Coleman Powermate Black Max slow to build pressure

by Len
(Idledale, Co)

I have two Coleman Powermate Black Max direct drive single stage oilless 5hp compressors (27 gal tank) model# BL0502710.

They both were slow to build pressure so I rebuilt one with a new piston/cylinder assembly and cleaned up the valve plate and reed valves which cut down the charge time from ~20 min to 7 min.

However, after about 2 weeks of moderate use the charge time is back to 18-20 min.

The reed valves seem to be in good shape, no bends or cracks, I replaced the gaskets and still the same story.

I also tried swapping the valve plate with the other compressor's and no change.

When the pump is running there seems to be a lot of air coming out of the front (piston side) of the pump. The air intake sucks in air fine and no blowback is apparent.

Also, there is daylight around the piston seal inside the cylinder through the whole stroke when turned by hand.

My thought is this gap in the cylinder is what is causing all the problems but shouldn't the air pressure inflate the seal on the upstroke? Is there something else I can check, or do you know a way to better test the valves to see if they are the issue?
Thanks

__________________
Bill says....

Len, I don't know what this means... "When the pump is running there seems to be a lot of air coming out of the front (piston side) of the pump" Where is the air coming from, exactly.

Depending on the type of piston seal, some will "inflate" with pressure. However, that you can see daylight all the way around suggests to me that you need new piston seals.

That cleaning the valves improved things for a while suggest to me, too, that the valves are part of your problem. Cleaning them might not be enough.

Cheers,

Bill