John Deere D Compression

[Grabatire]

I just acquired a '39 styled D. What would a reasonable compression be for an original bore low compression piston?

 

[buickanddeere]

I just acquired a '39 styled D. What would a reasonable compression be for an original bore low compression piston?

One could imagine the HP increase with 8 to 1 compression on 91 octane gasoline . Along with the dual exhaust .

 

[Rodney51Cub]

According to JD service bulletin 167-S, Feb 15, 50 - serial number 143800 and up is 60 psi.

 

[Grabatire]

Thanks fellas, I was guessing 80 psi. I was planning on taking the head off to check the valves and cylinder taper, but I'll belt it up my '39 unstyled and see what I get. If it's close to 60 psi after a wet and dry test I won't bother.