Cracked engine block

[Willsurf]

I’m one of those people who bought a cheap boat that had been sitting out uncovered for a number of years. It has a 3 liter Mercruiser and it turns out that the block is cracked up behind the manifold. I looked online and found that many people use JB weld to repair the crack. This boat is raw water cooled which I would think means that there is no pressure in the cooling system. Is that correct? If there is no pressure, it seems like flexibility would trump strength. So I was thinking that high temperature silicon or 3M 5200 might be better choices. Any thoughts? The 3M product has a service temperature of 190 degrees which should be adequate, but I’m favoring the silicon with a service temperature of 600 degrees. I was also planning to drill a hole at each end of the crack. I was also thinking of drilling and tapping holes about every inch and putting in a machine screw that I would grind flush. I think that this might help to limit differential movement along the crack which is about 9 inches. Any thoughts would be appreciated!

 

[scoflaw]

The crack you see may not be your only one

 

[wellcraft-classic210]

Hmmm -- Assuming the crack is from water left in the block and freezing -- you could have more than 1 area of damage.

Additional cracks in the block or exhaust manifolds would be common.

As you seem to be aware cracks do tend to propagate with thermal expansion etc.

Fixing them has had mixed results even when its only 1 accessible crack. -- But then again their is usually not a lot to loose except time -- Assuming you can limit the expenses.

That said you are correct in that the water pressure is low I am aware of cases where Welding , JB weld , Bolting a metal block with a Rubber gasket have all been used as patches with some success.

Not sure about 5200 or silicon -- Personally I would use JB weld or a bolted plate with rubber.



Where is the crack located you talking about ? ( PICs would help )

Does the engine run well and do you have any signs of water in the oil?

 

[nola mike]

Sitting out uncovered for years = rotten boat. I don't know that I'd even invest in a thing of JB Weld until you're absolutely certain that you don't have rotten floor/stringers/transom. Also, a neglected boat that wasn't winterized to begin with...yeah, I'd be worried about more than one crack.

 

[jp1669]

I had the same issue last year with my boat. I drilled both sides of the crack, cleaned it really good, sanded it down and put JB weld on it. It lasted right up until the end of summer in which I noticed it had made it's way through the JB weld in one little small area. I don't know what I am going to do now, either going to go through the same process and redo it or just try and JB weld over the already JB welded area, but that is my story so better luck to you.

 

[Scott Danforth]

the issue with cracked blocks is they tend to keep cracking. a block with a 9" crack will most likely have internal cracking too. the manifold is probably toast as well.

i agree, a neglected boat left exposed to the elements and not winterized has bigger problems than a cracked block

left neglected to the elements, the hull will get water in areas its not supposed to, which leads to rot and water soaked foam and damaged interior.

cheap and free boats are the most expensive, just be prepaired it is going to be a bigger suck-hole for cash than spending $10k on a well-cared for boat ready for summer.

 

[fishrdan]

I wouldn't use silicone or 3M 5200 (wouldn't want that getting into the crack and fouling up other repairs when it fails), use JBweld.

Drilling the ends of the crack - yes, but I wouldn't drill/tap the crack for screws. Clean it up spotless, jam JBweld into the crack, then cover it. If I had to do it, I'd be pulling the engine, so the crack is level and the JBweld flows into the crack instead of down the block.

As mentioned by others, you may have other issues, cracked manifold, exhaust elbow, internal engine crack, hull....

 

[Bondo]

I’m one of those people who bought a cheap boat that had been sitting out uncovered for a number of years. It has a 3 liter Mercruiser and it turns out that the block is cracked up behind the manifold. I looked online and found that many people use JB weld to repair the crack. This boat is raw water cooled which I would think means that there is no pressure in the cooling system. Is that correct? If there is no pressure, it seems like flexibility would trump strength. So I was thinking that high temperature silicon or 3M 5200 might be better choices. Any thoughts? The 3M product has a service temperature of 190 degrees which should be adequate, but I’m favoring the silicon with a service temperature of 600 degrees. I was also planning to drill a hole at each end of the crack. I was also thinking of drilling and tapping holes about every inch and putting in a machine screw that I would grind flush. I think that this might help to limit differential movement along the crack which is about 9 inches. Any thoughts would be appreciated!

Ayuh,.... Welcome Aboard,.... yer chances of success is 'bout 1%,.....

If there's a 9" crack under the manifold, there's most likely an 8" crack on the Inside(oil-side), opposite the drain plug,....

 

[tpenfield]

:welcome:

You only thought you were buying a cheap boat

As the others have said . . . the crack that you can see is probably the 'tip of the ice berg' . . . probably more cracks lie within. Best to get a new block. 3.0's are not all that expensive and you can use an automotive block and heads, and just swap out the head gasket and core plugs, then add all the marine fuel and ignition from the former engine. You will need to get a new exhaust manifold.

 

[Willsurf]

Thanks for all the advice. My first step will be to clean the crack and fill it with JB Weld and do a pressure test of the cooling system. If there are no more leaks, I’ll likely do more to shore up the crack.

 

[Lowchopr]

I use J-B weld on my crack where yours is located and it worked great but I'm still getting water in the oil and reading this thread makes me think I'm going to be engine shopping