4.3 OMC engine replacement info needed

Normspeed

Cadet
Joined
Feb 20, 2011
Messages
9
First an intro. I've been browsing this forum for a while and I see a lot of great knowledge here. I'm looking for some specifics regarding how to spot the best and most compatible used motor for rebuilding and installing in my 86 Galaxie Starion. I've owned this rig for 16 years and it's been a great reliable boat. Only 405 total hours since new.

Living in the southern U.S., in 16 years I had never drained my block and manifolds for winter but this year mother nature got me. This winter we had a record breaking cold snap and I fell victim to the freeze. Starboard head has a visible external crack and port manifold cracked. Even worse, plenty of water in the crankcase which I suspect means the block cracked as well. I'm heartbroken. The stringer outdrive is in great shape and the rest of the boat, although old, is still real serviceable. I would hate to part it out or donate it to charity. I'm mechanically savvy and have an engine hoist and plenty of tools, as well as OMC manuals. From reading other posts here, I see there were changes to the Chevy 4.3 liter motors over the years that could affect compatability with my drive, mainly the bolt pattern on the crank. Is there a source for me to find which years or block numbers would most likely be compatible with my setup? Is the crank flange different if the motor is attached to a standard versus automatic trans? It's an 86boat but has the stringer outdrive so I'm thinking it's an 85 powertrain.

Right now I'm on the fence about repairing the old gal. If I can do it without going completely upside down on cost versus boat value, I'd like to keep her. Many years of great times and much sentimental value here.

Any info, reference sources, shared experiences, would be greatly appreciated. My next step will be to check for cracked block. I read the sticky on milky oil and pressurizing the block. I assume that means pressurizing the water jacket, but with a cracked head spilling water, I don't think that will reveal much. If I pull the intake and do a visual, is it likely that block cracks will be in the valley area, or are there more hidden areas that are likely to crack?

Sorry for the long post. I look forward to hearing from other folks who have gone through this.

Here are some identifying numbers from the motor: From the thermostat housing, MOD432STMRCOM. Ser J842753. MOD984210. J403231. The number on the engine block is J842753. On the front of the port head is 1537.

Norm
 

Bondo

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Apr 17, 2002
Messages
70,465
Re: 4.3 OMC engine replacement info needed

From reading other posts here, I see there were changes to the Chevy 4.3 liter motors over the years that could affect compatability with my drive, mainly the bolt pattern on the crank.

Ayuh,... You need a 1986, or Earlier....
 

Normspeed

Cadet
Joined
Feb 20, 2011
Messages
9
Re: 4.3 OMC engine replacement info needed

Thanks guys, that helps. I'll keep an eye out for a motor that might work. Meanwhile, I haven't dug into it any further. I'm guessing that the block cracked since there's water in the oil, but then that could possibly be from the damaged head. Do you know, when the 4.3 blocks crack from freezing, is it usually in the valley area where you can spot it, or can they crack in other areas that are harder to detect? If it's just head and manifold damage the repair would be a lot easier and cheaper.

what he said, '87 was the changeover year, so anyhting from before that will work.
 

Bondo

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Apr 17, 2002
Messages
70,465
Re: 4.3 OMC engine replacement info needed

Ayuh,... Odds are Slim, to None that it's a Head....

The blocks crack in the lifter valley, or inside the block, opposite the drains...
 

Normspeed

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Joined
Feb 20, 2011
Messages
9
Re: 4.3 OMC engine replacement info needed

Well, this will take a lot of consideration on my part. I've done mechanical work as a hobby all my life and did it for a living in my younger days. But these days I'm getting kinda tired of beating myself up. I could part the rig out and recoup a fair amount, since it's a solid fresh water only boat with a healthy Stringer outdrive, good trailer, and some decent accessories, but I could never bring myself to dismantle the old gal after all the years and all the good times. I'll sit on it for a while and do some searching for a suitable motor. Guess I'll either fix or sell at a bargain price locally, maybe work up a trade for an aluminum rig with a running outboard. I guess the (expensive) lesson here is, no matter how warm a climate you live in, winterize your boat. For the sake of a few minutes' time to open those petcocks, I've pretty well lost my boat.

Thanks again for the comebacks, and if anyone else has more to add, I'm all ears!

Edit: This just occurred to me, anyone know the year the crank seal config changed? And would the new seal be compatible with an older crank? I ask because my crank is certainly still very good, and if a later block would accept the crank and cam from my early motor, and if the motor mounts were in the same location, I might be able to overcome the crank flange thing by re-using my crank. It would widen up my search for another block.
 
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180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
Re: 4.3 OMC engine replacement info needed

crank (and seal) changed in 87, balance shaft added in 92 and vortec heads introduced in 96.

TBI heads are the worst ones GM ever used, vortecs are arguably the best GM design, and can be put onto any year block.

As for reusing your existing crank etc in a "new" block - DON'T Internally, these engines are a parts swapping nightmare. Externally, all is good.
 

Normspeed

Cadet
Joined
Feb 20, 2011
Messages
9
Re: 4.3 OMC engine replacement info needed

Well, all things considered, I decided that it was time to part with my beloved old Galaxie. Found a buyer who has the mechanical skills and funds to get it right. I was completely up front with him about the damage I was aware of and the possibility of additional hidden damage. I also shared with him the great tips you folks supplied on this site. I tossed in all the extras I had, like the water ski equipment, and all in all he got enough good stuff that he can't really lose at the price I was asking. So today I waved goodbye to my old friend of 16 years as he towed her out of my driveway. A bittersweet moment to be sure, but there's a time for everything and I feel OK about letting her go to a new owner. I'm sure that in the future I'll end up with another runabout, most likely an aluminum hull/outboard rig. Lighter and easier to tow. That will still be a couple years off. But I'll sure remember that old Galaxie fondly. Definitely not the proverbial hole in the water etc etc.

Thanks again to all who shared their knowledge with me. Happy boating!
Norm
 
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