my #1 cylinder has 215 psi compression and 10% leakdown. it all comes out of the #4 spark plug hole.

my #4 cylinder has 230 psi compression and 2% leakdown coming out of the crankcase breather.
cylinders 2 and 3 are 225 psi and 3% out of the crankcase.

wtf?

if air can get into the #4 cylinder from another cylinder, how cant it get into that cylinder through the #4? do i have a checkvalve in my crankcase somewhere or some ****? does this sound like a piston ring issue or a headgasket issue somehow?

its not smoking and i dont have a cat so i would certainly see and or smell it.

 

Gay-Lussac's law pretty much answers your question. Or maybe it's Dalton's law. I don't remember, it's one of those gas pressure laws. Your numbers seem healthy enough to not worry about it.

 

i know the numbers arent bad, but honestly this is a brand new motor with 38 miles. i was hoping they would start off closer. its pretty much an itr motor with an ls crank at this moment, with just under 11:1 static

the previous time i used this engine it scratched the #1 intake cyl wall and dropped 40 psi compression. it was the same exact scenario with the whole leakdown into the #4 cyl after that incident

since then it was machined .020 over and i dont remember the scratch still being there. the head was milled, the block decked. the pistons and rings are new. the hg (obviously) and the headstuds are new. ugh im just worried the machining didnt fix the issue or there is another issue somewhere

 

Man that sucks to hear. I'm trying to think of a way compression could make its way all thee way over to number 4 but idk. Could be a freak crack in the head or something.

 

thanks guys, im used to things in my life sucking so its no big deal anymore.

things im concerned with at the moment:
1- would the pressure from combustion go up into the #4 cyl and cause some kind of ring flutter or unloading that will be bad

2 - can it be said with certainty that the rings are the culprit for the leakdown leaving cyl 1.

 

Poor valve seal. Remove both manifolds and rerun the test to identify which valves are leaking.

 

ahh interesting. i know my seals are leaking oil. new guides are ordered but i know my machine shop will take months to do it. i guess i better order another of these dumb cometic gaskets not sure if i can make it through this without taking the head off...

 

Valve seal on the seat is poor. Changing guides is a major repair and will require full disassembly, seats should be cut with new guides! As long as the viton coating is not damaged I would use the headgasket again.

 

not that im trying to get out of this, but how immediate of a repair would you guys put it as? i have certainly driven motors with more than 10% leakdown out of a cylinder for long periods of time.

 

Cyl #1 and Cyl #4 are connected via the Intake Manifold...so if your #1 cylinder is leaking compression out of the intake valves and the intake valves in #4 are open (because of the part of the stroke they are in, then you may here air in that cylinder.

You would also here it coming out of the throttle body in this case as well

 

ok i am in the process of getting a new head together and rebuild with new guides. it was from the stock b16 that came in my em1 which had an even 210 psi and 5 ish %. it was just leaking oil from the valveseals constantly .it may take a while though im going to stop by the machine shop this week to discuss it.

would my #1 cylinder be the one i should look for the leaking valves in rather than both that and number 4. this would be more so since the air is not leaking out of number 4 from the combustion chamber, only through number 1 cylinder from the combustion chamber

 

was the engine at OT?

 

yeah pretty much. oil temp was in the 170's when i shut it down and began testing.

i guess im just trying to formulate an approach to fixing this head when the time comes.

 

alright, took off the manifolds yesterday and put 100 psi back in cyl#1. it is coming out of the exhaust valve on the right, closest to the timing belt. the other valve is sealed up. it must have been getting into #4 through the header. i also plugged in cyl#4 and it was 2-3% leak into the crankcase on a dead cold motor.

whelp, for whatever reason that valve didnt seal. i guess it could be worse like a ring issue or headgasket issue. i guess i will tolerate it until i get a different head or can get one of these stupid .040 thick cometic gaskets to my house so i can take the head off and re lap or swap out that valve.