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2G Head gasket thickness low compression

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1kick

5+ Year Contributor
84
17
Mar 27, 2018
Santa fe, New_Mexico
What's up guys! I recently had my block decked due to exhaust gas entering my cooling system. My head was machined a couple of times and is at the service limit. The machine shop said combined 26 thousands had been removed so I put a .075 thick head gasket to make up for the material removed but i think it might be too thick. I did a compression test today and it was reading 130 psi previously it was 150 with a factory head gasket. I don't seem to have much blow by but I wanted to know what you guys think because I'm going in for another tune in a couple of weeks.
 
so if the block and the head combined has .026 off, and stock gasket is .051 (compressed), your head gasket seems to be the right thickness. Did you re-ring the pistons or anything like that?
 
I had them do a hone, rings and bearings the machine shop gapped the rings I told him I was planning on running over 20 lbs of boost so he said he would gap them a little loose. The compression test was done 800 miles after break in
 
hopefully the rings seated properly.
did they do a plateau hone on the cylinders?
did you use the correct oil for break in?
did you constantly vary the rpms while the engine was warming up or i guess how did you break in the engine is a better question.

a leakdown test might be better than a compression test to check ring seal
 
Not sure on the hone but the cross hatch lines were pretty fine not rough filled it with 5w20 conventional ran it for about 20 minutes first 5 minutes revving it up a bit then 15 minutes of driving after making sure nothing was leaking the drive was getting up in the rpm range without boosting much and letting the engine slow it down changed the oil put 5w30 conventional and changed it again at 500 miles and re-torqued the head. The car was tuned a while back and I'm wondering if timing has anything to do with it I would assume when I had the factory head gasket on. The head was already at it's limit so the timing would have been retarded due to the distance from the head to the block right so if the tuner added timing ( I don't know if he did ) but it would be advanced now right? I'm also noticing my vacuum is low at idle its at about 14 I know I don't have any boost or vacuum leaks ( I had to fix them because of a high idle issue. Sorry if I'm going off track but I'm trying to give as much info as I can
 
sounds like you did a proper break in.

the tuner would change your spark timing. head gasket thickness and head/block surfacing would mess with the mechanical timing.

if you change the mechanical timing so that it increases valve overlap, it will lower your vacuum. so if you had adjustable cam gears you could increase the overlap by
-advanced the exhaust cam
and/or
-retarding the intake cam

if my math is correct (its not alot of the time) you've got a difference of + 0.002 compared to before the rebuild. I don't think that would change the mechanical timing enough for you to really even notice.
 
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