Pain in the arse oil leak

FasterPlease · 11-03-2009, 07:07 AM

I have a 454 mag. It has been bored and stroked with a 4.25 crank. all the goodies are forged and balanced. I have a breather on the port valve cover and a pcv on the starboard going to the base of a 750 demon(sea)carb. I am still making too much crankcase pressure??? The oil is bypassing the dip stick Am I missing something? If i cruise around a 2k or less no leak. Put the throttle down and a gooey mess happens. Any help would be welcomed

ezstriper · 11-03-2009, 07:21 AM

at higher RPM's the PVC does little, better off with dual breather tubes and possibly a puke tank...but that engine should not need that....sounds like you might have some ring sealing issues possibly causing more blow by....

seafordguy · 11-03-2009, 08:31 AM

I used to have some oil coming out of the dipstick. I took a piece of Duct Tape about 3 inches long and ran the dipstick through the middle of it with the sticky side down. Then put the dipstick back in with the tape matting down around the tube - problem solved for years now.

Also - if you are blowing oil out of the valve covers and no breathers will fix it you might need to go to a puke tank.

I buy my breathers of all places at PEPBOYS and they do a great job - no leaks.....

502's with Weiand 177's on them - not much boost/HP

FasterPlease · 11-03-2009, 08:49 AM

I suspected the rings also. I broke the motor in in Jan. last year the water temp was about 50 degrees. I had a hard time getting the rings to seat. I changed oil to a non detergent 30 weight snd ran the boat for an hour or so with the rpms between 700 and 1200. Basicly putting. Changed back to a castrol 30 and that seemed to do the trick. I didn't smell oil burning. Shortly after that I had to tow a boat 15 miles so again there was alot of low rpm lugging.
Can any one make a recomendation of a good motor guy near Tulsa, Ok. I'm sick of screwing around with this. What is weird is sometimes there is a leak and sometimes not. ARGHHHH!!!

mrv8outboard · 11-03-2009, 09:08 AM

Perform a leak down test. It will direct you to the problem. The info from this test will help on the repair because you will know were to look. eliminating the guess work upon inspection. But it does sound internal. Piston to wall clearance or more probably rings.

FasterPlease · 11-03-2009, 09:20 AM

Forgive my questions but i'm assuming by a leakdown test it's a matter of doing a compression test and seeing if or how fast the pressure drops?

Young Performance · 11-03-2009, 10:51 AM

A leak down test is different than a compression test. In a leak down test, you put compressed air into the cylinders through the spark plugs hole. You have two gauges attached to the air hose(you will need to get a leak down tester). One gauge reads the air pressure going in the cylinders and the other reads the pressure that remains in the cylinders, expressed in a percentage. If you put 100 psi in the cylinders and only 80 psi stays in it, then you have 20% leakage. You are looking for 10-15%. My engines will leak under 5%, because of the rings, clearance and finish on the cylinders that I use. Actually, most will be 2% or less.
A cold engine will leak a little more than a hot one, so take that into consideration. This test will tell you much more than just a comp. test. If you have excessive leakage, you need to find out where it is going. You can plug up the breathers on the valve covers to see if the air is going past the rings. You can also open the carb or throttle body and listen there. Lastly, listen by the exhaust for leakage. This will tell you where the problem is.
Give me a shout if I can help. Good luck.
Eddie

mrv8outboard · 11-03-2009, 05:39 PM

Just what he said.

blue thunder · 11-04-2009, 06:32 PM

I had that problem when I first bought my current boat with "rebuilt" engines. Turns out there were no windage trays and the oil was splashing on the underside of the pistons making a wicked burnt oil smell and the dipsticks would pop out. It was so bad I could see the oil pressure dropping irratically from aereation sp? of the oil. Ended up wiping out the mains on at least one of those engines.

racinfever · 11-04-2009, 10:22 PM

Eddie,
My crankcase pressure is becoming excessive also.
Which piston rings are you recommending? Currently I am using Speedpro with hell fire top ring. My bore is 4.600 with a 250 stroke and my rings are only lasting about 200 hours. Could it be cylinder hone finish is too smooth for this type of hard ring?