I picked up an air compressor at a yard sale this weekend. I plugged it in
and it ran fine; only problem is when I got it home and let it run for a
long time, it wouldn't reach more than 40 psi. I tried to find rebuild kits
on the web, but came up with diddly. I've heard bad things about Sears
Repair (it's an old-ish Craftsman), so I'm at a bit of a loss as to what to
Look up the model number on the web site. Sears compressors owner's manuals
come with an IPB that lists all of the parts, right down to internal parts.
You may still be able to get rings, etc. through Sears. If not, you will
likely be able to get rings by removing the pistons and mic'ing them.
Before I did that I'd do some of the standard stuff though. Make sure the
air cleaner is clean. Take it out and wash it really well. A dirty air
cleaner will usually result in oil and moisture in the air stream, but can
also result in difficulty building pressure, and this is always a good
starting point when performing maintenance on a compressor.
Make sure the check valve in the pump head is not stuck or dirty. Take the
air line that runs from the head to the tank and inspect the valve that
seats in at the head. Make sure it's free. It should rattle if you shake
it. If this valve is stuck shut it will usually manifest itself in
difficulties spinning the compressor up (it's a relief valve), however if it
is not free it can cause the problem you're seeing as well.
Check your belt tension. A loose belt will keep you from building up
pressure as well.
From the "D'oh!" department - make sure the regulator is turned up all the
Most of these little compressors don't have any trouble building up pressure
if the above things are working correctly.
What Mike said with a couple of adds:
How old is the machine? Also, was there much moisture in the tank? Some of
these mass marketed machines seem to have a tank life of about 15 years,
even if drained regularly. Take a close look around the tank drain cock for
signs of rust, air leaks (soap solution with tank pressurized - even 40 psi)
or moisture leaks. If the tank is rusted your options are limited. Either
pitch it or find a similar machine and combine parts (usually very easy).
Most compressor or welding shops will not touch a tank repair.
How long does it take to get to 40psi and does it ever shut itself off?
Just wondering if the gage is accurate. If it does shut off you might have
a pretty cheap fix.
There's a check valve in the tank where the big tube goes from the pump to
the tank. If that's bad it won't build up pressure. This valve isn't brand
specific so any place that sells compressors farm stores usually sell parts.
Just take old one along and compare. Also the reed valves could be bad.
Remove the head and there will be 2 metal flaps that cover the holes held on
by 2 screws maybe the screws came loose or the valves are worn, sometimes
just flip them over since they're the same on both sides, if the casting is
grooved where they seal then just smooth it up with some sand paper Good
Most compressor rebuild kits are readily available. Check with a local auto
repair shop and find out who services their compressors.
However, if it is one of the oil-free types they may not be worth the
A few years ago I faced the same problem. Sears has parts but not a
kit, each one has to be individually ordered.
Checking with the local compressor repair place, I found that the
compressor itself is one of the better makes but the name escapes me.
I opted to let them rebuild it as it was far easier than doing it
myself, and if it didnt go right I had somebody to yell at :)
A knowledgeable repair guy can probably tell you the compressors
maker, and perhaps from that a rebuild kit can be found.
Sorry I cant be a lot more specific on this, age and time has taken
many of the details from me .
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