Rear Main Seal

PGtoy · Feb 13, 2005

What is bettwr a one piece and two piece rear seal. Is there any differnce in the way the early mercruser 5.7 bolted to the bell housing say 1985 and the 1996 Merc bolted up and the size of the fly wheel.

rodbolt · Feb 13, 2005

Re: Rear Main Seal

hello the one piece seems to seal better. the bell housings stayed the same. the flywheel and shaft coupler changed. unless your 85 is already fitted with the trainge shaped coupler.

jimmythekid · Feb 13, 2005

Re: Rear Main Seal

what do you have now? they aren't interchangable.

PGtoy · Feb 13, 2005

Re: Rear Main Seal

I have a 1996 Merc alpha 1. I have been looking at the GM crate engines circa 1970 to 1987 2 piece rear seal 8.5 to 1 pistons 4 bolt main 12 bolt intake, and was thinking if you changed the cam ( Marine )freeze plugs, and gaskets to marine could it be used in the 1996 alpha. The only thing I can see is the rear main seal. From the 1970-1978 to 1979-1996 I know there were other changes but the basic block looks the same.

TilliamWe · Feb 13, 2005

Re: Rear Main Seal

Don and Rodbolt, help me out if i am mistaken. He would need a flywheel for the GM crate engine, right? His bellhousing will bolt right to the block. And then the coupler would bolt right up to the flywheel, right?

PGtoy · Feb 13, 2005

Re: Rear Main Seal

I would have the fly wheel off the old engine unless the bolt patern changed on the crank.

rodbolt · Feb 13, 2005

Re: Rear Main Seal

tilliamwe yep the flywheels are vastly differnt. if he has the newer style triangle shaped coupler he can reuse the coupler. but I can tell you just go buy the correct part and its a done deal. the changes in design from the pre 85 motors to the 96 motor is vast.

PGtoy · Feb 13, 2005

Re: Rear Main Seal

Thanks I guess that is that, another good idea that wont work...... thanks for the replys

TilliamWe · Feb 14, 2005

Re: Rear Main Seal

Phill, your idea can work, but you are gonna need some extra parts, that's all. Flywheel to match the "older two piece seal" engine, and the correct coupler that will fit that flywheel. I just don't think your flywheel on the 96 engine (one piece seal, I believe) will match up to the crate engines that you speak of.

qystan · Feb 14, 2005

Re: Rear Main Seal

Phil Had a look at the parts list. Your flywheel p/n is 222-9520. This is listed all the way back to the 1982-86 series engines. Your crankshaft (bolt holes) p/n 429-9521 goes all the way back to 1987 (2 pc) series engines. Your 222-9520 flywheel is shown to be used on both p/n 429-9521 and 429-9519 crankshafts on the 1987 series engines. (Means your flywheel can fit the 2 pc seal crankshafts?) The 1982-1986 (2 pc seal) engines uses crankshafts 429-9519 or 429-6537. There is a possibility that you can reuse your flywheel as there is a chance the bolt holes will fit. Take a physical look before you write off this option. Let us know your findings.

PGtoy · Feb 14, 2005

Re: Rear Main Seal

Thanks Qystam, for the time you spent on looking up the info. I printed it for future referance. You can get a new Gm 350 crate engine 2 piece main for 1400.00 Marine gaskets 200.00 marine cam 80.00 brass plugs for 12.00 So if all the rest will fit you could have a new factory fresh 5.7, 8.5-1 comp rated 260hp if you use a 4bl carb for less than 2000.00. From what I have been able to get so far from 1970-1985 the 350 had a two piece main seal then from 1986-1996 a one piece main the same block. from 1996-present the vortek 350 that is differnt.

Buttanic · Feb 15, 2005

Re: Rear Main Seal

Qystan, your information is wrong. The bolt circle diameter on 1986 and newer crankshafts designed for one piece seals is smaller (3.00")than the bolt circle diameter (3.58") on two piece seal crankshafts. Also the the one piece seal crankshaft reqires a counterweighted flywheel for proper engine balance. Pre 1986 two piece seal crankshafts can be used in 1986 and later one piece seal blocks by using a seal adapter. One piece seal crankshafts can not be use in early two piece seal blocks. This information is direct from Chevrolet's power catalog. Some 1986 and later marine engines may have the early two piece seal because of the large stock of eariler two piece seal engines.

Bondo · Feb 15, 2005

Re: Rear Main Seal

Sooo,......... What is the price options on an 86 to 96 long block ???? It's a Better Block.... Already for roller lifters,+ cam..... Price 1 out for a pickup/truck application,+ All you Need to swap out is the Headgaskets,+ Core-plugs......... The Truck Cam is So Close to the Marine app., It Doesn't Need Changing....... 96,+ later 350s will also drop into your boat.... The differences are the Heads,+ intake manifold...... The Vortecs are the Best SBC Ever Built....Bar None..........I'm refitting My 1969 327 with Vortec heads.........Not the best racing heads, but their Real Torque Monsters........ Truth is, Any SBC from 1955 to the present 350s Will bolt up to your boat, With the Right Collection of Parts................... Although the Best, Simplest swap is a motor of the Same Vintage/Year Class as the 1 there Now....................

PGtoy · Feb 15, 2005

Re: Rear Main Seal

Bondo, Thanks for the info. Summit racing will have a 5.7 Gm crate engine Long block soon for truck use 3/4 ton one piece main for 1900.00 or so. that sounds like the one

Bondo · Feb 15, 2005

Re: Rear Main Seal

Your Local GM/ Chevy Dealer will sell you 1 over the counter.......... Why wait for Summit..... Do a Google search......

Reel Poor · Feb 15, 2005

Re: Rear Main Seal

For that kind of money and most probably a "VOIDED" warranty on a "NEW ENGINE" because of engine tampering, why not look into a quality MARINE REMAN WITH WARRANTY? Some of the better rebuilders give a 2yr PART AND LABOR warranty. hum.........

qystan · Feb 16, 2005

Re: Rear Main Seal

Buttanic The info is not intended to show that both crankshaft can be used interchangeably, I wouldn't even give it a try. Looks like it conveyed the wrong message. The info shows that the same 1996 flywheel is useable all the way back to the 82-86 and 87 2 pc seal series engines. There are 2 crankshafts p/n used in the 82-86 series engines, means one (or both??) of the crankshafts should fit the 96 flywheel. This should be confirmed by a physical inspection to determine which crankshaft is installed.

Bondo · Feb 16, 2005

Re: Rear Main Seal

The info shows that the same 1996 flywheel is useable all the way back to the 82-86 and 87 2 pc seal series engines.

Qystan, I don't know where you're finding this info,...... But, It's Wrong.......... The Flywheels for Pre-87 are Very Different than the post-86s................... They Will Not Bolt Up....... And, Are Balanced Very Differently........ There's nearly a 1/2" difference in the bolt patterns.........

MGallik · Feb 16, 2005

Re: Rear Main Seal

The auto/truck engine may also have dished pistons to meet emissions rather than a marine engines flat top pistons. The dished pistons will be more prone to detonation and make less power in a marine engine.

qystan · Feb 16, 2005

Re: Rear Main Seal

Got my info from the Merc Electronic Catalog, I am usually wary of publication data, which is why I recommended a visual. Coming from you guys, it is likely the info I have is incorrect. Below is the 1982-86 page. Item 7 for the flywheel. http://mercruiserparts.stemtostern.com/MercBlockDisplay.aspx?DocNumber= 99985 This is the 1996, item 3 is the flywheel. http://mercruiserparts.stemtostern.com/MercBlockDisplay.aspx?DocNumber=816596 96

Rear Main Seal

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