Topic: Chain Noise From Engine Area?

[Justin]

During my ride this past week with the recently revived (been sitting in a barn) '75 CB400F, I noticed a fair bit of whirling chain noise emanating from the engine area (not drive chain noise).

Further reading on here seems to show that this originates from the cam chain.

What causes the noise?
Aren't the cam chains on these bikes of the self-adjusting variety?
If not, what needs to be done?

Thank you.

[78 k550]

Justin,
This was covered a couple times in the last months. You should come up with something in a search. The FAQ section also has a write up as per the manual.

Paul

[eldar]

THe cam chain is self adjusting BUT you need to loosen a nut generally for the tensioner to do its job.

[eldar]

This nut should be retighten after adjustment!

[nashvegas]

Justin

You have just discovered the Achilles Heel of the infamous CB400F.  I too had this problem (as well as hell of a lot others) but I was one of the lucky ones that still had a working cam chain tension adjuster bolt.  Back then I was able to tension is properly and it sings a little.  In fact you should get a little sewing machine noise out of the cam chain.  If you are not getting a really nasty noise out of the engine then it is not that big of a deal. However this is what you do.

If you look in the manual, there is bolt at the front of the engine above the oil filter canister with a lock nut.  What you do is get the bike warmed up and idling at 1200-1300 RPM, next you very carefully break the lock nut on the bolt (I still have a burn mark on my hand from slipping once and touching the header while doing this).  Next you gently back out on the bolt about ½ to a full turn and the mechanism inside will push a rod down and auto tension the cam chain.  After you have backed out, GENTLY tighten it back down but don’t over tighten it, then secure the locknut back.  If all goes well then consider yourself in luck.  However this is what normally happens, you back off the bolt and it just spins in place or the bolt doesn’t back out at all and has become fused with the engine case.  This is because the bolt is in the worst damn spot it could be where it picks up dirt, salt, squirrel blood, you name it. If this happens, you may make the situation worse.

I will mention that currently mine is a bit too noisy for my taste.  This happened after I rebuilt the top end.  I assume that using the specks to torque the head back on put enough pressure on the cam shaft to make the cam chain just a bit loose.  I tried tensioning the chain the dangerous way (email me if you want details) but that didn’t help.  So this winter I will be rebuilding the entire engine just so that I can replace all the springs and tensioner slippers.

The Moral of the Story, if your adjuster bolt still works, GREAT! If not, don’t force it and ride on it till you have the chance to fix it properly come winter.

P.S. Nice Bike!

Matthew

[Justin]

Wow...thanks Matthew!