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g111sims
08-02-2006, 08:19 AM
I have a 3.5 hp 20 gallon craftsman air compressor. I was building a shed, used the compressor to drive a nail gun. The 4th day the compressor started to slow down and a hot metal smell was coming from it, like something was binding. Any suggestions?

imagineer
08-02-2006, 08:45 AM
My guess, the motor has burned up. I doubt that the piston/cylinder assembly is damaged because the compressor would have locked up quickly. I also doubt its the crank/connecting rod/piston pin or bearing because the you would be able to hear the worn parts banging around.

smithboy
08-02-2006, 08:56 AM
If it's similar to the ones I have seen, the motor and compressor are a single oiless unit. I see many of these oiless compressors for sale cheap after they break. I bought a one for a secondary tank for my plasma cutter. Generally, the piston rod breaks on these units...but, that might be caused by heat seisure. If this is the type of compressor you have, it may not matter if the motor or the compressor is the problem, they are often replaced as a unit. You can rebuild the compressor part, however. I think I do remember seeing rebuild kits, but if it's the motor like imagineer suggests, you may have to buy motor+compressor just to get the motor. If you are still in warranty, I would return it.

Sober_Pollock
08-02-2006, 09:22 AM
How long and what gage extension cord were you running it on?

dozer
08-03-2006, 11:38 PM
Yup, it sounds like a high RPM one-piece.

On one I owned 10 yrs ago, there were teflon 'rings' on the piston, which went bad; and allowed the tank to leak down every night. I have never seen one of these single-piece units survive any kind of 'constant' usage. They're fine for occasional use though.

If you use a lot of air at 90psi and above; try to get a "2-stage" compressor. Not the same as a "2 cylinder". The 2-stage units have a larger 1st-stage cylinder which pumps into a smaller 2nd-stage cylinder; and that one pumps into the tank.

At higher pressure-ratios, it's a lot more efficient to compress in 2 stages. I.e., you get a lot more air in less time, and with less power consumed and heat made.

gimpyrobb
08-15-2006, 02:37 PM
Also check on ebay for large cheap pumps. A buddy got a champion brand pump for 100.00 and it puts out 19cfm @ 120psi.

Ggg6
09-08-2006, 12:06 AM
The "oil less" or "high speed" compressors do not have any rods or pistons in them at all, its a different style of pump. They are very similar to an air inpact but the anvil is driven by the electric motor not air.

MAC702
09-08-2006, 03:00 AM
The "oil less" or "high speed" compressors do not have any rods or pistons in them at all...
I've personally replaced piston rings on an oil-less pump.

Bandit
09-09-2006, 11:58 PM
I own a Air Compressor Service Company. I was a Service Center for IR Energaire Compressors before they were bought out by DeVilbiss out of Tn. Not the Canadian Devilbiss ( Cast Iron Pumps ). I did Service DeV for 8 yrs.
The biggest problem I found with them was Contractors buy them , place the unit on the ground next to the house with a Really Long Extension Cord. They Then either Fried the Motor , or the Cooling Fan for the motor and Aluminum Piston with a Teflon Ring turning on a Roller Bearing ,Would Suck Up Sand and Wipe Out the Teflon Ring , Piston and Sleeve , ( Voiding the Warrenty ) :nono:

Just try telling someone with a 5 day old $600.00 Compressor it is Junk and Not Covered By Warrenty.
I still have a ton of parts left over , I will try to find one and post a pic.
Bob
Banditair@aol.com / Banditair@yahoo.com

Note
Sears Compressors are made by Devilbiss

smithboy
09-10-2006, 09:11 AM
They Then either Fried the Motor , or the Cooling Fan for the motor and Aluminum Piston with a Teflon Ring turning on a Roller Bearing ,Would Suck Up Sand and Wipe Out the Teflon Ring , Piston and Sleeve

I always thought these had rings made of a soft metal, like lead or something. I never knew they were teflon. That's good to know. I was always a tad bit concerned about vaporizing tiny particles of soft metal into the air.

My local Tractor Supply Store sells off some of the damaged units. ALL of the ones (a dozen or more) I've seen have a broken piston rods...some look like it was due to bearing seisure...others look like maybe a piston problem with cylinder scaring...just like you describe. The motors have all LOOKED fine, but you can't test them since the pumps are shot. These are mainly the $269 30ish gallon oiless compressors.

Ggg6
09-11-2006, 07:37 AM
I've personally replaced piston rings on an oil-less pump.

I will assume there is more than one style of oil less compressor then. The ones I have worked on had rotary vane style pumps on them no pistons. Then again maybe thats the reason why you were replacing the rings on a oil less compressor, it wasn't a oil less compressor to begin with. lol

smithboy
09-11-2006, 08:03 AM
I know the type you are talking about...I had never heard them called oiless though. I think the ones you are talking about are generally higher-end items. We used to have a big rotary compressor at a plant I worked at as a highschooler. I think it was lubricated, but the concept is the same, I think. They are pretty quiet as I remember.

The ones folks are talking about here are generally cheapies, like those from the local sears. The compressors are just aluminum cylinders and pistons with reed-type valves and a sealed bearing on the crank, which is turned by a high-speed electric motor. They are about as simple as they come. They use a self-lubricating ring (now I know they are at least sometimes made from or coated with teflon).

MAC702
09-11-2006, 11:30 AM
I will assume there is more than one style of oil less compressor then...
That is correct.

Ggg6
09-12-2006, 01:21 AM
smithboy, the rotary vane compressors I was talking about are cheaply made, very noisy, and definitely not for industrial use. You are talking about rotary screw compressors, fairly quiet, high output, high psi, and very durable. They do use oil lubrication, and they are big $$$. Real nice compressors to have in a big shop/factory.
MAC who makes these oil less piston pumps?

MAC702
09-12-2006, 01:42 AM
...The compressors are just aluminum cylinders and pistons with reed-type valves and a sealed bearing on the crank, which is turned by a high-speed electric motor. They are about as simple as they come. They use a self-lubricating ring (now I know they are at least sometimes made from or coated with teflon).
Ggg6, Smithboy described them well here. The vast majority of oil-less compressors on the market under $400 are this type. This includes my dad's Campbell-Hausfeld as well as just about all the oil-less pancake style compressors you see for carpenters, etc.

Personally, I'd never own one. Too loud, too fragile. But there's hundreds of thousands of them out there.