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A 1975 CB400F high mileage complete engine rebuild

jensen

Veteran Member
Joined
Jun 1, 2020
Total Posts
1,215
Total likes
380
Location
Blaricum, The Netherlands
I have a stock CB400f, and decided it is time for a complete engine rebuild.

The facts :

I bought this CB400f 13 years ago from the first owner, he bought it new in 1975 (I have the original bill of sale from the shop where he bought it new).

The owner putted 73.000 km (45360 miles) on it, always maintained the service intervals, and always used Castrol (RS) mineral oil. When he bought it he had to choose between a second hand BMW or a new CB400F.

His wife advised (forced) him to go for new, he always rode second used motorcycles and had to wrench a lot, so you guess what he ended up buying. The BMW and the CB400f couldn't be of a bigger contrast, and in fact he drove the CB400F as-if it was a BMW. He told me he only once did rev it on the German highway above the 7000 rpm, but not higher than 8000 rpm, but only once. He never exceeded the 8000 rpm, doing that, he never felt what the CB400f was capable off. Afterwards he was better of buying a BMW, it was fitting more to his riding style.

Fourteen years ago I met him on a classic event, and I noticed his bike, it was in showroom condition. He told me that he was suffering from balance disorder, and he was afraid of driving it (and his wife too). He was then 73 years old. Being afraid of driving it, I asked him if he wanted to sell. He said yes, and it took him a year to emotionally part from it. He actually cried at the post office during the paperwork, because then he realized that it not only meant that he sold his bike, but also that his motorcycle riding days were over. He rode motorcycle his whole life.

I drove it home and I fell in love with this little sohc four. It is my first four, but I have other classic Honda´s as well, but all twins (a few CB450's, CB72's, early dreams, and a Kawasaki KR1-s 250 twin stroker).

Like I said, it is in showroom condition, and everything was original, he cared for it like as if it was his child.
The original drive chain and sprockets where on there too. I got the cb400f with a can of grease, a stove and a few other things. He bought an extra chain with the bike, and he cleaned and lubricated one chain, while the other one was on the bike and changed it every 1000 km.

1975 CB400f 4.jpg

Odometer shows 78419 km, which is 48727 mls

P1050041_s.jpg


I did change a few things immediately, mainly focussed on safety like chain and sprockets, tyres, brake pads, brake fluid, and front fork oil.
Because an original rear sprocket is unobtainable, I made one from aluminium and I latched the special piece from the old sprocket to the new one.

I also changed to Castrol full synthetic oil (10W50), after cleaning the sump pan (wasn't that much sludge in it).

The engine was very, very lazy. I went to a friend of my with a dyno and measured the curves as I got it, and I measured the curve after pulling it a few times to 10.000 rpm.

dynorun CB400F.jpg

CB400F dyno run 2.jpg


The first run was very difficult for the engine, it hardly pulled to the 9000 rpm (took ages) and showed no more then 26 Hp on the rear wheel. I pulled it to 10.000 a few times, and found 3 or 4 extra horses in the second run (the red line is the first run, the blue line a run after a few times pushing the engine to 10.000 rpm).

We also synchronised the carbs (that was really necessary) and the engine became much more silent (it made a lot of mechanical noise before this).

We checked the compression, and 1,2,4 where good, but number 3 was lower (but not below specifications). The logical reason is that the screw for the tacho cable was never released while doing valve adjustment, so he never took out the tacho cable, and that makes it hard to adjust properly.

He advised me to ride it for a few thousand of km, and then see what the engine did afterwards, so I did.

In the beginning it was doing only 110 / 120 km an hour in fifth gear and wasn't strong enough to pull in sixth gear, besides that, the acceleration was poor. But after a while, the engine had to get used to me, it pulled to 150 in fifth gear, but still not able to pull in sixth gear, and the acceleration got a little better.

But when hitting 7000 rpm, the clutch started to slip, so I decide to get some decent clutch plates and stronger clutch springs. After that, it didn't slip any more, and every time I hit the 7000 rpm, the engine appreciated it more and more.

I took the CB several times to Italy for my work, did some long distance rides to customers, and after 10 years of riding it, the tacho reads 2.000 km, so it actually did 102.000 km. Below a picture of my bike in front of the Grolsch brewery were I was working on a new type of inspection system.


CB400F at Grolsch.jpg


At 90.000 km the cam chain started rattling, and couldn't be adjusted any more. The primary chain also rattled a lot, and the compression of the 3th cylinder was getting better, but always stayed behind compared to the others. I figured out that it was necessary to start thinking of an engine rebuild.

So I started to collect the necessary parts from ebay and other sources. I soon found out that it is more difficult to get parts for this CB400F then for the older twins I have. But when you have patience, you can achieve a lot with little money.

It took me two years to I find and buy two new cylinders blocks (I couldn't resist the price, and it was cheaper then boring / honing), std pistons, std. piston rings, valves, valve springs, main shaft, silent rubbers, packings, oil seals, kick starter shaft, secondary shaft, clutch outer, clutch inner, primary gear, etc.

Jensen
 
Gosh that brings back memories - my second bike back in 1978 was a blue used CB400 F1, with the footrests on the swing-arm, identical to that one of yours Jensen. Two of my friends had the later F2 models, one in bright yellow, and the other in the more traditional metallic burgundy/maroon. Fine bikes - all three of them

I did a little bit of work to mine in terms of getting the heads gas-flowed by Dixon racing in the UK (they also used to do a 460cc conversion kit if memory services correct) and fitted a lighter Yoshimura 4 into 1 pipe. Not sure it it made any real performance difference, but it certainly sounded a lot faster :) Like this..

https://www.youtube.com/watch?v=Vtd0aKq-OsU

Often wondered how the later 400/4 compares to the earlier 450 twin. On paper I think the 450 twin is more powerful and a little quicker, but was never sure if that translated to much difference in real life. Be interested to hear your take on it.
 
Hi Alan,

When I got the CB450 K0 it was an old (dated) bike with low handling capability's. Over the years I worked on the bike, I modified a lot of things, not noticeable, keeping all details of the CB450 K0 intact. I changed the inner parts of the suspension (front and rear), chose for modern tires (BT45), new steering stem bearings, bronze rear fork bushings etc. The list is too long to display here, but all these modifications made the CB450 K0 a much better bike, not only at handling but also in reliability.

The CB450 K0 is now a very reliable bike and brought me save home after a lot of trips. But one things makes the CB450 K0 an uncomfortable long-distance commuter, and that is the vibration mostly in the lower frequency's. I know, it's a twin, I like the bomber for nice trips on backroads. However, the bike behaves very nice at high speeds, from 120 km/hour and on, only then the engine feels like a turbine, with only some high frequency vibration, but it's not possible to do that constantly (law).

The CB400F on the other hand, is not particular vibrating at any given speed, making it a much better long distance rider. The only things that lacks the CB400F is torque at lower revs and top end power. I don't think I can give the CB400F more torque at lower revs (unless using a big bore kit), but I thinks the top end power can be raised a little to meet the power of the CB450 K0 (my goal is 35 HP at the rear wheel).

By comparison the dynocurves from the CB450 K0 and CB400F, and you see what I mean (rear wheel power and torque curves).

CB400F 1975 powercurve and gas analyser.jpg


CB450 K0 1965 powercurve and gas analyser.jpg


@2500 rpm the CB400F has a torque of 20 Nm, the CB450 K0 28 Nm.
@8500 rpm the CB400F has 30 Hp, the CB450 K0 has 32 Hp.

The differences seems not to be much, but should be seen relative. Then there is the shape of the torque curves, the CB450 curve is almost flat, that's nice, but won't give a "kick in the back" like the CB400 does between 5K and 7K rpm. But on top speed, the CB450 K0 wins, just by an inch...And if you're good with the clutch the CB400F can keep up with the CB450 K0 at full throttle through the gears.

However, two years ago I went to Spain and back, and had a choise between the CB400F and the Cb450 K0. I took the CB450 K0....but next time I'll take the CB400F. Not that regret the choice, I had lots of fun in France and the Pyrenees, back roads and small winding roads, but on the highway I had to get of the bike every 45 mins...

Jensen
 
From those curves, there's very little difference in the peak power - but with the twin having slightly more torque low down. Couple that to the four cylinder bike actually being a little lighter (c10kg maybe ?) and I can see how they are actually very close performance wise on the road. Good point about the four being smoother though. Its easy to overlook the 450 is a twin and complain about the vibrations - even for a well engineered bike - but it is still a twin. I can imagine how the 400/Four would be a much more relaxing ride over long distances.

They do handle quite well too. I remember a badge of honour for the 400/Four rider was how far you managed to grind down the little blobs of metal below the footrests - the 'Hero Blobs' as they call them nowadays. If you really tried hard - you'd not only get them to touch (usually in roundabouts - the best surfaced/constant radius turns near us) but eventually manage to grind them away completely. After that, the next hard point that would start grinding was the bottom of the exhaust collector-box. How any of us survived beyond the age of 20 I shall never know :)
 
Hi,

Four months ago I started to soak all important bolts and nuts in penetrating oil. The nuts of the headers, cylinder head and all the bolts of the engine cases. I did this once in two days. After a while I could free the nuts from the header without damage. I found a lot of carbon deposits in the exhaust ports, at least 3 to 5 mm thick (see pictures).

This was clearly one of the reasons that the CB had only 30 HP, the exhaust ports where a lot smaller in diameter. Like I said in my previous mails, the PO never understood how these engines should be driven, he never ever revved above 8000 rpm. However I revved it up from time to time, and did ride some fast routes through Germany with it. The engine never used oil between the oil changes (3000 km).

I also dismantled the cylinder head cover and looked for the first time into the valve train and camshaft. From a distance it did not look bad to me, but when I took a closer look I found severe damage on the camshaft lobs and rockers.

After soaking in penetrating oil , I freed the cylinder head, all nuts came out undamaged, also the nuts just before the spark plug holes. I was warned about the cylinder base gasket, and I soaked the studs and also the gasket from outside. Today I freed the cylinder too, the base gasket was completely wet from the penetrating oil, and no problem any more.

uitlaat poort_1.jpg

Exhaust valve area cylinder 1

uitlaat poort_2.jpg

Exhaust valve area cylinder 2

uitlaat poort_3.jpg

Exhaust valve area cylinder 3

uitlaat poort_4.jpg

Exhaust valve area cylinder 4

The chrome on the rockers was gone, some parts broke out and damaged the camshaft lobs. The middle of the camshaft lobs was much thinner then the outside, so some rockers where also damaged because of that. The bearings of the camshaft - head where good, also the bearing surfaces in the head itself, so the head can be re-used, the camshaft not. Luckily I tracked down a new camshaft, so that problem is solved for now.

damaged rocker.jpg

damaged rocker

damaged rocker 2.jpg

damaged rocker

camshaft left side.jpg

Camshaft left side

camshaft right side.jpg

Camshaft right side

The cam chain was loose, there was no tension on it any more, and I think I stopped riding it just on time.

Jensen
 
When I took the head off, I found a lot of carbon deposit on the head and piston floors. The valves where not really burned, not one of them. I was very happy I was able to pull the head and cylinder without any damage, all studs are in perfect condition, as the bolts and nuts. The only thing I have to do is re-plate (sink), saving a lot of hassle and money. In the past I bought a few boxes of Honda sohc NOS parts like valves, rockers, cams, cranks, clutches, camshaft bearing parts, but no parts numbers on it. I have found at least 7 camshafts, but all larger, probably CB500/CB550 and CB750. But after comparing the valves, I found all the valves and rockers I needed (I replace all valves, all rockers and all springs).

verbrandingskamers 1 en 2.jpg

combustion chamber 1 and 2

verbrandingskamers 3 en 4.jpg

combustion chamber 3 and 4



I removed the valves, and cleaned the head. Afterwards I beat blasted the combustion chambers and in and exhaust ports with the finest bead I could find. I use a very low pressure while blasting. The result is a very fine structure, and the bead also closes the surface. I made pictures of all the ports and inner side of the head.

After measuring the valve guides I decided not to replace them, not one of them was worn out, and all within specifications, and that means saving a lot of trouble.
The combustion cambers are a little rough, but that's the material itself.

A friend of my will start to port the head and make the combustion chambers nice and smooth. I also will make the exhaust chambers precisely the same in volume. Next to that it' also necessary to re-cut all the valve seats for the new valves and the modern petrol.

facts :

valve stem diam. ex 1 = 5.30 valve stem daim. in 1 = 5.42
valve stem diam. ex 2 = 5.32 valve stem daim. in 2 = 5.40
valve stem diam. ex 3 = 5.29 valve stem daim. in 3 = 5.41
valve stem diam. ex 4 = 5.30 valve stem daim. in 4 = 5.42

the play of combinations was less than 0.3 mm, except ex. 3, but the play is too much for me, so I decided to renew all valves.

All springs where within specifications, but I decided to replace them all, better save then sorry.

Camshaft lob height ex 3 = 27.8 mm (too small), rest was within specifications. But the surface of the lobs made me decide to search for a new one.

The exhaust 3 has suffered the most, My assumption stated earlier is that this is because the the adjustment should be done after removing the tachometer cable, the PO never did this. Does has someone another explanation ?

Jensen
 
Jim,

Yes, that's correct. The CB400F doesn't have vacuum carbs like most twins, but directly (cable) controlled carbs. When opening the carbs to much at low revs, the A/F mixture get's way to lean.

Jensen
 
Hi,

Porting, or rather cleaning-up the intake and exhausts ports

It was difficult to clean-up this head because Honda made everything in this head as difficult as possible. The valves are angled in two planes, the intake ports are not straight in the vertical plane. Due to the way the head is made the area around the valve guide seems apart from the rest of the intake port, intake and exhaust ports are really small and angled in two ways etc.

When cleaning-up I realized that this is one of the first Honda’s with angled valves in two planes. Every early Honda twin I worked on had the valves angles in one plane. Does the 1969 CB750 sand-cast also have this feature ? It must have been a pain in the … to machine the valve seat’s surfaces in that time. I actually don’t understand why Honda engineered it this way, very very difficult and expensive to make it like this.


P2060022_s.JPG

blasted surface only, clear to see the rough area's.


P2060023_s.JPG


What I’ve tried to realize :

My working order with cleaning-up a head is maybe different then other people, but it worked for me in the past.

I always start with the entrance of the ports, and normally I start with the intake side. It’s very important not to shape the port itself yet, first I make all transitions between the different parts smooth and there are four of these transitions :

1. intake manifold – entrance of the intake port
2. intake port – valve seat
3. valve seat – exhaust port
4. exit of the exhaust port – muffler / muffler packing

I’m using the original carburettors and muffles after the rebuild, so I use the original intake manifolds. I did this with making a calibre with the same diameter as the intake manifolds and then compare this with the intake ports entrance. When the entrance is almost finished I mount the manifold and make it fit precisely.

I also do this with the exhaust port exit. I make a calibre which fits precisely in the pipe of the muffles, and copy it’s shape and size into the head.

The second step is make the transition from valve seat to the aluminium of the head very smooth. I’m always very careful when shaping two materials at once, the steel of the valve seat is much harder then the soft aluminium of the head itself.

After this is done I have shaped everything but the port itself.


P2140010_s.JPG

Cleaned-up surface
 
Nicely done there, it's a bother getting all the casting seams removed but it does allow a more even flow. It's one of those "little" things that make a difference.
 
Hi Jim,

Yes, it's a lot of work, but not only the casting seams are smooth now, also the diameter of the intakes are made exactly the same, as well as the diameter of the exhausts.

Jensen
 
Hi,

After the painstaking process of finalizing the cylinder head I brought it to a machine shop to flatten the head and to cut the valve seats. Just to be sure, now it's straight within 0.005 mm for sure, but looking at the milling face I guess the head was straight already. As modern patrols are lead free, and I don't like to add lead or something like that in my tank every time, I let cut the valves at 45 degrees and faced them at 1 mm. Like I wrote earlier, all the valve are new but the guides are original.

milling structure of flattening the head.jpg


valve and seat_2.jpg



valves in combustion chamber.jpg

Ready for mounting ....
 
Hi Jim,

Thanks, I know it's not a twin, but certainly worth the trouble. This engine has to be done ASAP to make room for the Twin engines for the K0, K1's and the K2.
I may have a lot of room for parts and bikes, but my bench area is limited to one engine at the time, and this engine is taking all the space for too long now....

Jensen
 
I just like engines, doesn't matter the number of cylinders. I'd love to get hold of a CBX 6 cylinder just to play with but then I'd have to get the bike also to be able to test the engine and then one thing leads to another. Then there's the CX650 Turbo or the Suzuki RE5 rotary engine.
 
I'd love to get hold of a CBX 6 cylinder just to play with but then I'd have to get the bike also to be able to test the engine and then one thing leads to another. Then there's the CX650 Turbo or the Suzuki RE5 rotary engine.

Jim, you'd love the CBX engine, to me it's some of the best technology they brought to the street from their road racing days. If only they'd used gear drive for the cams (all 4 of them, lol)
 
Indeed, it really doesn't matter how many cylinders your engine has, the work is mostly the same, times 2 for this bike compared with the twins. Although, a four is easyier to work on compared with a CB450 tiwn engine, but that's not due the two extra cylinders of the four.

Anyway, oilpump rebuild time:

When doing a full engine rebuild, it’s necessary to take a good look at the oil pump. Normally, an oil pump cannot be rebuild, or sometimes parts are not for sale separately, just like the oil pump in this bike.Since NOS oil pumps are rarely seen on eBay and other market places, it’s worth doing the best you can, and find some good used pumps to make good one from the best parts.

When I dismantled the rockers and saw the damage on the cam, I knew I should have a look in the oil pump for any damage. The chrome of the rocker surface was mostly gone. These chrome particles are very hard, and sometimes brake out of the surface in pieces. On at least two rockers this was the case. These pieces are not filtered out before they can reach the oil pump, so these particles will grind the pump lobs. Small damages or not so bad, but bigger damages or a lot of small damages can lead to the fact that the oil pump doesn’t pressurize the oil enough for the main bearings especially when the oil is hot (low viscosity).

Over the years I bought two other second hand pumps from low mile engines. I want to build one good pump out of three pumps.

3 oil pumps dismanteld.jpg

First of all I dismantled all pumps carefully, and cleaned the parts thoroughly with petrol (see picture)

My own (original mounted on my CB400) pump (pump 1) :

I found that my pump was indeed damaged (inner / outer rotor), and since it’s from a high mileage machine, it also showed (normal) wear between the outer rotor and pump housing (see pictures).

damaged rotor of pump 1 and 2.jpg

damaged inner rotor of pump 1 and 2.jpg

Pump 2 (according to the previous owner the engine did only 10.000 miles and the price 20 USD) :

I found that this pump also had damaged rotor lobes, less that mine, but nevertheless, damaged. I also found that the pump gear was damaged (see picture). Overall the parts showed less wear then pump nr. 1 I would say that indeed the pump did less then 65.000 mile, but 10.000 miles is a little too positive, or the PO never changed oil during the 10.000 miles.

Pump 3 (I bought this pump on a local swap meet, the seller said something like low mileage, but didn’t know how much it actually did, but the price was 1 euro, so I bought it).

I found an almost perfect rotor set in this pump, no damaged rotor lobes, nothing at all. The pump did however turn a little heavy, but smooth. I also saw that the gear on the pump was different then the other ones, I checked with my parts manuals, but there’s no info about parts in the pump, and there’s only one part number for a complete pump, strange, but after working on older Honda’s you get used to these things. The dimensions of the important area’s where exactly the same as the other ones.

After the first impressions I started measuring. The most important dimensions of an oil pump are the size of the lobes, the amount of play between both rotors and the play between the rotor and the pump housing.

measuring play with a feeler gauge.jpg

Play between the inner and outer rotor (measured as in picture) :

Pump 1 : 0.15 mm
Pump 2 : 0.10 mm
Pump 3 : 0.05 mm

I choose to go further with rotor set of pump 3, and measured the play between outer rotor and the pump housings :

Outer rotor 3 - rotor housing 1 : 0.05 mm
Outer rotor 3 - rotor housing 2 : 0.10 mm
Outer rotor 3 – rotor housing 3 : 0.10 mm

I decided to use the rotor set from pump 3 in the main rotor housing of pump 1, and measured it again, resulting in the same numbers.

The gear and shaft from pump 1 was the best, and also a had the tightest fit in rotor housing 1, so another part selected.

Now, I only have to choose between 3 oil pump main body's, and the best secondary pump rotor set (the pump of the CB400F consists of two pumps, one (big) for the crank and head, the other one (small) for the transmission (see picture to see the pump main body rotor surface).


surface pump body 2.jpg

I measured the small rotor sets in the same way and found out that rotor set of pump 3 was the best (0.05 mm), and the play between the outer rotor and oil pump main body number 2 was the best fit (0.05 mm). Non of the rotors where damaged in any way (see picture)

secundairy pump rotor sets.jpg

measuring rotor o.d.jpg

The secondary oil pump cover of oil pump number 2 was really smooth,, so I use that one too (see picture).

So, the complete assembly is consisting of the main rotor set of pump 3, main rotor housing of pump 1, gear / shaft from pump 1, secondary rotor set from pump 3, the main pump housing of pump 2 and cover (and bolts) from pump 2. I also used the pressure relief valve from pump 2, but the spring from pump 1 (stiffer).

The next step is to measure the space between the main rotors side ends and the housing. This space is regulated by the height of the main rotor housing. I used plastigauge. to measure it, and found out that the play was more than 0.2 mm The rotor is made of steel and the housing is made of aluminium, and thus the expansion coefficients differ a lot (steel has a much bigger expansion coefficient then aluminium. From that point the play between rotors and housing can be 0 / +. For safety I choose for 0.02 mm play between the surfaces (20 micrometer). I grinded off the main rotor housing 0.18 mm to make sure not going too far. This resulting in 0.02 mm play between rotor and main rotor housing.

measuring secundairy rotor cover.jpg

After assembling it turned very smooth and so I now I only had to figure out what size of O-ring to use between the main rotor housing and the main pump housing.

As this O-ring is not mentioned in the parts manual, I did measure depth and diameters (I.D. and O.D.) of the O-ring grove itself. I chose a vitton O-ring that is 25 % bigger in diameter (thickness) then the groove.

Now I only have to assemble the O-ring in the oil pump, and store it for later use when building everything together. From all other parts I made another pump (reserve), in the same way.

The play between the rotors is 0.1 mm, the play between rotor and housing is 0.1 mm, and I refurbished the lobs of the inner rotor a bit with very fine sanding paper. The rest of the parts are for spare (or when I find another good pump or two to go through the same process)

What Honda says about the specs of the oil pump :

Maximum play between the rotors : 0.30 mm
Maximum play between rotor and housing : 0.35 mm

There are no further specifications of play between parts, so you also can conclude that all the oil pumps I started with where in fact within specifications, so, why all the hassle ?

My impression on these specifications are different then Honda had in the 70’s. it’s also known from the 70’s that these sohc4 engines where prone to early cam and rocker wear. One reason was the use of low quality mineral oils (there are also good quality mineral oils), and the other reason where the tolerances of parts in an given engine.

I always use full synthetic oil in rebuild engines. I have very good experiences with Castrol ( power 1 GPS 4T 10W-30 or 10W-50 or 10W-60). I don’t want to start an oil debate, this is what I use.

complete rebuild oil pump.jpg

When the engine is real hot, on a hot day, the pump should be capable of building up pressure. The smaller he play between the important parts, the less leak between the parts and rotors self . So the better the specifications are, the more guaranteed this will be. I’m investing a lot of time in this rebuild, and therefore I don’t want to ruin a my engine with a bad oil pump. I like to ride it fast and reliable, for a long time.

Another night of hard work resulted in something useful :)

Jensen
 
It's the attention to detail that makes the difference between engine builds and success. It's always the little things that make a difference. When I did my 350 engine I discovered that the oil passage from the crankcase to the pump pickup was partially blocked by casting flash. Just removing that increased the area by @25% so now I know I will have good oil supply to the pump.
 
Hi Jim,

Yes, as always not only the devil is in the detail, but also success :) Talking about details and devils:

After opening the crankcase everything seemed nice and shiny, but as usual, the devil is in the detail, and the devil was in my transmission. The first impression was good, but I knew something should be wrong, because my oil pump just was too much damaged. After disassembling the gears from the shaft and cleaning the gears thoroughly, I found heavy pitting on the the top gear combination.

complete trans_1.jpg

I tried to make a good pictures of it, and it clearly shows that this gear has severe damage. These images show exactly what pitting looks like, the top layer of hardened steel is completely disintegrated. Both top gears where damaged, but not in the same way. The counter shaft top gear is damaged the most.


top gear countershaft_1.jpg


minimal pitting.jpg

I expected a lot, but not this amount of severe pitting in gears from an engine always maintained good with good (mineral) oil. I saw a lot of this pitting on my early Honda's, but these are known for the hardening errors, and thus pitting.

normal structure from fabrication proces.jpg


looks good, but detailed examination showed pitting.jpg
 
In all of the Honda transmissions I've had apart, I've never seen that much degradation to any gear teeth that was not caused by horsepower-related damage.
 
That damage does look like load failure, either from horsepower or too low an rpm (lugging) operation. Low rpm and attempting acceleration places some extreme loads on the gear faces. I know the CB450SC 6th gear has that issue.
 
Hi,

I know, and I guess it has everything to do with the riding style of the bike by the original owner.

Like I wrote in the beginning of this thread:

His wife advised (forced) him to go for new, he always rode second hand motorcycles and had to wrench a lot, so you guess what he ended up buying. The BMW and the CB400f couldn't be of a bigger contrast, and in fact he drove the CB400F as-if it was a BMW. He told me he only once did rev it on the German highway above the 7000 rpm, but not higher than 8000 rpm, but only once. He never exceeded the 8000 rpm, doing that, he never knew what the CB400f was capable off. Afterwards he was better of buying a BMW, i t was fitting more to his riding style.

He rode the bike as it was a BMW, I think there you have your answer. A BMW is a large displacement bike with a lot of torque at low rpm's. I think he rode this bike in sixth gear while doing 50 km/hr. The sixth gear is meant to be an overdrive, but not at these low rpm's! My assumption is that the sixth gear set (top gear) is damaged by this. A CB400F is an SS, a super-sport bike and must be ridden likewise. That's also the reason that the bike was so lazy in the first few dyno runs. For the original owner it would have been better that he just had a 4 speed gearbox I guess.

It's the same reason that a lot of owners of a CB450 K0 wanted an extra gear (they got it with the K1), but honestly, 4 would be enough if it would be ridden as a supersports bike. And if people should do that, there are no issue's with the generator not keeping the battery healthy, no issue's with fracturing chain covers due to heavy vibration and no issue's with carbonising the heads. There was a discussion on FB about removing the top engine mounts for less vibrations, but if people ask the question, I know that they are not riding the bike as it should. Above 6000 rpm the bike is almost free of vibrations ! Keep the engine above 4000 rpm at all times, especially in higher gears, same with the CB400F.

Today I had a nice ride on the CB450 K0, and yes I keep the bike around 4000 to 5000 rpm at back roads, only using the first three gears, but I always like to ride it on the highway for longer periods, and I use the fourth gear from 80 km/hr and above. Here in the Netherlands we are aloud to ride 130 km / hr (80 mls/hr) after 18.00 hour. The engine will do a nice 7000 to 8000 rpm, no vibrations, no issue's. The sound out of the mufflers and air boxes is is marvellous and ear-pleasing, even with a helmet.

Jensen
 
Hi,

Examination of the shift forks and shaft:

All shift forks where in perfect condition, all measurements where within specifications, and the surfaces looked like they never touched anything. The bores on every shift fork where as new.
The gearbox never gave any problem, so I didn't expect any issues related to the parts of the selector group.

shift fork detail.jpg

The shift drum was very nice, especially the "bends" in the groove. I've seen a lot of damaged drums, always look at the places, as pictured. The side play with the pin on the shift fork was as new, again, no signs of damage at all. I checked everything and couldn't find anything what give away the fact that it did the job 65.000 miles.

shift drum detail.jpg

The shift fork shaft was another story, it is bend, not much, but it ain't straight, although it is within specifications I decided to replace it, especially because of the fact that the surface wasn't very nice anymore too. It's difficult to see in the picture, but if the shaft was straight, no light would come through the flat surface and the shaft itself.

shift shaft.jpg

The shift shaft itself is in used condition, There is some wear at the point where the shaft comes through the case, but this is within specification. The shaft is straight.

shift fork shaft.jpg

All other small parts where as perfect as can be, and no further action is required. I bought the shaft already a few years back, because I knew that this would be a risk part.

Jensen
 
The last important part is the crank. I decided to measure the crank with plastiguage for a quick and dirty check on the bearings and crank condition, but before measuring I had to clean the crankcase surfaces.

First I removed the crank bearings after cleaning the surface and marked with a permanent marker.

Then I cleaned the empty cases in engine cleaner, and after drying I start to scrap the old packing material from the surfaces.

After removing the packing material with a tool (see pictures), I take a wet stone to remove small pieces from the mating surfaces.

packing removal tool_1.jpg

packing removal tool _2.jpg

This must be done with care, you don't want to ruin a otherwise perfect mating surface.

wetstone method.jpg

Never use the whetstone dry, always use petrol or something like that. Never use the wet stone balancing one one surface, the change that you destroying the surface by rounding is big. Always place the whetstone on at least to points on the mating surface, don't apply much power, but wipe it gently but straight over the mating surfaces.

After this work (it takes a few hours) clean the engine cases good, because every part of dirt on the cases can mislead the measurement. Working with plastiguage is easy, nice and accurate, but only when everything is clean.

Put the bearings back in there places, put in the crank (dry and cleaned) put plastiguage on the bearing surfaces and place both crank half's together (don't put the plastiguage under the crank, the weight of the crank will interfere the measurement).

Now put the eight special crank bearing bolts into place (cleaned and lubricated with molycote) and torque them to specifications and in the right order. Wait a few seconds, and get the bolts out (in the right order, and remove the crankcase half gently.

The only thing you have to do is reading the play directly.

crank bearing_1.jpgbearing_1.jpg

Bearing surface and shell 1

crank bearing _2.jpgbearing_2.jpg


Bearing surface and shell 2
crank bearing_3.jpgbearing_3.jpg

Bearing surface and shell 3

crank bearing_4.jpgbearing_4.jpg

Bearing surface and shell 4

crank bearing_5.jpgbearing_5.jpg


Bearing surface and shell 5

My crank (main) bearings where 0.042, 0.045, 0.042, 0.042, 0.045. All, except nr. 2 and 5 are within build-in the specification (new), and that, as you can imagine was a great relieve, nothing to renew here.

Jensen
 
Hi,

The best way to document a rebuild is to take pictures of every single part of the engine, and close-ups when in doubt. I label the pictures with the part number and the results of the measurements, the pictures labelled with an F (fault) should be replaced. This set of pictures marked with an F is direct input for my search list. When the (new) parts arrive I can directly compare the parts and decide it's the wrong or right part. With the older Honda's there are many different parts used in one type of engine, sometimes these parts have the same part number, or the part number on the particular part is written down wrong somewhere in time.

The above sequence seems to be a lot of work, but there's always a moment when you think, glad I did it. I never regretted this way of working.
And another benefit of this way of working is that if you are forced to pause the work due to events in live, you wont have to start from the bottom up when picking up again.

piston pins.jpg

piston pin surface.jpg

When you look closely to the piston pins you can see that the wear is not linear over the whole area, in fact the piston pins show asymmetrical wear. My assumption is that this is due to an misalignment of the crank in the cases or cylinder to cases, but with this minimal damage on the pins after 100.000 km, it's not something to worry about. The pistons seems to be ok, but measurement shows that the pitons are close to the maximum wear specifications (ovality). The piston ring groove is also showing wear.

piston skirt.jpg

Piston skirt

piston crown_1.jpg

The piston shows a live of blow-by and burned oil area's. However, it's also good to see that the air filter and oil filter did the work they designed for. Almost no vertical stripes on the piston skirt, and that is a good sign.


piston rings close up.jpg

A close-up reveals that the piston and rings are at the end of there life cycle.


The con-rods were within specification, so another reason to let it as it is. Of course replacement of the pins is necessary, as I will replace the pistons and rings.

Jensen
 
Hi,

Yes, indeed, never saw that before. But honestly, I never looked at piston pins of a 100K km small capacity bike from 1975, so I have no comparison.
The con-rod ends are in perfect shape, no issue's there. I will re-use them.

Jensen
 
Yesterday I did the carbs. In the last two years I found some interesting spare parts for these carbs, and I decided to replace all the important items like needles, needle jets (Honda), all packings and O-rings. I also changed the throttle valves, not really needed too, but I had these lying around. I found that the third carb had a different float height (float was 2 mm higher, so nr. 3 got more mixture compared to the other three), so I set the float height properly.

carbs before rebuild.jpg

Before

carbs after rebuild.jpg

after
 
Hi Jensen, thank you for taking the time to share your project. I have enjoyed reading about it and learning about the bike and your process to inspection and rebuild.

Do you have plans to share the condition of the cam chain and tensioner assembly? I assume they all show wear from usage and will be replaced with new parts?
 
Thanks Steve,

Unfortunately I don't have much spare time to spend and being more active on the forum.
Here, all projects came to a standstill, except the projects at work. Today, we closed the deal for 4 machines, on top of 2 we are now building.
Each machine is 8 mln euro's, options not included. We don't know were to find good technical people to accomplish this task, so very busy for the coming years too ...

Jensen
 
Today, I ordered all O-rings and oil seals. It took some time to dive into the world of rubber and making the right decisions. All critical O-rings that contact oil and should withstand temperatures above 120 degrees Celsius are Viton rings, the rest are made of NBR. Some O-rings are not made in Viton, so unfortunately, not all critical O-rings are Viton. The same for the oil-seals. Sometimes I changed the type of oil seal and added a dust seal where Honda did not.


All Honda NOS O-rings are made of NBR, even the newly made O-rings for this bike. Since it's an air-cooled bike, I always look for better materials with a higher temperature resistance and chemical resistance. Since Viton and petrol are not compatible, all O-rings for the carburettors are NBR-type O-rings.

For the Honda CB450's and the CB72's I use the same strategy, and I have complete lists and vendors who supply them. But doing it for just one bike (CB400F) was a lot of work.

O-rings and seals.jpg
 
But before I can start building-up the CB400F, I first have to make the Kawasaki Kr1-s winter ready, it's a 2 cylinder 2-stroke. I took the engine out, to do maintenance, and afterwards I'll park it in a dry and cool place.

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Frame is very light, the complete bike weights only 123 Kg (271 Lb)

20210320_204102.jpg

Engine during overhaul (new pistons)


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This is how the bike looks like.
 
The Kawasaki is stored for the winter, so time and place to start the build the CB400F engine.

The secondary as well as the primary shaft are NOS, just as all the small parts and bearings. After building up both shafts and gear selector drum, I placed both assembled shafts in the upper crankcase. I found that the first gear on the secondary shaft had to much play, so I shimmed with 0,5 mm shims both sides. I also shimmed the primary shaft, with 0,5 mm shim. The total end play of both shafts is now within 0.25 mm. More important is that the first gear on the secondary shaft is not able to "touch" the opposite gear at the right (in the last picture). I also replaced the badly worn gears by other, better gears.

IMG_0069.jpg

IMG_0071.jpg

After shimming, the first gear (largest gear) doesn't touch the opposite gear sideways

IMG_0072.jpg

The shim on the primary shaft can be seen

IMG_0074.jpg

The gears are all running smooth and free, shifting by hand is smooth (rotating the fork selector drum by hand).
 
In an other post (and this one) I mentioned plating I added some pictures of stuff I brought to the zinc plater. Every once in a while after accumulate parts to plate (approximately 25 Kg / per batch) it's time to sort the stuff that's coming back. Since I throw in fasteners, springs, sprockets and even larger parts, of the bikes I'm busy with, this sorting takes a while. Pictures of before help me to identify the parts after plating.

IMG_0075.jpg
After sorting out, put the parts in boxes per category (bike-type)

IMG_0079.jpg
Before plating I take the time to get the parts as smooth as possible, the result after plating is much better then just throw the parts in....

IMG_0083.jpg
Carburettor parts are also plated, this is a part of a batch of CB450 carb parts.

IMG_0078.jpg
This is why I needed to bring the stuff to the plater a little sooner (approx 20 Kg in total), the engine bolts for the CB400F, the bike of this thread. When you look closely, you'll see one dark thread per bolt, this is the position of the steel wire that hold them during the plating process.

The price I pay for plating depends on what I want. For example the bolts in the last picture are plated piece by piece (hang-plating), because I want them to be perfect. Putting the same bolts in a rotary plating process won't give this quality. The batch in the pictures is partly rotary plated, partly hang-plated, and set me back a little above 150 euro. It seems to be a steep price, but the value of all the parts I throw in is much, much higher.

These 8 mm bolts (special bolts for connecting the crank cases around the crank) for the CB400F in the left bag alone, are worth over 100 euro, if available. The process of plating takes only 2 to 4 days, cleaning-up and smoothen the parts takes hours and hours, sorting them is also time consuming....

bolts.jpg

Is it worth the money ?

Before I start a restoration I make a calculation of costs. Restoring this CB400F was on the edge of costs-value when I started the resto 12 years ago. In the past 12 years I acquired parts for the bike to replace the worn or bad parts.

I bought the bike for 1250 Euro back then, and considering it's condition, a good price, even when you add the 65.000 miles on the odo. The first owner I bought it from maintained the bike well, so most parts are in perfect shape (chrome / paintwork).

A simple calculation :

Total cost of the bike : 1250 Euro
Paintwork (not powder coating) frame and a few black parts like triple tree etc : 850 euro's
Total costs of all the new parts acquired over the last 12 years : 2300 Euro
Plating / chroming : 100 euro
Engine work (cutting valve seats) : 250 Euro

Total costs of this bike when ready is 4750 euro's, and that's a lot of money.

In my search for parts for this bike I bought some batches of parts, knowing that I didn't need them all. For example I acquired 2 camshafts, but needed only 1, my seat was nice, but found by accident a NOS one in the box, I bought a batch of 12 intake valves and 12 exhaust valves but needed only 4 of each, 2 NOS cylinder blocks, needing only one, etc, etc)

Many of those extra parts are sold during the last 4 years and until today it gave me back over 1500 euro, but I expect getting more. For example in my search for spokes I bought 30 Kg of unsorted Honda spokes, containing spokes for the CB400F, but also dream's, CB72 / 77 and CB450's, CB750 etc.

I expect to gain another 1000 euro from those parts alone, so the total costs when the bike is ready to ride will be around 2250 - 3250 Euro.

12 years ago this bike wasn't worth that kind of money, but times have changed....

btw, I'm not in for the money, because the hours spend on searching parts, working on the bike are not counted....
 
Sounds like you have a good handle on what this is really all about.
 
Yesterday I prepared the assembly of the upper- and lower crank case, but unfortunately it seems I'm missing two important bolts. The project was lying around for 12 years, and I cannot find them anywhere. CMS and DSS don't have these bolts. Does anyone has two of those bolts laying around ? P/N is 90086333000, it's a U.B.S. bolt. Without these bolts I cannot proceed with the build. I really would appreciate help in finding those bolts, used or NOS.

I GOT THEM. I made a view phone calls and one of the guys found the bolts and was happy to part with them. Next week I can finally close the cases after 12 years !

IMG_0109.jpg

IMG_0111.jpg

CB400f bolt.jpg

bolt2.jpg
 
In my search for the missing bolts for the past two days, I stumbled onto a box I could not remember having it, nor what would be in it.... Opening the box showed a lot of NOS CB450 and CB77 parts. Pistons, rings, bearings and a complete set of CB450 K0 camshafts.

IMG_0108.jpg

No bolts for a CB400F '75 :sad:
 
Engine rebuilding goes slowly due to work (too many large projects, not enough people). However, the bolts are in place, so upper and lower engine cases can be re-united after 12 years. In my search for the bolts I discovered that a performance part for the CB450 K's can also be used for the CB400F. This is a needle bearing set-up for the swing arm, instead of the bushings set-up. Always nice to un-pack such old parts out of there original package. Luckily the parts where rust free, like these where made yesterday...

20220130_181813.jpg

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Loving this thread and I don't even have a 400!!

Detail and pics are great, and I was particularly impressed with the costing rationalisations. Great stuff!! And, you'll end up with a magic bike!!(y)
 
Thanks, the only four in my collection of twins, a fun bike it is to wrench on. Cost calculation is always part of the plan for any bike I restore, I think one has to be realistic on the choices you (have to) make.
 
The last three weeks I suffered from Covid, so got time to work on the engine. I had two days high fever, and after that I felt fine, but a few days later I had to cough like and old man with a history of 50 year smoking. That was the only inconvenience I suffered, no energy loss or anything else. The last 12 days I walked 12 km a day without any problems. I'm not allowed to go to the office due to the cough, and have to work from home.

In the mean time all parts are plated, including the U.B.S. engine casing bolts, so finally the engine half's are reunited ! Crank and transmission are running smooth, and should be running smooth because I replaced both gearbox shafts for NOS ones. All rubber parts are replaced by new parts, including the old hardened transmission damper rubbers in the primary shaft (the part where the chain from the crank is delivering it's power to the clutch).

After assembling the top-end I will put the engine in the frame, before I put the clutch, oil pump, starter motor and lower engine case on the engine. This way I engine is not as heavy, and much easier to handle.

IMG_0179.jpg

Nice plated bolts connecting both engine cases. From now on, it will go a lot faster !

IMG_0181.jpg

Clean surfaces, ready for taking the gaskets and top-end parts...

IMG_0183.jpg

In another thread it was discussed that the original FSM was always better then other FSM's, I wasn't agreeing, and this book on top of the original parts list and FSM is an example of that. The whole disassembly and assembly process is covered in this book. this book is written by a Dutch writer, so in Dutch only. Very detailed pictures (not a copy out of the Honda FSM) AND text on how to and what is important, including correct torque tables etc.... Over 200 pages valuable information only on the CB400f and CB550f.

The books are relative cheap too : https://www.marktplaats.nl/l/motore.../2/#q:peters|searchInTitleAndDescription:true
 
Getting sick sucks but sounds like you're coming thru this ok. Good progress on the engine, looks beautiful.
Now if I only knew how to read Dutch. From your description that book sounds like a valuable resource unlike the typical Clymer versions.
 
Hi, thanks for the heads-up. This was my second time, I also had it in march 2020, and now again in march 2022. btw, I'm not vaccinated nor boostered. The first time was very mild, the second time a little worse, but I recovered completely. I did travel and fly a lot, I think I picked this one up in Hungary or Serbia where I was just before I got it. These are one-day travels, fly in in the morning, fly out in the evening, no hotels etc.

Anyway, next step is the top-end, and then the fun starts, by merging the engine into the frame and put all parts back.
 
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