Allis Chalmers B

Holmanc · Apr 13, 2020

I have a 47 allis b I purchased last fall
with a woods under belly mower to make
quicker work of our large lawn. I only put
maybe 10 hours at most before winter but I
noticed it would run fine for a while then
it would start running irradically and
would be down on power and would begin to
miss when it was under more load. Among
other things I suspected it may have a
blown head gasket. Upon removing the valve
cover I found coolant sitting under there
on top of the head confirming to me that
there was definitely an issue. However,
when I removed the head I did not find any
obvious signs of a blown head gasket
although I cant be 100% sure. There were a
couple suspect areas but the gasket was
also glued down quite well with gasket
sealer so it was damaged quite a bit when
I lifted the head off. Should I proceed
with the head gasket replacement or is it
likely there is another underlying
problem?

Crazy Horse · Apr 13, 2020

I think a head gasket glued down is a bit of a red flag. Not sure on that but it might be.

jm. · Apr 13, 2020

I would take the head to a good shop and have it checked.

Ted in NE-OH · Apr 13, 2020

Check the "freeze plugs" in the head, there are 3 of them, they can get a pinhole.

Steve@Advance · Apr 13, 2020

Sometimes those slow leakers can be impossible to see a bad gasket.

While the head is off it would be a good time to take it to a machine shop, have it gone through, magnafluxed, checked for level, valves and seats touched up.

Ted says there are freeze plugs in the top, replace them for sure.

Another possible source of coolant in the crankcase is the wet sleeve orings. It's a messy and involved job to replace them, but with the head off, no way to pressure them up and see if they are leaking.

It's your gamble, probably a 50/50 chance they are leaking, or could start leaking now that they have been disturbed. If any liners rode up from turning the engine with the head off, they will for sure need to be replaced.

Ron W · Apr 13, 2020

I have a 41 Allis C. It ran wonderfully all summer and fall. I double checked the antifreeze and it was good. The next spring there was antifreeze in the oil. Before I pulled the head, I filled up the radiator and putting a cloth over the opening and using the air gun, water bubbled up through little tiny pin holes in the freeze plugs. I tore it all down, pulled the freeze plugs, and found one of the plugs full of rusted out divits.

I have heard from many people this is very common. At shows, many guys shake their heads when you bring it up.

Bottom line is that you should change them no matter what. Since I did, I have not had any troubles. Good Luck.

Holmanc · Apr 14, 2020

I will check the freeze plugs in the head. I was hoping to not have to go so far as to pull the valves and take the head to a machine shop but if the freeze plugs seem fine I think I will tear it down the rest of the way and take the head in and I'll probably get the valves reground while I'm at it

4wdtom · Apr 14, 2020

If the plugs in the head are ok you might want to take the pan off and see if you have water leaking around the cylinder liners.

Holmanc · Apr 18, 2020

I have an update on the allis. It was warm and sunny today so I broke out the pressure washer and cleaned up all the baked on grease of the head and upon closer examination the center freeze plug had rusted through. Monday I am going to head into our local machine shop and get 3 new freeze plugs. I am also going to lap the valves while I have it apart. I wasnt going to remove the valves but I figured since I have it torn down this far I might as well go the rest of the way with it

Dennis K (WA) · Apr 18, 2020

Thanks for reporting back. It's always good to know the out come.
Easy fix too.
Dennis

Allis Chalmers B

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Crazy Horse

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