Compression test / Piston re-ring

[yeyo_racing]

Ok guys, I recently finished the break-in on my engine and last week I decided to do a compression test on it. Numbers are very low. Cylinder pressures range from 100 to 115 . I used dino 5w-30 oil with 3oz of Lucas Zinc Plus additive on every oil change during the 3000 mile break in period.

I think the rings are shot. The engine it's a 2.8 iron head with forged slugs std size running on 6 pounds of boost. I used Hastings moly rings on this previous rebuild.

My question is should I use moly rings again or regular rings on the next re-ring? I have read that moly rings shouldn't be used on worn cylinders. Anyone has more information regarding this? Bear in mind i'm going to do the honing myself so I won't be able to check cylinder roundness.

I already bought a set of Speed Pro Moly rings (E-411K) but I'm thinking of using the non-Moly version (E-411X) from Speed Pro. I want to be able to use this engine reliably while making good power until my next build. I'm planning to do a 3.2 DIS setup with the 7730 ECM for next year.

Also, should I break-in the rings with the turbo hooked up or without? How do guys with boosted engines perform the ring seating procedure?

[yeyo_racing]

Anyone?

[pocket-rocket]

If you want to break in without the turbo, up the wastegate so it opens sooner. Knowing that cylinder pressure that works its way behind the ring helps force it out against the cylinder wall, I would probably want to break it in with a little boost, but not a lot.

[yeyo_racing]

Does 6 psi sounds too much? What about using Moly rings vs Standard Ductile Iron rings? Any preference for turbo applications? Can Moly rings be used on worn cylinders?

[pocket-rocket]

IIRC, ductile use a rough cylinder surface for oil retention and moly use a smooth surface because they have a rough facing to use as oil retainers. They say moly need almost no break in because of this in the blueprinting book I read not to long ago, but I don't know about using moly in a worn cylinder. It might be a better idea to call your local machine shop on that one.

As far as 6psi, that's when you go WOT, so you shouldn't see 6psi at the break in period since you won't be going WOT.

[Joseph Upson]

I've heard they take longer to seat than standard rings. Whatever the case make sure you use the right stone roughness to prep the cylinder bores. I believe I made a mistake there on my recent engine build along with some other bad things. Oh well, do it right or do it over.

[trotterlg]

You can tell if the low compression is from bad rings by putting about a tea spoon full of engine oil down the spark plug hole and cranking the engine over a few times before doing the compression test. If it is not higher with the oil then it is not the rings. Larry

[yeyo_racing]

Trotterlg,

I didn't tried that because I didn't want to damage the Wideband O2. But just by looking at the numbers you can tell something is not right and I'm almost cerain it's the rings. I noticed that the vaccum at idle dropped from 18 hg to 15 in the first two months or so since I started the engine. Today it's at 13 hg, so it's been dropping.

I think it was my method of break-in that fussed it. The car was running pig rich the first time so it might have washed the cylinders while running it. Also, I did a couple of WOT runs once I got the engine partially tuned, mixture was all messed up. In theory, the engine went from light throttle runs to 3/4 - WOT runs, nothing in between to set the rings.

Pocket-rocket,

I'll ask my machinist to see if he measured the cylinder bore for this previous build I did. Either way, I won't be taking the block to the machine shop this time. I will be rebuilding the trans and re-ring the engine in one weekend, so I won't have time to take it to the machine shop for measuirng or honing. I've been reading that 320 to 380 grit is what is recommended for moly rings. I'll be doing 400 grit with regular three stone hone (not flex hone).

I have one more question. Has anyone used ductile iron rings with forged slugs on a boosted build?