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Oil pan/rear main seal replacement

ascuro

ascuro

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After my last trip in to the hills, my crate 350 seems to have developed a fairly significant oil leak. I'm hoping it's just leaking out the back of the pan, but it really looks like it might be the rear main seal.

My question is - how hard would it be to fix either problem? After some reading, it seems like I can jack or lift the engine up in order to remove the pan and replace its gasket...but I'm unclear if I can replace the rear main seal without removing the engine from the truck? Is there an easy way to tell if the main seal is bad?

Also, how involved would either job be? I've rewired/replaced/serviced almost everything else in various cars and trucks I've owned, but I've generally left the transmissions and engines alone. If I do end up tackling it myself, would a jack underneath the pan be sufficient/safe to lift the block with, or would I be better off investing in an engine hoist?
 
It depends.

If its a one piece rear =fix with engine in truck, but pull tranny to get to it, pull main seal replace and reverse steps.

If its a two piece rear =get your wrenches ready cause your gonna have some fun pullin that motor. As far as I know, you have to pull the crank to properly replace main seal on a 2 piece block.

If its just the oil pan, just get a one piece oil pan gasket and be done with it. They are a bit expensive but pretty much idiot proof if you squirt a little rtv in the corners. A lot of them have limiting retainers that keep you from over tightening and breaking the gasket. Also, pulling the pan can be done with out doing anything with the motor, you just have to work at it. Its one of those things that gm designed with a little too close of tolerances.

On a more positive note, its prolly your oil pan gasket callin in for a coffee break.
 
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you can do one or two piece seals while the motor is in the truck, just slide the seal under the crank after it's been liberally oiled using the included strip of plastic that will protect the seal from rubbing on the block edges and you're set.
 
As was said, if you have a 1 piece rear main seal then you have to pull the tranny/T-case rearward enough to access the seal retainer and remove old seal and reinstall new seal then reverse procedure for assembly. If you have a 2 piece rear main seal then it is alot easier since you don't have to pull the tranny/T-case but rather drop the oil pan and the rear main bearing cap and oil pump and the seal in the cap is obviously easy but the seal half in the block is a little trickier but can easily be changed without pulling the engine or even dropping the crank. You just need to have someone help you to carefully rotate the crank while you use a small screwdriver or the like the start with helping the seal rotate along with the crank as it is being turned. Do the same to install the new upper half and (make sure that you install it the correct way or it will leak worse than before.) The lip of the seal always points towards the inside of the engine. Make sure that the same is true for the cap when changing it as well. :thumb:

Forgot to add, the 1 piece oil pan seal is an excellent choice and makes it even easier to reinstall while you're working upside down and they don't leak either.
 
There is a kit made by Lisle that is called a Sneaky Pete for removing and installing two piece rear main seals. I don't know how well they work as I have never used one, I just know that they exist.
 
MoonMan said:
There is a kit made by Lisle that is called a Sneaky Pete for removing and installing two piece rear main seals. I don't know how well they work as I have never used one, I just know that they exist.
Click to expand...

Those are for rope seals and not neoprene (rubber) seals.
 
Thanks a ton for the info guys. Guess I'll give it a shot myself and see how it goes, hehe.

A couple other quickies though...once I pull the pan, are there any tell-tale signs I should look for to see if my rear main is indeed at fault? Oh, also - where did you guys find one-piece pan seals from. NAPA and such only seems to have the two-piecers.
 
If you have a 1 piece rear main seal then it is a FEL-OS34500R
If you have a 2 piece rear main seal then it is a FEL-OS34510T

These part numbers came from summit racing.
 
Make sure..

Before tearing the oilpan off,I'd make 100% sure its not the valve covers,oil pressure sending unit,distributor "O" ring,or the intake manifold's rear sealing area leaking before blaming the rear main seal!..I've replaced a few rear main seals without doing a thourogh check of all those,and it came back leaking the next day,with an unhappy customer at the wheel!.. :blush: - :doah: :tongue1: ...do it ONLY if it needs it!.. :crazy:

If you do pull the pan,its a good idea to look for any nylon gear teeth in the pan,and the oil pump pickup screen..if you find any,it would be wise to put in a new oil pump and new screen,and put a steel collar on the oil pump drivshaft in place of the nylon POS chevy uses factory..and plan on doing a timing chain and gears too,while the pan is off..some motors used steel cam gears,some didn't..I replaced all of the above in my 86 305 I put in my 79 C10--including the oil pan gasket,for about 60 bucks!..cheap peace of mind.. :crazy:
 
Thanks again 4x4high, that was just what I was looking for.

And yeah, I've been desperately searching (and hoping) for something else to blame for the leak, but I can't find any evidence up top of the block. The only source I can see for the oil is right between the flexplate (auto trans) and the back of the crankshaft.

The only strange part is that it only leaks oil when the engine is running and warm. Not when I first start it up, or after it's cooled off/been sitting. Don't know if that tells you guys anything - all it tells me is that my driveway isn't getting as stained as it could be =)
 
I'm probably going to have to do an oil pan gasket seal too. However, I thought about replacing the rear main as well but I don't know if it is a 1 or 2 piece. My 350 is an 88 tbi, all factory.

Also, I need to replace the o-ring that goes between the block and the factory engine oil cooler. Does anybody know what size the hex bolt is that screws into the filter on one end and into the oil cooler on the other end, mine always comes loose when I take the filter off.

Thanks
 
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A 1988 engine will be a 1 piece rear main seal engine so in order to change it you need to pull the tranny/t-case. The bolts that hold the adapter to the block usually havd a 3/8" or 7/16" socket head.
 
4X4HIGH said:
A 1988 engine will be a 1 piece rear main seal engine so in order to change it you need to pull the tranny/t-case. The bolts that hold the adapter to the block usually havd a 3/8" or 7/16" socket head.
Click to expand...

Dang from the other posts it seemed like a 2 piece was mildy easier. I know its not 3/8" because that's the same size as the brake caliper bolts and I've already tried that hoping that was it. 7/16" sounds like a good place to start.

Thanks
 
I would like to second what a couple of guys said previously. Get the one piece oil pan gasket! After fighting with my gasket the last time i pulled the pan, I swore i'd get a 1 piece every time I pulled the pan with the motor in the truck.
 
Ok, now i remember, the bolts with the oil cooler are allen bolts and not hex head bolts, IIRC they are a 1/4" allen wrench.
 
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