Motorcycle Repair: 1977 Honda CB 750 K7 w/31K miles, honda cb 750 k7, honda cb 750

Question
Hi Rich,
I have a fairly general question about cam chains. I just purchased the bike mentioned in the subject. I am not a motorcycle mechanic and it has been years since I've ridden motorcycles.  The seller of the bike did not disclose that the cam chain was in bad shape. I did notice a rattling noise at idle, but it went away at higher rpms so I ended up buying the bike (for $1,500). I knew it would need a bit of TLC and found a good shop who attempted to adjust the chain, but found that it could not be done. In an attempt to become more informed, what factors lead to the inability to adjust a chain and have to replace it?  Secondly, what do you think is a fair market price for replacing a cam chain (parts and labor)? Finally, how long can I expect the new cam chain to last, if interim adjustments are done? And is 31K miles a bit premature to have to replace a cam chain?  Thanks in advance for your opinions and information.  

P.S. the bike runs pretty strong otherwise, and does not use any oil (no smoke). I have read where the CB750 Fours were built to last up to perhaps 100,000 miles with proper maintenance. Your experience?

Answer
The 750 motors are good little motors.  I've seen them with a lot of miles but 100,000 may be a little beyond their reach.  With excellent maintenance, I suppose it could be possible. I'd be amazed of you have to replace the cam chain in 35K miles. Before tearing into the engine, loosen up the lock nut and pinch bolt. Remove the point cover so you can rotate the crank. Put an allen wrench or something in the end of the plunger housing where the tensioner plunger and spring are.  Then slowly rotate the crank backwards.  You should feel the plunger rod push out as you tighten the back side of the cam chain.  If it doesn't move the plunger rod is stuck and you just need to pull the tensioner housing off and free up the plunger.  I've seen those freeze up in their bore.  

If it does move freely, rotate the crank in the forward direction and feel when the plunger travels in to the furthest point and then lock down the pinch bolt and lock nut.  Don't over tighten the bolt or you run the risk of breaking off the bolt and that's bad. You can even put a little pressure on the plunger to overcome any friction in it movement.  Just don't put to much pressure or you will over tighten the chain and it will wear out faster.

Let me know if that doesn't fix your problem. If it doesn't, I'll tell you what's involved with a camchain replacement.

Regards
Rich