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Old 07-28-2009, 11:10 AM
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Marine 454 Leaking Rear Main Seal?

I've got oil coming from.... somewhere. Can't find it because the oil pan sits almost on the hull and EVERYTHING is covered in oil. I've cleaned it with 3-4 gallons of simple green but it's just impossible to get it all because it's too tight.

Oil plug is tight... that leaves the rear main seal and oil pan gasket, right? How much clearance do you think I need to get under the engine to check these/replace them? Do I need to completely pull it and put it on a stand?

Boats! It never ends!!

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Old 07-28-2009, 11:58 AM
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Quote:
Originally Posted by wotan
Boats! It never ends!!
I watched a show last evening, something about pawn shops. A guy sells the owner's son a boat, the father freaks out (at first, anyway) and tells his kid, "A boat is a hole in the water that you throw money into!"

I always heard, "The two happiest days of a boat owners life is the day he buys his boat- and the day he get rid of it! lol

First, check the oil pressure sender. Wouldn't hurt to look at the base of the distributor, too. Anyway, you could have a rear main gone on it. Was it a sudden thing, or gradual, or?

In any event- IF it's either a rear main seal or a pan gasket, the pan needs to come off. This will mean at a minimum, you'll need the height of the pan, plus some to clear the crank counterweights/throws and the oil pump pick up in order to get the pan off. Removing the engine would sure make things easier. I hesitate to say it's absolutely necessary, but it's close.

For the RM seal, there are complications involving having to remove the rear main cap, oil pump and old seal. The bottom half is a piece of cake, but the top half can be a bit more trouble.

If the engine has been together for a long time, the RM seal will have stuck in the upper half pretty darned good. If you take an 1/8" BRASS drift, you can try popping it loose by hitting it on the end. This has worked for me in the past.

There's a tool made for installing and removing the RM seals, called a SNEAKY PETE. I know some swear by them, others AT them- personally I've never used the one I own, I always did just fine w/o it.

Cleaning the top seal groove is important. You need to have it real clean so the new seal will slide in easily and so it won't leak, but the job is basically blind. I've had luck using a long piece of gage stock, trimmed for the job (below, usually available from NAPA or a machine shop). You can use some spray gasket remover to soften the rubber if there's a lot adhering to the block.

Many builders have taken to using the "offset" or "clocked" method of installing the seal- that's up to you, as well as where (or if) to use any sealer. I don't use sealer on the seal itself, but use a small amount on the block, adjacent to the seal.

Then there's the front seal that will have been disturbed by the pan removal.
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Old 07-28-2009, 12:24 PM
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Don't forget that many Boats are running a Mark IV or Mark V 454 which has a one piece rear main seal-
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Old 07-28-2009, 01:47 PM
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It's an 86 boat.... how can I tell which engine is in it?
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Old 07-28-2009, 01:52 PM
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What is the drive system? Merc or OMC will be GM blocks. Where is the distributor located? Is it a ski boat inboard type?

Salt water or fresh?
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Old 07-28-2009, 01:55 PM
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Originally Posted by Jsup
What is the drive system? Merc or OMC will be GM blocks. Where is the distributor located? Is it a ski boat inboard type?

Salt water or fresh?
Supra ski boat... full inboard... PleasureCraft Marine did the marinization. Distributor is an HEI located on the back. It's a GM block, 454 and I'm 90% sure when I rebuilt it I did a 2-piece rear seal..... but it was about 5 years ago and I just don't remember. If I lift the engine up a foot I think I'll have enough room to pull the pan.... once I do that, it shouldn't be that tough of a job. Is there a seal I should put in there that will guarantee I never have to do this again??
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Old 07-28-2009, 01:57 PM
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Quote:
Originally Posted by 35WINDOW
Don't forget that many Boats are running a Mark IV or Mark V 454 which has a one piece rear main seal-
Good point, my bad- automatically thought 2-piece when he talked about leakage...
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