Cracked block - fixable?

[Vanguard08]

I've got a b7100 HST that had a leaky radiator that I've replaced. I haven't had issues since I put the new one in but I'm guessing I've got some nasty cold damage. I started it up a few days ago and noticed my radiator was empty so I filled it up but saw a pretty tragic drip of water underneath and traced it back to a crack on the block.
1) What did I likely do wrong or didn't do right that would cause such a crack? I can only think of running it hot or freeze damage
2) Can this be repaired with a weld or do I have to tear this whole thing down to replace?

Here's a picture: the left side shows where the crack is, it's on the backside near the fuel tank. The right side shows the crack itself.

I can take more pictures or a video or something if it's helpful. Hoping this can be repaired but guessing not so much so hopefully I can at least learn a lesson here.

 

[Hugo Habicht]

Well, we had that subject a while ago: Link fixing hole in side of the block , not to be taken too seriously.

If it was frost damage there could be more than just this crack in the block. But if you want to risk the rest of the engine you can try JB weld, as Joe Smith used in the thread above.

 

[North Idaho Wolfman]

That does not look like the block that looks like the head, more pics and zoom out a little.

If it is the head that's cracked, then you're more than likely looking at a head replacement.
Much cheaper and easier than replacing the block.

And over heat or freezing can cause that style of crack.

 

[#40Fan]

I want to say that is where the head meets the block and they are both cracked.

 

[Vanguard08]

I want to say that is where the head meets the block and they are both cracked.

yea... I was gonna go out and take another picture but I'm fairly sure you're spot on. The crack started below but just traveled right on up. I'm gonna try some JB weld to see how much more I can get out of it... other than hopeful duck tape limp-a-longs, I guess I'll start looking for parts and salvage rigs to see if I can rebuild it.

 

[Mark_BX25D]

Well, if you are going to go that route, make sure you clean it cleaner than you think is possible.

 

[#40Fan]

Well, if you are going to go that route, make sure you clean it cleaner than you think is possible.

Yep, take a propane torch to it and get it hot to boil off any oils/fluids.

I doubt it will hold, though. Maybe if you pull the guts out of the radiator cap to keep it from building pressure.

 

[North Idaho Wolfman]

Yep, take a propane torch to it and get it hot to boil off any oils/fluids.

I doubt it will hold, though. Maybe if you pull the guts out of the radiator cap to keep it from building pressure.

This is a thermosiphon system.
Altering the radiator cap in itself will make it overheat.

 

[BT3101]

Likely since the radiator was leaking the PO was just adding water, assuming it would leak right back out. If you are going to use JBW, I'd at least try to grind a small V-shape into the crack. Not only gives significantly more surface area for adherence, but also a nice contaminant free zone.

 

[Vanguard08]

Curious what you mean about grinding a V-shape into the crack. I'll clean it off as well as I can and I'll torch it to make sure to boil off any remaining residue to give the JB as much of a fighting chance as I can, but what would be the point in grinding into the crack? Is that just to grind away a small surface area so to have fresh clean metal to apply the JB to?

 

[North Idaho Wolfman]

Curious what you mean about grinding a V-shape into the crack. I'll clean it off as well as I can and I'll torch it to make sure to boil off any remaining residue to give the JB as much of a fighting chance as I can, but what would be the point in grinding into the crack? Is that just to grind away a small surface area so to have fresh clean metal to apply the JB to?

Yes that typically would be what you want to do.
But in your case don't do it, as that metal is so thin that you will be opening a real can of worms.
If that crack is only the head, then your chance of success is possible but low.
If the crack extends from the head into the block, then your chance of success diminishes into almost nothing.

 

[Vanguard08]

Well I'm filled with encouragement now...
Maybe I'll take a Dremel and just lightly buff the area around the crack

 

[Hugo Habicht]

I would not cut a groove. The rough crack has best adhesion for the glue against pressure from inside. Clean everything meticulously, brake cleaner may work well here. And then heat everything if you can. Epoxy glue get very soft then and creeps into the gap.

 

[airbiscuit]

I had a Farmall H with a crack at the bottom of the rear end. I cleaned it well, touched it with an angle grinder to expose bare metal, cleaned it with lacquer thinner and applied JB Weld. It lasted for decades.

 

[L35]

I hate to be a pessimist but I’m in the “don’t waste your time” camp. JB weld has its uses but in a pressurized cast iron situation with large temperature swings it usually fails due to expansion/contraction. It’s a cheap experiment and I hope to hear the end result after a dozen or so heat cycles. Don’t leave us hanging!

 

[airbiscuit]

 

[airbiscuit]