New to the forum

[cb750kjake619]

Hello to all the 750 fans, i have some well needed advice for my 1980 cb750k. I recently took the bike to a shop because it randomly does in my driveway from what i thought was a spark issue, the shop told me the spark was just fine on all four plugs, but my compression was low on all four cylinder. About 55-63 psi each. My biggest assumption was that it had jumped time, because it happened immediately, why else would it do that so quickly? I have taken it all apart, the entire top end. I found beautiful cylinder walls still with hone marks, and very clean pistons with almost new rings, this bike has 30k miles idt these pistons are original. Enough about the background BACK TO THE QUESTION AT HAND, both timing chains were tight to a point that i wouldn't expect them to jump especially when i was just sitting in neutral giving it about four little typical revs before it died and all this happened. I'm faced with the problem, 1. Do i put it back together right. 2. Buy a new chain tensioner, 3. Buy everything chain tensioner and chains. Also consider all the work that is for someone who's never done it, i won't bring it to a shop either to much money. THANKS FOR ANY INPUT!!

 

[amc49]

The engines are super easy to put together with the cams out of time and even for those who have done some engine rebuilding. As soon as the engine is whirled over with the starter then you bend all the valves. Almost impossible to jump time while running though unless tensioner loose or breaks, they commonly don't just jump on their own. If you didn't find bent valves then likely nothing was wrong there, compression testing is often flawed and needs to be done more than once and correctly before you rely on any numbers there. At 60 psi it should not have even started or run they are commonly pretty dead and/or giving problems at 100, normal is 170.

You will most likely fail trying to put back together with no experience and that work is not done well over the net at all. You MUST get a manual, the service manual is available online.

You may HAVE to shop it, zero skills doing that is most likely a disaster that hasn't happened yet but WILL.