High Crankcase pressure after complete rebuild ; what went wrong ???
 

I had a buildup done on the 1970 BB Coupe a couple years back with an Edelbrock Power Package and Total Seal Ringset.... and while the power increase is phenominal, the rear main seal started leaking from almost day one , even with a correctly functioning PCV . After trying different rear main seals, the problem continued to occur . He assures me that the motor/trans are properly aligned, and there is no vibration whatsoever. The block was sent out to be bored .060" over , honed, and cleaned . The Mechanic who did the rebuild has done many in the past and had several Corvettes in the family .

The performance is MUCH to my delight and estimated at 550 gross h.p. (up from 390 stock) and im somewhat reluctant to have the motor teared into again .

. Is it likely the rings didnt seat properly / or were incorrectly gapped ?

Thanks for any insight.

Have you done leakdown or compression tests?

:iagree: do a leak down test. pull off the PVC while the motor is running and rev it up. See how much blowby you actually have. I can't imagine a refreshed motor building so much internal pressure that it pushes the gaskets out.

How many breathers do you have on the engine? Most high perf. engines will need one breather per valve cover instead of a pcv valve.

Leak down and compression checks would be another good idea.

I have heard of stock 5.0 ford engines n crown vic's blowing out the rear main because the pcv's were getting clogged.

I'm voting on it being a main cap/crank issue. I couldn't imagine crank case pressure pushing a rear main seal unless there was no breathers at all.

I run a pcv and a small chrome breather ony 496" with no issues at all....and I race it often.

throw away your pvc set up and go with breathers on the valve covers to the atmosphere....this is a common occurance with total seal rings...just call them and they will explain why....also it should have been with the instructions that came wit the rings......:cheers:

Ive tried a breather on each valve cover and i still get rear main seal leakage ; the oil ends up on the gearbox. Im going to try breathers plumbed to the Header Collectors for a cheap exhaust purge system. I may get a leakdown test done as well.

Thanks to all.

If you have twin breathers you do not have any crank case pressure.

Also header breathers only really work in a system that has no back pressure like uncapped headers. It just uses venturi effect to draw a vacuum. That doesn't happen on a mufflered full length system

Are you using the Total Seal rings again, with a gapless top ring or gapless second ring ?

i used the check valve off a brake booster in place of the PCv valve kind of a cheap vac u pan

It's hard to imagine you'd have enough blow-by on a fresh engine to blow out the seals and/or gaskets. A couple of questions:

1) Have you used the dye to diagnose the origin of the oil leak? "Dye don't lie". You may have a leak at the rear of the intake or rear of the valve covers that can look an oil pan gasket leak or real main seal.

2) What engine and which PCV valve are you running and to where does the hose go (vacuum source)?

2a) How does fresh air enter the crankcase? A breather on the other valve cover?

1. Havent tried Dye. Its definetely the rms as its been replaced twice now . (Didnt have the problem before the engine build) . No leakage from the valve covers at all.

2. 454 bored to 468 cid. Factory block. Dont know the brand of the PCV but it sucks good and vaccuum source is a big port at the bottom of the carb (Demon 800 cfm) .

2.a. Yes, breather on the other valve cover.

Im pretty sure its a TotalSeal gapless second ring.

You didn't mention much about the rear main seal. If the crank was originally set up for a rope seal it will have some small groove's in it and will tear up a neoprene seal unless they're machined off.

I've seen several new engines over the years with enough crankcase pressure to blow the dipstick out of the tube and push oil at almost every spot.
Good pcv was the cure, but these were pretty stock sbc's.

You can connect a vacuum gauge to valve cover opposite the pcv and test for pressure or vacuum, should be negative except at WOT.

Had similar issues with my (then) freshly built 489 - it was using significant amounts of oil - using atmospheric vents from each valve cover - didn't seem to have too much crankcase pressure - then found one of the culprits (dipstick tube not sealed into block - oil mist being pumped-out under car and burning-off exhaust. Cured that, then tried to cure constant oil weeping from valve cover breathers - so went to PCV valve set-up which helps drivers side oil weeping, but not passenger side - swapped PCV side to side & same issue on opposite side. Did some thinking and came to conclusion that as I am using 'tall' Brodix 'non-baffled' valve covers, with oil pressure that goes of the gauge there is a lot of oil being flung around inside the valve cover and I reckon the 'squirter' for one of the rockers ejects oil right underneath the valve cover vent. I intend riveting/welding some baffles within the covers over the vents and see if that helps reduce the problem.