Topic: 1977 CB750 Project Gone Wrong

[rastocky]

So im looking for a point in the right direction with a project I've been working on for 3 years , so basically in a nut shell I have a 77 F2 motor with Carrillo rods and a set of dynoman 836 pistons. the problem im having is I can check compression when cold and it will average 180-190 across no issue Ill hit the ignition starts up no problem one by one every cylinder drops out with no explanation so I check compression with the engine had been running for about 5-10 min and I have less than 40psi all together. so I started with replacing the head gasket and redecking the head............. nothing. so then I thought maybe a valves were sticking so I did an entire valve job from guides to valve replacement and nothing at all same issue. now im stuck on deployment and debating on if I need to resleeve the engine.

[754]

I hope you checked valve clearance before teardown.
Anytime you get a cammed motor, check them and write it down..

[Don R]

 I'd look at the valve lash too, have you tried a leakdown test?  If it's valves you can hear it leaking through in the carbs or exhaust pistons you can hear it through the crankcase.
 You do have the throttle wide open for both tests right?

[madmtnmotors]

I hope you checked valve clearance before teardown.
Anytime you get a cammed motor, check them and write it down..

+1

Is the valve lash "tightening up" when hot? What valve lash are you using? What cam are you using?

[rastocky]

its the stock cam and im using the Clymer manual for the spec for valve lash I cant remember what it is off the top of my head. and I have tried a leak down test with no problems found there. the only thing I can think of is maybe if im not reaching for the stars here and the cylinder walls are cracked, and so once they heat up the crack expands.

I wish I had the bike in front of me but im not going to see it for a few months