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Thanks in advance for reading. Have some heavily rusted bolts on my hubs, trying to do as much of a needed hub replacement as I can myself. Got a mixed bag of auto repair tools from someone a while back, among them a 1/2” air wrench and some assorted bits. I like to do my own repairs, and have run into this problem a couple of times so far. So thinking of buying an air compressor to run the air wrench.

Question is, though, a lot of random literature says I need about 6cfm to run them, but compressors that have that kind of output are at least $700. What happens if I use one with an output of 4 or 5cfm?

Just a guy
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5 Answers5

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4cfm is the usual rating for most air tools - including intermittent work with an impact wrench.

Also consider buying an Electric Impact Wrench (not a battery powered one - they're usually too low in power). And breaker bars with long (4ft) extensions can persuade most bolts..

PeteCon
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If the air wrench does not get enough air then it does not develop the full power it is capable of, which means it won’t always undo the nut. (I don’t have that problem - even by hand I can undo , break or shear nuts I have to undo...)

Either buy a large enough compressor or consider using a secondary tank to have a larger reservoir of air...

If you go the second reservoir route, then use rated tanks - truck brake tanks are a possible option - but consider that the small compressor will have to run much longer to fill a larger reservoir and that may lead to overheating.

Solar Mike
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The size and pressure in the tank determine what tools it can supply, not the output CFM of the compressor.

However, a small and/or low pressure tank might only give you a few seconds of runtime on a large impact wrench, and then the small compressor would have to struggle to refill the tank.

Keep in mind there's a huge difference between 10 gallons on an oil-less compressor running 120psi and 10 gallons of compressed air from the oil bath "industrial" models at 175psi. If your tank is small and you regulate to 90psi (typical) at the tool, that 120psi will drop below 90psi in a hurry.

SteveRacer
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If the air wrench is the only tool you intend to drive from the compressor, consider and electric impact gun as, for the same money as a cheap and cheerful compressor, you’ll get a really nice electric or even better impact gun.

Steve Matthews
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Get a corded impact wrench, all that torque on tap and cheap. My 78 280z have a 35mm nut holding together the rear hubs. 40 years of rust makes for a tough customer. I got a $30 impact from menards and after about 4 minutes of hammering with it they came loose! That corded impact is unbelievably strong

DatsunZ1
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