40 crankshaft journal sizes

[Vintageman]

I have 2 of JD40 scrap engines which I hope to make up 1 runner. Interestingly, when I measured the crank journals, I noticed that the Main journals are the same on both cranks (2.39) however with the Bigends, on the one crankshaft they measure 2.25 and on the other they measure 2.25. Did the M/40 cranks change during the production lifespan or do I have 2 different model engine or why would the Bigend journals be different sizes on the 2 cranks?

 

[M-MAN]

The crankshaft has main bearing journals and rod bearing journals. No idea what you are looking at when you say Bigend journals???

Normally main's are the same size and rod's are the same size. Occasionally you will run across one where a journal was damaged and the owner was too cheap to have the crankshaft turned properly.

 

[Mike M]

M's have smaller rod journals than the 40 does. IIRC it was done because the 40 runs faster RPM's.

 

[J.Wondergem]

I think I missed something, what did I miss??
on the one crankshaft they measure 2.25 and on the other they measure 2.25.

 

[Glen D Anderson]

I don't have the OEM manual in front of me but the specs. from our IT manual for the 40-330-420-430-440 engines as well as 320 engines after S/N 320854 are as follows:

Rod journal 2.498" - 2.499"
Main journal 2.397" - 2.398"

The IT manual goes onto to say that 320 engines prior to S/N 320855 have rod journals that are 2.249" - 2.250"

Perhaps you are working with a 320 engine?

(quoted from post at 01:12:11 12/20/22) I have 2 of JD40 scrap engines which I hope to make up 1 runner. Interestingly, when I measured the crank journals, I noticed that the Main journals are the same on both cranks (2.39) however with the Bigends, on the one crankshaft they measure 2.25 and on the other they measure 2.25. Did the M/40 cranks change during the production lifespan or do I have 2 different model engine or why would the Bigend journals be different sizes on the 2 cranks?