seeing lower cylinder compression AFTER valve job- any ideas?

[Mn_Z_Man]

OK, so I did a valve job to fix a bent valve, and am seeing something weird- lower, but more even compression across all the cylinders. Before I was seeing 175 +/- 5 psi, now I am seeing 155-160. 2 ideas- valve timing is slightly advanced (2 deg on the cam), maybe due to new timing chain guide which is giving a slight inward curve to the tight side of the chain. My other thought was could the carbon buildup on the head and pistons have raised the comp by 15psi? It didn't look that bad, but I don't have much experience to judge by. Obviously its all cleaned up now after. Head was milled 0.003".

Valve lash are all properly adjusted, wipe pattern double checked and OK, cam OK, new Felpro gasket. Engine runs OK, maybe not quite as punchy as before. I've put on about 100 mi since the build. Some one on another forum suggested maybe the Felpro gasket having a larger cutout for the L28 engine, as they claimed to have had the same experience, but I can't remember how close the fit was.

I was hoping the compression would go UP with a shave and valve job.

Any ideas appreciated, thanks

Eric

[Walter Moore]

If the engine is running correctly, check it again in about 3000 miles. I have heard that sometimes it takes a while for even correctly machined valves to "seat" fully.

I don't know how accurate that story actually is, but I have heard it more than once.

[bigoak]

I assume, you did all compression checks with the engine at operating temperature.

[Mn_Z_Man]

yep, and throttle wired open