A little background on the engine:

Over the summer we pulled the 305 out of my 88 Iroc and built up a 350 we got off of craigslist with a top end kit and a freshened up bottom end(bearings, gaskets). The 350 was out of a 1987 van. The build went pretty smoothly, except for finding out that the pistons were not a standard size. They appeared to be an 18cc bathtub looking piston, and the standard replacement oil rings did not fit, so we re-used the original oil rings(the engine looked brand new on the inside, visible crosshatches and no oil gunk buildup, maybe only 20k miles?). The top end was an Ebay kit, all Erson/PBM parts which fit together pretty nicely. 200cc aluminum heads, 230/230 cam, knock-off air gap, and a 600cfm vac-secondary carburetor.

After a few months and about 700-1000 miles on the engine, I can say it pulls pretty nicely and has great top end power, but we started getting plug fouling on 1, 2, 3, 5, and 8. We pulled the intake and found oil seepage on 4, 6, and 7. Solved those with a new gasket, but the car still smokes. It's a white smoke, gas/oil smell only on startup and initial idle.

I did a compression check and I get 170 across the board.

At first it sounded like valve stem seals, but they are new aluminum heads that we're assembled in the US by a speed shop.

I then did a leakdown test, and I got 55%, and 45% after squirting oil down the cylinder(yes, it was on top dead center). I was able to hear the air through the dipstick tube. I've only done it on #1 cylinder so far.

My question is, is it ring related or is it leaking through the head gasket into an oil passage? I did use the original oil rings with new compression rings(probably the cause of this mess), but is it possible to get 170 cranking psi with 50% leakage past the rings?

I also used a thin metal gasket to increase compression. Maybe the block is warped, and it's leaking through an oil passage? My coolant is clear and uncontaminated. So far, it's used about a quart of oil after changing out the break in oil.

Thanks for your help,
Brian

 

oil burning can only come from a couple places, such as the rings and valve seals. Is the speed shop reputable? Sometimes even the best speed or machine shops make errors. Honestly, the fact that you reused the rings makes me think that they aren't sealing properly to the cylinder walls. My worn out 305 smokes exactly like you say and my diagnosis is both bad valve seals (bad quality new gas destroys them) and the rings being worn out, just due to regular wear. I'm by no means an expert, but check the simple things first, like maybe a bad PCV valve? excessive crankcase pressure can cause those symptoms. Is there any blowby with the oil fill cap off?

 

A compression test is not really testing the worthiness of the oil rings. Neither is the leakdown test (which makes me think the test was performed incorrectly to get those high values). My guess is the oil rings are shot OR the intake gasket is still leaking.

 

Absolutely 100% not true .

 

Questions:

About the piston rings. It's not clear in your post; you re-used the original oil rings....what did you do regarding the two compression rings?

The pistons were not standard size; how much over sized were they? And did you measure the cylinders and compare these measurements to see how much actual wear there is?

 

I apologize if that was wrong, I always thought that ethanol in the new gas (at least around here) damaged the seals. That's what my engine builder said, maybe he misspoke or I misunderstood him.

 

maybe that person meant valve seats if your running older heads like double humps you have to have the vale seats redone and hardened or the new gas will eat them up

 

Worn valve guides will cause this also. And it will also mes with your leak down test results. I would redo the test again and go from there.

 

Did you see the engine run before the rebuild? Go out and run it wide open twice with someone following you. If it's the valve seals it won't smoke much cause they leak under vacuum. Rings leak under load. I had a local guy redo a set of heads for a sbf and if turned out he didn't even have all the tools to do it right and it smoked good but only on startup and idle. If it needs rebuilding it would be a great excuse to ditch those garbage dished pistons, and I would never run a metal gasket without decking the block.

 

Rings are the item that makes the engine seal, never rebuild with used rings. We all learn I guess.