1WD21 pump on a 4XA59 compressor motor knocking at high pressure

by Justin
(Clovis, CA)

I have a 1WD21 pump on a 4XA59 compressor I believe from 2007. Used very rarely. The pump will have no problems filling the tank from empty and cycling a couple times. An issue arises around the third cycle when the tank is almost full that sounds as if a rod is knocking or a demon is trying to escape from the inside of the pump.

The cycles are more than 20 minutes apart.
I have pulled the head thinking it was a reed sticking but there were no issues. Cylinders look perfect. I checked all lines for any clogs but there were none. Oil level is perfect.

The tension on the belts is just barely off. Would the unloader valve cause this issue? I removed it and did not see any issues.

Comments for 1WD21 pump on a 4XA59 compressor motor knocking at high pressure

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May 14, 2014
knock
by: Doug in s.d.ca

"The tension on the belts is just barely off. Would the unloader valve cause this issue? I removed it and did not see any issues. "

I can't see how the unloader could cause this, but if I say it can't, it will.

Sounds like a heat problem. Belts heat up and start slipping enough for the comp to sort of 'backfire' if you will...Could be weather related.

So, I'd start with that, especially if the belts haven't already been replaced recently.


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