Low compression on a total rebuild top end

[Jake]

I have a 1980 CB 750 I acquired a couple years ago. The engine only had about 120 pounds per cylinder so I rebuilt the engine new pistons 823 Wisconsin and had to cylinder head with all valves redone. All work was done by a professional machine shop. Did reassembly with All punch marks and locations exactly as specified now I only have 125 pounds for cylinder. I warmed the engine up approximately 1/2 hour still reading 125 pounds per cylinder. I am coming up with low compression and also on the vacuum side. I am reading late valve timing. Can the crankshaft chain stretch enough where it would give me these issues and if so can I slip the crankshaft chain one tooth without having to split the lowercase.

 

[dirtdigger]

Did they set the valve clearances for you? Get adjustable cam sprockets if they are available then you can time it correct with a degree wheel. Are you sure your compression tester is accurate?

 

[Jake]

The valves were set at 5° for the intake and 7° for the exhaust. I don’t think they make an adjustable camp sprocket for the 1980 hopefully I’m wrong. I went and bought a new gauge to put on my compression tester just to be sure and they both come up the same number as they did before the rebuild I do believe my chain that goes from the crank up to the cam is stretched out because all marks exactly where they’re supposed to be. I also bought a new cam chain that goes from Cam to cam still the same issue low compression and lead valve timing.

 

[dirtdigger]

I dont understand you valve numbers, valve clearance needs to be .005" to .006"

 

[Jake]

.005 on the intake and.007 I need your trust what I am trying to simply explain even with the.003 to .005 that I had previously before the rebuilt I still had low compression and also had a late valve timing on my set of vacuum gauges and now after I rebuilt the top and completely with new patient every done valves, I still have the exact same issue