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Discussion Starter · #1 ·
I have a CB400N with a rattle that follows the revs. Local mechanic said it probably was the stabilizer chain that had some slack, and just "ignore it". As long as it does not wreak havoc on the engine that part is fine, but it's loud enough to be annoying. Common problem I guess, but I would prefer to not have it ticking away like that.
Easy fix or more complex for a four stroke novice? I have a lot of experience with two stroke engines, but four strokes are new to me.
Could this be rectified without splitting the engine, or am I looking at a bigger job here?
 

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The top of the chain guide and the tension spring is accessible under the head but the bottom pin is tied into the crankcase.

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You will need a Honda full service manual . What 01-7700 shows is the timing chain and it can be adjusted by loosening and tightening the screw on the head under the carbs . Part # 10. With the motor at idle loosen the bolt and let the chain self adjust. The balance chain adjuster is under the right side cover. The manual will tell you how to adjust the balance chain. You might need a gasket for the cover and it might be the time to change the oil and filter since you will have to drain the oil to remove the cover. You can remove the seat and tank then the valve cover and see the top of the timing chain and sprocket and the tip of the slides and maybe see if something is wrong. You will have to split the cases to get to the balance chain. Some of the 400 motors have an access port to get to the balance chain adjuster but I dont know if yours does.


Bill H
 

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DO NOT adjust cam chain via the bolt ten in the head. This bolt should be tight, do not shear it off, it's a 6mm bolt, 10mm af.

Adjust the cam chain via the nut on the back of the cylinder below the carbs, part 11.

If your bike where mine....

Seat and tank off. Cdi removed so it's out of the way.

Flywheel cover off, mark with tipex, F ( fire ) and T ( time, tdc, top dead centre ).

Remove cam cover with gasket, a bit of a juggling act but there is a sweet spot.

Inspect the valve springs, yellow marking up. Check cam loves. Lots of oil in there ?

Set flywheel to T, the engine runs anticlockwise looking at the flywheel.

Look at the cam sprocket from flywheel side. You see the two lines on the sprocket, they should line up exactly parallel with the cam cover cylinder head sealing face.

Take some pictures to show cam timing at T, and cam loves/valve springs etc...

Now, turning flywheel back and forth a few degrees, much "sloppp" or play in the cam chain ?

How much cam chain lift is there on the cam sprocket ?

I assume cam sprocket bolts and head bolts are tight ?

You have a manual for torque settings ?

To auto adjust spring loaded cam chain adjust system, position flywheel to T, slacken the adjusting nut and watch auto adjust happen.
Nip up nut and tighten, do not shear it off !

Repeat flywheel back and forth movement a few degrees, much play or slop ?

How is chain lift now ?

Check valve working clearance with feeler gauge, cb400n,

Internet being a pita, pm me your email address...easier using email today....
 

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Cb400n valve clearances, cold, 4 inlet and 5 exhaust, that's thou.
From memory the 250 was 5 and 6 thou cold, but will check later.

Pictures of cam area, perhaps we can spot something.

Any evidence of sealer at the front of the engine in the middle, or oil leaks there ?

Balance chain.

You should see a relatively large slotted plug close to the rev counter cable ?

Using a good fit washer, undo this plug. You will see a 12mm af lock nut in a slotted arm. Any slot left at the top ?

Engine cold and stationery, slacken the locking nut. DO NOT drop anything inside the engine !

The arm is spring loaded and should automatically rotate anticlockwise. It may be suffering from "sticktion" and need some excercise.
When it auto adjusts, nip up the lock nut.

Any slot left at the top ?

Looking thru the hole, at about 2 o clock, you will see a 14mm self locking nut. The threaded end protruding thru the nut has a "dot" which is a bit difficult to see, but not impossible.

Using a clock face, what position is it in ?

Engine stationery, using a long thin probe, with practise you can "feel" slop or slackness in the balance chain.

Looking thru the hole, looking thru the slit between casing and main bearing ladder casting, you will just about see the balance chain, but this takes practise.

The spring loaded arm is repositionable on its shaft, but clutch cover etc. off for that pita of a chore.

So, cam box area for pictures and what position is the dot ?

Any "lean back" on the cam sprocket timing marks ?

Noisey cam chain, balance chain and clattery vales is not good ?

Do not put these chores off, or oil and filter changes.

Engine done about 35k miles ?

How long you had this bike ?

The 400's are better than the 250's, more get up and go.

The 250's are great on back roads here in Snowdonia, Wales, UK.

You know of CMSNL for the very informative exploded views ?

Get a manual with wiring diagram.

Take your time, don't break anything, those cam cover bolts, and enjoy...
 

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Notice the dot.....

So, with slit lock nut right, slacken the 14mm shaft nut so it can be removed, then remove the 12mm slit nut, and the dot nut.

Remove the arm.

Let the system self adjust.

Where is the dot now ?

Picture shows dot at about 1 o clock.

If dot moves to 9 o clock, you have problems.

You will see the balance chain thru the slit between c/case and main bearing ladder.

When you remove the clutch cover, flush out the engine with low pressure spray. Crap will be seen on the sump floor labarinth.

Where the kick start would be you will see an oil trough that will have crap in it.
 

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Suspicious...

When was that picture taken and why did he show it to you ?

Green cyl base gasket, so has this engine been apart ?

Awaiting cam area pictures and dot position as it is now...
 

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Discussion Starter · #11 ·
It was one of a ton of pictures on the ad when I bought it. It was a picture of a clutch change I think. I have the complete service history on the bike. It has been owned by a Honda collector/mechanic before the previous owner (who only had it for 2 years). Carbs, brakes, clutch oil changes, new chain + sprockets and so one have been done at regular intervals. It runs smoothly and it starts like new every time. The only "problems" I have with it is the rattle and the neutral light not working. Everything else seems to be in perfect working order I have a spare gasket for the clutch cover, so I can remove it (just have to get some new engine oil and filter first).
 
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