Fresh rebuild L-36 - Main seal leak

[Keith B.]

Just gone thru the ardious re/re of my org 427/390 for past several months. Complete near OEM rebuild top to bottom. Engine has only run for approx 15 minutes, had a minor electrical problem so repairing that now. Meanwhile at the bottom of the Bell housing inspection plate in the center I have a small drip of oil...ahhhhhh. I followed a recent restorer article and used the best Fel-pro RED seal over the blue or gray one and my machistist ensures me he took extra care and lube upon install.

The thought of taking this 700 LB monster out again makes me want to cry after months of detailing and work.

Should I give it some more time, break it in officially for 500 miles, add an additive maybe to seat the seal ??, Best advice and thoughts are extremely appreciated....Thank-you !!

[Joe L.]

Re: Fresh rebuild L-36 - Main seal leak

Just gone thru the ardious re/re of my org 427/390 for past several months. Complete near OEM rebuild top to bottom. Engine has only run for approx 15 minutes, had a minor electrical problem so repairing that now. Meanwhile at the bottom of the Bell housing inspection plate in the center I have a small drip of oil...ahhhhhh. I followed a recent restorer article and used the best Fel-pro RED seal over the blue or gray one and my machistist ensures me he took extra care and lube upon install.

The thought of taking this 700 LB monster out again makes me want to cry after months of detailing and work.

Should I give it some more time, break it in officially for 500 miles, add an additive maybe to seat the seal ??, Best advice and thoughts are extremely appreciated....Thank-you !!

Keith-----

The leak will not cure itself with time.

You don't necessarily have to remove the engine to fix the leak. The rear main seal can be replaced with the engine in the car. It just involves removing the oil pan, oil pump, and rear main cap. The seal can then be replaced. Assuming the problem relates to the seal, itself, or its installation, this should solve it. The areas shown in the GM Service Manual which adjoin the seal parting line MUST be treated with sealer as shown. If this was not done when the engine was rebuilt, that's why it's leaking now.

If the actual problem involves the crankshaft seal surface, that's another matter. If the seal surface is damaged in any way, an "offset" seal may solve that.

[Keith B.]

Re: Fresh rebuild L-36 - Main seal leak

Joe: Thank-you. Not sure if you read the article in the Summer 2008 Restorer by John Bissell relative to using the better # FPP-2912 seal. I used this one and am assured it was installed correctly, I have to dbl check with him though about sealer on the line and can only trust he installed it correctly. It's very disappointing but......

I did not know one does not have to remove the engine again. Pardon my ignorance Joe, just he pan, pump, and cap has to be removed, not the bell housing, transmission, etc.?? Once inside I gather its a matter of double checking the seal, its installation, and proper lube. I was hoping you would say it would seat itself and go away.......Keith

[Joe L.]

Re: Fresh rebuild L-36 - Main seal leak

Joe: Thank-you. Not sure if you read the article in the Summer 2008 Restorer by John Bissell relative to using the better # FPP-2912 seal. I used this one and am assured it was installed correctly, I have to dbl check with him though about sealer on the line and can only trust he installed it correctly. It's very disappointing but......

I did not know one does not have to remove the engine again. Pardon my ignorance Joe, just he pan, pump, and cap has to be removed, not the bell housing, transmission, etc.?? Once inside I gather its a matter of double checking the seal, its installation, and proper lube. I was hoping you would say it would seat itself and go away.......Keith

Keith-----


The transmission, flywheel and bellhousing do not need to be removed for seal replacement. That would only need to be done if your engine was equipped with a 1 piece seal. But, if you had one of those you probably wouldn't have a leak now anyway. GM went to a 1 piece seal for small blocks in 1986 and for big blocks in 1991. They didn't do this because the 2 piece seal worked just as well. Unfortunately, the 1 piece seal is not retrofittable to Mark IV big blocks or pre-86 small blocks.

If I was going in to check a seal, I'd always replace it at the same time. There's no real way to check it for the possibly infinitesimally small problems that could result in a leak. It's just not worth it to go to all the effort to get at the seal and then not replace it. The only exception would be if you found that the sealer was not used as I previously described. In that case I'd carefully clean and apply the sealer and "button it back up" without replacing the seal.

If you do replace the seal, make absolutely sure that you use the little plastic "shoe horn" that comes with the seal kit when you replace the upper half.

[Bill S.]

Re: Fresh rebuild L-36 - Main seal leak

i have had this same issue since reinstalling my 66 L72 3 years ago after a fresh rebuild from a well known builder. i was going to check the rear pan seal. any chance of that being the cause?

[Ray G.]

Re: Fresh rebuild L-36 - Main seal leak

Just gone thru the ardious re/re of my org 427/390 for past several months. Complete near OEM rebuild top to bottom. Engine has only run for approx 15 minutes, had a minor electrical problem so repairing that now. Meanwhile at the bottom of the Bell housing inspection plate in the center I have a small drip of oil...ahhhhhh. I followed a recent restorer article and used the best Fel-pro RED seal over the blue or gray one and my machistist ensures me he took extra care and lube upon install.

The thought of taking this 700 LB monster out again makes me want to cry after months of detailing and work.

Should I give it some more time, break it in officially for 500 miles, add an additive maybe to seat the seal ??, Best advice and thoughts are extremely appreciated....Thank-you !!

Hello Keith;
Experience indicates the most common source of oil leaks is other than Rear Main seal.
Check thoroughly above the seal. Oil sending unit area, rear of intake manifold, distributor, valve covers, etc.
The smallest leak/seepage will collect at the bottom of the oil pan and inspection pan areas.
Hope this helps.
Ray