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Argess 08-07-2010 07:29 PM

How to tell if SBC has 1 or 2 pice rear seal
I have a Mercruiser 260 HP engine (basically a SBC 350) in my boat that seems to have a leaky oil pan, no doubt from all the years being around salt water. It's a 1985....right around when they changed them, so other visual clues such as valve covers and dipstick locations might not confirm the seal type being used.

To change the pan, I need to jury rig a hoist and lift the engine out of the hold and change the pan with the engine suspended in the air, so it would be nice to already have the pan at that point, rather than to leave the engine suspended for a week or two while the correct pan is on order.

I think I can see under the pan with a mirror and trouble-light, but am unsure what to look for at the back end of the pan. Is any of the rear bearing cap exposed on one and not the other? I've got a feeling nothing is obvious unless I had two engines to compare.

hemi joe 08-07-2010 07:45 PM

it's a two piece seal.

DoubleVision 08-07-2010 07:49 PM

Chevy made the change in late 1985 for the 1986 model year.

greenmoonshine 08-07-2010 07:50 PM

The one piece is 86' and later,
Whats your block #?

Argess 08-07-2010 08:26 PM

Dont know the block number (I'll check if I can find it....not much room in there to look is it located?). I do have the engine model number, 02608344 and the engine seerial number 6774526, but I'm fairly certain they are both Mercruiser numbers.

The Mercruiser parts list show both oil pans, but you have two know which type rear seal to order. To top it off, Mercrusier discontinued both pans, but Seirra sells an aftermarket of either type. None of the oil pan pics showed enough detail for me to use to ensure which pan I currently have.

But I agree it's probably a 2-piece seal. Just looking for "extra info" to confirm 100%.

Thank-you all for your replies. Sure faster getting a reply on a SBC than a Ford FE......LOL.

ericnova72 08-07-2010 08:33 PM

Block casting # is at the rear, on the block to trans mating flange, drivers side, behind the distributor/drivers side head.

oldBodyman 08-07-2010 09:04 PM

"Chevy made the change in late 1985 for the 1986 model year."

that is also when they changed the valve cover bolts from perimeter to center bolts, should be an instant tell-tale. :thumbup:

Argess 08-08-2010 04:47 PM

Thanks all. I think I`m certain enough that it`s a 2-piece seal to order the proper pan. Trying to get one more month of boating in, I may try some epoxy putty as I found the leak. Right hand side, about 1 inch up and back from the deepest sump portion of the pan.

Original paint on most of the pan except for spots, so I`m hoping the whole think will last another month, or a bit longer. Hole is too small to see, but if I wipe it dry, after about 2 or 3 minutes, a little weepage shows up.

After I get it out of the water, I guess it`s time to fire up the chainsaw and cut some spruce trees for a scaffold of some sort (actually, I`ll use sawn timber and bolts). While I`m at it, I`ll probably get the starter overhauled as it`s another thing that is almost impossible to change with the engine in the boat.

Thanks again.

trees 08-08-2010 05:09 PM

I changed the oil pan on my Mercruiser I/O (302 Ford motor) for the same reason, but I was stubborn and young enough to do it in the boat. I basically laid on my stomach and removed the bolts from the pan. Not an easy task since the salt water had rusted the heads badly. I used three different size sockets:SAE, Whitworth, and Metric in order to get a good bite on the heads. Had to drive most of them on. I placed a mirror in the bilge so I could see what I was working on instead of being totally blind. Having said all this, I would pull the motor.

As a note, if you are planning on keeping the boat a while, try to locate a stainless oil pan. If not, use a very good coating on the new pan and use stainless bolts and lockers


Argess 08-08-2010 05:27 PM

Young and stupid? I'm not sure age has much to do with it as I am old and stupid. I replaced my exhaust Y-pipe and didn't remove the engine. I did move it forward about 8 inches, but both bottom exhaust bolts were all done by feel. I couldn't see anything. And laying on top of the engine really adds to being stiff and sore.

Just to change the sparkplugs, I need to remove both batteries, squat down on the battery tray and reach back along the engine. Luckily I have long arms.

The engine compartment looks spacious, but only a midget"little person" or a small child could get in there.

I actually went to the dollar store and bought a fairly good size hand mirror. I mounted it on a light piece of aluminum channel and then had another piece of channel a little wider so I could hinge it. Helps immensely to find the oil leak. I also tried a digitial camera, but no matter where I thought I had it pointed, all I got was glare from the flash and what is left of the oil pan paint.

Mercruiser has discontinued the oil-pan, and so far all I can find is a Sierra, P/N 18-0613 and a 4 piece gasket set, 18-0411. Wish I could find a pan in SS, but no luck so far. Wish I could find a 1-piece oil pan gasket as well, but again, no luck. Not sure about the pan and gasket compared to a regular SBC, but there seems to be a problem with the dipstick tube. In a Mercrusier, the tube extends all the way to the bottom of the pan for oil removal (has a threaded end up top to connect a oil removal pump). I can't see because of the starter, but I suspect the oil tube is different and somehow partially external to the block so regular SBC aftermarket stuff may not work.

I like your story about all the different sockets you used to fit rusted bolts. I've been there, but luckily not crawling around a boat engine compartment. Does build character though, doesn't it?


Moral: When you can't afford new stuff, and you buy old stuff, be prepared to work your arse off....i.e. that would be me!

Rickracer 08-08-2010 06:11 PM

The hole in the block where the dipstick tube comes through is the same, so a 1 piece pan set with the tube on the correct side, and for a 2 piece rear main should fit just fine. :cool:

cobalt327 08-09-2010 10:08 AM

If you use your mirror and see an aluminum housing like the image below, it will be a 1-piece rear main seal engine.
The housing shown doesn't have the seal installed, but is basically what you'd see bolted to the rear of the engine.

Argess 08-09-2010 10:12 AM

Ahh.....I see. And if it was a 1-piece seal, I should see some of that casting even with the pan and bellhousing on, and I don't. I'll look again though. Thanks for the pic!

Hogg 08-09-2010 12:00 PM

Right 2 piece RMS
Left 1 piece RMS



greenmoonshine 08-09-2010 10:10 PM

Heres a pic I had also
Top is a 1 piece RMS
Bottom is a 2 piece
P.S. I snagged this pic from CarCraft :thumbup:

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