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Old 11-08-2007, 06:34 AM
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Thinking of buying a used compressor--what should I watch out for?

Hey all-

I've been reading these forums for a while and finally decided to make a post as I need a little help.

Anyway, Im looking to buy my first compressor, and I found a guy locally who is selling a craftsman at a decent price.

What should I be looking for to make sure that the unit is in good working condition? From what I've read, it seems important that there be no leaks and that the unit be drained regularly. Is there any way to make sure this has been done? Are there any other checks I should do to make sure everything is in good order?

Many thanks.
-Mike

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Old 11-08-2007, 07:30 AM
F&J F&J is offline
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I've had several Sears in the last 35 years. Most were good values except one was a 4 or 5 hp "special priced" cheapie. It had a cheaply made pump and you can spot it by what type of air filter it has. It had 2 small foam filters just sitting in 2 recesses. It eventually started blowing head gaskets due to warping.

The other one that I don't like is a 4 to 5hp "oiless" one with a 30-33 gal tank. It is just too noisey.

Run it through several cycles to see if it restarts OK with air in it. They usually kick back in at 90 psi.

If it's old, check the bottom to see if the tank has been welded or brazed due to leaks.

Some have a check valve (where the air pipe enters the tank) that was cushioned with a teflon seal. If the seal gets worn, then the check valve will be metal-to-metal and almost sounds like a rod knocking....usually when it gets past 90 psi or so.

For the most part, I think "most" of them are a good purchase.
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Old 11-08-2007, 08:57 AM
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Quote:
Originally Posted by superkaz661
Hey all- Im looking to buy my first compressor, and I found a guy locally who is selling a craftsman at a decent price.-Mike

You did'nt tell us much about which compressor it is and we could give you a better idea if we had more info, F&J covered the most important things but I would drain the tank and see what comes out. If it is light brown to yellow-ish with what looks like a trace of oil then that is normal but if it is dark brown and appears to have trash in it that is a sign of rusting and the tank may be a short-timer. Also, like F&J already pointed out, if that tank has been "repaired" by welding or brazing don't even think of buying it since not only is the tank trashed it is extremely dangerous! Most people know better than to do this but it does happen. If you do find any of the leaks that were mentioned then the compressor has probably just about reached the end of it's service life and they are not worth repairing unless you already own it, don't buy someone else's problems. Also don't buy an oil-less compressor since those things are junk when they are new, they are VERY noisy, run VERY hot (lots of water in the air lines) and don't last long at all.
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Old 11-08-2007, 09:10 AM
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I would post the model number, but the guy says he isnt sure. He did say though that it is a Sear Craftsman Professional 3hp 4 gallon model. Here's the thing though, he says its rated for 8cfm at 40psi and 5.7 psi at 90. I know a lot of you may suggest for me to go bigger, but right now I rent a small house and share space with roommates, so it would be very difficult to get something bigger.

Unfortunately, the model is an oilless. Thats strikes 1 and 2 already I take it?

My compressor use experience is pretty much nil. I guess Im looking for something that will take care of jobs around the house, and possibly throw some paint on some parts.

Thanks to both of you for giving me some instructive comments. I think I can figure out draining the tank and looking at the composition of what comes out like you suggested. How should I cycle it to test for leaks?
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Old 11-08-2007, 09:53 AM
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The size may be ok as long as you are talking about airing up tires, using an air brush, etc or painting small items and not large car parts but I would recommend not buying an oil-less under any circumstances because they usually fall apart in short order and they are not worth repairing. Honestly those things are so bad IMO they should not even be allowed to sell them! If you take one of those pumps apart you will see what I mean, the internals are made from "pot metal" and plastic.
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Old 11-08-2007, 08:09 PM
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Thanks oldred for all the advice. This guy isnt getting back to me, so it may be a lost cause on this particular model.

Maybe I should just look into getting another unit. Basically, what Im looking for is something is something that can run a framing nailer and a small hvlp gun (yes, I know Im going to get yelled at, but I want to try to paint a teeny project car with this gun Harbor Freight Cheapo )

I'd also like to be able to throw it in my trunk to take to my Dads house so we can work on stuff there, so Im hoping that it can be somewhat portable.

Any thoughts on this guy Second Piece of Harbor Freight Cheapness ?

Again, I know Im going to get yelled at for now getting something better. But at this point, Im just looking for something to fill this stage of my tinkering and not a "forever" model.

Thoughts on both compressor and gun?
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Old 11-09-2007, 05:48 AM
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I am not going to knock that gun because it will do a really good job of laying down paint it's only fault is that it is cheaply built and will wear out fairly quick, after a few cleanings you will probably start to get leaks, drips, parts coming loose, etc but it will have paid for it's self by then. That compressor is another oil-less so I don't recommend it at all however it is probably way too small anyway. Look around for a belt driven pump with about 6 or 7 CFM, maybe a bit less. I am not really all that familiar with those really small compressors so I can't offer any suggestions on models/brands, maybe someone else here has a small belt driven model they like?
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