how high compression should I be getting after a rebuild?

[kr.k]

I am on about 4K miles after a rebuild and I am getting 10-11-11-10 bar compression on my engine from right to left. Is that low or in spec? I have 8.5 pistons in there.

 

[Mike 99GSX]

I'd say thats a little low. Stock 2g compression is supposed to be 178 PSI and your looking at between 147-161. Everything should be plenty seated by now. Are you sure all your timing marks are right?

 

[92redman]

Well, that is low and I believe it is still in spec but those numbers are very low for a rebuild. Were the cylinder walls honed and checked for roundness and proper diameter? Also what piston rings did you use and are you sure they seated properly? If it were me, I would cut open my oil filter to see if there are metal shavings in there...

 

[kr.k]

Originally posted by Mike 99GSX
I'd say thats a little low. Stock 2g compression is supposed to be 178 PSI and your looking at between 147-161. Everything should be plenty seated by now. Are you sure all your timing marks are right?

Marks are ok but I am burning oil also. nothing major but a liter per 500 miles or so. Someone has told me that my engine is not worn in because I started using synthetic oil right aftre the rebuild. That the synthetic oil has too good oiling and the rings will not fit in as they are sopoused to in a very long time. any comments?

 

[92redman]

That may be a factor because usually you run cheap oil for a little while to break it in, but I would think even with synthetic, after 4000 mi it should be broken in.

 

[ecr1055]

what type of head gasket did you use? If u used a thicker or metal head gasket, that could of lowered your compression.

 

[kr.k]

Originally posted by ecr1055
what type of head gasket did you use? If u used a thicker or metal head gasket, that could of lowered your compression.

yes, I actually have a metal head gasket. how much would it influence?

 

[ecr1055]

can't actually give you an exact number. Was the head and block decked when you did the rebuild. Shaving the deck and head actually raises the c/r, but the metal head gasket is a lot thicker than stock. Most likely it is the head gasket. I mean does the car run ok and haul? If so there is no real complaining. What you said about the synthetic is true and not. Basic oil today is refined so much that it is relatively just as good as synthetic. The synthetic oil however will not break down and loose it's properties after time. Always use basic 30w motor oil for future reference. If the rings did not seat right, after 4k miles they are prolly f**ked, but you can run the motor at 2-2500 rpms for like 1/2 an hour, but at this point it prolly won't do anthing. Also, what foot lb did you tourque the head down to? Recheck the timing and if it is off, take the head off since you have to redo the timing belt and look at your intake valves. Let me know....