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Username Post: DIY : convert weak electric air compressor to GAS powered??        (Topic#222758)
74elco for73SS 
Senior Member
Posts: 575
74elco for73SS
Loc: so cal
Reg: 04-30-04
08-01-09 12:50 AM - Post#1745728    

Hey folks,,

I have a old craftsman 3hp 30gal horizontal air compressor. I'm a mobile mechanic, and this thing really needs a homeowner with a good sized breaker in they're garage to be able to start up my compressor. I believe the 3hp electric motor is on its way out, because it trips almost every breaker of the house I plug it into.

I need a gas powered compressor anyway, but they go for a lot of money. I figure, I have a good tank, I have a good "compressor" so why not remove the wimpy electric motor and add a 5 or 6hp gas engine?

I guess my question is, has anyone ever heard of doing this, and can you point me in a direction as far as pressure relief valves and what not to work with the motor. I know all this stuff already exists, but don't know what the parts are called or where to get them?



Senior Member
Posts: 3221
Age: 62
Loc: D/FW Texas
Reg: 02-18-03
08-01-09 08:20 AM - Post#1745819    
    In response to 74elco for73SS

I have never really studied a gas powered compressor but my roofing crew uses one every day and I practically trip over it when I am out there on the jobs. I doubt anyone sells a kit to build one. There has to be some sort of a clutch controlled by a pressure switch to engage and disengage the compressor and some sort of governor to raise the engine idle speed when the clutch engages and puts a load on the engine. The governor is likely mechanical and part of the engine. The pressure switch likely activates electrical contacts to engage the clutch. Logically, that means the gas compressor has to be plugged in to an outlet to run the clutch or it has to generate some level of electrical power on its own. I will be interested to see where this goes and I will take a look at one next week to see if I can tell how it works.

I would think that by the time you cobbled something together you could take the same money and buy one. Or maybe get a broke down one at a pawn shop and fix it.


To each problem exists a think.

The ZD Nova Page

Posts: 689

Loc: Sault Ste. Marie, ON, Can...
Reg: 03-14-05
08-01-09 08:43 AM - Post#1745828    
    In response to 74elco for73SS

Don't change everything just yet. I have an old Craftsman compressor(1979) that blew fuses as well. The bearings in the electric motor were seizing up. I changed them out, and compressor has been fine since. It is on a 220V 30A circuit. Check them out first, you may be okay.

74elco for73SS 
Senior Member
Posts: 575
74elco for73SS
Loc: so cal
Reg: 04-30-04
08-01-09 10:27 AM - Post#1745868    
    In response to Algoma56

Ok thanks guys for the help. Im sure my electric motor could be repaired to pull much less of a amperage draw, but being mobile I pretty much need to do this upgrade, or buy a generator to run my electric compressor as is. A generator capable of powering the start up amperage spike of a compressor will probably be at least $500 for a chinese knock off.

But I think I pretty much found my answer: -powered-...

these things are expensive, but I already have the tank, and compressor head. So it looks like all I need are a horizontal shaft engine (craigslist/harborfreight for cheap @ $150)
and a unloader valve:

@ $60.00, : es-engines-p-386.html

a throttle valve:

at @ $50 or less :

and about 20 trips to home depot to figure out the plumbing of said parts.

Looks like if I can get a cheap engine, I can do this conversion for around $200 plus misc. plumbing pieces, a belt and a pulley for the engine.


08-01-09 04:18 PM - Post#1746028    
    In response to 74elco for73SS

Try this for what you need:


Posts: 754

Loc: Albany,Ga. Gold Member
Reg: 05-23-02
08-02-09 08:21 AM - Post#1746304    
    In response to Bobs85PU

74elco--Having worked on air compressors for a number of years I won't tell you that what you want to do can't be done, but it will be difficult, to say the least. Even though those parts are readily available, it's not just a matter of putting them on, and piping them in. All components of a combustion engine driven compressor must work together for the unit to compress air, store air, and unload air when the appropriate pressure is reached. Good Luck, David

"12th Year" Platinum Supporting Member
Posts: 5356
Loc: Always garaged
Reg: 02-23-02
08-09-09 01:14 PM - Post#1750720    
    In response to 74elco for73SS

Hey elco.

Don't blow yourself up.

As noted, systems are engineered to keep that from happening.

Personally, I'd look for something 'out of the box'.



Juergen and Ana's Webpage

'54 Bel Air
'57 Townsman 210
'07 Dodge Magnum R/T

Senior Member
Posts: 811
Loc: OR
Reg: 02-01-05
08-09-09 03:42 PM - Post#1750779    
    In response to 57Townsman210

This is not something that should be very difficult at all, and not dangerous in the least unless you're a complete moron. The major important thing you need is simply a standard blowoff valve that will go off when your tank is full. That way it will never, ever blow up. Also, with something like that you don't technically need to even control the engine - you can run it on high all the time, and just allow the excess air to escape from the blowoff valve. Of course that adds more wear and uses more fuel, but it's cheaper....

Senior Member
Posts: 251

Loc: Ks.
Reg: 11-17-05
08-25-09 08:45 PM - Post#1760533    
    In response to Number21

That is the valve (either one) you need, the port on the right side of the picture goes to the valve in the head of the compressor and also to a air cylinder mounted to the carb butterfly to let the motor go to idle. When the pressure goes down the cylinder retracts and the motor throttles up. The problem is that most elect powered compressors don't have the proper valving in the heat to do this, without this valving the compressor will never unload (more or less freewheel) and when it pressures up and the cylinder cuts the throttle to idle the load will stall the engine. North Central Air in Downs Ks. could point you in the right direction.


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