Help rear main leak

B

bigdaddyslotrat

Junior Member
Hi guys i have a question !! THIS IS A NEWLY BUILT MOTOR my oil leaks out the back of the motor is as follows, running at idle steady stream out the hole in the bell housing slightly higher rpms the leak seems to stop until you turn of the motor then a stream starts up again for about 4 table spoons of oil. ok this motor has about 1 hours running time and i did not build it! but was told by the builder himself that he changed the gears in the oil pump and it should make around 100 psi ??:eek: will that much pressure make the oil leak out the back?? thank you all very much
 
Stock oil pump is very low pressure around 2-3 PSI max, high volume.


The usual reason for an A to have a pressurized oil system is if you are running an oil filter kit system. Even then 100/lbs. seems high to me, am uneducated what an A pressurized system normally runs. Seems you may be running a modified Motor?


If no one here knows, then perhaps ask on the HAMB forum, or perhaps ask on the Barn Hot Rods and Custom forum.
 
The stock oil pump will put out at least 40 psi. The reason you only see 2-3 psi is because there is no back pressure. The pump pumps oil to the valve chamber and it drains back to the dipper pan or runs down to the main bearings and the timing components.
 
midgetracer said:
The stock oil pump will put out at least 40 psi. The reason you only see 2-3 psi is because there is no back pressure. The pump pumps oil to the valve chamber and it drains back to the dipper pan or runs down to the main bearings and the timing components.
Click to expand...

Thanks for correcting me, learned something new.
 
please forgive i forgot to say the motor is a 1932,33,34 "B" diamond block.


has high comp. head and pistons with a isky cam. and an oil leak out the back:p.
my next question is will an oil filter system lower the pressure in the motor and relieve the pressure after turning off the motor???:confused:
 
Good afternoon...I would contact the engine builder and let them know what is happening. If you can drive the car over to them, do so and let them see what is happening. If you can't drive to them, can they come to you? A fresh engine should not be opened except by the folks who built it, or they might well claim that the problem is not theirs. Ernie in Arizona
 
Do you have babbitt or inserts, and pressure oil system? The oil pump will not cause a rear main leak no matter what the pressure unless some modification has been made.
 
IMO: A couple things could be causing your leak:
1) The rear main clearances are excessive
2) The rear main seal may not be installed with the proper sealant
3) The cap may not be set or machined correctly
a) The cap or mating surface my not be flat
b) The oil passage in the rear main cap may be restricted
c) If the engine has inserts, the thrust washers may have excessive gap between
them
The clue to your problem is the leak after shut down. The oil from the valve chamber is running down to and through the rear main faster than the drain system can remove it. This typically indicates a component in the rear main that has excessive clearance.
Good Day!
 
Had a customer with a new motor and the rear leak problem.
It turned out to be the flywheel housing was not flat over the cam opening.
Yes, this was a pressurized motor so it is exaggerated but none the less a new housing corrected the issue.
J
 
Make sure the gasket between the flywheel housing and the engine block is installed correctly . If it is installed backwards it will leak oil out the camshaft and it will run down the rear main area . I'm not sure if the Model B engines are the same .
 
Pc/sr
what do you mean by modification ??
This pump has been modified and all i know is he put different gears and told me it should have 100 lbs.




Well now it looks like i will have some more work ahead of me now.


Thanks for all the information guy
i'll keep you posted
 
What I meant by modification was inserts, pressure oil, modern rear seal, that sort of thing. A stock rear main properly installed will not leak more than a few drops. Other posts point out what defects to look for.

I cannot imagine an A oil pump, even modified, being able to pump 100 psi, and if it did you do not want it to. Would be curious teo know what gears were installed.
 
bigdaddyslotrat said:
please forgive i forgot to say the motor is a 1932,33,34 "B" diamond block.


has high comp. head and pistons with a isky cam. and an oil leak out the back:p.
my next question is will an oil filter system lower the pressure in the motor and relieve the pressure after turning off the motor???:confused:
Click to expand...
Sounds like the builder didn't know how to rebuild the B engine. The pump in an A or B has the capability of as much as 100 PSI but without any restriction in the system, it won't push but about 2/3 # in an A and 5/7# in a B with the stock system. There is a marked difference in the A bearing design and the B bearing and one won't work in the other application without leaking. I can be available for consult if you want to know more. Just go to my website for the phone #.
 
well sorry i haven't been on for a while but guess what?????:cool:

i went ahead and made a new valve cover for the motor and in it i drilled and tapped 3 holes 3/8 national pipe threads.:eek:


then i routed the oil from the tapped hole and back to the oil pan through the fuel pump block off plate.:D


today ran the motor for about 1 hour and not one drip out of the rear main.:cool:
so i ordered an remote oil filter adapter kit and will install it Wednesday.
so my conclusion is that the pump just put out to much pressure . i hope this won't make the pressure rise to muck after.:confused:
i want to thanks everybody with all the ideas to help and they were good ones too !!!:):):):):)
 
So to be clear, you put a bypass line from the oil galley to the pan with no restrictor?

Are you making any oil pressure to feed the bearings?

Typically the oil is picked up from the block pump retention hole, passed thru a filter and then back into the oil galley thru side cover.

Better make sure you have pressure to bearings, better sooner than too late.

John
 
I had a pilot friend that owned a Funk airplane.

The Funk used a Model B engine that was dry sump and inverted (cylinders down).

He changed the valve chamber gasket and went for a test flight.

Upon take-off, the oil pressure gauge was pegged (lots of pressure).

Just as he cleared the end of the runway, the engine started to clatter.

Luckily, he throttled back, circled and landed without incident.

Turns out that he forgot to poke a hole in the valve cover gasket that would feed oil into the galley that provides oil to the mains and camshaft.
 
If the flywheel housing gasket between the housing and block is installed backwards, oil will leak badly from the end of the camshaft exactly as you describe. You can easily check this by looking at the starter side of the engine where the housing meets the block and see of you see a round portion of gasket sticking out....it you do see it, the gasket is in backwards.
 
I am not sure tapping three holes directly into the oil galley and externally drawing off oil flow will leave enough flow to the bearings, cam and timing gear area. I guess time will tell. Hope it works.

The attached photo shows an alternate way to decrease the oil pressure to the rear main bearing. The installed pop off valve will keep some flow to the bearings and the modification is hidden from sight. If the small size of the pop off will not handle the flow of the pump, an additional one can be installed on the other side of the oil galley. If you are wondering about the carb jet you see: I have restricted the oil flow to the cam bearings in the photo by installing a carburetor jet. The opening over the cam gear is also restricted. When this photo was taken, I was developing about 45# of operating oil pressure in the system.


Good Day!
 

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