1940 Model B cylinder / piston options

Hi,

I am working on a 1940 Model B s/n 85243 that belonged to my uncle since before I was born. A cousin was using it to pull logs out of the woods when it ate an exhaust valve, so now I need to bore the cylinders and buy overbore pistons. Seemed simple enough, but now I've discovered that ‘39 – ‘40 replacement parts are rare as hen's teeth. What can I do to get this (sentimental) johnny popping again?

If I can't buy replacement parts for this cylinder casting, can I bolt a later serial cylinder casting & matching head casting to this crank case? Do the studs line up? Will the skirts clear? Will the rods, bearings & crank take the additional load?

What do people do with these ‘39s & ‘40’s? Any recommendations as to how I might be able to get this tractor running again would be greatly appreciated.

Thanks,

Dave

Did it bust your piston ? or if you can find a standard piston used you could have your cylinder bored out and sleeved if it is damaged.

I did what Mike M stated with my '36 B. Had the cylinders bored out and sleeved for standard pistons. Worked like a champ and the tractor runs very well.

Kris A NC (now IN)

rileys list m&w style piston for 39 and 40 b's. yes a mid year block will bolt in but you also have to use newer head and water pipes. Mid year b's have a larger rod journal on crank so you must reuse orig rods. Beware with mid year block and m&w piston it will put piston right at top of block if not slightly higher. Lots of compression if hand start.

Hinrich's repair 815-778-one900. He has all kinds of replacement pistons or can point you in the right direction. If the bore didn't get messed up to bad you may get away with .045 over. sleeving a block is a waste unless the block is really messed up and even max rebore cant fix it. because then you can't rebore it later without spending way more than it should cost. Someone did that to my 50 sleeved one cylinder and now its a paper weight as far as I'm concerned. If the damage is above where the compression ring stops and the rest of the bore is OK and within specs hone it real quick but don't take a lot out and clean up the damage at front of block with a die grinder and a flapper wheel to take high spots off before honing. Remember these tractors sometimes have an inch to an inch and a half or more between the block deck and compression ring. As long as the piston has room to float and doesn't drag it isn't going to hurt a thing. Just make sure there is nothing stuck in the block from the valve breaking. If you want a refreshed motor that is in a budget .045-.09 over is a good range and most of the time the pistons cost the same across the board from stock to max overbore. Have the head cleaned up with new valves and springs and it will be a good little motor that will last a long time.

What all is damaged in yours ? My cousin had a 520 eat a valve. Head was good surprising enough,piston was beat up too bad and it bent a rod which broke the back of the block. So new valves,keepers,piston,used rod and had the one cyl. of the block sleeved.

So I'd also make sure and check the connecting rod !

I haven't spoken to anybody at Riley's directly - but talked to one of the dealer's they list.

According to him - Riley's owns the machinery to make the 4 1/2 pistons, but stopped making them about 10 years ago. They have sold all their stock.

So - like me, you're out of luck unless you can find some used or old stock somewhere.

I guess it's either bore to 4 11/16 and deal with the associated issues there - or sleeve.

Guy I talked to recommended using the original pistons with larger rings (ie. 4.5 + .045) - machining the pistons to fit them... I'll have to talk to my machinist about that. I've never heard of anybody doing it, but who knows.