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Andrew
05-05-2003, 12:01 PM
After reading Forrest Addy's thread on air compressors and the responses it got me thinking about making a compressor from an old engine. Do any of you guys know where I could find more information on this?

I live in the suburbs, and my shop is a 2 car garage, so I would need to power it with an electric motor as I can't put it outside, and I obviously don't want to run it off gas inside the shop. How many HP do you think I would need to run something like a small 4 cylinder engine? What about an engine off a bike?

I'm looking to build this thing fairly cheap, and would mainly be using it to run a spray gun, however, more air tools will come in the future. My goal is to have something that can put out 15 cfm (or more) @ 90psi, and use a fairly small reserve tank as space is limited. Do you think this is a reasonable project? Any help is greatly appreciated.
Andrew

Al Messer
05-05-2003, 02:04 PM
If you're going to have to look for a scrapped engine as the basis of your project, you'd be better to 1. keep an eye on the classified ads in your local paper. 2. shop the pawn shops. 3. while scouting for an engine, also look for a junked air compresor off a semi truck engine or a junked Freon compressor.

Paul Gauthier
05-05-2003, 02:58 PM
I once made a compressor from a 5 HP tecumseh engine. I did not need it I just did to see if I could. I can say that it worked, made a lot of air, but it also pumped some oil, so no good for spraying. I dicarded the original head and made another that would accept two reed valves. If I were to do it again I would also discard the rings and make new ones from Delrin or some other plastic material. Might even bore and hone the cylinder in an attempt to reduce oil consumption. I think that was my problem I used an older engine. A three to five horse motor would be sufficient. Wait a minute??????? OK I am back I just went out and checked, I still have the head I made with the valves I can put them in a box and you could have them for the cost of shipping.

Northern Tools sells compressor pumps for which you would need to supply a motor and tank. A single stage 13.2 cfm @ 90 psi=$299.00 and a two stage 15.9 cfm @90 psi = $369.00. IMHO a lot of bucks, may as well buy a complete unit.

An idea that I have had for a long time is to make a compressor from a running VW engine. Two cylinders will run the unit and two will pump air. It can be done. I have seen plans in some mag. years ago to make one from a V8. Four running and four pumping. I thought of using the VW because #1, it is smaller and #2, it is air cooled.


------------------
Paul G.

darryl
05-05-2003, 03:50 PM
I've thought about doing that, using an old snowmobile engine, driving it with an electric motor. The four cylinders would give a reasonably smooth pressure delivery, maybe enough so to eliminate the tank altogether, of course, that means running the motor constantly, and some kind of valve would be needed to bypass all unused pressure. Much like a power steering pump is set up. My reasoning had to do with the large flow capacity possible with a four cylinder, coupled with the small capacity of a reasonably sized tank. The motor would be cycling on and off way too much, may as well run continuously, no tank required. Just a suitable valve. Of course, you could run the 'engine' slowly enough to be adequate for the most hungry air tool, but no more so. That might reduce the horsepower requirement for the electric motor driving it. Another benefit would be that the temperature rise of the compressed air would be lessened having four cylinders doing the pumping, so the heat loss, ergo energy loss would be less. These are just some of my theories on this , so take it as that. I've not yet built my own compressor, though I plan to, and am looking at a tankless setup. One other thing to consider is the 'engine' will essentially be sucking a high vacuum, which is the worst case scenario for oil passing the rings. It would have to be in good shape. All comments and criticisms welcome on these ideas.

Oso
05-05-2003, 05:44 PM
Well, as a project for fun, why not?

As a practical way of getting a compressor, maybe not.

There are a fair amount of compressor pumps with no tank around, due to tanks rusting, etc.
Used to be refrigerator pumps, back in the bad old days. I have a friend whose farm has a fridge pump compressor, works great.

Those things were designed to pump air well.

Since engines are usually available because there is a cylinder or major bearing problem, that is one issue. Also the oil throwing issue.

And lifetime as well. Oil distribution may not be very good on a splash-lube engine at lower speed. And some of those engines are low hour life engines , usually available because they are about wore out.

Finally, most are low compression, meaning they will not push as much air as a real pump with equal swept volume. You would have to fill up the chamber somehow to get better efficiency.
If you make a new head, might as well make the whole thing.

Still, its an OK fun project. And better than no compressor if that is the only option out in the sticks, or a remote location.

Kerry.S
05-05-2003, 06:50 PM
If you use a four cylinder engine you could make it a four stage compressor. have one cylinder feed the next so each clinder only needs to compress the air a little bit. but since most engines create 120 to 180 psi in one shot I don't think overworking it will be and issue
kerry

[This message has been edited by Kerry.S (edited 05-06-2003).]

Spin Doctor
05-05-2003, 07:10 PM
Back in the days when AMC still existed as a seperate enitity they did a quite substatial business in supplying motors for various aplications. International was using the inline sixes and v-8s until they installed their own v-8 machining equipment and still continued to use the six. One other custumer at one time was a natural gas pipeline company in Canada that bought AMC v-8s with a special cam shaft and intake manifold. Four of the engines cylinders operated as internal combustion while the other four were used to maintain the pressure in the pipeline. And the four that were running in the combustion mode ran off of the gas supply in the pipeline

Cass
05-05-2003, 10:25 PM
Air compressors are too cheap to make it worthwhile to build one from junk parts. Rebuilding a good cast iron compressor makes sense if you get a good one. Ingersoll-Rand is expensive and hard to rebuild. Quincy, Kellogg, Curtis, Saylor-Beal are all good solid compressors and pretty easy to rebuild. Get as big tank as you can. The bigger the tank the less often the compressor will cycle and it is the starting and stopping that wears them out. The compressor should not start more than once every ten minutes or it will most likely smoke the motor or the compressor. Constant running is not hard on the compressor. Get a big piece of pipe say 4-5 inches in diameter to use as the first receiver and put a ball valve on the bottom with the pipe standing vertically. This big piece of pipe will condense and catch a large part of the water and oil vapor coming out of the compressor. Put another ball valve on the air tank so you can drain the water there also. After that you can put on a refrigerated air drier to give you real dry air and then put on a coalesing air filter. The air you get from this set up will do a great job for painting and for most instrument air applications. The air is still unsafe to breath though. You don't need the refrigerated air drier for most painting but it extends the life of the the air filter a lot so you save some money on filters and are less likely to screw up a paint job.

Thrud
05-05-2003, 10:46 PM
If I was going to waste the time to build a compressor from scratch, it would have to be a rotary screw compressor. No point screwing around - I always say - or was it "poo or go blind"? For what a good Cast iron compressor cost, why bother? Or better yet, find an old one no one wants and rebuild it! (Yeah!)

I knew a guy that was given a tree stage for free - worn out. It cost him $500 for the sunnen CK10 hone job, parts, and a 10HP single phase motor. It could run 3 snap-off impact wrenches and a 1-1/2" impact wrench all day and stay at 200psi. A commercial unit to do the same would have cost $5000. So it was worth the effort.

CCWKen
05-05-2003, 11:01 PM
Just one more sugestion: If you plan on running air tools, go with a compressor that makes at least 15cfm @ 120psi. More (cfm) is better. Also, 90psi at the regulator will be down to 80 or less by the time it gets to the end of a 50' hose. Some of the new sanders and die grinders use only about 4cfm @ 90 but most others need 9cfm and above. I've got a few that take 15 and a spray gun that takes 17! Make sure you check that when buying air tools.

jfsmith
05-05-2003, 11:11 PM
I got my air compressor from a seniors assisted care living center. They have to replace the fire sprinkler compressor after so many hours of running, so I got a nice 5 HP compressor from them. Then I called around to the places that repair auto shop equipment, they a 100 gallon tank that they took the compressor off of and gave me the tank for $50. This was a poor mans way of doing it.

From HF, I bought a 4.5 HP compressor with a 21 gallon tank. I use the 100 gallon tank to build volume, works much better and doesn't run all of the time. Things are so cheap, that building one is for the experience, not the need.

Jerry

wierdscience
05-06-2003, 12:06 AM
I once worked on a steam driven air compressor but not the usual type,it looked and operated like a walking beam steam engine,had a big cylinder on each end one for steam and one for air,I don't see why you couldn't make one with an electric motor driving an eccentric just a thought,I have a Linsay 80 cfm that is a 360 Dodge v-8 that runs on four and pumps on the other, they did away with the factory head and made their own with popet valves instead of the automotive type,as long as the rings are new and not subjected to combustion temps. they seal good and don't introduce any more oil than a regular compressor would.I like Thrud's idea if you are going to do it build a screw,or better yet find a commercial unit that the engine is blown up in and modi. it.Maybe even build a vane type compressor they are pretty simple.

x39
05-06-2003, 08:03 AM
I have a book I bought about fifteen years ago called "Build Your Own Sandblaster". The compressor for this rig is a 390 Ford engine set up simular to what weirdscience posted above. The book was written by Donald E. Ribbing and Robert D. Kirk, published by Design Publications, PO Box 102, Columbia, Ill.,62236 and is item no. 3697. Not sure if it's still in publication, nor did I ever attempt to build one, so I can't address the accuracy of the plans.

[This message has been edited by x39 (edited 05-06-2003).]

Oso
05-06-2003, 01:21 PM
OK, if you are gonna use a 4 or maybe even an 8 cylinder engine, a litle efficiency won't matter. And if you want volume, that will indeed help a ton on that too.

I don't wanna move that sucker, though.....

docsteve66
05-06-2003, 04:54 PM
We kind of discussed this a while back (I said we "walter mitty engineered" the gas engine idea. I did not know they were so common. We thought using three cylinders to feed the fouth (in a V8) would give much high SCFM than running al four in parallel (which is what I gather is being discussed). The three feeding four would allow for a heat interchanger between stages.

And on any home made rig- don't forget the unloader valve if the compressor will have to start against tank pressure.

Alistair Hosie
05-06-2003, 06:12 PM
I once saw an old timer use his truck to cut lumber he would drive it in to work in the morning and jack and block it up, and take of the rear wheel and put on a wheel without tyre and then put a belt from this wheel to run his big saw which he used to mill timber.When the days work was done he would put the wheel back and drive home and come back next day to start over he must've wedged the gas pedal with something.I was just alittle boy at the time but I thought it was a great trick then Alistair

x39
05-06-2003, 10:12 PM
<font face="Verdana, Arial" size="2">Originally posted by Alistair Hosie:
he must've wedged the gas pedal with something.</font>

I've seen older trucks with a second throttle control on the dash board. The ones I've seen could be set at the desired RPM. Very handy when running equipment off a PTO.

docsteve66
05-06-2003, 10:18 PM
Alistair: They used to make a "cat head" to slip over lug nuts and run a belt. When I was "water tanking" the company furnished a tractor trailer. We used the tractor to lift things by rigging a pulley (single block) and putting a line between the dual wheels. sounds dangerous but never had a rope snag. Replaced the rig with a war surplus winch. Truck had a hand throttle as described. but we ran it at idle with a safety line to snatch the gear shift to neutral should anything snag. We were very safety aware men http://bbs.homeshopmachinist.net//smile.gif
Steve

Thrud
05-07-2003, 02:27 AM
Alistair, X39

My dad had oilfield sevice trucks with a PTO shaft welded on the rear hub cover plate. They would put both wheels up (posi-trac) and use the rear wheels to power Ridgid Pipe threaders. There was a manual throttle control mounted either at the rear of the trucks under the gin pole roll, near the deck winch, or in the cab. It works great BTW.

Andrew
05-07-2003, 01:24 PM
Thanks for all the replies. From what I gather I'd be better off just getting a normal compressor. I was hoping to build something cheap that could put out a decent amount of air, but it seems like that would be a fair amount of work and I don't have enough time to spend on it right now (too many other projects). Also,I need to save money for college, and I like buying my tools once, so I guess buying new isn't really an option.
I come across a fair amount of used compressors, however they are usually 7 real hp and up, and I don't have enough power in my shop to run one (30 amps @ 220). Unless.... and this should probably be a new thread, but has anyone made a 3 phase generator by hooking up a 3 phase motor to a smaller single phase motor (say a 10 hp 3phase run by a 1 hp single phase). From my limited amount of electrical knowledge it seems possible, however I'm probably overlooking something or else everyone would be doing this.
Thanks
Andrew

ibewgypsie
05-07-2003, 01:37 PM
Andrew..
The older ford AC freon compressors on the cars I have built a dozen compressors off them. You just weld the clutch up and drive it with a electric motor. Last one I made I used two of them on one motor and it put out as good as the campfield hausfield I had next. You could paint with it, not so the 2hp roll around.
You can find a hundred reasons "NOT to do something" you have to look at Why. But I am as stubborn as a mule.
Do it your way, it is easier just to buy what you need. If you have the money.
I sold my 2hp nail gun roll around for $150.00, shop around for a used one. A Motor will cost you 1/3 that at least.

ChadL
05-07-2003, 01:43 PM
Another idea is to use an old york AC compressor off of a car. I'm into jeeps, and it is pretty common to mount these compressors to the engine of the jeep (or whatever) and use it to fill tires, or run air tools.

There are several different size, and they larger ones will put out enough air to run an impact easily (10 cfm +)

I have one on my jeep and it works great, I have an extra sitting in the shop, and plan to use it to replace my cheap compressor (craftsman) when it finally dies.

Chad

ibewgypsie
05-07-2003, 03:22 PM
My school bus & trucks has a decent compressor, I never saw anyone work on one. I kinda think they hook to the motor oil pressure thou. 130psi for the air brakes. You might get one of them gave to you. I just remembered hooking quick connects to the air tank on a semi for a air ratchet.

x39
05-07-2003, 05:45 PM
Oh boy, here we go... I just scavenged an old compressor tank from the dump and happen to have an AC compressor from my old Cadillac still laying around, then I read this, say no more....

docsteve66
05-07-2003, 11:11 PM
ibewgypsie: Strange you mention campbell huas. Son in law has one- he says it a piece of junk. but per specs it is good compressor. So I looked more carefully at the specs. It supposedly is 7 cfm. We calculated volume of the tank and it should have pumped up in a minute or less. Of course it don't!!.

Then measured bore and stroke and rpm. came out very near 7 cfm. Went to some other catalogs, discoved about the same thing. Seems like they are calling the cfm pumped same as cfm displaced. WW Grainger was honest- they rated cfm availalbe at different pressures.

No compressor is going to have 100 percent volumetic efficiency, but if you figure the cfm swept out as 7 cfm, then figure 15 psi (14.7 for nitpickers) as start, then 30 psi halves the cfm, 60 psi halves it again, and 120 halves it again. Am I missing something? 16 minutes to fill the tank at 120 psi. But son claims the thing took a very long time to reach pressure.

If thats what the advertisers are doing, they should be jailed!
Steve

wierdscience
05-07-2003, 11:26 PM
Doc I think there was a checkvalve failure involved,I see them everyday at least 2 a week.But you are right there is a difference between free air cfm and cfm at the spec pressure.The pressure on the spec end is usually determined by the volume avalible at top dead center,about .0625"x(3.14 x r2)x compression ratio- that is if this is correct.I like the converted engines for the small volume blasting I do,but for commercial use I still prefer an air screw or a vane pump.

Oso
05-08-2003, 12:46 AM
That's the problem with engine compressors. Good flow, bad pressure.

Since the "compression ratio" in a compressor is huge, but only say 8 or 9 in an engine, the way it delivers air is diffrent.
Assuming you have a check valve, it won't open until it has a differential across it. The compressor develops a greater-than-tank-pressure earlier in the stroke, devoting the rest of the stroke to flow.

An engine against 110lb will not develop that pressure until later in the stroke, and won't exceed it by much in any case *. Flow is related to differential and flow resistance, So the lack of differential means good flow at low pressures, but much worse than expected flow at high pressures.

To improve it, you need to fill the chambers to raise the compression ratio. Now the tank pressure is exceeded early, and the rest of the stroke can be flow.

If you only want 40lb, you can get a lot of flow with an engine based compressor, especially a 6 or 8 cylinder.

* at 8 to 1 ratio, you get just to 120lb, neglecting heating effects, which would raise it a bit.

[This message has been edited by Oso (edited 05-08-2003).]

lightswitch
05-08-2003, 02:36 AM
I have a freind who rebuilt a mopar airconditioning compressor, & mounted it under the hood of his landcruiser, powered off teh motor with an extented accessory fan. That thing Kicks out! both pressure & volume!

docsteve66
05-08-2003, 12:12 PM
Oso: Good explaination -and you said enough to keep a man in the design phase a long time (if your comments are carefully considered).

I suspect a long stroke would be bettter than the same cubic inches with a short stroke and same compression ratios. Have NOT done a single calculation, just a gut feeling I had as I read your explaination.
Steve

ChadL
05-08-2003, 04:37 PM
<font face="Verdana, Arial" size="2">Originally posted by lightswitch:
I have a freind who rebuilt a mopar airconditioning compressor, & mounted it under the hood of his landcruiser, powered off teh motor with an extented accessory fan. That thing Kicks out! both pressure & volume!</font>

Yeah, it's pretty cool, the York compressors have their own oil resevoir, they were used on lots of different cars in the 70-80's, a modern sandean (sp) compressor doesn't work as well cause it counts on the refrigerant for lubrication.

Last week, I pulled my jeep down around the back of my house, and used the compressor to run an impact while I drove 4" long 5/16 diameter lag bolts, beats draggin the big one out from the garage.

ibewgypsie
05-08-2003, 11:28 PM
Chad.. I have built about thirty or more tube type bumpers and put a air quick connect on them. (to carry air) Them off roaders are trips in thierselves. did you see the exto-skeleton on the model 3 bender site?
We are rapidly losing all the places to off road in the south.
I have always wasted my money on harleys and beer, except for the 46 dodge panel truck with wagoneer chassis.. it was fun. Real posi's on both ends.. one wheel touch it would go.

ChadL
05-09-2003, 10:31 AM
<font face="Verdana, Arial" size="2">Originally posted by ibewgypsie:
Chad.. I have built about thirty or more tube type bumpers and put a air quick connect on them. (to carry air) Them off roaders are trips in thierselves. did you see the exto-skeleton on the model 3 bender site?
We are rapidly losing all the places to off road in the south.
I have always wasted my money on harleys and beer, except for the 46 dodge panel truck with wagoneer chassis.. it was fun. Real posi's on both ends.. one wheel touch it would go.
</font>


Yeah, we are kinda' a different bread http://bbs.homeshopmachinist.net//smile.gif Now that I have the engine powered air compressor, I'm working at adding a second alternator to use as a welder http://bbs.homeshopmachinist.net//smile.gif

If your interested in off-roading, and keeping the trails in your area open, look up some local clubs in your area. There are 100's around the country, we need all the help we can get http://bbs.homeshopmachinist.net//smile.gif

Chad

ulav8r
05-10-2003, 11:26 PM
[QUOTE]
I come across a fair amount of used compressors, however they are usually 7 real hp and up, and I don't have enough power in my shop to run one (30 amps @ 220).

Get one of those, replace the motor with the largest you can run from your power supply. Use a smaller pulley on the motor and/or a larger pulley on the compressor. This will give less air than originally, but should extend the life of the compressor. Another alternative would be to put a gas engine on it, set it outside and pipe the air into your shop.

About using an engine with some cylinders pumping air, the main reason for replacing the head is to eliminate the chamber in the head, thereby increasing the compression ratio. This is also why reed valves are used, they work without having a cavity for the air to compress into.

David Hafnorske
05-11-2003, 06:18 PM
ANDREW
Don't know if this is what you are looking for, but Enco sells static phase converters of different sizes. They list one as heavyduty 1-3 for $128.

cutter
05-13-2003, 05:46 PM
X39.....
How large is that book??
How many pages, that is......Any chance of getting a "Xerox" copy of it?
WOuld be happy to pay copy/shipping costs......

Thanks.....


<font face="Verdana, Arial" size="2">Originally posted by x39:
I have a book I bought about fifteen years ago called "Build Your Own Sandblaster". The compressor for this rig is a 390 Ford engine set up simular to what weirdscience posted above. The book was written by Donald E. Ribbing and Robert D. Kirk, published by Design Publications, PO Box 102, Columbia, Ill.,62236 and is item no. 3697. Not sure if it's still in publication, nor did I ever attempt to build one, so I can't address the accuracy of the plans.

[This message has been edited by x39 (edited 05-06-2003).]</font>

cutter
05-16-2003, 01:23 PM
LET ME TRY THIS JUST ONCE MORE.........

X39.....
How large is that book??
How many pages, that is......Any chance of getting a "Xerox" copy of it?
WOuld be happy to pay copy/shipping costs......
Thanks.....


quote:
--------------------------------------------------------------------------------
Originally posted by x39:
I have a book I bought about fifteen years ago called "Build Your Own Sandblaster". The compressor for this rig is a 390 Ford engine set up simular to what weirdscience posted above. The book was written by Donald E. Ribbing and Robert D. Kirk, published by Design Publications, PO Box 102, Columbia, Ill.,62236 and is item no. 3697. Not sure if it's still in publication, nor did I ever attempt to build one, so I can't address the accuracy of the plans.
[This message has been edited by x39 (edited 05-06-2003).]