401 diesel overhaul

I recently purchased a 1955 401 diesel from my grandpa. It sat in a shed for 14 years and I was able to get it to run after going through the fuel system, rebuilding the starter and replacing the batteries. The only issues that it has are that it burns oil (I was told this) and it is pumping engine oil into the coolant. I suspect that it has bad head gasket(s) or a cracked head since the only other place I can think of where oil could get into the coolant is the oil filter housing and it isn't leaking there. Is there any other place where oil could get into the coolant that I'm missing?

I plan on overhauling the engine to remedy the oil issues and freshen it up the but have a question. It is my understanding that pistons are no longer available for the 251 cu. in. engine (4" bore). One available option is to get sleeves that have been bored from 4" to 4 1/8" and use pistons for the 267 cu. in. engine (4 1/8" bore). I was wondering if someone has done this and what they thought of the results? I'm a little concerned about removing 1/16" from the sleeves, mostly overheating and longevity of the overhaul. I plan on pulling the 4-14" plow that its rated for when I'm done with the restoration and I don't want to have to baby the tractor because of the thinner sleeves.

Is there a place to get the correct (4" bore) sleeves and pistons for this engine? Case claims their not available.

Thanks,
Eli

My understanding is that you bore the block and use sleeves from a
267 engine along with the 267 pistons, not that you bore the
sleeves. Those 251 engines have been bored out much bigger than
that. I doubt you'd have any problems at all.

4" Sleeves are still available, but CASE, in their wisdom, does not furnish the 4" Pistons anymore. Neither does anyone else. We have teamed with a machine shop to bore the 4" Sleeve to 4-1/8". 4-1/8" Pistons are very economical, & readily available. Boring the inside of the correct sleeve for your 251, as well as the 6cyl. models, saves removing the block, taking it to a shop & having the block altered. There will be no consequence to sleeve integrity, or engine cooling in boring the sleeve.

So if I understand this thread correctly. In order to put the 267 liners and pistons in a 251 the block has to be bored for the 267 sleeves? For some reason I was under the impression that they fit without mods.

The 4 1/8" Sleeves I furnish will drop in without modification to the block. Sleeves specifically designated for the 267 will not.

I use 930 sleeves and pistons in my 251's. 4 1/8 and fit with no modifications. 970 sleeves will also fit with a few thousands machined off the top flange