Air compressor won't go past 80 PSI?

[StaggeringGoat]

I don't use my air compressor all that much, thus I have a cheapie from Harbor frieght. It is a 23 gallon/2hp/oiled compressor which basically looks the same as all the chinese oiled compressors.

Problem: It won't compress air past 80 PSI, and it takes a long time to get there.

Anybody have any idea what could be causing this? I took the motor/compressor cover off but I don't see anything wrong, it's not leaking anywhere. It sounds like normal once it hits 80 PSI and keeps pumping but the air pressure doesn't go up.

I even tried filling the tank from another compressor, it fills up to 120 just fine with no leaks or anything.

Any ideas?

 

[pstnbly]

Bad rings

 

[KenC]

My first guess would be bad reed valves. Either broken or not closing all the way. Easy to fix, assuming you can find the parts. Just need the valves, may be serviced as a plate with valves as many are, and gaskets.

 

[6768rogues]

I would take it apart just to check it out. I had as small compressor that had a cheap plastic filter. A tiny piece of the plastic filter broke off and got ingested, making a reed valve not close fully. Chances are it is worn out and scrap anyway, so taking it apart is not risking anything and you might get lucky.

 

[srmofo]

My first guess would be bad reed valves. Either broken or not closing all the way. Easy to fix, assuming you can find the parts. Just need the valves, may be serviced as a plate with valves as many are, and gaskets.

I was going to say the same thing.

I had to retire my fathers old craftsman compressor last year because of it. Couldnt find valves and the morons at the sears shop were useless in helping me find any that might work. Funny thing is it still had a repair tag hanging on it for broken reed valves.

 

[kvanderploeg]

If there are fittings going from the actual compressor to the tank, check to be sure they are tight first. I was having a similar issue with my cheap tank and found one of the brass fittings was vibrating loose. Not a ton, but enough pressure wouldn't build quickly or very high. Good luck!

Kent

 

[StaggeringGoat]

Alright, I finally tore the whole compressor down today. Took off the head, the valves look good to me. Very little wear. The rings and cylinder bore looked the same. All the fittings I could find from the compressor to the tank are tight.

Put it all back together...it seems to pump even slower than before. Now I can't get past 60PSI. I don't understand! Anybody have any other ideas? I spent $160 on this thing and barely touched it...

 

[ibedayank]

most of these cheapies use a diaphram pump
contact Hf for a manual and availability of repair parts you may get lucky

 

[StaggeringGoat]

most of these cheapies use a diaphram pump

Not oiled ones....

contact Hf for a manual and availability of repair parts you may get lucky

Parts won't do me any good if I don't see anything broken...

 

[NUTTSGT]

The think the answer is in your first sentence.

"thus I have a cheapie from Harbor frieght."

 

[StaggeringGoat]

The think the answer is in your first sentence.

"thus I have a cheapie from Harbor frieght."

Actually when I took it apart I was pretty impressed with the quality. The compressor cylinder is cast iron and the piston has 3 rings, all with good machining.

I just don't understand why it won't work, everything looks perfect to me....though I'm no expert....

 

[Kbota]

Just an idea, and I am also not an expert, but what you describe is classic for leaking reed valves. Reed valves can leak, while "looking" great. there are tests you can do, but the best test will depend on the configuration and mounting of the reeds.

If the reeds and seats are okay, then check carefully for a leak elsewhere. I have also seen a hairline crack in the reed valve seat, that was tough to locate.

If everything above checks okay, then here are some "rules of thumb" for piston bore, and ring measurements.

You might want to check the ID of the cylinder bore in 2 or 3 different locations. Check for egg shape and taper. If either are off by more than .009" per inch of bore dia, then that's probably excessive wear. If the cyl bore is okay, then use a ring spreader, remove the rings from the piston (one at a time), and place the ring into the cyl bore. turn the piston upside down, and use it to shove the rings about an inch into the bore. Use a feeler gauge, and check the end gap.

The end gap "should" be in the range of .0025" to .0045" per inch of bore diameter. Clean the piston grooves carefully, and reinstall the rings in the same location. Make sure you get them back in the same profile. Upside down rings do not work well. Use a feeler gauge to check ring side clearance. Should be less than .0015".

One other thing..... Remove the crankcase vent, and hold your thumb over it when the compressor is running and still a few psi from shutting off. If you feel a lot of "blowby", then piston rings or cylinder are suspect.

I'm sure there are some guys on here with a lot more knowledge than I.

 

[stevefasano]

removed due to

 

[StaggeringGoat]

You can also check the on the one way valve ..It will be on the line from pump to tank..in that valve you will find a ball n spring in the housing..clean the ball and housing ..I think the spring is tank side n ball pump side..

I was assuming that part was good since I was able to pump up the tank to 120 PSI with another compressor and nothing leaked out, does that sound right?

 

[Greatbear]

If you want to do a quick check to rule out rings and/or scored cylinders, put your finger over the crankcase breather (depending on how it is set up, you might have to unscrew it or otherwise remove it) run the unit near the max pressure it is trying to produce and see how much blow-by air pressure develops, and how fast. If the rings are shot, it will try to push your finger off in 30 seconds or less. If no appreciable amount of pressure builds up after that time, you are looking air bad reed valves, worn valve plates or leaky head gaskets. Don't overlook the unloader valve and the air lines connecting it.

 

[addconcepts]

I've repaired a number of these compressors. It's the gasket between the aluminum head and the reed plate. Remember seeing the triangle shaped chamber? The maybe 3/16" wide wall between that chamber and the one next to it doesn't seal well with the stock gasket. Make a new gasket from thicker material and try to make sure that aluminum plate is actually flat where the gasket sits on it. When these compressors get really hot trying to keep up with an air tool, that aluminum plate warps slightly allowing that gasket to start leaking.

Darren

 

[taumac]

first I would get a spray bottle of soap water and go to town and check all fitting from the head to pressure switch. Theres a leak somewhere from the point of compreesion to the check valve.