1500 mile on rebuild.. still low compression

[98GSt_4life]

i finished my rebuild a wile back and im having truble figuring out why my compression isnt going up yet? is is a stock rebuild. 2g pistons stock rods rebuilt head, decked block cometic HG.... i did install a new clutch with the rebild so the first 500 miles i was really easy on the engine. but after that i still did the basic breaking, in 2nd gead bring it up in rpm then let the engine slow the car back down, and repeat each time raising the rpm.

i now have 1500 miles on the engine and drive it normaly but my compression is only at 150 across.. i was thinking it would be more like 180.. i check the compression every week with the engine fully warmed up and the throttle open fully charged battery.. its stayed the same every time i do it. the only time it was different was when the engine only had 100 miles on it, and it was 175 across.

 

[Jeff_Ciesielski]

It could be possible that your rings didn't seat right. The first 100 miles are crucial when it comes to the rings setting in. The last 2 rebuilds I've done were broken in by driving it like it was stolen for 20 miles or so, then normal driving. 155 across the board ( 1g ).

 

[98GSt_4life]

well ive read other threads and it seems some people break there engine in hard and some dont, so i figured it wouldent hurt to break in my clutch the right way, then the engine

 

[98GSt_4life]

also the pistons are standerd size, and the block was honed... if any of that matters

 

[1gcrazy]

Hmm.... I always thought you would have issues with compression if you used the std piston like that. I guess we'll find out if its true. I can see the rings filling the gap but wouldn't that kind of stress the rings?

 

[98GSt_4life]

Hmm.... I always thought you would have issues with compression if you used the std piston like that. I guess we'll find out if its true. I can see the rings filling the gap but wouldn't that kind of stress the rings?

no, there new pistons, but i was just saying that ther are stock mitsubishi 2g

 

[Jeff_Ciesielski]

Being that its a solid 150 across the board, I doubt that its headgasket or valve related, but I could be wrong. Just for the hell of it though, have you done a leakdown test?

 

[95tsiawd6blt]

the compression is equal across, your fine, dont test it drive drive the damn thing

 

[Sharadon]

Do you know any of the spec's on the cylinders. Like actual size. How far out of round the cylinder is. (assuming) because you only mentioned honing the cylinders. and using stock pistons. Ring end gap. Piston to wall clearence.

Un hook your pcv and look for blow by. If you have a lot. it's the rings.

It takes longer to brake in the rings with a used bore (even with honing) because the cylinder is still slightly egg shaped and the new rings are round trying to be egg shaped.

Not saying this is your problem. Don't have enough info.

 

[AKGEN1DSM]

As long as they are all the same you should be fine, but my recomendation would be to go to Napa, buy the silver can of RESTORER and run that with a fresh oil change. That might help seal the rings better. Did you lap the valves when you installed them? I don't know the specs on the HG you used but is it the stock compression? Just my $.02

 

[98GSt_4life]

Do you know any of the spec's on the cylinders. Like actual size. How far out of round the cylinder is. (assuming) because you only mentioned honing the cylinders. and using stock pistons. Ring end gap. Piston to wall clearence.

Un hook your pcv and look for blow by. If you have a lot. it's the rings.

It takes longer to brake in the rings with a used bore (even with honing) because the cylinder is still slightly egg shaped and the new rings are round trying to be egg shaped.

Not saying this is your problem. Don't have enough info.

the pistons are standerd size 2g mitsubishi

my shop told me that the cylinders were almost perfictly within spec and all i needed was to hone it out.

the rings came pre-gaped

if im getting blow by though the pcv that means the rings just havent set yet right?