#1 cylinder low compression HELP!

[supreamS14]

My Sr was running 100% . I went to the track and on my 6th run I ran 13.5 @ 110mph like always, It was like 95 degrese out side and after the 110mph my car started to stumble a little. I parked and poped the hood. The valve cover started to leak on boost! I got it home, did a compression test (fully warmed up, all plugs out and WOT). #1=80 psi #2=155psi #3=155psi #4=149psi

I put a cap of oil in cyl. #1 and it went to 85psi . The weardest thing is IT DONT SMOKE! AT ALL!!! The plugs are dry and a good tan color. When I tested #1 cyl. it turned over faster than normal and sounded like the timming was off. I pulled the valve cover and everything is in place but I forgot to check if the cams might of skiped a tooth. when I melted a piston last time I switched it out, had the head resurfaced for a mls HG but the guy put all the rocker guides and shims in a bag. I know they go in by size but I dont know how to shim it proper. I put them in and it was running great before my 6th run that day. I know it could be rings or valve stem seals but wouldent it smoke? Maby a cam skipped a tooth? Im LOST!Im calling an SOS from you nico PLEASE do your MAGIC and HELP MEE!!!

[david200095367]

maybe your headgasket is sealing right in cylinder 1 anymore?

[supreamS14]

It could of knocked at the track even thow its a new Cosworth 1.5 mls HG with Arp head studs just cous it was sooo hot. Would a leak down test narrow it down? It must be leaking pressure in the crank case cosing the valve cover to leak. NO coolant or oil is being burned, thats what makes me believe its something in the top end. Thanks

Can Any one think of anything elts?

[sicairos_2007]

bad rings?

[supreamS14]

Wouldn't it SMOKE? Wouldn't the psi go up more when adding oil to the cylinder? Thanks for the help.

Is there anything elts in the top end that it could possibly be? Other than piston rings, head gasket and valve stem seals? correct me if Im wrong, dont these 3 things make the exhaust smoke?

[s13_silvia_redtop]

have you checked your headlaight fluid, when your low you tend to have less compression. jk i hope you find out soon.

[Hijacker]

Low compression can be caused by a number of things. Leaky valve seats or a damaged valve head would cause it without any smoking as there is no oil involved in those two pieces.

A quick and easy way to eliminate a holed piston or cracked rings is to pull the stock catch can and see if you have some extra air pouring out of the block tube.

Also, I've had pistons melted/holed in SRs and not smoke.

My money is on the piston or rings right now.

[supreamS14]

A quick and easy way to eliminate a holed piston or cracked rings is to pull the stock catch can and see if you have some extra air pouring out of the block tube.

Wow, thats a great idea ! That is probly why the valve cover started leaking oil on boost! I will try that tonight!

If there is no extra air from the block tube (piston or ring) then will there be extra air from the top end T if there is a valve stem seal leak? THANKS HIJACKER!

[Hijacker]

valve stem leaks typically don't affect compression. the reason why is because the valve has to be sealed against the seat to form a compression seal. You loose compression from the head because something has ruined the seat's sealing surface. This is usually due to the seat being worn down, which usually only alots for a few PSI, a bent/damaged valve, or a damaged seat.

Now, when those go bad, the leaky air goes back into the runners and out either the intake mani or exhaust mani (path of least resistance).

tl;dr, you will not see air come out of the valve cover T due to a leaky valve stem seal

[supreamS14]

Thanks Hijacker! That tells me that the valve cover gasket is leaking because of the rings/piston not sealing and boost is leaking pressure into the crank case. It looks like I will be tearing the whole motor apart for the 2nd time in 3 months