Ok so i have this motor noise(scraping/grinding)that sounds like it is coming from the top front of the motor. Im assuming cam chain or tensioner or cam related... Before I order and gasket and tear the top off the motor etc.. i was wondering if somone on here can give me a better step by step instruction of how to adjust the tensioner on a 1981 cb750k obviously the DOHC. Video would be ideal, pictures would be great but ill settle with a step by step directions. Ive heard that if you do it wrong the tensioner will fall into the block causeing me a major headache. I cant figure out what im doing wrong with my research but I personally dont like the manuals way of explaining and people online are saying different things and confusing me. You people have never set me up for failure so I come here again for an answer.
Thank you for all who answer.
Army Combat Vet (Iraq 2005-2006) 4th Infantry Div.
1981 Honda CB750k
Scraping and grinding are not good noises. I had a similar problem with my 79 model. In my case, the cam chain from the crank to the exhaust cam would never tighten up. At idle, it made more noise than I liked. The chain between the two cams was fine.
After the long cam chain broke (sad story, to be read elsewhere), the teardown revealed the problem. The long cam chain adjuster was worn through the plastic part. This meant the chain was running metal to metal. The slop was so bad, it made grooves in the head where the chain ran up and down. I have a pic of it somewhere. Needless to say, the motor was repairable, but would have cost too much in parts and labor. So I parted it out.
If you have to replace it, I recommend you get the Factory Service Manual (found in the Manuals link on this forum's home page), and read up on how to inspect/replace it. I believe it'll call for removing the engine from the frame, and at the very least, pulling the head.
Good luck, and keep us in the loop. I'm sure we'll be able to help if you need it.
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
fyi - you don't necessarily need to replace the gasket. If it's still in good condition it can be reused. If you're going to use gasket sealer on the dimes (I found it made no difference) make sure you use the flexible kind and don't use too much.
Also, you don't need to take the cover off to adjust the tensioner. If you do take it off, make sure you check the valve clearances at the same time.
One other thing to watch for - do NOT over tighten the valve cover bolts. It's easy to do using just your hand. Use a torque wrench. Even with a torque wrench the threads may already be damaged and tightening it to within spec could be enough to strip them.