350 sbc oil leak

[YoSammyT]

I just finished a rebuild on a 1990 sbc 350 roller motor mated to a 350 turbo tranny and put it in my 1978 280Z. I probably don't even have 100 miles on it. 

I have a difficult to find oil leak. No leak at idle, but after driving it it will leave a puddle under it, and it smokes from oil slinging on the header when driving. So, I put the car up on stands and let it sit and run for around 15 minutes. Again, there is no leak at idle when hot or cold. No noticeable leak at 1,500 rpm either. However, if I rev past that it drips very noticeably from the bottom of the rear main seal housing. Some of the drops hit the outside edge of the fly wheel which slings oil on the header and up in the transmission housing.

If I rev the car up a few times to 4,000 rpm or so and then quickly get under it, I can actually see it leak several (7 plus) drops of oil, then it stops leaking.

I had two breathers with no PCV, but they pretty quickly became saturated with oil, so I utilized a K&N part that vents the valve cover directly to the side of the air cleaner and I'm not using a PCV valve, just a straight vent to the air cleaner on both sides. 

It's my understanding that a one-piece rear main seal... 1. typically doesn't leak 2. when they do leak, they'll leak at idle as well as any other rpm. Am I wrong? I've never had this happen and I'm at a loss here and could use some advice. I really, really don't want to have to pull the engine back out.

Thanks for any advice. 

[rsicard]

Sounds like there is too much piston ring blow-by.  The more RPM, the more crankcase pressure build-up.  What is the mileage on the engine?  Was it from a carb or EFI induction system?  EFI always runs a lot cleaner on the cylinders.  Carbs tend to wash down the oil on the cylinders and accelerate piston ring wear.  Sounds like at the least it needs a rering job.  More likely, bore and hone the cylinders with replaced pistons and rings.  This should drastically reduce piston ring blow-by.

[nullbound]

Have you talked to Paul?

[YoSammyT]

It is a brand new build. Definitely not a wearing out challenge.

 

I have talked to Paul. He called me this morning with an idea. Hook a drill up and 'prime' the oil pump and turn it for a few minutes to see if it leaks under a good constant pressure. That will help isolate/exclude where it's coming from.

Edited May 1, 2014 by YoSammyT

[MONGO510]

did you seal the sides of the main cap?

[rsicard]

Priming the oil pump will NOT reveal the problem.  The positive way to go about it is doing a cylinder by cylinder leak-down test.  The tool to do this with has two air pressure gauges.  One for line pressure and the other for cylinder holding pressure.  Once a cylinder is pressurized at top dead center, for that cylinder, note the reading on the cylinder hold pressure gauge.  The instruction sheet that comes with the tool has a chart of how much leakage per cylinder pressure read.  Open the valve cover cap and get near it with your ear when the cylinder is pressurized.  If you hear an air leak, then it is the piston rings for that cylinder.  Also listen at the exhaust and carb intake for air pressure leaks.  It will tell you whether there are valves leaking.  There are quite a number of variables when an engine is being rebuilt.  The more experienced the re-builder is, the better the outcome.  Don't be afraid to disclose facts about the rebuild and there are many of them.

[dexter72]

 

This may be related to oil pressure, What is the oil pressure of the engine above 2k rpm???..

Did you silicone the oil pan gasket to the block or to the oil pan??.. Could be the pan gasket leaking.  I know on older small blocks ( 1970's ) you silicone the gasket to the block. I rebuilt a small block and had a leak from the rear of the engine and i glued the gasket to the oil pan. The first thing a senior tech asked me was, how i attached the oil pan gasket. He said pull the pan and silicone the gasket to the block. Did it and no more leak for me. Not sure if the same thing goes for newer small blocks.  

[skirkland1980]

Is the bottom of the intake sealed to the block?

[grumpyvette]

the first step should obviously be to locate the source of the oil leak, Id suggest getting several cans of spray brake cleaner and totally degreasing the area, and then blowing a bit of talc powder over the area so any new oil flow leaves a very obvious track back to its source,

but in the area you mention, rear seals,

the rear intake gasket and the oil pressure sensors

that screw into the block are all suspect as are the rear cam plug and rear lifter gallery oil passage plugs

 

 

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=464&p=39647&hilit=rear+seal#p39647

 

http://forum.grumpysperformance.com/viewtopic.php?f=51&t=1718&p=38740&hilit=rear+seal#p38740

Edited July 1, 2014 by grumpyvette

[YoSammyT]

Just realized I never posted my findings on this. The rear main seal was broken. Had to be faulty as it had a huge crack in it. Pulled the tranny and replaced it... I'm dry.

 

Never had a one-piece RMS leak (much less break), but I guess there's a first time for everything.