SOHC.co.uk Forums > CB350/400

400 four whistle

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Piki:
I open this thread to see if someone can help me, the issue is the famous "whistle" or "reverse" sound that many 400Fours have. Through a Facebook group, someone commented that the problem comes from the primary shaft pinion when its teeth wear out (it is the pinion that meshes with the clutch). That sprocket is no longer available and I had to buy it in a store in Japan, this weekend, taking advantage of the oil change, I changed the sprocket but the problem was not solved, the annoying whistle continues to sound......does anyone know where is the problem really?
Thank you in advance.

Oddjob:
If the pinion gear is wearing out then surely the gear on the back of the clutch would wear at the same rate? so maybe both need changing?

I can't remember ever hearing this sound BTW, so is it present when the engine is ticking over or does it only appear when the bike is rolling as knowing that should point to what it's not and maybe what it is, for instance, if you run the bike up to 30 then shut off the engine does the noise continue, (pull the clutch in to disengage or put into neutral) in which case it's on the drive/gearbox side of things, if it stops with the engine stopping that points to something either on the clutch or before the clutch.

I have heard final drive bearings make that noise when they've been overstressed with a really tight chain but not on the 400.

Deano400:
Ken / Diego. What are your thoughts on this? Something in the back of my mind from 40+ years ago to do with an overtightened cam chain. Done by loosening the lock bolt and using a screwdriver down the top hole to push the rod down. Maybe take it with a pinch of salt as my memory is terrible, as you know Ken.

Athame57:

--- Quote from: Deano400 on September 13, 2023, 04:25:24 PM ---Ken / Diego. What are your thoughts on this? Something in the back of my mind from 40+ years ago to do with an overtightened cam chain. Done by loosening the lock bolt and using a screwdriver down the top hole to push the rod down. Maybe take it with a pinch of salt as my memory is terrible, as you know Ken.

--- End quote ---
This happened to me as well. I would describe it as a sort of whirring sound rather than a whistle though.  :-\

Oddjob:
That’s a good point John. Turning the engine off whilst running should point towards if it may be or not. Well remembered

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