View Full Version : Air compressor from a small engine

05-09-2007, 05:41 PM
Well i got it hashed together -more or less.

I know someone here was asking for some more info on another thread so i thought i'd post some pics of my attempt.




I still have to make a guard out of the expanded sheet metal you can see on the floor. I'll clean things up a bit, give it a coat of paint and make it look a little more purdy. The gaurd will help hide the fact that the engine is on there crooked... oops ... and keep fingers away from the fan on the bottom of the motor. Thats somewhere you might accidently reach for and get a finger whopped off!

Not too bad considering it only took me about 1 1/2. That included all the time i spent sitting on a stool figuring out what i could make with the scrap i had.

I can run it as is, but i really would like to modify the camshaft. It seems silly to have a power and compression stroke on an air compressor. A lot of wasted energy since i am effectively compressing and then expanding and then recompressing before allowing it to enter the tank. This means more loss of air and psi on the tank end and excess heat on the compressor end.

I'm thinking about making me own cam and just free-hand grinding two lobes for each valve, each lobe 180* apart. I can't think lobe geometry is too critical in this application.

What do you guys think?

The B&S camshafts are plastic lobes and gears so its kinda hard to modify but the other option i thought of was buying some 35 pitch sprockets and put one on the crank and one on the cam so the cam turns once for every one reveloution of the crank. That requires that a buy something though :(

05-09-2007, 05:48 PM
The mounting bracket for the engine was the most trouble since they have kind of funky mounting bolt circles. The crank cover is all knobly and bubbly so there can only be some small contact pads where the engine bolts to. Oh, and i welded the whole bracket assembly to the pad that had previously held a small integral motor/compressor. I didn't want to weld directly to the tank...

I used the crank cover with out the rest of the engine for mock up so it was much lighter and easier to deal with one handed (the other hand being occupied with welding)

I chucked a B&S crank in the lathe and set the compound to match the taper on the crank so i could cut the taper inside the pulley (after mis-measuring/calculating the taper once). I think my compound ended up reading about 12* but i'll have to check. Can't remember right now.

Aside from that i cut some slots to allow vertical movement of the motor and used washers to tension the belt by pushing the motor outward.

Then, where the muffler had been, i'm making a 3/8" plate with threads for 1/2 black pipe which then connects to an old piece of copper tubing from our kitchen sink to the unloader valve on the tank. I still have to wire the motor into the pressure cut-off switch. And i think thats basically it for the construction aspect of it.

05-09-2007, 06:41 PM
Hi Fasttrack,

You have a good start on this idea. Using a vertical shaft engine is difficult to do.

You commented on the camshaft. I think that you may want to consider removing it all together, and making you a couple of check valves to put in the head. An inlet and an outlet. This will let it pump every stroke. You could also remove the intake valve along with the camshaft and use the intake for the inlet check. You will have to stop up the intake valve guide. Use the spark plug hole for the outlet.

Just a couple of ideas.

Good luck on your build.

05-09-2007, 07:42 PM
Thanks! I actually built a check valve deally for the tecumseh block i had planned on using. It was a pretty fun build that required some goofy little passages to be milled and a couple of ball bearings and springs to act as the check balls. Not sure how well they'd seal - i've tried before and only had moderate sucess at building my own check valves but that was before i got a three-in-one.

Trouble is the crank and con rod in the tecumseh were junk so i went to this briggs one instead. Of course the part i made actually bolted on in place of the cylinder head (looking back that was stupid) so it only fits tecumseh blocks :( I was too lazy to attempt it again when i didn't even know for sure if it will work.

05-09-2007, 08:28 PM
take out the tappets and cam replace valve springs w/ light springs replace sparkplug w/ check valve it will now pump every revolution like a regular compresser

05-09-2007, 09:48 PM
Yeah what Gene said, I've made a few like that myself

works very well.

check valves can be purchased or home built easily.


05-09-2007, 11:50 PM
Ditto,ditch the cam.

05-10-2007, 12:06 AM
'Twil be curious to see what pressure max, the machine will put up. With standard B&S compression, maybe 60 psi? If you are looking for 100 psi, or so, will shaving the head be an answer? Thinner head gasket? Moving the checks closer to the piston? Complete new head (alumyum)? I dunno.


05-10-2007, 02:30 PM
Unless the motor is very low compression, it should hit 120psi easily, if not, shave the head or use a thinner head gasket.

before sealing up after removing the cam, be sure to plug or restrict any oil passages that will dump pressure to the crank. if it's a splash system no worry.

on V8 compressor conversions I normally leave the cam and lifters in position to maintain oil pressure.


05-10-2007, 03:50 PM
The compression ratio on the old tecumseh engine was very low - the piston hit TDC about an 1/8" before the top of the cylinder and the head had a pretty big (compartively speaking) combustion chamber. The head i built for that one actually occupied some of the 1/8" space (not much about .100) and had a block on top that housed two 3/8" check balls for in and two for out along with a little adapter dealy so i could plug into a tank easy. Ditched the cam, plugged the tapet guides, just in case and was pretty happy. Until i started thinking about how much slop there was in the conecting rod... i was just going to run it as is, but i was affraid it would tear itself to pieces, even at low rpm, or at least make a huge racket. I checked with a mic and telescoping gauge the two dimensions - .119 :eek:

Anyhow thats the story of my first attempt - i guess i will try my homemade check valves again since they never really got tested. I just think they're not going to work... may have to buy one.

I think i'll keep the cam in place since it has a little eccentric oil pump attached but i'll ditch the tapets and put it lighter springs for the valves. With the crank breather there and the valves operating the way they should i dont see how pressure would be dumped to the crankcase...

Yeah - i know compression gauges normally read about 60 psi but i reckon i should be able to hit 110 which is where the switch is preset to cutoff at it with out too much trouble.

05-12-2007, 06:27 AM
take out the tappets and cam replace valve springs w/ light springs replace sparkplug w/ check valve it will now pump every revolution like a regular compresser

Hope to convert a 6 cylinder ford engine to a compresser, (drive with tractor PTO)using the above valve idea.
Would like to know the maximum revs that this set up could be operated at,
and if valves would receive enough lubrication with the rocker gear removed?
Thank You,

05-12-2007, 09:24 AM
You could make a new head out of alum. plate to bolt to the block. Remove the valves and cam. A good gasket to seal around the cylinder to block out the valve area. Put a check valve in the head with a filter for the suction side. Put a line out from the head to the tank with a check valve in it for the pressure side. You will get max. compression that way. Be sure to check piston to head clearance.

05-12-2007, 10:25 AM
Years ago, I saw in a farm magazine a compressor some guy built out of 2 Chev. 292 sixes, one driving the other that was converted to a compressor. He had check valves in the spark plug holes for outlets, I don't remember what he did for intake, prob. light springs on the valves. A local painter had a comp. that was a Ford 302 V8 w/one bank used as the comp. This was some kind of factory-built setup & had a special head for the comp. side. Interesting...
Ron in CO...

05-12-2007, 12:03 PM
Not too many of you, are as old as I. But, when dirt was new and Roebuck was a partner with Mr. Sears, every auto parts counter sold 12 - 20 ft pieces of air hose with a tire inflator bib on one end and a simple check valve on the other. The check valve included a crossover thread, which would temporarily replace a removed spark plug, on most any engine. This was when 90% of auto and tractor engines used one size hole threads.

For less than $5, everyone carried their personal/emergency 'compressor' under the front seat. Great for airing up tires, especially on the farm and no one ever worried about filling a tire with gasoline vapors.

An aside concerned Chevy 6 bangers, which at one time were quite common in the vacuum truck industry. Driven via a PTO and equipped with a finned aluminum head with reed valving, they made an economical vacuum pump or low pressure air pump, depending on the position of a 3way valve.


05-12-2007, 05:05 PM
"I still have to make a guard out of the expanded sheet metal..."

No, you don't. Mine's been running for almost 40 years without one.

You can see the flat plate and check valve that replaces the original cylinder head and spark plug. The cam is still there, since the oil slinger runs on it, but the tappets have been removed. The exhaust valve is closed off. There's a light spring on the intake valve, and a small relief is cut in the head from the intake valve over to the check valve.

I can get about 90psi max, but the cutoff switch is set for 35. That way I don't have to use a gauge when I pump up my truck tires.

You can cut the oil fill tube off and cap it, too. Mine has been running on the original slightly used engine oil since I built it. That's my air storage on the left of the photo. :D


Wow, I'd forgotten about those emergency tire inflators that connected to the spark plug hole. Nothing like having your tire filled with an explosive mixture of air and gasoline when you go to have it fixed.

05-12-2007, 11:29 PM
winchman, they still make them. http://www.stopngo.com/inflation.asp

05-13-2007, 10:32 AM
I like that. Nice conversion and should last a long time.

05-13-2007, 11:04 AM
I have a friend who made a compressor out of a 4 cylinder he made the head out of plate steel and put reed valves on each hole .

05-13-2007, 12:15 PM
Well to be a full-fledged air compressor it needs a bit of work yet. I run at about 1300 rpm on the engine and even spinning that fast it takes a good 3 or 4 minutes just to get to 50 psi. (i'm filling an 8 gallon tank)

I need to improve all of my valves. The check valve i'm currently using is one i pulled out of a junk pit. The plastic disc that had been in there had long since disappeared (where i dont know) so there was just an open hole and a spring. I tossed a ball bearing in there and got it to seal up but it still leaks a bit. I think if i improve all of the valves i should be able to get up to pressure a little faster.

What do you guys think? Any thoughts on how to make it more efficient? Its got a ~2.6" bore and i think ~2.5" stroke so about 215 cc displacement.