Hey guys I had a quick question. I haven't really messed with my Z lately, but one thing that crossed my mind that I had forgotten about was awhile back after allowing the Z to idle for a while and get warmed up I did a compression check. My compression came out 150 for cylinders 3,4,5, and 6.

Cylinder 2 was 130-135 and Cylinder 1 was about 140-145. I think the gauge I used reads high, but the car idles and revs up seemingly fine. It does pop if you rev it up quick and then let off, but it also has no exhaust on it. I have yet to actually adjust my valves, so I went today and started checking clearances. All of the cylinders with 150 compression I was able to fit my .007in feeler gauge under when the cam lobe was pointing up, some a slightly tighter fit than others. Cylinder 1 & 2 the clearance was much tighter and I couldn't get the .007in blade to even fit between the cam lobe and the rocker arm.

I don't think my lower compression in those two would be any sort of headgasket issue as it seems to idle and run decent, plus it wasn't smoking or overheating. I had about 17inHG of vaccum at idle when warmed up.

What do you guys think, can having the valve clearance be too tight cause a loss of compression? Can it have the intake valve stay open longer or not close all the way?

Sorry for the noob questions, but I'm still pretty new to alot of the valvetrain stuff.

 

i suppose it is possible. but i really doubt it. that be tough to achieve. and is this a hydraulic head? if so shouldn't you not be able to take clearances on it? cause the hydraulic lifters move by pressure under them, one might just be sticky but doubt it could keep a valve from closing. something else is up with that 130-135 cylinder that's not so good, not a disaster but not so good. the 140-145 is nothin to worry over yet.

 

This is a solid lifter P90 head. I changed the head. Then put an n/a cam in it. Could that indicated a problem with a headgasket though? The compression between those seems too high to be a headgasket. Plus the readings were very consistent. When I get a chance and actually remember to bring the right tools I'm going to adjust those valves and see if that makes a difference. I mean it seems like if the clearance is alot smaller than it should be the valve would open earlier and also close earlier, which you'd think might leak and have a loss of compression?

 

welll... usually in a HG case and theres no oil/coolant burning then its a bad HG between two cylinders, but then the two cylinders sharing that bad seal in the HG would have closer lower compression readings. i'd say more likely a ring or valve seal. re-do the tolerances and try again. also bring an oil can with you with some motor oil in it. then you can squirt some down in that very low compression reading cylinder n take the compression reading again. if the compression reading goes up its bad rings. if no change in the compression reading its a valve or headgasket problem.