About the thousandth Rebuilt engine burning oil question...

Frankensteinteg

New Member
Ha..Ha...funny story. I didn't gap the rings...

My reasoning is that the the cylinder walls are worn, from the engine having about 300,000 on it, the diameter of the cylinders were within spec mind you, but at the edge of it. None were out of round my more than a thousandth or so.

This is the first motor that i have rebuilt.

The NPR rings that i used were standard size bore, and did not state that filing was required (i know that some things need not be said, and should be common sence, but bear with me)
 
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Muckman

Not a M0derator
Ok so the ring gaps are likely loose if the bore is large. I cant believe you'd check the bore but not the gap. Anyways, what was the bore diameter?
 

Frankensteinteg

New Member
I measured the bore and not the rings soley to determine if the bores had been bored out to oversize. Thats a good point mind you, and that possibilty didnt occur to me , although i never wrote down the figures, i believe the largest was 81.15mm, or so and the smallest was a hair under 81mm (probably a carbon build up where i measured.)

Wouldn't the compression test show if the rings were loose enough in the bore to cause an issue? Seeing as a compression test would show the sealing ability of the 2 compression rings, without the aid of combustion gasses forcing them against the cylinder walls?

To me, if the rings were loose, wouldnt they not fully seal? meaning that i would have a low compression figure, and a substantial, and almost immediate leak down of that pressure? (the leak down was minimal to none after 45sec of leaving he cylinder pressured up.).

I appreciate your help with this btw.
 

Muckman

Not a M0derator
.15mm is a large spread. Thats .006" between the largest and smallest bore. That difference alone would equal .019" in ring gap difference. A block with this many miles should have been bored to the next largest size to make everything square and consistent. Sigh

Anyways the compression test is consistent, somehow, albiet low. Id expect it in the 180s for a lower compression LS motor. Yes its a new motor but you have 100+ miles on it so the rings are broken in. Compression test really only shows the top ring seal therefore it has nothing to do with burning oil as thats the middle ring and oil rings.

Honestly you dont have much of a choice at this point if you've ruled out the head. Run it and hope it seals up with more miles.
 


Frankensteinteg

New Member
Well, being that its my first complete tear down and rebuild, doing 90% of the work myself, I think that its an achievement that it even works, haha. But, thanks for your help, ill keep you posted. I just drove it again. Overall, it really does seem to be improving, power wise, and oil consumption. ill re check compression after a few hundred more miles.
 

white4d96

Burning oil like a boss
My oil-burning LS with 180k+ on it comps at 200-210 across the board. Unless you're running 8:1 pistons, something's not right. Do a leakdown test and see where your losing compression.
 


Frankensteinteg

New Member
Did a second compression test after about 175 miles this time.

I've been beating fairly hard on the motor in straight line pulls (basically like a 16 year old kid after watching Fast and Furious) to force the rings and other components to seat, and i have noticed that this has made the engine feel a bit more responsive, and, by the "seat of the pants dyno", seem a bit more peppy as well.

Compression has also increased, And the oil burning is not quite as prevalent, although it is still present.

#1 - 165 PSI
#2 - 162 PSI
#3 - 168 PSI
#4 - 171 PSI

All 4 cylinders seem to hold their respective pressures, as I don't have a leak down tester, the best i can do is watch the gauge on the compression tester to see it if drops, which it didn't for any of the 4 cylinders.

Despite the issues I am having with oil being consumed, its hard not to feel some sense of accomplishment when im able to rev a motor i have re built myself in each gear to nearly redline down a country road, that only weeks ago i was holding those very pistons in my hands.

I am optimistic with the improving figures, and am expecting the numbers to increase a bit more, as more miles are put on the engine.
 
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