What was your compression after a rebuild?

[AWDlaserRS]

What was your compression after a rebuild? I ask because mine is quite low, 135,125,125,115. I plan on doing a leakdown test to pinpoint the cause.

 

[Echo5Zulu]

By the book turbo should be 165 and non turbo 195. My non turbo engine (I have a turbo kit on it though) made 195 across the board. Could be lose rings or something. Valves not sealing? That is quite low though.

 

[AWDlaserRS]

I know , its pathetically low. I think Im gonna have to pull the head off again. This time Im gonna have it pressure tested to make sure there are no leaky valves. im also going to recheck the ring endgap clearance, maybe I mismeasured before or something. First however Im gonna find somebody with a leakdown tester because that will save me some time in figuring out the cause.

 

[half-cocked]

How many miles do you have on the rebuild?

 

[GalantGst]

I would wait atleast 500 and before u take it apart Like u said I would do a leak down first to pin point the problem.

 

[AWDlaserRS]

Its got about 80 miles on it so far, It just seems like the numbers should be higher than that even if its not broken in yet.

 

[UnityDSM1]

My engine read well into 130's before I reworked the head, now it is mid 150's across. It's most likely the valve's but like they said Leakdown test should be done...

 

[half-cocked]

Wait until the engine has passed its break in period then do another test.

 

[anomalyinva]

Wait until at least 800 miles for the first test. It should come up another 20-30psi.

 

[Mr96GSX408]

My engine was rebuilt by the guys at Mitsu and when I did a recent compression test I had 145 on all four cylinders. Maybe they didn't deck the block correctly or the head gasket is too thick?

 

[1fast97gsx]

I tested my compression on my new motor after 250 miles. It was 185 across the board. This is on a 9:1 motor. I believe your compression should be pretty close to where it will end up staying after the first 50 - 100 miles.

 

[AWDlaserRS]

The head was redone with all valve seats reground and the valves were lapped. Maybe they did a lousy job or something. Will the compression really change that much over the break in period on theses engines?

 

[1fast97gsx]

not significantly. If your valves aren't sealing then driving it for 1000 miles or so and checking again won't fix it. Rings will seat after the first 50 miles or so IMO. I doubt your compression will change a whole lot from where it is now.

 

[AWDlaserRS]

Thats what I thought, looks like I have more work to do.

 

[DJpHGotBanned]

What cams do you have?

 

[AWDlaserRS]

stock cams

 

[TargeT]

quick question...


the car was at operating temp when you did this right?

 

[notractiongst]

also check your timing and how long are you letting the motor crank over for and make sure the throttle plate is open

 

[TSIfreek]

Also check your camshaft timing. Both dowels should be pointing upwward when the crank arrow lines up. What is your engine vacume?? If you didnt have any valve work done to the head as far as a basic valve job I would highly recomend that at least with new valve seals and bronze guides. One of these two are likely your problem.

 

[AWDlaserRS]

Yeah the car was at operating temp, Ill let you know the vaccuum after I do the leakdown test today because I dont remember what it was. There was valve work done to it, the seats were reground and the valves were lapped. Also there were a few exhaust guides that were bad that got changed. I got all the parts together to make a leakdown tester today, I just gotta put it together now. Ill update later with my results.

 

[AWDGrayBird]

I don't know man 50miles after my rebuild mine was 130 all the way across. But i also have 272 and with the over lap I have heard it will read about 30-40 psi lower not sure though. :thumbdown

good luck

 

[Turbo Talon DL]

After my FIRST rebuild..my compression was 190psi accross the board after about 10 miles

 

[1fast97gsx]

awdlasrerrs - any update?

 

[greathuskie]

mine was about 200-210 all the way across....

im on an 9:1 comp pistons though

 

[AWDlaserRS]

Okay, heres the update> I did the leakdown test, by the way the engine was at operating temperature. It apears that the head is not leaking at all or too little to detect which Im kinda glad about as Ive paid...... damn ... alot for the work done to it. Its losing compression past the piston rings because it was blowing alot of air out of the crankcase when I presurized the cylinders. The headgasket is fine, no air was lost into the cooling system. I did discover my oil cap leaks though . Oh I redid a compression test with a different tester and it read a little bit higher it was 137 137 127 137. And the vaccum was -20psi at idle, according to my boost gauge.