Low compression numbers on new rebuild?

[GSXRolla]

I don't have a damn clue what is going on here. I followed the proper break in procedures, and this is what I've got. 160, 165, 165, 165 compression numbers. It would seem ok except for the fact that I rebuilt this thing with 2g pistons. Shouldn't the compression numbers be up there around 180 or so? I finally got this thing running, and now I'm dealing with low compression numbers.

I put a teaspoon of oil into cyl number 1, and did a wet test. 180psi. Any ideas? Does it sound like the rings didn't seat right or what? This is pissing me off. There's only about 5 miles on the whole thing. I don't have a clue where to go from here. Would the 15 psi be worth stripping this thing down again to rehone the cylinders?

 

[espinelli]

Would the 15 psi be worth stripping this thing down again to rehone the cylinders?

I would try Lucas first. When you did your compression test, did you make sure your car was properly warmed up, pull out all the plugs, disconnect ignition, and floor the gas pedal before turning it over?

 

[Sk8er07999]

A friend of mine has a newly rebuilt 6 bolt with 2g pistons that has the same compression. hmm...

 

[jott5555]

if everything is going ok with the engine no smoke ect... i would run it after a couple hundred miles retry it. with only 5 miles the rings havnt even come close to seating..

 

[Darksyne]

Definitely make sure your throttle is open all the way. If you didn't open it all the numbers would read equally low.

 

[92awddsm]

It takes more than 5 miles to seat the piston rings. Try a hundred or so miles with light to moderate throttle pressure and little to no boosting. Then recheck compression.

 

[GSXRolla]

Yeah, I followed the compression steps to the letter. When I tried it w/o WOT, it measured around 150, 153, 155, 155. After I went WOT, it bumped it up into the 160's. I'm assuming that I need a bit more time to let the rings seat, like you guys are saying. But I also remember someone saying that after a hard break-in, that the rings would be as seated as they ever would.

What do you mean, try lucas? Lucas on the cylinder walls?

 

[espinelli]

When I had low compression on my old motor I mixed a 3/4 quart of Lucas with my oil changes. My compression ratios were very low and on top of it 1 of the cylinders were off by 15-18psi.

Basically, it helped stabilize and make my CR consistent across the board as well as raise slightly raise my CR.