Mercruiser 3.7 cracked block

[HT32BSX115]

Re: Mercruiser 3.7 cracked block

Couple of thoughts; I have a 470, so am particularly sensitive to its problems and always read every 470 post and in the last 3 years or so I think that this is the first real case of a cracked 470 block that I can recall, so I do not believe that it is a very common problem, as opposed to freeze cracked seawater cooled engines. A lot of guys suggest a 4.3 from a "donor" boat, but they are donor boats for a reason (including frozen engines) and would very likely need a rebuild anyway. Besides a standard 4.3 is not that much more powerful than a 470 and weighs about 200# more. IMHO a rebuilt well maintained 470 is just as reliable as any other engines of that vintage. Good luck with whatever you do.

I am not sure I have EVER read about anyone with a "cracked" 470 (3.7L) unless it was due to a SEVERE overheat.... which would probably result in a different type and location of a crack(s)...and of course entirely possible if someone just put regular water (or not enough xx-glycol) into the cooling system....

If it was definitely cracked due to freezing, there could absolutely be more than one (external) crack.......

Just about all boats made, have been offered with different engines and drives. A boat that could be ordered with a 470 could probably also be ordered with a V-6 or V-8 if there available in that model year as an option.

There's likely more than enough room for a V-6 or even a V-8.

 

[achris]

Re: Mercruiser 3.7 cracked block

..

Just about all boats made, have been offered with different engines and drives. A boat that could be ordered with a 470 could probably also be ordered with a V-6 or V-8 if there available in that model year as an option.

There's likely more than enough room for a V-6 or even a V-8.

Not necesselary Rick,

Mine boat was available with either an inline 6 (165) or a Ford 302 V8 ('888'), but it was no easy job to drop one engine into a hull designed for the other engine. The engine bay size and shape in the floor was cut differently in the factory, as was the engine box, for each engine.

Just saying,

Chris.........

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

here's the pics after disassembly. I'm not thinking JB Weld or welding is going to fix this. what do y'all think?

 

[Don S]

Re: Mercruiser 3.7 cracked block

I agree, that's not fixable.
It's probably from previous freeze damage when the po forgot to check the antifreeze and it was all water. It froze and cracked the block. He may have dumped in a bunch of stop leak to stop it long enough to sell it. Now the stuff is past it's useful life and it leaks again.

 

[ricohman]

Re: Mercruiser 3.7 cracked block

I weld aluminum and I've used JB weld on aluminum cylinder heads to fix casting flaws that couldnt be welded. If you can clean and prepare the area I wouldn't doubt JB weld could repair this. If you can't weld this is the best option.
That is a long crack but if you prep the area carefully you might get away with JB weld. I would weld it if it was my boat.

 

[aerobat]

Re: Mercruiser 3.7 cracked block

i would not put any money in welding. you might consider a last chance epoxy repair. we have one guy at the marina which had a freezing cracked manifold on a aq170 volvo and he just cleaned and epoxied it. it holds now the third year.

before even spend some dollars on this make sure that you have no water in oil etc- so internal cracks. also consider to contact the seller since this damege is freezing for sure .

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

so, yesterday after posting the pictures, I decided to jump on the motorcycle for a long ride in the country to give me time to think. Seems the best thing to do for the long run is to find another good block and have my machinist do a rebuild for me. However, since I really have nothing to lose, I think I'm going to try to clean up the block and epoxy it to see how it works. Worst case is that I'd have to rebuild anyway, huh?

I sure do appreciate all the help, input and support from this forum. If you guys were closer, I'd buy you a beer or a cup of coffee!


thanks!

 

[MarkSee]

Re: Mercruiser 3.7 cracked block

Worst case is that I'd have to rebuild anyway, huh?

That's true. Maybe you'll luck out enough where you can get another season out of it while shopping for a replacement to have ready when this one finally gives out.

Good luck.

Mark

 

[HT32BSX115]

Re: Mercruiser 3.7 cracked block

Not necesselary Rick,

Mine boat was available with either an inline 6 (165) or a Ford 302 V8 ('888'), but it was no easy job to drop one engine into a hull designed for the other engine. The engine bay size and shape in the floor was cut differently in the factory, as was the engine box, for each engine.

Just saying,

Chris.........

Well, I didn't say ALL boats......I said "Just about" all boats. That would cover me for the one out there (like yours) that was different wouldn't it? :happy:

 

[tazrig]

Re: Mercruiser 3.7 cracked block

Good luck with the epoxy. Just make sure to watch your temp gauge closely! You have nothing to loose EXCEPT if the crack gives way completely and you seize the engine. Then you won't have much left to even rebuild. You've put so much into the boat. It would be a shame to see that happen.

 

[HT32BSX115]

Re: Mercruiser 3.7 cracked block

I weld aluminum and I've used JB weld on aluminum cylinder heads to fix casting flaws that couldnt be welded. If you can clean and prepare the area I wouldn't doubt JB weld could repair this. If you can't weld this is the best option.
That is a long crack but if you prep the area carefully you might get away with JB weld. I would weld it if it was my boat.

That crack is on the outside. If there was none on the inside, I too might try drilling, grinding and welding. BUT, after that I think the block would have to be surfaced to ensure a flat and true surface for the cyl head and gasket.



But again, Before I did anything, I would probably find someone that uses those engines in circle track racing. That's where some of them go these days and they do a LOT of things to keep them running. It's probably been tried (welding a long crack) and it either worked or it didn't.


After you did all of that I think you'd STILL be right up there with just getting a good used core engine to rebuild.

 

[ricohman]

Re: Mercruiser 3.7 cracked block

You need to drill both ends of the crack and use a wheel to open the center. Going to be tricky where its raised. Obviously the paint is going to need to be removed around the crack.

 

[generator12]

Re: Mercruiser 3.7 cracked block

Couple of thoughts; I have a 470, so am particularly sensitive to its problems and always read every 470 post and in the last 3 years or so I think that this is the first real case of a cracked 470 block that I can recall, so I do not believe that it is a very common problem, as opposed to freeze cracked seawater cooled engines. A lot of guys suggest a 4.3 from a "donor" boat, but they are donor boats for a reason (including frozen engines) and would very likely need a rebuild anyway. Besides a standard 4.3 is not that much more powerful than a 470 and weighs about 200# more. IMHO a rebuilt well maintained 470 is just as reliable as any other engines of that vintage. Good luck with whatever you do.

I'm with Stony. If this boat is going to provide entertainment for a bunch of twenty-somethings - running WOT for long periods, pulling skiers all afternoon, running offshore for hundreds of miles at a time - look for something else.

If, on the other hand, you intend to do some nice comfortable cruising, get out for some fishing, in short - some "gentle" boating, your engine is just fine and should remain fine.

As everyone says about this rig, watch the temperature. And I suggest, respect her age.

 

[fat fanny]

Re: Mercruiser 3.7 cracked block

The history of the 470 is skeetchy @ best or they would still be making them for marine use epoxy it for now and start looking for a donor 3.0 with all the accessories there all over e-bay,craigslist and maybe worth going the re-man route! Good luck!!!

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

I'm in the midst of the epoxy route and am not holding any illusions that it will be of value long term, but perhaps it'll get me through a little bit of use. I've found a potential donor motor locally and am going to head down the route of a rebuild. If by some chance the epoxy does hold, maybe I'll have a spare motor for the next problem that comes along! lol