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Old 11-24-2005, 07:13 AM
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SBC rear main leak ?

Subject engine 76 350. I rebuilt this last year and installed it in my S-15 Jimmy. It always had a small, very small oil leak that dripped out of the holes in the transmission inspection cover (r700). Figured it was the darn 2 piece rear main and decided to wait until it got worse since I would have to pull the engine to replace it. Well it's gotten worse finally after 25K miles but now I'm wondering if it is the rear main. I pulled the inspection cover off the trans this morning and the cover has oil in it but the flex plate and torque converter are clean and dry, the converter is even starting to rust some??? I guess my question is wouldn't you think they would just be covered in oil if the rear main was leaking?? It's tight to look at the engine but it almost apears that the right side (starter) is a lot wetter with oil than the left. Could I have a topside leak? and any suggestions where to start looking or how to tell if it is the rear main without pulling the engine?

Things that I have checked, valve covers are sealed and not leaking, oil pressure gauge line not leaking.

Thanks in advance,
Lance

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Old 11-24-2005, 07:21 AM
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It's possible the oil pan may not be sealing properly around the rear main bearing cap. At any rate if you pull the pan I would go a little further and replace the main seal also. When you install the split seal do not align the ends with the bearing cap mating surfaces. Rotate the seals so the seal mating surfaces are not in the same plane as the bearing cap surface. Place a small dab of high temp RTV on the bearing cap mating surfaces and bolt together. I would consider a new oil pan also. I purchased a Milodon oil pan when I accidentally crushed the GM pan that came with my crate engine.The Milodon pan is thicker at the front-rear and sides. The side rails have an extra thick strap. Overall a much higher quality pan than the OEM pan.

Vince
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Old 11-24-2005, 07:36 AM
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Good advice........but to go 1 step further.......FelPro makes a one piece oil pan gasket for the older 350's now......like the one GM designed for the 86 up engines. I always use the improved gasket and have never had a oil pan leak yet...

DEUCE...
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Old 11-24-2005, 07:39 AM
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I agree with 320/Z28 could be oil pan or the oil pressure sending unit on the back of the block behind the dizzy. I have seen those leak and drip down. In most cases you can replace that seal without pulling the motor. Godd luck
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Old 11-24-2005, 07:56 AM
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Been looking more but it's tough, this is a shoehorn fit, just about zero clearance between rear of the engine and firewall. But I'm wondering how much of a oil leak can you have at the rear of the intake? I can't see back there but I stuck my hand there and it came back with some oil on it...

To reply to the above posts,
After market oil pan, one piece oil pan gasket, rear main seal installed as decribed above. Oil pressure gage fitting not leaking.

With this being a 4X4 and the engine set back the way it is there is no way to drop the pan in the truck otherwise that baby would have already been off! So I'm really trying to exhaust all of the other options before pulling the engine. I'd hate to go to all that work only to find it was something that I could have fixed with the engine in the truck. Could the rear intake seal leak that much oil?

Lance
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Old 11-24-2005, 08:32 AM
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What aftermarket oil pan? If it is a Chinese or Taiwanese knockoff that may be your problem. All aftermarket oil pans are not created equal. I have seen some really terribly fitting oil pans from Mr. Gasket.

Deuce, forgot to add about the FelPro one piece gasket, greatest thing to come along for the SBC IMO.

It is certainly possible that the rear seal on the intake is leaking, I have seen it slip even after it has been installed for a long time. If that were the case you would have oil all over the top of the bellhousing and transmission.

Vince
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Old 11-24-2005, 08:40 AM
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Quote:
Originally Posted by 302/Z28
Deuce, forgot to add about the FelPro one piece gasket, greatest thing to come along for the SBC IMO.

Vince
I figured as savvy as you are on the SBC's you knew about the FelPros.
And I agree.....best thing for sealing to come along in a long time.

Have you seen/used the FelPro thermostat gasket ? It is plastic with a O ring in it. It is reusable....and works great.

I have one on all my stuff..except the new cars....

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Old 11-24-2005, 08:56 AM
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Quote:
Originally Posted by 302/Z28
What aftermarket oil pan? If it is a Chinese or Taiwanese knockoff that may be your problem. All aftermarket oil pans are not created equal. I have seen some really terribly fitting oil pans from Mr. Gasket.

Deuce, forgot to add about the FelPro one piece gasket, greatest thing to come along for the SBC IMO.

It is certainly possible that the rear seal on the intake is leaking, I have seen it slip even after it has been installed for a long time. If that were the case you would have oil all over the top of the bellhousing and transmission.

Vince
It's a custom pan from Jags That Run for the SBC S-15 swap. Very nice pan, much better than stock.

I've decided to pull the intake, in my reaching around I'm finding that bellhousing is oily on the top and it appears that the oil is running down. Considering that there should be no oil there I'm really beginning to think this is where the problem lies. I figure it's worth a shot, and if this is it then it will be an easy fix, if not, oh well, nothing ventured nothing gained Thanks everyone for the suggestions, I'll let you know what I find when the intake comes off. Happy Holiday all

Lance
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Old 11-24-2005, 05:28 PM
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Good news, for me at least, pulled the intake and sure enough the rear seal had moved during assembly and was sealing by a piece only about 3/32" wide in one place, which over time gave up the ghost. So tomorrow off to fight the crowds of happy shopers to pick up a set of gaskets. I didn't think the rear main was leaking
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Old 11-24-2005, 08:29 PM
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I've had better luck laying a bead of oil-resistant RTV on the rails rather than try to use the black rubber seals.
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Old 11-25-2005, 06:28 AM
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Quote:
Originally Posted by techinspector1
I've had better luck laying a bead of oil-resistant RTV on the rails rather than try to use the black rubber seals.
Same here.....
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