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Old 12-13-2013, 03:51 PM   #1
SilverGhost
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Default strange rear oil leak, advice needed

Hello friends
My Model A, has a very good and strong motor. But on driving it leaks oil out of the flywheel housing cotterpin hole. If I let run the car in idle for about one hour there is no oil leaking out, but if I am driving it leaks about 0.15 quart per mile.

The motor was completely rebuild about 2000 miles ago. Rear cam is sealed. The crankshaft is modified for a modern seal. No pressure in the oil pan.

I would be thankful for all hints you can provide me.

best regards from Switzerland
Eric
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Old 12-13-2013, 03:58 PM   #2
Patrick L.
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Default Re: strange rear oil leak, advice needed

The problem could well be the rear seal. When you say no pan pressure, I'm thinking that you mean the fill tube and cap are clear.
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Old 12-13-2013, 06:10 PM   #3
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Default Re: strange rear oil leak, advice needed

I suspect your rear main seal is not working. Talk to your engine rebuilder.
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Old 12-13-2013, 06:34 PM   #4
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Default Re: strange rear oil leak, advice needed

First things first. Did you overfill? Where is the oil level on the dipstick? Remember you leave almost a quart in the valve chamber. Is their anything in the oil filler cap to keep the motor from breathing? Some people will put a steel wool pad in them to keep the blow by to a minimum. All this does is pressurize the motor and pushes it out the rear main. Start with what is easy and then move to the big stuff.
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Old 12-13-2013, 07:44 PM   #5
James Rogers
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Default Re: strange rear oil leak, advice needed

The rear seal has failed. I stopped using them a year ago because none of the available ones will work for more than 1000 miles. The slinger can be replaced but, not without removing it from the block and, in your case, sending it to the states to be repaired.

Sorry for the bad news.
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Old 12-14-2013, 10:28 AM   #6
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Default Re: strange rear oil leak, advice needed

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Hi friends
I will try to answer all mentioned points in one reply.

- fill tube and cap are clear. It even leaks without the cap.
- no pressure in the pan. Even a small plastic bag over the filler tube does only breath.
- oil level is half on the dip stick, not overfilled.
- we changed already the rear seal without success, slinger is removed.

Thank you all very much for your help until now.
Perhaps one of you has one more idea.

Thanks for your help and best regards
eric
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Old 12-14-2013, 10:34 AM   #7
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Default Re: strange rear oil leak, advice needed

Hello James
First, congratulation for your informative web site.
I try not to send the crankshaft to US because this is very expensive. Alone transportation and reimporting, customs and all is about 500 Dollars, without any work or material.
What I can not understand is why it does not leak if I run the car for more than 2 houres in accelerated idle. If the rear seal has failed I think it should even leak in idle.
Am I wrong?

best regards
eric
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Old 12-14-2013, 11:20 AM   #8
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Default Re: strange rear oil leak, advice needed

I fought this for a couple of years . changed rear main . in my case it is because the pan damn near cuts the rear cork in half . take the lower inspection cover off . you can see the rear main with a lite . mine was dry . thus watching where the oil is coming from & where it is not may help you . it took me several times to be sure . good luck ..... steve
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Old 12-14-2013, 11:48 AM   #9
SilverGhost
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Default Re: strange rear oil leak, advice needed

Hi Steve
Thanks, yes I did until now the same story as you some years ago. T took the inspection cover off, but I did not see the source of the leak. I am looking now since about 8 months and was not able to solve the mysterie. This year I was with my Ford on a Europe Trip for about 3000 miles with no problems only a leak which leaked about 0.15 quart per 100 miles.

thanks
eric
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Old 12-14-2013, 01:22 PM   #10
Terry Burtz, Calif
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Default Re: strange rear oil leak, advice needed

Hi Eric,

We had one leak because the seal rubbing surface was not concentric with the rear main bearing.

With engine stopped and inverted on an engine stand, we pressurized the rear main drain tube to 60 psi and there was no leak.

The engine would not leak around town (up to 40 mph).

The engine leaked at high speed (over 40 mph).

At slow speed the seal lip was able to flex and maintain contact with the seal rubbing surface. At high speed the seal lip was whipped out and was unable to maintain contact with the seal rubbing surface.
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Old 12-14-2013, 01:56 PM   #11
SilverGhost
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Default Re: strange rear oil leak, advice needed

Hi Terry
Thank you very much for your input. That could really be a reason.
I will try to make test drive with very slow rpm and look what happens.
At the moment the conditions are not good for test driveing. We have temperatures blow 0 centigrade and some snow.
But better wether will come.

Thanks
eric
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Old 12-14-2013, 02:07 PM   #12
Dave in MN
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Default Re: strange rear oil leak, advice needed

Terry is explaining my experience with modern main seals. When the crank is prepared for a modern seal, the seal surface should be cut before sending to the crank grinder. When at the crank grinder, ask them to index the rear main journal from the seal surface. The two surfaces should be concentric within .001" or less. Another point to remember...when polishing the crankshaft seal surface spin the crank in the direction the crank turns in the engine. I have found that modern seals, both front and rear will fail if you don't.
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Old 12-14-2013, 03:48 PM   #13
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Default Re: strange rear oil leak, advice needed

Had similar experience. My oil return drain pipe had come loose.
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Old 12-17-2013, 08:54 AM   #14
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Default Re: strange rear oil leak, advice needed

Hi Bigdave
Thank you for your input.
I already checked the return pipe. Perfect mounted and not to long.
James and Terry brought two (form me) new aspects. I will check this and keep you all informed. But at the moment there is no chance for further test drives because we have nice snow outside.

best regards from sunny and cold Switzerland
Eric
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