Shop Air Compressor Problem

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today the air compressor pump started to slow and squeel the belt near the end of one of many cycles.....there was also an apparent knocking sound as it neard' the end of the cycle at higher pressure...sounded like a knocking rod..in the next cycle the pump slowd repeatedly and the knocking grew louder and louder then would almost completely stop and run , then just began smokeing the belt..i shut it down.  i had to finish my paint operation , just kicked the breaker back on at 60psi and it was fine until  100-110+psi...then i have to shut it down  manually...and the 15" pump flywheel is extremely hard to turn inches , after i've shut it down at 110,120+ but seemed easy at lwr pressure.i thought i was a compressor wiz , it being my main machine of operation .any ideas appreciated.        thermal arc 252i  -  millermatic 350P -   miller XMT, cp300ts, 30a 22a feeders, buttload of other millers, handfull of lincolns, couple of esabs  -   Hypertherm 1250 G3
Reply:Could be either reeds going bad or bearings.   Tear it down and find out.My name's not Jim....
Reply:Originally Posted by BoostinjdmCould be either reeds going bad or bearings.   Tear it down and find out.
Reply:Nope, the check opens with pressure from the pump side which the pump can overcome unless it is bad.  I would bet that the reed valve on the exhaust side isn't closing and pressure from the tank is holding the piston down.  Pop the head off and take a look.My name's not Jim....
Reply:Our compressor was doing something similar. Opened it all up and found that the small screws (M3???) that held the check valve strips (reed valves???) in place had broken/vibrated loose. The valves and block were OK, so I drilled them out to #6-32 (or was it #8-32???) and reassembled with Locktite. So far so good.Andrew