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Old 05-27-2019, 09:41 AM   #1
Conaway2
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Default Rear main oil leak >

I just installed a professionally-rebuilt engine in my 31 Model A, and have a pretty bad oil leak in the rear. I can see the oil running down on either side of the inspection plate, and am pretty sure itís not leaking from the cork seal at the rear of the oil pan.

Iíve been stewing over this for several days, and am really puzzled. Before I started the engine for the first time, I added about a half quart of oil to the valve chamber via the hole for the distributor shaft. 15 minutes later, there was a significant puddle of oil under the bell housing.

I have made sure that the oil return tube is not screwed in too far, and oil breather tube and cap are both clear. Now when I run the engine, only a few drops leak when the engine is running. After itís been shut of for 20 or 30 minutes, a puddle of oil forms under the rear of the engine.

This has me stumped - somehow the oil in the rear of the valve chamber must be accumulating, rather than draining though the rear main cap oil tube or the external oil return line.

Any thoughts what may be causing this ? Iíll probably drop the pan this week and remove the rear main cap to inspect it.

Many thanks - Jim
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Old 05-27-2019, 10:04 AM   #2
100IH
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Default Re: Rear main oil leak >

Did you install the flywheel housing? or did the shop install it. There is a gasket that goes in between the block and the housing. Rear cap is the next likely issue. Look at crankshaft end play first. Valve chamber normally runs flooded, exits over the timing gears and though the external return tube.

Last edited by 100IH; 05-27-2019 at 10:12 AM.
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Old 05-27-2019, 10:15 AM   #3
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Default Re: Rear main oil leak >

If you only added 1/2 quart or so of oil and the engine was never started before you saw the leak, it is most likely not the oil pan gasket or the rear main. Be sure to check that the gasket was added between the flywheel housing and the block. A leak at the rear camshaft bearing would do just what you saw.
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Old 05-27-2019, 11:01 AM   #4
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Default Re: Rear main oil leak >

Put car on stands,chock wheels and set E brake.Pull inspection plate,wipe rear main bearing cap and surrounding area clean,start engine let it idle,pinpoint where the leak is coming from,it will save you time and effort.
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Old 05-27-2019, 11:07 AM   #5
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Default Re: Rear main oil leak >

Might try checking the black light dye and flashlight. Less guessing.
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Old 05-27-2019, 11:16 AM   #6
Ernie Vitucci
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Default Re: Rear main oil leak >

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Good Morning...You might consider speaking to the folks who rebuilt the engine for you. If they are local, drive over and ask them to take a look. Ernie in Arizona
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Old 05-27-2019, 11:18 AM   #7
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Default Re: Rear main oil leak >

Agree with those who suspect the gasket between the block and flywheel housing. On all but the earlier A's there was an oil feed hole from the rear of the valve chamber down to the rear camshaft bearing. This will leak in the way you describe--ie, just sitting with oil in the chamber. Also agree with Railcar to put it on blocks and wipe all oil off, but repeat the test of putting oil in the chamber and letting it sit before starting the engine. Let it sit couple of hours or until you see oil. Trace the oil. After that, start the engine and check again. I do not think that oil to the rear main while sitting would be enough to leak there unless the tube was blocked, and lack of oil while running seems to me to eliminate a rear main leak.
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Old 05-27-2019, 12:38 PM   #8
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Default Re: Rear main oil leak >

Thanks to all for your responses ! I installed the flywheel housing and did put the gasket (with sealer) in. Sounds like the rear main cap may be the culprit. I have spoken with the re-builder, but moved since the rebuild and now live 13 hrs away, so a bit tough to get the engine back to his shop.
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Old 05-27-2019, 02:11 PM   #9
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Default Re: Rear main oil leak >

Did you overfill the crankcase??
Paul in CT
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Old 05-27-2019, 03:26 PM   #10
John Stone
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Default Re: Rear main oil leak >

My experience with the block/flywheel housing gasket. Many years ago (about 44) I put my first A engine together. Why I did it, I'll never know but I put the gasket on backwards. I guess I thought it was symmetrical. When I started the engine, the oil did not leak and ran fine. Upon shutdown, a pool formed under the car bigger than a dinner plate. After checking a few things, I pulled the engine and corrected it. After that I have been very careful with the gasket.
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Old 05-27-2019, 03:34 PM   #11
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Default Re: Rear main oil leak >

Crankcase is not over filled - oil level is slightly below F.

John Stone - doesn’t the gasket go on only one way ?
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Old 05-27-2019, 03:57 PM   #12
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Default Re: Rear main oil leak >

Quote:
Originally Posted by Conaway2 View Post
Crankcase is not over filled - oil level is slightly below F.

John Stone - doesnít the gasket go on only one way ?
It can be reversed but the part that goes over the camshaft hole will be on the wrong side. I checked mine by taking off the inspection plate on the flywheel housing and using a mirror could see the gasket sticking out where it wasn't supposed to. I'm not saying you did it, just saying I was not careful and did it. Inspection is easy. With the cover off, start the car, turn it off and look inside the flywheel housing. It should tell you where the leak is.
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Old 05-27-2019, 04:46 PM   #13
Kohnke Rebabbitting
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Default Re: Rear main oil leak >

I added about a half quart of oil to the valve chamber via the hole for the distributor shaft. 15 minutes later, there was a significant puddle of oil under the bell housing. "End Quote"

That is normal.

Oil comes through the shims, top and bottom of the main bolt, uneven cap and block mating surface, shaft clearance, thrust clearance, oil tube screwed in to far, with out cleaning out with a 3/8's bit.

When you pour a Model A rear cap, the little soft plug should be pulled to make sure that the passage is all clear.

With a half plugged, passage, with Babbitt, you would never know it by blowing 175 pounds of air through it.

Herm.
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Old 05-27-2019, 05:19 PM   #14
Conaway2
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Default Re: Rear main oil leak >

JS - good suggestion on how to check the gasket - I will double check on the gasket, but am positive I put it in correctly and used sealer on the gasket.

KR - How do you remove the Welch plug from the rear main cap ? And....how do you put it back in ? Do you use any sealer ? The rebuilder asked me to hook some tubing to the drain tube and blow through it - which I did, and there seemed to be no pluggage ....with air.
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Old 05-27-2019, 05:36 PM   #15
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Default Re: Rear main oil leak >

KR-- I had one that would blow free but had a small flat piece of babbitt floating in the main cap line. Sometimes it would leak and other times no leak. Acted like a random check valve. You are right, pull the drain tube and welch plug to make sure.
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Old 05-27-2019, 05:48 PM   #16
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Default Re: Rear main oil leak >

Quote:
Originally Posted by Conaway2 View Post
JS - good suggestion on how to check the gasket - I will double check on the gasket, but am positive I put it in correctly and used sealer on the gasket.

KR - How do you remove the Welch plug from the rear main cap ? And....how do you put it back in ? Do you use any sealer ? The rebuilder asked me to hook some tubing to the drain tube and blow through it - which I did, and there seemed to be no pluggage ....with air.
To remove the little soft, I have a very small round punch, that I ground at a 45 degree angle. Put the cap in a vice, surface side either direction, in the vice, just tighten lightly. Take the punch and punch through the center of the plug, and pry, side ways, and it will come right out.

It is just a common 3/8's soft plug, and install like any other soft plug.
I take a 5/16 round punch, and hold it above the plug, about an 1/8th inch, and tap with a small hammer, in the middle of the soft plug, and take down the crown, in the middle.

Use a little Indian Head on the lip, inside the hole.
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