how do the spec-s of an air impact wrench relate to the air compressor? i need to loosen a crankshaft pulley bolt that is torqued at 134 ft- lb. on a 1998 honda civic LX. i have a sears craftsman 1.5hp 4- gallon 4.7SCFM@40psi--3.3SCFM@90psi air compressor. i don't yet have an air impact wrench. what should i look for in terms of psi when i go to buy one, such that i can use that air compressor to drive the impact wrench to loosen the bolt? tia.
Usually PSI and CFM are the main requirements for tools. There are also electric impact wrenches available. Have you tried a 3/4" drive socket with a 4' pipe over the breaker bar.
The problem is you'll have adequate pressure but highly unlikely to have sufficient volume (cfm) to drive a sizable impact wrench. Most will need in the 7-9+ cfm range at 90-100 psi to come close to the spec's you're wanting.
A bolt that was torqued down to 134 ft lbs may take a hell of a lot more torque to remove depending on how long it's been there and how much rust is on the threads or weather thread lock was used on it.
Your compressor may give you 30 seconds of impact wrench time then you'll have to wait for it to build back up.
a 4 gallon compressor wont give 2 seconds of impact with a 1/2 inch drive impact.
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Buy a twin hammer impact like the IR 231 (I have a Porter-Cable knock- off, $105) and it will take off the bolt in a heart beat. Been there, done that. Old fashioned puny impacts simply won't get the job done. Look for a lb-ft rating of 400 or better (600 is good) and don't worry about PSI. Just set your compressor to something over 110 lbs or so if you can and go for it. The bolt will be off before the compressor needs to cycle again. The twin hammer impacts are also perfect for removing lawn mower blades, putting on snow tires (use wheel chocks) and similar chores. Have fun.
Joe
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Well, 4gal --> ~0.5cu-ft and a typical 1/2" impact wrench will need roughly 5 cfm@90-100psi (I was thinking of the big 3/4" jobbie earlier needing almost 9). So, not accounting for any losses at all would be about 1/10th of a minute (6 sec) and poof!--tank's empty.
I really doubt if he'd get it to spin up to speed even, what more actually make an effective impact.
As others have mentioned, that compressor may be too small to drive an impact wrench. Harbor Freight has an electric impact for sale, which is supposed to deliver 200# foot pounds. Just plug it in, and no compressor needed. It's rather long, from back to socket so it won't fit in some spaces.
For your application, how about a socket and a long breaker bar? Impact wrenches do have the advantage of "rattling" which tends to break up rust. With a breaker bar, you may need to heat up the nut.
Don't knock it 'til you've tried it. My twin hammer Porter-Cable works just fine with my Hitachi twin tank portable (1.5 gallon, or whatever) set at 110 PSI. The OP stated 135 lb-ft torque is reached by many impacts in less than two seconds. Calculations are trumped by actual facts every time.
Joe
Joe wrote: ...
Well, mayhaps yours does; even my 1/2" I-R certainly won't off the small roughly equivalent to OP's oilless de-Vilbiss compressor...and I wouldn't venture to recommend someone plan on making a purchase on the basis of a grossly undersized compressor.
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Fastest way to get that bolt off is a 6 point 1/2" socket attached to a long breaker bar extended with a piece of pipe. Attach and bump the starter. Used this method repairing Saturns. Works every time.
Is that a valid computation?
A 4 gallon tank may be 0.5cu ft in volume, BUT the air inside it is compressed so I think a 4 gal tank holds a lot more than 0.5cu ft of compressed air.
But maybe not... does anybody KNOW?
Mark
If you can get a solid 6 point socket on it with a good breaker bar. Hit the breaker bar with a large rubber hammer. It will come off. If you have the room, a good impact wrench will get it off. Good and made in China are not synonymous:) BTW: I have a 30" long Snap-On breaker bar. It would be worthless for this job as it's springy. The breaker bar needs to be solid.
Reminds me of a mechanic up the street. Was trying to get the axle nut off an old Studebaker. Put a large pipe wrench on the nut. Told his helper to put it in gear and let the clutch fly while he stood on the wrench. Tossed him about ten feet, broke his arm and shoulder. The helper put it in reverse:)
Al
I've had some success with pulling on the breaker bar, and then whack the breaker bar (about halfway down the handle) with a metal hammer. Sends a shock wave into my hand, and also into the nut. The OP will probably have to remove the radiator to get an impact wrench in.
Sorry to hear about the guy turning the gearbox the wrong way. That's no good, to send the boss flying through the air.
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