with a 638 4 bolt main sb350 , I rebuilt boring 40 over and decking at .020. This engine does not pack performance until I run it for a while.. The usual Spark Plug fouled up in cylinder 7 from Oil deposits. Its noticable in the rear when you step on it..
I did a leak down and pressure test of all the cylinders. TIGHT compression at 190lbs/ square inch.. The problem really is the consumtion of oil and performance degredation after about 2-3 weeks. I mess up o2 sensors as the oil just cakes the sensor being located right underneath the cyl 07 .. So Under hard excelleration it burns out the oil in the cylinder and clears up,, then stopping at a light and idling it developes the oil.. Making me think its Valve stem seals.. But I have brand new Seals installed. Looking hard for things like Why ? I wondered can reversed installed Picton rings do it ? or the bottom intake port leaking on hte manifold gasket.. ? Is the stem pushing over enough to create an opening large enough for the oil to get sucked in ?
Also this engine seems to push oil up the dip stick tube..Not under serious presure but its not a perfect seal.. and the Valve cover with the filler cap also always shows oil coming out of it.. Any diagnostic help or thoughts on where to narrow the search down to would help.. thanks in advance
Hank- 1989 iroc t-roof manual t5 350 TPI. AFPR 24Lbs INjectors, Custom tuned PROM, zz4 roller cam design, 7cc KB120 hyperU pistons, Total Seal rings, upper instake plenum hogged out, Ventury throttle body Air foil, MAT sensor relocate, MSD IGN system , under drive pulleys, 11.35lbs flywheel . 3" cat eliminated flow master exhaust

 

i'd guess the intake gasket leaks

 

What ring gap did you measure for the top and 2nd compression rings during assembly? Did you have the machinist do the finish honing on the cylinders?

Some amount of blowby/consumption during break-in is normal, so I only get worried if it continues past the first 100 or so miles.

You can check for intake gasket leaks as Ed mentioned by either pulling the intake, or removing the TPI runners and using a flashlight to look down the intake at the heads' intake ports...oil present there indicates a likely intake gasket leak. If you pull the intake, be careful removing the gaskets so you can inspect the crush points where the heads and intake compressed them.

 

What kind of valve guide seals does it have? If they're O-rings or umbrellas, and the guides weren't replaced or sleeved, they're inadequate.

Try a set of FelPro "positive" valve guide seals.

With Total Seal rings, end gap is not really a factor. Failure to seat could be though, but it doesn't sound like that.

Sounds more to me like the heads didn't get as much attention as they should have, and inferior ineffective seals were used besides.

As far as the pressure in the crankcase, how is your PCV routed?

 

I was wondering this too.

 

Whoops, didn't catch that he used zero-gappers...

In my very limited experience w/ Total Seal rings, the final honing is even more critical than w/ regular ductile iron/moly rings. Two engines is the depth of my knowledge, but both had to be torn down and re-honed because the darn rings wouldn't break in and seal.

Cranking compression tested fine, but leakdown test was hideous on both.

We never got to the root cause, just called the local machine shops and hit one that said "Oh you're running Total Seals, bet you're having trouble...we have the right honing stones for those." and that was it. Also used Marvel Mystery oil instead of 30W engine oil for cyl wall and piston assembly lube the 2nd time around, at the machinist's recommendation. Happy customers resulted in both cases, engine oil at the end of the boating season was visibly cleaner (not black like the rest of the fleet).

 

I've got one right now not sealing with gapless.
But on the other hand, there's no mention of any head work sitting on top of the fresh block.