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1951 JD B compression spec

R

Royse

Well-known Member
What should minimum compression be on a 1951 JD B?
Got 100 PSI on both cylinders, dry and wet. Good enough?
It does run, sometimes, but backfires when trying to start
it at other times so I was looking for a sticky valve, etc.
 
100# sounds real good. I think new they weren't much more than that. The 2cyl. engines are amazing. When I got my 60, I farmed for a season before I found that it had a pie shaped chunk out of one ex. valve and '0' compression !! When repaired it was 125# in ea. hole.
 
I haven't taken anything apart David.
My nephew just bought this tractor.
What was done to it previously is unknown of course.

I know it has carb work coming, as it leaks.
It also hunts when running.
Maybe carb, maybe governor. Maybe both.

So I figured a compression check was a free test to start.
I had a Case with a bad valve that backfired on start up.
On the Case the compression test pointed it out.
On this JD, that compression test all but ruled out a bad valve.
 
If timing has not changed, the back fire would probably be do to a lean condition or possibly bad cap.
 
Lean condition would also fit with the governor hunting.
That carb's got to come apart anyway, so we'll start there.
Thanks!
 
you need not worry about a sticky valve...with 100 P.S.I. you're okay....check quality of ignition/timing/condition of carburetor....
 
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