A 1975 CB400F high mileage complete engine rebuild

[crazypj]

That really is in remarkable condition for an early model CB400F (rear footrests on swing arm instead of frame mounted)
Not revving the motor probably did a lot more harm than good, several area's require 'splash lubrication' and are under lubed at lower rpm (small ends in particular rely on oil being centrifuged from big end bearings, hitting piston crown and dropping back onto connecting rod).
The state of pistons shows they were getting a bit hot so 'cooking oil instead of staying clean.
If it were 1980, the most impressive thing to do would be fit a 490 kit and a PIPER cam, but, PIPER don't want to be involved with old bikes. (like Quaife, way more money to be made from the race car crowd)

 

[jensen]

Added the engine guards, rear fender (back from plater), mudflap and tail light.



Ready for the ridingseason 2023

 

[Maraakate]

Looking great!

 

[fxray]

Beautiful work on a beautiful motorcycle, jensen! While you wait for the 2023 riding season, here is an old YouTube video that I like. I stumbled onto this several years ago when looking for RD250 videos. This has the best of both worlds, an RD250 being chased by a 400F. Since the camera is on the Honda, the RD is almost always in view, but the Honda exhaust note is what you hear as the rider works the gearbox. He had one missed shift at WOT, but it was brief. The only disappointment is that I wanted to hear the RD as well. Oh well, I still like this video.

Full screen and volume up for best effect!

 

[jensen]

Nice video indeed, sound is great too. I saw it a few times, a few years ago and forgot how good the sound of that video is. When I was young I owned an RD350, the later water-cooled version with YPVS, and a Kawasaki KR1-s. The RD350 is long gone (sold it and it's not registered any more), but the Kawasaki I still own. I would like to make a video like that, but then with the CB450 K0, the CB400f and my Kawasaki Kr1-s (no doubt that the Kawasaki would be faster with it's 63 HP), but the CB450 and CB400f have to dogfight for second position.

Sounds of all three bikes are completely different, but all a lust for the ears (to me).

 

[Tracks450]

What a great thread. Awesome work Jensen.
I have a HP question though, Is there a difference in the way HP is measured on European bikes vs Canadian bikes? Or are the Canadian ones just higher HP? With the numbers you quote on page one, (I know my Kawasaki numbers are much higher) but my CB450 K1 Hellcat shows 54 HP on the brochure below. Even the 350 Sport shows 40 HP.

 

[crazypj]

DIN and SAE HP figures are different. The original brochures used Japanese horses though, much smaller than 'normal' ones so you get more

 

[jensen]

Today we did break in the engine on the dynojet, and adjusted the carbs (sync and air/fuel mixture). As you can hear and see in the movies, the engine is doing well after the total rebuild. No strange sounds, no overheating and no oil where it doesn't belong.

No measurement of torque and HP jet, first I have to break-in the engine in the coming 1000 km.

https://flic.kr/p/2oi9FKa

https://flic.kr/p/2oi9FLT

 

[ancientdad]

Nice to hear it run finally, it sounds good.

 

[LongDistanceRider]

Looks real good and sounds better

 

[Richard Pitman]

That looks really great, I'm envious ..

Regarding horsepower figures, brochures over here refer to PS, as in 20PS for the CB175. A tongue in cheek Bike journalist suggested that PS stood for ' pretty small ' , although I actually think that is something to do with the German word for horses, Pferde, if I remember my 'O' level German correctly.

 

[ballbearian]

Sounds perfectly smooth and even. Carb synchronization is impressive. Were the carbs that good from your careful assembly, or did they require further adjustments?

 

[jensen]

Yes and no. Synchronisation was more or less good when we started, but the mixture wasn't. But if you start chancing the mixture per carb, the synchronisation will change too. This iteration, going back and forth from left to right and back, took us an hour.

 

[Maraakate]

Did you use an EGA to adjust the mixture? I have an older two gas unit coming my way next week, itching to give it a try.

 

[jensen]

Did you use an EGA to adjust the mixture?

I don't know what you mean with EGA, but I guess it's a mixture measurement tool, and yes, we used a tool like that to measure the COx, NOx, Air/fuel ration etc.

 

[ancientdad]

I don't know what you mean with EGA, but I guess it's a mixture measurement tool, and yes, we used a tool like that to measure the COx, NOx, Air/fuel ration etc.

Exhaust Gas Analyzer

 

[jensen]

Exhaust Gas Analyzer

Yes, we used this to analyse the exhaust gases, however, after 1000 km we have to do it again because the engine has to "set" while breaking in.

 

[jensen]

Maiden trip today ! After 12-13 years the bike saw the road again. It's so much fun to ride that little 4. Some pictures :

 

[stl360+450]

I'm glad to see this! We've had a cold March in my area, but I'm happy to see others enjoying the start of a new riding season. It should begin here soon and when school shows down in May the wrenching season will begin for me, too.

 

[ballbearian]

Love the first pic, the old and the new(ish) together. Glad it's as much fun to ride as to look at. Nice work.

 

[jensen]

Thanks gentlemen ! Did I mention that the bike is a pleasure to ride I'm starting to wonder if I will ride the twins so much this year.....


Next project in my little workshop:



The CB450K1 candy sapphire blue parts are ready for painting, and since these bikes share the same colors, I took this bike to see what parts should be painted.
For now, the only parts that are candidate are the headlight holders and one side cover. The rest of the paint work is in good shape, it's only original once ...

 

[Maraakate]

Maiden trip today ! After 12-13 years the bike saw the road again. It's so much fun to ride that little 4.

Great work Jensen!

 

[LongDistanceRider]

Maiden trip today ! After 12-13 years the bike saw the road again. It's so much fun to ride that little 4. Some pictures :

Looks great and it has to feel great to get to the finish line.

 

[jensen]

Looks great and it has to feel great to get to the finish line.

Yes, it does. One of the hardest restorations I did. For wrenching, singles and twins are more my thing, for riding a small agile four is preferred on faster roads due to comfort and the lack of vibrations.

 

[ancientdad]

Those 400Fs are great bikes, I wish I still had the one I owned in the late '70s.

 

[jensen]

Spring arrived !, the first 200 km's on the odo



Cleaning the left overs of my desk, and finishing the CD50-H Project.



Cleaning wiring and testing the electrical functions. Meanwhile fixing the front fork (both bend) at the machine shop.

 

[Maraakate]

Great work Jensen. Looks like you're having lots of fun!

 

[LongDistanceRider]

Still looking good there, wish spring would pop here.

 

[jensen]

The last 30 Kg of re-plated hardware. Part from the CD50-H, SS50, PC50, CB450 and CB400f. I hope my memory doesn't fail me (luckily I made picture before bringing away the parts). This time I added all the yellow pasivated parts (mainly carburation and electrical hardware). Costs are relatively low, just 50 euro for the whole bunch. The hours I spend to re-cutting threads, cleaning, polishing, and fixing JIS bolts not counted.....

 

[LongDistanceRider]

The hours I spend to re-cutting threads, cleaning, polishing, and fixing JIS bolts not counted.....

:lol:And the hours spent sorting out what goes to what now that everything is pretty.

 

[jensen]

And the hours spent sorting out what goes to what now that everything is pretty.

Pictures in groups of parts before, including a ruler, makes it relatively simple.....




CB450 group 1



CB450 group 2,

All parts in the boxes are pictured like this, 30 kg's on parts makes give or take 60 pictures (including detail pictures).

Original and correct hardware is difficult to find, I always do my best to save every bolt, nut etc. I re-cut the threads with high quality tools (cutting also cleans the threads) If a head is damaged, I repair it, either with a file or on a lathe with milling head.

 

[LongDistanceRider]

Smart man! That's really the only way to do it. I went thru the same thing doing the CL, clean each and every piece, tap and die nuts and bolts, file heads, etc. Fortunately I was only dealing with one bike.
It's getting cost prohibitive here now since the local place is doing "barrel" pricing, $300 for everything that's in a 55 gallon oil barrel. No more small batches. I need to look around for another shop.

 

[jensen]

This long weekend (due to Kingsday), I reached the first 1000 km. Replaced the oil and filter and checked everything today (loose bolts, leakage etc). However, it's not running as it should, between 3K-5K rpm the engine doesn't run perfect. One header pipe is a little hotter then others, so I think I have to wrench again. I have to work on the engine anyway, since the head bolts needs to be re-torque-ed, taking the carbs out is just an extra point on the list while I'm in there.

Since the issue's are between 3-5K rpm, the issue is complex. This area of rpm has three major influencers, being the stationary jets, the float height, and last but not least, the throttle slides cut-of. Needle hight is ok, because it picks -up good from 5K to 10K. I'll start with chancing the float height and increase with 2 mm and go from there. Giving the engine more fuel in that region, will also interfere with the stationary mixture, so the mixture has to be changed as a result of that. that also will fix the header pipe temperature, because I think the major reason for that is uneven float heights.

Changing the stationary jet doesn't solve much since it's running perfect between 1.2K - 3K rpm mixture is good too. Changing the needle height doesn't fix it either, since this is the area that the needle is straight. Changing the throttle slide cut-away, thus changing the throttle slides is difficult, try to find them !

 

[LongDistanceRider]

2mm float change is a rather large one.

 

[jensen]

2mm float change is a rather large one

Yes it is, however, the issue's around that rpm era are also big. I have to close the choke a few % to get a workable mixture, we guess that represents close to a 2 mm float high, based on my opinion and from my dyno-friend. It also depends on how much difference I measure between the float heights between the carbs. If the float high difference is large between nr.2 (blue-ish header) and the rest the float height difference will be set less then 2 mm. However, I cannot imagine that I introduced such a difference while assembling the carbs.

 

[jensen]

1900 km's and counting. I took the bike everyday to work, every day at least 120 km, plus "extra" km's taking the long way home. Next week I take the CB450 K0 out again, otherwise it will get jealous.

 

[Richard Pitman]

Lovely looking bike. A chap in our bike club back in the day had a brand new blue one just like yours, I was very envious. First thing he did was to remove the stock silencer and replace it with pattern 'Dunstall Decibel' pipe, cut and welded to give it an upswept angle. Sounded ( to my teenaged ears ) very nice ..

Not sure if this is the bike in question, this is a photo I took back then.

 

[ballbearian]

View attachment 21754

1900 km's and counting. I took the bike everyday to work, every day at least 120 km, plus "extra" km's taking the long way home. Next week I take the CB450 K0 out again, otherwise it will get jealous.

What an interesting photo.

 

[stl360+450]

I have to work on the engine anyway, since the head bolts needs to be re-torque-ed, taking the carbs out is just an extra point on the list while I'm in there.

Will you need to pull the motor from the frame to retorque the head?

Changing the throttle slide cut-away, thus changing the throttle slides is difficult, try to find them !

Would it have been easier (possible even) to find alternate throttle slides for these carbs at the time of production? Hopefully the float height adjustments will fix the issue in any case.

 

[jensen]

Will you need to pull the motor from the frame to retorque the head?

No, but I have to make room for that procedure by disassemble a few things like gas tank, seat, coils, horn, clutch cable, rev cable and cylinder head cover. I also plan to take the clutch cover off to see if everything is ok. Oil pan re movement is also a subject of the job.

Would it have been easier (possible even) to find alternate throttle slides for these carbs at the time of production? Hopefully the float height adjustments will fix the issue in any case.

Yes, after market (and maybe Honda) throttle slide were made for the tuners, all history now. Float height adjustment will make it better, the real question is "how much better" ?

 

[jensen]

After breaking in the CB400F, and put it on the bike lift for the earlier mentioned work, I took the CB450 K0 to work today. I was forgotten how agile this bike is compared with the "lump" CB400F, and I love the availability of torque compared with the CB400F. Earlier measurement show that the CB400F and the CB450 have more or less the same power, but the way it's delivered is so different.


On the way back I had very heavy rain for an hour, but the bike brought me home !

 

[stl360+450]

I'm surprised the difference is so large that you would use the word "lump" to describe the CB400F, but it's interesting to hear your comparison. Riding the two bikes in close succession and on a familiar route makes for a nice test. I guess you don't expect the planned float height adjustment to substantially change the calculus on this head-to-head comparison?

 

[jensen]

Re-torque the head bolts, check cam chain play, check how the parts set-in.



All wet from oil, that's good !



New parts did set nice



New camshaft has no visible "hot-spots" where force is higher or lower, all bearings are showing more or less the same pattern, that's good.

 

[LongDistanceRider]

Looks good Jensen.

 

[jensen]

One of the most annoying things to do on a four, particularly a small four, are taking the carbs off the bike. Even worse is to put them back again. I managed the get them off, using a heat gun and a lot of patience. Set the floats 2 mm higher, and perfectly equal, now time for putting them back :lol:



Picture is taken before adjustment, the two middle floats are set a little higher to compensate for the cooling factor (My dyno man was suggesting this, and with his experience with those bikes, who am I to dispute that). Standard setting is 21 mm, when I took them out I measured 22 on the two outer floats, and 21.5 at others. Measuring the float height is very difficult, so I made a stand at my work to make it more simpler and more accurate.

I thought I had put them on 21 versus 20.5, but measured on the stand, it clearly showed that the height wasn't right. Now I did set them to 20 mm for the two outers, and 19.5 mm for the the others.

 

[stl360+450]

Did you bench synch the carbs after removal or will you use the previous position as the baseline after this change to the float heights?

As far as the inner/outer carbs, I assume the idea is that the inner carbs will provide a richer mixture to compensate for the fact that the inner cylinders do not dissipate heat as well. Will this be noticable in terms of the header temperatures? Would the goal be to end up with all of the cylinders running at the same temperature?

 

[jensen]

I will use the previous positions, until mid June, then the bike is ready for the final adjustments after breaking in the first 2000 km after rebuild. Yes, it is to compensate the lack of dissipation of heat. Only the mid-range is compensated for this, no needle height differences or main jet differences. Using the bike in the city often, mainly using between 1/8 to 1/3 throttle, no speed, thus hardly any wind to cool down the engine, it is suggested to make an adjustment only in this region. It will has some effect on the higher rpm,'s but hardly noticeable. At stationary the adjustments of the air screw will compensate for this.

In the old setting, this area was lean, engine got really hot, especially the two mid downpipes (blueish) compared with the two outer downpipes. I hope it's equalised now.

 

[LongDistanceRider]

Sounds like you're on the right track here. Hopefully the 1mm increase will be sufficient so you don't have to take them off again.

 

[stl360+450]

Is the CB400F still on the lift?

Addendum: A question occurred to me based on my current project, a CB350. The question is about the side plate for the rear sprocket, which seems to be part of the original Honda design for the CB400F and was added to the CB350 apparently in it's final year. Do you know the intended purpose of this side plate?

I went back through this thread and found a post that shows your rear sprocket. It seems that your rear sprocket doesn't have the side plate and was made in France. Was this the sprocket on the bike when you purchased it or a replacement? I have been assuming that your bike is a German model, so I would guess this is a replacement.

 

[jensen]

Hi,

Yes, the CB400f is still on the lift, but I didn't found time to work on it yet. Went to a customer in the US for 3 days (Kentucky) and to Greece as a gift for to my youngest son as he finished high school (gymnasium) by visiting ancient Greek mythological places for a few weeks. Yesterday we came home, this week I will put the carbs back.
The rear sprocket is a replacement, and indeed, the original sprocket has the side plate. I have a few aluminium rear sprockets, the aluminium sprockets are ready for laser cutting the holes in, but time....

I have a few side plates which I will combine with the aluminium sprockets, then everything seems to be as it should.