# Craftsman Air Compressor not pressurizing



## slingshot (Sep 14, 2009)

I have a Craftsman 1 hp 12 Gallon air compressor, Item# 00916640000 Model# 16640. It was running this weekend, building pressure, then all of a sudden the motor started making a different noise. It was a lower tone noise than the motor usually makes. My first thought was something was wrong with the motor, so I quick shut it off.

It had gone to 60 psi before I shut it off, and I have regulator set for like 110 psi. So, I took the head off ... piston appears fine ... not stuck .. can rotate by hand. Put back together, turned it back on with check valve removed. I put my finger over the check valve and was definitely pumping air in bursts out at that point. So I put it back together.

My next thought was to try and find a leak somewhere. So I turned it back on and sprayed a soapy solution around the cylinder base and head, around all fittings, etc. I did not find anything major.

Everything appears to be fine with me. It will turn on fine, run just like normal, but pressure gauge will not move. It is putting some air in the tank bacause after a minute I can pull the relief valve open and some air comes out, but not like it should. The unit is not that old and does not even get used that much. Any ideas ???????????


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## Mr Chips (Mar 23, 2008)

slingshot said:


> It had gone to 60 psi before I shut it off, and I have regulator set for like 110 psi. So, I took the head off ... piston appears fine ... not stuck .. can rotate by hand. Put back together, turned it back on with check valve removed. I put my finger over the check valve and was definitely pumping air in bursts out at that point. So I put it back together.


did you happen to check the check valve when you had it apart?


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## slingshot (Sep 14, 2009)

Mr. Chips. THe check valve is just a brass cap, with a spring, and like a nylon or plastic button inside. Everything appeared to look normal ??? The spring was not broken, and the plastic cap looked normal (not broken or cracked).


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## Mr Chips (Mar 23, 2008)

right, but make sure it's not stuck.

i tried to look up your model to look at parts breakdown, but couldn't find it.


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## micromind (Mar 9, 2008)

If the motor appears to be operating at normal speed, and the belt isn't slipping, and the head gasket isn't leaking, I'd suspect the valves. 

Most of these compressors use reed valves in the head. It's possible one of yours is broken. 

When its running, does the intake pull air in, or does it pull and push? If any air is pushed back out of the intake, there's a problem with the intake reed valve. 

When you had your hand over the discharge tube, did it actually push air out, or did it just pulse the air? Again, if it just pulses the air, the exhaust reed valve is bad. Since the exhaust valve operates at a higher temperature than the intake, there's a chance that it's simply gummed up with solidified oil. 

Reed valves are usually nothing more than a thin piece of metal that covers an opening, and is fastened at one end only. The idea here is to allow air flow in one direction only. 

Many times though, the head gasket is leaking. With the unit running, feel around the cylinder to head joint. It'll be obvious. Simply replacing the gasket doesn't necessarily solve the problem though. Frequently, the head is warped. 

It could also be the unloader valve. If there's a small tube at the pressure switch, make sure that this valve doesn't leak when it's running. It opens only when the unit shuts off. 

This is sort of a generic troubleshoot. Each compressor is slightly different. 

Rob


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## slingshot (Sep 14, 2009)

THank you everyone for the information. I assumed the head gasket was not leaking because I sprayed around the head while it was running and there was no air leakage. HOWEVER, the gasket runs between the intake and exhaust inside of the head ... and there was the problem !! A section about 1/2" long was gone. 

So luckily I had some gasket material left over, cut a new gasket, put it back together and presto ... works fine again !!

Thanks again everyone.


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