Alright, Need Some Smart Guys!

Bryce Frazier

Well-known Member
Here is the question:

Will a set of 1939 JD A Short Stroke Pistons fit and work properly in a 1940 Early Styled JD A?

My 1940 A has a bad block, and is bored .045 over. I can get a replacement block in very good, useable shape for $125, and it is going to be a standard bore.

Once I do that, I then either need to come up with rings for my .045 pistons, OR I have been offered the above pistons ready to go for just the cost of shipping.

Anyone have any thoughts? Thanks very much! Bryce
 
Right, I understand that, you combined both options! :)

Either I need to buy the block for the $125 and bore it out to .045 and then buy rings for my pistons and put them in,

OR,

I can buy the block, and get the pistons that are being offered to me for free. They are out of a 1939 A Short Stroke.

Thats what I wanted to know, will pistons out of an Unstyled A fit into an 1940 Early styled A??
 
I would say if the pistons are 5 1/2 they should work. 39 pistons are A 61 R. and they go up to serial 487999. I also have set of 5 1/2 A pistons and rods from a 44 A I would let go for cheap and shipping. Ron Mn.
 
According to "Mr Thinker's John Deere Almanac" the bore is the same. The difference is in the stroke which is shorter in the unstyled A. As to the difference in where the wrist pin is placed (if any) I don't know.
 
So in theory if the wrist pin is in the same spot, and they measure the same from the top of the wrist pin hole to the top of the piston, then they should be interchangeable right? Bryce
 
Bryce; 39 & 40 are some odd years for 2 cyl. parts interchanging. I'd have to check by your serial number but yours may be closer to a 41 ?
Good news is that A's models do offer a lot better interchangeability than B's

JD parts books will hold the answer for what will directly fit. But not for those that will fit with a little rework. I was always a by the book stock guy so I don't know much about the reworks.

Compile a list of your block casting number (may be on bottom or top ?) ,your piston casting number (may be on inside of skirt)
Then you have had a lot of offers for parts at good prices. Get the casting numbers for these as well.
That will give me a starting point to see what's what in the parts books.
Parts books for these old machines are now to be downloadable from jdparts.com also. Not sure how good that works out ? If you get into a parts book you have to look carefully at the description line for other numbers as many times these will reference your casting numbers.
 
Unstyled A pistons have smaller wrist pins than all later A's and 60's, also different compression height. Standard pistons for your block are not hard to find. I have two or three sets and am not real proud of them dollar wise.
 
They will work, but it will be down on power, and you'll either have to use the unstyled rods, or get bushing to fit the later rods, and the early pins.
 

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