Mercruiser 3.7 cracked block

[Old Yeller Boater]

Ok....at this point I'm pretty much heartbroken over this boat. I purchased an 87 Larson DC190 early last year and it turned into a real project to get things going. First step was overheating which I corrected with a head gasket replacement. That, along with an adjustment of the timing (it's got an aftermarket alternator and electronic ignition now) had the motor running MUCH better. My next step was to repair a bad water leak in the transom along with repairing the floor where the previous owner had scabbed in a piece of plywood. I finally got all that work done by a professional a few weeks ago. While that work was being done, I found that the alternator bracket had broken and I welded up a new one and now have it installed and working fine.

So now the bad news. After getting the boat back, getting the repaired alternator bracket on and getting the boat running, I have now found a crack in the block on the port side of the motor. it is just below the exhaust manifold and somewhat behind where the starter is located. My plan is to remove the starter, exhaust manifold and coolant reservior to have a good look at how bad the situation is.

Since getting the boat last spring, I've always run 50/50 antifreeze in the block and of course, it has a heat exchanger, which I drained water from prior to parking it for the season in October. Here in NC we've not had any really hard freezes so far this year and I just can't imagine the crack was due to the block freezing. That only leaves that the leak was there when I bought it and I've not been able to notice it due to all the water it had been taking on. However, is it possible when I put the head and exhaust manifold back on I over torqued or something? I used a torque wrench and did things according to the specs in the manual. I'm at a bit of a loss.

So...I realize I don't have pics yet to see the extent of the damage, but could anyone give me some ideas on what I may be facing? If the crack is not too bad, can it be fixed with JB Weld? Could I have the block repaired? Am I facing installing a new motor?

Any input appreciated.... :blue::blue::blue:

 

[Bondo]

Re: Mercruiser 3.7 cracked block

That only leaves that the leak was there when I bought it and I've not been able to notice it due to all the water it had been taking on. However, is it possible when I put the head and exhaust manifold back on I over torqued or something? I used a torque wrench and did things according to the specs in the manual.

Ayuh,.... My guess is, it's been there all along,...
Over tightenin' bolts, strips threads, it don't crack blocks...

Strip it down, grind out the crack, 'n try epoxyin' it,...
At this point you've got Nothin' to loose...

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

thanks for the reply. I also just got off the phone with my local machine shop that did my head work. he told me he does not do block repairs but has someone that does. He said as it's an aluminum block, it could possibly be welded, but this guy charges 50 bucks an inch to weld, and I think this crack is well over 6 inches long, maybe longer. Step one is to remove the exhaust manifold and coolant reservior and starter and he can take a look at it and give me an idea. The JB Weld would work on the aluminum block???

He also told me if I could find another good block, he could bore it to 30 over to match the current pistons and swap everything over for about $1200. I suppose that would be worst case other than my time pulling the motor and such.

Any other input or suggestions greatly appreciated!!!

thanks guys!!!

PS. The really good news about the transom is that the guy used a composite material to put it back in, so it should never rot again!

 

[Don S]

Re: Mercruiser 3.7 cracked block

I doubt epoxy of any kind will work on your block. Unlike raw water cooled engines, yours builds up 12-15 lbs of pressure and runs at 180?.

The weld could work, but who knows what the alloy of that aluminum is and if you can be welded at all. Also, if it was up near the top of the block, you could end up warping the sealing surface for the head, then you would be in a mess.

A new/used block would be your best choice, and you wouldn't always be wondering if the repair is going to hold.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

I'll look into it. Thanks Don!

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

....and if anyone in the south-east happens to have a line on a good 370 block, I'd be interested.

thanks all!

 

[stonyloam]

Re: Mercruiser 3.7 cracked block

There is a reasonably priced one in Georgia, on e-bay.

 

[Capt Ken]

Re: Mercruiser 3.7 cracked block

Those things are getting near impossible to find. Epoxy may be your best bet. Problem with tig or mig, if the aluminum wire used is a different hardness than the surrounding metal, it will expand and contract at a different temp and due to metal fatigue, recrack again.

 

[ziggy]

Re: Mercruiser 3.7 cracked block

don't know if it's compatible. but here's one in my hood w/ a boat. donor boat in your case. no idea how good the price is or anything else about it other than it says 470 on it.

 

[tazrig]

Re: Mercruiser 3.7 cracked block

Ok....at this point I'm pretty much heartbroken over this boat. I purchased an 87 Larson DC190 early last year and it turned into a real project to get things going. First step was overheating which I corrected with a head gasket replacement. That, along with an adjustment of the timing (it's got an aftermarket alternator and electronic ignition now) had the motor running MUCH better. My next step was to repair a bad water leak in the transom along with repairing the floor where the previous owner had scabbed in a piece of plywood. I finally got all that work done by a professional a few weeks ago. While that work was being done, I found that the alternator bracket had broken and I welded up a new one and now have it installed and working fine.

So now the bad news. After getting the boat back, getting the repaired alternator bracket on and getting the boat running, I have now found a crack in the block on the port side of the motor. it is just below the exhaust manifold and somewhat behind where the starter is located. My plan is to remove the starter, exhaust manifold and coolant reservior to have a good look at how bad the situation is.

Since getting the boat last spring, I've always run 50/50 antifreeze in the block and of course, it has a heat exchanger, which I drained water from prior to parking it for the season in October. Here in NC we've not had any really hard freezes so far this year and I just can't imagine the crack was due to the block freezing. That only leaves that the leak was there when I bought it and I've not been able to notice it due to all the water it had been taking on. However, is it possible when I put the head and exhaust manifold back on I over torqued or something? I used a torque wrench and did things according to the specs in the manual. I'm at a bit of a loss.

So...I realize I don't have pics yet to see the extent of the damage, but could anyone give me some ideas on what I may be facing? If the crack is not too bad, can it be fixed with JB Weld? Could I have the block repaired? Am I facing installing a new motor?

Any input appreciated.... :blue::blue::blue:

Sorry to be the bearer of bad news but especially with a 6 inch crack in it, the only realistic long term option is to replace the block. You can find them all over google. Some as low as $400.

 

[achris]

Re: Mercruiser 3.7 cracked block

...but who knows what the alloy of that aluminum is and if you can be welded at all....

It's Merc's XK360 alloy, same as their outboard engine blocks and the castings of the drive housings. Very weldable...

Chris.......

 

[HT32BSX115]

Re: Mercruiser 3.7 cracked block

I doubt epoxy of any kind will work on your block. Unlike raw water cooled engines, yours builds up 12-15 lbs of pressure and runs at 180?.

The weld could work, but who knows what the alloy of that aluminum is and if you can be welded at all. Also, if it was up near the top of the block, you could end up warping the sealing surface for the head, then you would be in a mess.

A new/used block would be your best choice, and you wouldn't always be wondering if the repair is going to hold.

Cast aluminum heads and blocks are welded all the time.

I have a pretty nice TIG welder and have welded quite a few different aluminum things and have found that aluminum castings are fairly easy to weld.

But, considering the availability of of 3.7L Mercruiser engines and parts on craigslist, ebay etc,

I too would find a good used engine and/or do a rebuild ........ and then do a recycle number on the cracked block. Aluminum is worth around $0.45 per pound [for more than 100lbs] around here if it's clean.......

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

Man, this is really a tough one. I really do appreciate everyone's comments and input. Sounds like welding might be an option depending on what I find when I get all the parts off to see the extent of the damage. I'll post up a pic on this thread in case anyone should ever run into the problem on theirs. This particular motor was a quicksilver replacement in 2005 and has less than 100 hours on it based on what I'm aware of from previous owner and his friends. it was a .030 overbore when rebuilt. I'm thinking there's good reason to try the welding if not too expensive to try to save an otherwise good motor.

If I were to buy another used one, who really knows that I'd get....or I'd pay a premium price for it. if I have to, I'll probably go the rebuild route with my local machine shop. he said 800 to 1200 depending on how things look inside.

By the way...I did find a used motor about 300 miles away that the guy wants 700 for and he had a video of it running. My only concern is not knowing how many hours are on the motor if it will last or not. Any comments or words of wisdom on that front????

Hopefully tomorrow I'll get the parts off and see what the real damage is.

More to come and thanks again for the input! I just love the value of this forum!!!!!

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

I thought about going with a 4.3, but doing some research here, I found some comments that it was harder than just "swap". Anyone have specific input on that idea?

 

[achris]

Re: Mercruiser 3.7 cracked block

I thought about going with a 4.3, but doing some research here, I found some comments that it was harder than just "swap". Anyone have specific input on that idea?

What input are you looking for? I did the swap from an in-line 6 to the V6 a few year back. Essentially the same as what you're talking about.

For starter you will need to:
Widen the engine box (If it's not wide enough)
Fabricate 2 engine mounts to accommodate the side mounts on the V6 (The in-lines have a front mount)
Change the exhaust Y-pipe...

That's about it...

What year is your current engine (please post engine serial number, not year. We're just been though the drama of someone posting a year, and the engine is clearly not that year).

Chris......

 

[Don S]

Re: Mercruiser 3.7 cracked block

It's not that bad a job if you do it like bubba said and replace everything from the front of the engine to the back of the drive. Then it all fits. Still a lot of work, and depends on if you have enough room under the engine cover for the V engine and if you have stringers to set the side mounts on of the V6.

When you get into trouble is trying to adapt the V6 engine to the drive and transom shield of an inline 4.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 cracked block

given that I JUST had the transom, bilge and rear floor section re-done, I don't wanna really get into ideas of widening to accomodate the motor either. Plus the cost part. I've put more money into this boat than it's worth already. thinking if the block repair isn't possible, I may just part it out and start over. Hate to do that, but the expenses just keep going up and up.

 

[achris]

Re: Mercruiser 3.7 cracked block

given that I JUST had the transom, bilge and rear floor section re-done, I don't wanna really get into ideas of widening to accomodate the motor either. Plus the cost part. I've put more money into this boat than it's worth already. thinking if the block repair isn't possible, I may just part it out and start over. Hate to do that, but the expenses just keep going up and up.

BOAT = Break Out Another Thousand....

Nobody said owning and maintaining a boat is cheap... (If anyone did, they're lying)

Chris.......

 

[MarkSee]

Re: Mercruiser 3.7 cracked block

...I don't wanna really get into ideas of widening to accomodate the motor either.

Here's a link to some dimension plans for the Merc. 4.3 so if your stringer system is narrower than what this shows, might help your decision process on what to do.
http://www.perfprotech.com/store/app_themes/ppt/images/product-specs/43L.pdf

Mark

 

[stonyloam]

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.