swap auto block for a marine? Mercrusier 4.3

ercstric · Sep 15, 2005

i have a 1985 wellcraft elan,20' -- with a 4.3l mercrusier v6. just bought it this year, and has run great except for water in the oil... uh oh.. that's right, previous owners did not winterize. now i have a major internal crack all the way accross. (by the way the tried to cover this up with JBWELD) my boat guy says i need a new short block $1200 - 1500, but i am handy with cars and can get one at the junk yard for $50 everything else is great on the motor, but the block, can i use an auto? if so, what do i need to do to it to make it work, and off of what kind of car should i pull?

WillyBWright · Sep 15, 2005

Re: swap auto block for a marine? Mercrusier 4.3

You can, but it won't hold-up as well. You'll want to use your heads at the very least. Changing cams would also be wise. The Boat versions don't have to meet EPA guidelines, so they're engineered quite a bit differently. They also tend to get more horsepower than the car 4.3s. After all, how many car motors will tolerate redline for hours at a time? Boat motors do it all day long.

4.3sunbird · Sep 15, 2005

Re: swap auto block for a marine? Mercrusier 4.3

your proplem will be fuel pump mounting auto's were fuel injected and dont have a boss to mount a pump other than like 85 model blocks which are pretty much impossible to find the entire engine in my boat I built out of automotive engine parts .. which are no different other than gaskets , freeze plugs ,cam but car cam would work I have alot better engine now than came in it 88 up s10 trucks are full of 4.3's

KaGee · Sep 15, 2005

Re: swap auto block for a marine? Mercrusier 4.3

Buy a truck motor and you won't have to worry about the Cam. Should you end up with a short block without provision of a mechanical fuel pump, just convert over to a marine electric pump with proper output. May want to consider a Vortec upgrade?

Bondo · Sep 15, 2005

Re: swap auto block for a marine? Mercrusier 4.3

The Key to working on/Playing with SBCs(Yes, the 4.3 is the little sister of the SBCs)......... Is to stick to the Year of Production of whatever you're dealing with............. Your boat is an 85,... Chances are the motor is an 85 vintage also,...... Serial #s,+ Casting #s can be used to verify this,........... These Mercruiser engines are Standard Production Chevy Truck motors,....... Right off the assembley-line,... for whenever Merc. bought them........ If you were to Find,.. or Build a 1985 Truck motor,.... You'll find All the holes are Exactly where they belong,............ The up-grade to a Vortec motor would be a Great Move,............ But then you're right back to the Dollar$ that your Mechanic is talking now........ It All depends on the Amount of the Work You're going to do Yourself................

ercstric · Sep 15, 2005

Re: swap auto block for a marine? Mercrusier 4.3

if i can use just a straight automotive engine, i will do it my self. i mean i work on cars/trucks with no problem. i have just been a little intimidated with this boat -- not having ever done much with i/o before. so if i am understanding correctly, a s10 motor should work -- i mean just match up? my mechanic says that automotive motors were not made to run like marine engines, at those RPMs.

ciliento · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

I have done that job, you need to change a lot of stuff you have to change all the gaskets and freeze plugs, the cam, the flywheel, fuel pump. water pump and others, wish I would have just bought a marine engine, they are cheap enough

KaGee · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

Originally posted by hardluck: my mechanic says that automotive motors were not made to run like marine engines, at those RPMs.

Your mechanic is mistaken. The basic block is the same except for the cam, gaskets and freeze plugs. My OMC Factory manual tells me to consult my local Chevy parts dealer for engine internal parts. The cam grind on a Chevy truck motor is very close to a marine grind so it will work without any noticable difference. If your existing motor is a closed cooled system, or you boat in fresh water only, you can get away with using standard gaskets and freeze plugs. Otherwise you should have brass freeze plugs and marine gaskets. Like Bondo said... get a motor from the same vintage. Strip it down to what you would consider a short block and build it up from there using the tin and "marine" stuff from your old motor.

whywhyzed · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

I, like Keith, have a v6 chevy I rebuilt with a short block. During the swap, I compared everything to the original OMC marine engine. Same crank, same block, same heads! castings, valves everything, same pistons, same rods, same rings. part number by part number.... everything, except the cam, was identical. The cam grind was quite different.. I have the measurements somewhere for the 2 different cams, and that's where basically ALL of the extra ponies come from in a marine engine. It's ground smaller on the base circle basically to provide more lift. Like others here, I used an automotive head gasket as I am in fresh water and it's working fine 2nd season now. I used brass core plugs, but next time I would probably just do the rear one.

rbezdon · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

If you replace the head gasket again, stick to the marine. It has stainless borders to stand up better to the high load in the conbustion chamber. I have also heard that the rings were different, the equivalent of the Chrome molly rings we used to put in the racing engines when I was a kid. I guess it is possible that is all that is used now but I am a little out dated.

whywhyzed · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

my original head gaskets were 1 pc all stainless... as I was reusing the heads without resurfacing, I thought best to have an automotive gasket that could better conform to any imperfections...

Bondo · Sep 16, 2005

Re: swap auto block for a marine? Mercrusier 4.3

I could argue the Headgasket Myth All Day..............

Most of the engines out there are running a Composite Headgasket,........ It really Doesn't Matter whether the Fire-Ring is made of Carbon, or Stainless Steel,... It Doesn't See Water,......... Hopefully.......

If by chance you Had to use a Shim Gasket,..... You could go with Copper, or Stainless..... I use a Good Quality Fel-Pro Composite on Most All of the motors I do.............

KaGee · Sep 17, 2005

Re: swap auto block for a marine? Mercrusier 4.3

Originally posted by Bondo: I could argue the Headgasket Myth All Day..............

Just to back my 'ole buddy Bondo... On the engine that Hystat and I have, The "Marine" gasket is hard to come by unless you buy a complete overhaul kit. Then you better take out a second mortgage to get it. I personally talked with tech support at FelPro and they assured me that the stock gasket in stock at AutoZone for about $22 a set (or there abouts) would work fine in most applications.

ercstric · Sep 17, 2005

Re: swap auto block for a marine? Mercrusier 4.3

all righty then, it is decided.... i am going to grab an auto 4.3 and get back into the water. next question, as i previously mentioned, i work on cars, but never boats. what is a good -- illustrated -- source for i/o? is there like a HAYNES manual for mercrusier?

Bondo · Sep 18, 2005

Re: swap auto block for a marine? Mercrusier 4.3

i am going to grab an auto 4.3 and get back into the water.

That's Truck Motor.................

what is a good -- illustrated -- source for i/o? is there like a HAYNES manual for mercrusier?

Mercruiser's Own,..??......

swap auto block for a marine? Mercrusier 4.3

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