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CB400T

Regarding the coil.
As of a couple years ago DSS was selling a coil with high Primary resistance for the SOHC's, 1.1 ohm or higher. S I would check that, it should be .8 or lower.
I would also check the Secondary resistance.
Are you using the NGK XD05F plug caps? With D8EA or DR8ES plugs?
I would guess at Yellow to Black w/White and Green to Black. Technically this style of coil doesn't care which goes where but I don't know about this aftermarket version.
Brass in the oil:
I can't recall any brass or bronze anywhere in this engine unless there's a bushing on one of the gears, it's been years since I was into the trans.
What worries me is the foreign material and the kickstart issue. When the left rod bearing goes the engine will turn over by hand most of the way and suddenly lock, rotating backwards gives the same condition. I would pop the left case cover off and both plugs out. Using a wrench or socket try turning the engine over 2-3 revolutions. I really hope I'm wrong here.
 
Hello Mr Rider
As much as I am pained by this, I am equally pleased to be heading towards a diagnosis.
With the stator cover off, rotating the engine by hand (to find TDC and set valve clearances) the stator drum rotates for almost a full revolution then hits a stubborn, hard to turn patch. It can be turned at this point, but with significantly extra effort. In either direction.
If this is bad news, so be it.
I am philosophical about it.
What does this mean and what’s needed?
Thanks again
 
Sounds just like what Jim described, which probably means it's actually a good thing it never started for you. The ugly sound of a bad rod bearing would have been all you'd have heard.
 
Hello Mr Rider
As much as I am pained by this, I am equally pleased to be heading towards a diagnosis.
With the stator cover off, rotating the engine by hand (to find TDC and set valve clearances) the stator drum rotates for almost a full revolution then hits a stubborn, hard to turn patch. It can be turned at this point, but with significantly extra effort. In either direction.
If this is bad news, so be it.
I am philosophical about it.
What does this mean and what’s needed?
Thanks again
You have the classic spun left rod bearing, caused by someone riding without checking the oil level first.
Minimal repair is a fresh crankshaft, 1 rod, all the rod and main bearings, gasket set, rings x2, etc. Usually cheaper to replace the engine. Any of the SOHC CB/CM400 or 450 manual transmission engines will bolt in and work. Don't get confused with the earlier DOHC CB450 engines, those look different and won't work.
 
I've found an engine
It looks right to me
Grubby, but the right engine?
Claims to have been set aside a couple of years ago as part of a planned, then panned refurb project
Claims to have done c14k miles
Claims to turn easily by hand
It's local to me
I can go and prod and fettle before handing over the cash
Any tips?

2.jpg1.jpg3.jpg4.jpg
 
Regarding this:

I would guess at Yellow to Black w/White and Green to Black. Technically this style of coil doesn't care which goes where but I don't know about this aftermarket version.

Both DSS and Rex confirmed that it doesn't matter which way round the wires go
As you said
Thanks

I've also asked DSS about this:

As of a couple years ago DSS was selling a coil with high Primary resistance for the SOHC's, 1.1 ohm or higher. S I would check that, it should be .8 or lower.

No reply yet
I'm sure that they will reply
 
I've also asked DSS about this:

As of a couple years ago DSS was selling a coil with high Primary resistance for the SOHC's, 1.1 ohm or higher. S I would check that, it should be .8 or lower.

DSS said they didn't have the technical datasheets, but offered assurances that as they sell many of these (without return or complaint) AND fit them to their own bikes without problems, i can be assured that the resistance is fine.
 
That engine is the early version CB400, may be a 5 speed. The right side cover doesn't have balancer chain adjuster access. Clutch adjuster says the clutch is in place and wasn't worn out.
Take your shift lever and front sprocket with you. While turning the front sprocket you should be able to engage all the gears to tell which.
You might take your starter, +bolts, jumper cables and battery with you also so you can check compression. Dead cold I would be hoping for 150 psi.
Needs a good bath and here's hoping it's a good engine.
 
Thanks Mr Rider
Our bike is an early 78 CB400T so it might be a like for like swap?
I’ll do as you suggested regarding gears, starter etc.
Hoping for some better luck.
Trying very hard not to let this experience drag me down
 
New old engine is here
Taken apart
On the bench
Is there a bottom end flush I can or should do before fitting it?
It’s free of oil
I drained the old mucky stuff
All the top end parts are off
 
The only thing you can safely do to clean out the old cruddy oil would be to tilt the engine and add gasoline or kerosene thru the drain plug, @1 quart, then put the plug in, let it down and let it sit for a day before draining again. Other than that it's frequent oil changes with filters for the first 500 miles. You cannot put any kind of engine flush into the oil and run it.
 
Update

I have taken the top end bits of the "new" engine

I have taken the top end bits of the engine that's on the bike

I've been comparing the equivalent parts

I have a question about the rocker arm assembly

On the original engine, both rocker arm assemblies have springs

On the new / old engine that I picked up late last week, only the left hand rocker arm assembly has springs
The right hand one has no springs at all

Photos attached

Which is correct?

Rocker arm assembly no springs on right.jpgRocker arm assembly springs both sides.jpg

Also....


And this is a head scratcher..

The original engine
The one in the bike
The one that turns by hand (using the stator rotor), bit sticks at every rotation, needing some extra effort to budge it
The one that's almost impossible to kick start

As soon as I'd taken the top end trio of parts off
As soon as the pistons were flapping loose in the breeze, but still attached to the con rods

It turned freely
By hand
Using the stator rotor

Might the sticking-on-every-rotation have been something else?

I had replaced both pistons and piston rings with aftermarket products
Might they have been utter garbage?

That wouldn't explain why it was an *rse to start before I changed the pistons and rings though
And why it was a b*gger to kicks start before the new pistons and rings either

The pistons in the "new" engine are original Honda pistons
Clean them up and buy original Honda piston rings (they're far from cheap) and try again?

In the new or the old engine

My head hurts

But I have beer

And you lot

So it's not all bad

Thanks in advance

Elwyn
 
The rocker assemblies should have springs. Easy fix.
I wasn't aware of the new pistons being installed prior to the engine binding up. It's hard to keep track of every thread at times.
So the engine freely turns with the cam/rockers removed. This could be that 1 valve was sticking open or cam timing was wrong. Has the head lifted slightly after turning the engine? If so that would indicate a valve was sticking open since the piston would push the head up on contact.
 
The rocker assemblies should have springs. Easy fix.
I wasn't aware of the new pistons being installed prior to the engine binding up. It's hard to keep track of every thread at times.
So the engine freely turns with the cam/rockers removed. This could be that 1 valve was sticking open or cam timing was wrong. Has the head lifted slightly after turning the engine? If so that would indicate a valve was sticking open since the piston would push the head up on contact.

Rocker assemblies will go back complete with springs

The pistons and rings are new
As are the valves and valve stem seals
Valves gently lapped in
All move freely

The head hadn't lifted, no

I've ordered Honda piston rings to replace the aftermarket piston rings
The aftermarket rings felt rubbish
They looked oversized
They're not oversized
I wondered whether they were part of the problem

I'm still enjoying the experience
 
While you're waiting for the rings flip the head upside down and fill the combustion chambers with acetone. Then inspect the intake and exhaust ports for signs of leakage. No leaks mean a good valve seal, leaks mean a bad seal or possible slightly bent valve.
 
Replaced the bottom end of the engine with a “new” one.
Replaced aftermarket piston rings with Honda piston rings.
All back together.
Still won’t start.

Recap:
CDI replaced
Coil replaced
Starter solenoid replaced
New plugs and ht leads
New regulator / rectifier
Heated grips fitted (for a bike that never goes out!)
Stator rewound
Starter motor bushes replaced
Carbs stripped down, cleaned, some parts replaced, all following LDR’s guide
New top end gaskets
The three top end parts were cleaned up
Diameters, bores etc measured, checked. All ok
All service manual torque settings were followed and applied.
New valves and valve stem seals
Timing is right
Valve clearances are right
New oil and filter

It started a few months ago with the “old” bottom engine with easy start / starting fluid

I haven’t tried starting fluid again this time.
I’ve read a few things online that advise against it.
And references to starting fluid achieving combustion under pressure only, ie not needing a spark, so limited as a true test.
Possibly nonsense.

It kicks over
The “old” bottom end engine was pretty much stuck.
Almost impossible to kick over.
Equally difficult to turn using the rotor.
The “new” engine turns with the rotor.

The electric start turns the starter motor

Spark plugs are sparking
How powerful is the spark?
No idea.

It just doesn’t fire up

Not even a splutter

The petcock was replaced 2 years ago

Fuel runs through and out of it but it’s not what you’d call a gushing flow.

Fuel is getting into the carbs

It used to run with the current petcock.
It was always difficult to start.
But now leaning hard towards impossible.

I think that sums up where I am

No progress

Wallet lighter

Less skin on my knuckles

Any questions?

Better still, and ideas?
 
Last edited:
Let's go with basics. Valves adjusted, correct NGK plugs, stator resistances are in spec., fuel is fresh. Don't bother with compression since it'll read low until the engine starts breaking in.
There's no reason not to give a shot of starting fluid, doesn't take much. It's possible that the carbs have created an air lock in the jets/passages from sitting dry and just need a good suction/vacuum of the engine firing to clear.
 
Update
Progress
Of sorts

The engine started

I tried it with a squirt of easy start first

It did nothing

Well, not quite nothing
It made one bloody loud bang
A small-ish puff of black smoke came out of the right hand silencer

I left it for a while

I changed the spark plugs again

I drained the fuel and replaced it with higher octane fuel, fresh out of the pump this morning

The bike started

It ran at c4000 revs

I assume I need to fettle with the carbs to get that down?
One screw to adjust idling speed?
Then balancing

I switched it off after a minute or two as it became clear that the earlier loud bang had blown a crack in the exhaust collector box

On closer inspection, it looks like the collector box had been repaired in the past, with today's crack opening up an old wound

I've found an aftermarket replacement on ebay (uk) for c£99

It feels like progress

I hope so

Thanks for all the help and suggestions to date

Regards


Elwyn
 
Great news!
Did you bench synch/balance the carbs? I got mine pretty close by looking thru them at the sliver of daylight at the edges of the throttle plate.

Your power chamber/collector may have been plugged. Mine had a ton of rust dust in it. I tapped with a hammer to get out what I could then soaked it in a large bucket with white vinegar and cheap toilet bowl cleaner for a day. Then I rinsed it out with lots of water with a garden hose. Then dried it out on top of my Kerosene heater before I spray painted it with barbeque paint. Alot of them have been tossed out and run without them, but they do run real good the way they were designed.
 
Hello
It’s been a while
Work and my car project
Anyway…

The bike now starts
The exhaust is fitted with no blowing

However….

It runs at 4-5k revs
Straight from cold
And when warmed up
No change to the revs

The choke makes no difference either
Either with the plunger pulled fully out or with it pushed in
It runs at c4k revs

The large balance adjuster screw on the carbs (sorry, not sure of it’s official name / description) also has no effect

With the engine running (at c4k revs) I turned that large black plastic adjuster screw head in both directions, hoping to see the revs go up / come down

It made no difference

The revs might have gone up slightly when turning in one direction, but when turning the other way, the revs stayed at c4k

No lower

Any thoughts, suggestions, wise words?

Thanks in advance

Elwyn
 
Replying to an earlier question:
Yes, I balanced the carbs on the bench following LDR’s guide.
Including holding the throttle plates up to the light for the new moon sliver.
I expected to have to do more at this stage
 
Sounds like the balance adjuster screw is misassembled. There are 2 washers that go on either side of the aluminum bracket.
201_4644-002.JPG

Or the fast idle cam linkage on the right side of the left carb is stuck.
 
Hello

Thanks for the help again

The balancer adjuster screw set on my bike has only one washer
The CMSNL website parts assembly diagram thing, plus their product listing also shows only one washer as below
The diagram is very poor quality, but it's clear enough to show where the 1 washer sits

Idle adjuster diagram spring and washer parts photo.JPGIdle adjuster diagram spring and washer.JPG

Or am I looking in the wrong place?

Regards

Elwyn
 
That picture is the main idle screw and yes there's only 1 washer. Look at my picture again, it's the linkage screw between the carbs for setting the sync that I'm talking about
 
Or am I looking at the wrong screw set / washers?

This one has two washers
Screw set with 2 washers 3.JPGScrew set with 2 washers 2.JPGScrew set with 2 washers.JPG

Also from CMSNL

Which should I be adjusting to reduce the revs?
 
The main idle screw is supposed to adjust idle speed. When the balance screw is assembled wrong it hold the right carb open so the main screw is doesn't work.
Your picture shows the balance screw assembled correctly so I would be looking at the choke fast idle cam on the left carb for being stuck. I know :cry: it means pulling the carbs out again.
 
The main idle screw is supposed to adjust idle speed. When the balance screw is assembled wrong it hold the right carb open so the main screw is doesn't work.
Your picture shows the balance screw assembled correctly so I would be looking at the choke fast idle cam on the left carb for being stuck. I know :cry: it means pulling the carbs out again.

Is there a way of checking the choke fast idle cam in situ?

i pulled and prodded, rotated and simulated all moving parts before reassembly

Everything worked / moved / returned where required fine

I don't mind taking the carbs off
I quite enjoy it
But only if I have to !
 
If I pull the choke plunger out and push it back in and I can see the cam rotating and returning, ie doing its thing...is that enough to tell me the choke fast idle cam is ok?
 
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