Compressor stopped building pressure, it is an oil based unit. i replaced the piston assy, now it builds pressure to 25 psi, unit keeps running but will not build past 25psi, cannot find any leaks, unit is only 14 months old & has hardly ever been used, it is a craftsman upright, small garage unit, supposed to build to 140 psi
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I have read both your questions and after taking both into consideration it sounds like it needs new piston rings. On a gas engine it is called blow by but both have a piston with rings on them, as they wear the end gap gets bigger and bigger allowing compressed air to bypass the rings into the crankcase where the oil is, the breather is there to allow air from the room to enter and exit as the piston goes up and down to avoid pressure or vacuum in the crankcase, the air on the top side of the piston is supposed to go into the tank but in your case some of it is going around the piston rings and into the crankcase building pressure and blowing oil out. There is not much inside a compressor like a gas engine, taking the head off and the oil pan should let you take off the connecting rod bolts and push the pistons out the top. This answer is based on the two comments of cant build all the air pressor and it is blowing oil out the crankcase breather. If you hit the 80 psi and unplug the compressor can you hear air coming from the limit switch box that the power cord goes into ? I will wait for your answer to continue.
If your compressor is oil-less type, most likely pressure is leaking past piston ring. To verify, remove cover to expose bottom of cylinder (unplug compressor and let out all air). With flashlight, examine the upper-most part of the cylinder (turn motor by hand till piston is at top of stroke). If top of cylinder is scratched, then pressure is leaking past. If cylinder looks good, most likely problem with reedvalves or broken gasket in pump head. Parts are not too expensive for most small compressors. If your compressor is oil lube type, problem sure to be in the head assuming no leaks. Good luck
I can not find a Craftsman compressor with that model number anywhere so here are a couple things to look into. If the compressor fills to 70psi and keeps on running check the valve plate and piston/cylinder assemblies. Check that the valve reeds on the valve plate are not bent, broken or warped from heat. Then check that the wiper (oil less) or pistion rings (oil splash) are not damaged and that the cylinder wall is not scarred up. Any of these will let the compressor fill up to the point where the air pressure leaks past the valves or piston and won't fill any further. If the compressor fills to 70psi then shuts off the problem is in the pressure switch. Some have an adjustment screw or bolt to control when it turns on and shuts off. If you had a drop from 100 to 70 the springs may be weak or broke and you'll have to replace the switch.
The air is always warmer coming out of a compressor. As air is compressed it builds heat, also the mechanics (friction) of the compressor builds heat. So you add these two together and you get some rather warm air out of a compressor, especially if it runs for a while. I hope this helps.
Oil free pumps do tend to blow the piston ring (not too expensive) available at searsparts.com. Remove covers to pump and manually turn crank until piston is at top and look at the condition of the cylinder neer top, If it looks scratched, order cylinder kit with piston ring. If it looks good and shiney, could be the valve plate in the head. There are reed valves that tend to break. Run pump however with covers removed and check with soapy water for air leaks and repair as needed (air leaks under the cover will prevent unit from filling). Good luck
If the unit will not build up pressure you need to remove the compressor head from the compressor and inspect both the intake and the exhaust reeds as well as the piston ting on the compressor. Without the model number of the compressor this is about as far as I can help with.
If this compressor is dry type with no oil needed, then it may have a worn cylinder and/or piston ring. With flashlight in hand, look under cylinder with piston in upper most position. If you see scratches most likely it needs cylinder / piston kit. Not to worry, not too expensive. If you compressor has a crankcase with oil, then you may have problems with valves in the head. Cracked or dirt under headvalves will prevent pressure from building. Finally there may be one or several leaks in the tubing, check leaks with soapy water. enjoy
Many craftsman compressor are built by champbell hausfeld using a dry type of cylinder and piston (no oil, no crankcase). If dry type, check for worn cylinder and piston ring. Pieces of the vinyl ring can jamb between the reed valves in the head causing air to escape from the intake. If your compressor has a crankcase and oil, check for broken reed valves in head. Spray soap solution on hoses, checkvalve, drainvalve, and fittings to check for leaks. Most likely problem is reed valves broken or open. Parts are available from sears or match parts to chpower.com. enjoy