Cracked cylinder head leaking coolant

[MiCarl]

My '48 Cub has an external crack on the head. I'd noticed it in the paint before but didn't worry about it since it wasn't leaking. Today it started leaking coolant. It only leaks when it's good and hot, shut the engine down and it stops almost immediately. When it's hot though it leaks pretty fast.

I replaced the coolant about two years ago right after I got the tractor. There was a lot of sludge on the bolster drain plug. I suspect the coolant might have had stop leak in it to keep the head sealed but it eventually opened up with straight 50/50 mix in it.

I'm not real keen on replacing the head right now. The tractor is burning some oil and at some point I'll need to tear it down for a rebuild and would prefer to do the head at that time.

Short of replacing the head I can think of 3 options:

1. Add a stop leak product to the coolant and hope that closes it up
2. Attempt to solder the crack with the head on the engine
3. Attempt to braze the crack with the head on the engine

I'd appreciate any thoughts/experience on which approach to take.

[Barnyard]

Since there is no water pump I doubt the stop leak will circulate enough to get to the crack.

[Jim Becker]

Option 4: Attempt to patch the crack with an epoxy material like JB Weld. Grinding a slight groove along the crack will give it a place to bond.

Advantage over solder or braze is it is done at room temperature while the other options require getting quite a bit of heat into the head while the rest of the engine is a heat sink.

[MiCarl]

Option 4: Attempt to patch the crack with an epoxy material like JB Weld. Grinding a slight groove along the crack will give it a place to bond.

You know, this was my first idea but I discarded it thinking the epoxy might work loose. The more I think about it though the more I like it. It did belatedly occur to me that since the system isn't pressurized it doesn't need a lot of strength. Chewing gum would probably do the job until the coolant dissolved it.

Better yet, I recently opened a package of epoxy for another job. Now I can get a second use before it either dries up or leaks all over the bench.....

Supposed to rain Tuesday. Will do the job then.

Thanks for the input Jim.

[Barnyard]

There's a crack somewhere in this picture of the side of my block. Dan England patched it with JB Weld back in 2007. I bought it from him in 2008 at the last Texas Tumble and it has been holding up since.

[John *.?-!.* cub owner]

Before you use something on the order of JB Weld, clean the paint from around it. They make a stick type that will work where something is seeping.

[coppersmythe]

Option 4: Attempt to patch the crack with an epoxy material like JB Weld. Grinding a slight groove along the crack will give it a place to bond.

Advantage over solder or braze is it is done at room temperature while the other options require getting quite a bit of heat into the head while the rest of the engine is a heat sink.

the last time i tried to braze a crack in a head , it did not go well . i think jim has the best reason why . i have a lot of experience at brazing , have been doing it for 40 years . as john said ,clean clean clean , maybe drain some coolant so it does not seep while working on it . coppersmythe......................

[MiCarl]

Yes, I'll drain some coolant, sand away the paint, cut a minor V to lay the epoxy in and give it a thorough cleaning.

[MiCarl]

Tackled it this morning. Crack was so tight it was difficult to see. I tried pressurizing the system with a shop vac to get it to blow soap bubbles. Cold it's tight enough it wouldn't bubble.

Shined light on from multiple angles trying to see it all and get it marked with a sharpie. Ground a slot over it with the die grinder. Was easier to see where I'd ground the slot.

Filled with epoxy. Tomorrow I'll sand and paint.

I wonder if it wasn't just paint sealing it all along........