Farmall M- Help with ordering the right Overhaul Kit

Hi All,
My name is Jay from Illinois. I have been reading YT for quite a while and learning what I can. I recently bought a non running Farmall M that I intend to get restored. I bought the tractor with a stuck engine and have since tore everything down and cleaned in the process. I need to send the block to get boiled and the crank to get polished. I have learning from reading many threads that an "Original" M doesn't really exist. Likely over the years they have been overhauled once if not more than once and usually set for higher horse power. So here is my question, what Overhaul kit do I order? The serial number is 155242 which makes it around a 48' model. I know this engine has been into before. It has stepped head pistons and a 8060DB head which I believe is a SM head. I've made as many measurements and notes as possible.

Block/parent bore is 4-1/8"
Pistons- 4" Stepped Head
Rod & Main bearings- 0.002
Wrist pin- 1"

I thought originally that this M had a SM kit put in, but now i am leaning towards a 400 or 450 264 cu" kit. The wrist pin diameter is what is throwing me off. I know i can get a 264 Overhaul kit that will include new wrist pins & bushings. I would like to stay with what the tractor has in it or at least not lose any potential horsepower. Hard to say when i have never seen the tractor run. Do i order a SM overhaul kit or a 400/450 kit? I'm pretty sure I'm over thinking on which kit to get. I just need someone to chime in and point me in the right direction. I really have no intention of farming or tractor pulling. Just parading around and maybe occasionally a plow day or pull. Any help or advice would be greatly appreciated.

Thanks!!

JV

You can check the engine serial number, by looking at the Boss,up front near the top, of block, and see what size block is it for sure !

4" is Super M. (264 ci) the 4 '1/8 is 450(282ci) Regular M is 3 8/8(248ci) The bigger sleeves wont fit into the bore with out boreing the block.,which you won't want to do. Just go with the 4" piston set.Order M/SM kit. Give those specs to the person you are ordering the parts from. They can help get it right.As far as I know,the wrist pin is the SAME. Ask your parts supplier. That is their job to know and help guide you.

Probably pistons from IH with one inch pin. Unless the connecting rods were changed the pin end will have a thick pin bushing, called adapter bushing at one time. If the rods have 5 numbers ending in D something it's probably the regular M rod. Rod with 6 numbers and end with R1 would be for a small pin bushing only. With a M rod you can use the regular M bushing or adapter bushing depending on piston pin size used. Most if not all aftermarket pistons use the standard M pin size now. 8060DB is pre SM. 8060DC was the SM one along with near end of M with that number.

you got the piston size and rod size so thats the important thing . order to replace those.
i have yet to find the smaller 248 sleeves in any blocks. they are pretty well all 4" pistons. run into some 4 1/8 " pistons in super's.
the thing was back then , farmers would say "i have the super pistons in here" when talking about there tractors. meaning the 4" pistons.

You're already planning to spend a bunch of money. So do it RIGHT and take it to a machine shop and have it measured up and find out what needs to be done (if anything) then order the parts.

Crank throws wear "egg-shaped" over time.

Have the rods checked for straightness, "big end" bore size and roundness, and have the new wrist pin bushings installed and fitted to the pins. All that takes specialized equipment and knowledge.

For my own common knowledge, the 1? wrist pin really won?t dictate what kit I need to get so long as I install new pins and bushings, correct?
Also I do have the original M rods. They are the 5 digit numbered rod. What was the reasoning for the 1? wrist pin versus the 1.13? wrist pin?

The smaller wrist pin was for internal weight reduction,and with the 450 cam, it made for a snappier engine!

Correct on piston pin bushing, put new one in for piston set sold this site. Bushings should be sized after installing and best to be expanded in rod before sizing. No machine shop near me does that anymore though. IH changed rods to small pin during 400 tractor production to cut down on rotating weight and made lots of replacement pistons with the small pins for use in M through to 400 tractors before rod change. After most cast iron pistons were dropped they decided the big pin wasn't needed. Don't know if the dealers even sell the small pin pistons for a M now. Another thing to watch for if replacing bearings. Crankshaft diameter was increased and bearings made thinner. Don't think they say the serial break is on engine numbers not the tractor number. Your 48 is below the serial break if original. For valve length you have a gasoline head and should be the longest valve length listed for a regular M head.

Congratulations on getting the block tanked. That gets all the corrosion from inside the oil and coolant passages. It will come back bright and shiny and will
take a beautiful coat of paint. I did that with my new/old block. Someone, before I purchased my M had bored it and was running against the cylinder walls. It
was ruined for rebuilding. Good luck. Ellis

Wait to order any materials until you get all parts back from machine shop and measures.

They will let you know how the crank comes out.