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View Full Version : What's the best material and fit for an oil-less air compressor piston seal?



winchman
11-30-2010, 05:31 PM
I've got a Task Force air compressor which wasn't making pressure. The cylinder was scored and the seal on the piston was folded down and split on one side.

I've turned and polished the cylinder bore. Now I need to make a new seal for the piston, but I'm not sure what to make it from. The piston is about 2" in diameter. It doesn't have a piston pin, so it rocks as it goes up and down in the bore. The seal is clamped to the top of the piston with an aluminum disc. This is the old seal:

http://img.photobucket.com/albums/1003/winchman/Miscellaneous053.jpg

It appears to be some sort of plastic, but there are no markings on it.

I've got some UHMWPE and some Delrin. Would either of those work for the seal?

Also, what kind of fit should I have between the piston and the bore?

I've tried to find a source for parts, but Lowes no longer carries TF compressors. The place they recommended for parts only carries parts for items still sold in the store.

JoeBean
11-30-2010, 07:09 PM
UHMW is used in some pneumatic and hydraulic seals as it has fair resistance to oil. But have you checked with seal manufacturers/hydraulic supply shops for the seal? Forget what it came from, you just need the specs on the seal. Looks like a typical design, and seals aren't that expensive, what with cylinders and pumps being rebuilt all the time. Just google "hydraulic seals" and you'll find a ton of sites with info to peruse.

becksmachine
11-30-2010, 07:29 PM
Any Delrin (acetal) that I am familiar with would be much too rigid for this application.

The seal needs to have a thin flexible edge to seal in the bore as the piston rocks to follow the crank pin.

UHMW might work if the cycle was limited to one tank fill up, but I don't think it would tolerate the heat for any kind of continuous use.

I think some kind of teflon would be the best.

Dave

Bruce Griffing
11-30-2010, 08:01 PM
Repair kits for that type of compressor are very cheap.

winchman
12-01-2010, 12:37 AM
Where do you get them? I've searched online for about an hour. The closest thing I could find was a link to the Sears parts site that says the item is not economical to repair:
http://www.searspartsdirect.com/partsdirect/part-model/Taskforce-midwest-air-Parts/Air-compressor-Parts/Model-37235/3251/0703000/P0506125/00001

Maybe that's why it was in the dumpster. :)

Bguns
12-01-2010, 06:17 AM
After listening to my neighbors similar compressor from over 600 ft away, without my hearing aids in..

The cheapest repair is to chuck it right back where it came from. Hearing aids cost BIG money...

Worthless 40 hour life, NASTY LOUD machines...

Beancounters over brains.. Buyers the same...

My dad was a commercial painter for 30+ years. Told me long before those cheap ones came out, to get a cast iron pump (pref with pressure oiling) with seperate belt driven motor.

Black_Moons
12-01-2010, 06:40 AM
Bguns is 100% correct
Toss that cylinder out, Buy a nice oil lubracated *LOW RPM* piston compressor. $200~ or so, And change the oil once a year, insted of the seals once a month!

My low rpm 2hp piston compressor is quite enough to talk over, What a consept!
My higher RPM 5hp compressor.. Maybe you can shout over it. But then, its a much bigger unit.

Every 1hp oilless compressor iv heard is even louder then my 5hp compressor.

mike os
12-01-2010, 09:49 AM
on the other hand, they dont mind falling over......being sat at an angle or even being pushed over while running....... all real risks out of the shop....:rolleyes:

Herm Williams
12-01-2010, 11:22 AM
mcmaster carr has cup seals. If it is very old it may be leather.
re

Bruce Griffing
12-01-2010, 11:27 AM
Sears sold kits in the past. If you look up Porter Cable, or others, you will find kits for them. Sears seems to have copped out. I am not sure who makes the Sears compressors, but maybe they still sell them.

vpt
12-01-2010, 11:33 AM
I always wondered (if a guy wanted to) could a 4cycle gas engine be used as a compressor? Say something with an oil system and two cylinders like a lawn mower motor.

kbertoson
12-01-2010, 12:06 PM
There was a company that made kits to convert VW engines into a compressor. They were based in North or South Carolina. Also years ago when spark plugs were more accessible they sold a spark plug replacement to put into a cylinder and use for emergency air for tires. Did see it used once sometime during the 1960's. He aired up a flat tire.

winchman
12-01-2010, 12:12 PM
I built this compressor in 1967 from a junked lawnmower which had a bent shaft. The motor came off a junked washing machine. The pulley is off a '55 Chevy. Everything else on it eas either free or from the junk pile, except teh new hose I installed about ten years ago. I put the original oil back in it after I cut off the shaft and it's still there.

http://img.photobucket.com/albums/1003/winchman/Air%20Compressor/000_1405.jpg

I made the new seal out of UHMW-PE this morning, and the old Task Force compressor has rejoined the living, at least for a while. :)

kbertoson
12-01-2010, 12:15 PM
I also understand winchman and his desire to repair the compressor. More fun fixing junk. If there is time and parts cost are low go for it. However the opinion is, the oil free compressors are the worst sounding pieces of junk ever built. For that reason alone it may be best to put it into the scrap or turn it into other uses.

becksmachine
12-01-2010, 08:30 PM
Good for you winchman!

I, for one, would be really curious how well the UHMW holds up, could you let us know? Did you take any photos of the part you made?

Thanks, Dave

bruto
12-01-2010, 11:24 PM
I have yet to find any place that sells just the seals for those compressors. You can buy a kit with the whole piston, rod and cylinder, but it's more than the thing is likely to be worth. I'm actually a little surprised that (as far as I know, at least) some enterprising entrepreneur has not tried selling the seals themselves, which must be pretty cheap to make if you have material sources. It seems like a good little ebay business for someone.

I don't much like those compressors either, but for portable air tool use it's hard to beat one. They're light and reasonably fast.

winchman
12-01-2010, 11:51 PM
I didn't really expect the first seal to work as well as it does, so I didn't take any pictures. I made it 0.025 over the bore diameter, had to start someplace.

Noise isn't really an issue with the compressor. The only thing I'll use it for is this:

http://img.photobucket.com/albums/1003/winchman/Miscellaneous055.jpg

It's also an item rescued from the trash. Should make an ideal combo. It'll look pretty bad, but the sound of that 24" horn is really nice. It's just a little lower than this:

http://www.youtube.com/watch?v=ElruJMYilow

vpt
12-02-2010, 08:02 AM
I am curious about the gas engine conversion. Do you use a one way valve to keep the compressed air in the tank, do you change the cam lobes in any way so there isn't a compression stroke or exhaust stroke? Are you taking the compressed air from the spark plug hole or from the exhaust port?

photomankc
12-02-2010, 10:29 AM
I am curious about the gas engine conversion. Do you use a one way valve to keep the compressed air in the tank, do you change the cam lobes in any way so there isn't a compression stroke or exhaust stroke? Are you taking the compressed air from the spark plug hole or from the exhaust port?


Yes, details please! I just happen to have an old broken lawn mower I will not be using anymore. This looks like just the ticket to make my wife's eyes roll!

:D

Guido
12-02-2010, 12:07 PM
Toss the camshaft, fab new cylinder head using an intake and an exhaust (compressed air) port. Use two 0.006 feeler gages, each to cover two 3/8 inch holes, and held with loctited screw mounted in the center. One pair for air intake, other pair for compression port.

New head to provide actual max compression, as top compressor pressure output is governed by the 'clearance' volume, ie. compression ratio.

Stock valves should be below finished deck height of the block surface. We checked for good sealing of the stock intake/exhaust valves, sealed with locktite, then covered over with J and B weld, to remove every last bit of compression volume.

Compressor still running after 12 years, slow but quiet with an air filter of sorts. Max pressure about 105 psi.

--G

winchman
12-02-2010, 03:55 PM
I made a new cylinder head from aluminum plate. It has a relief to permit flow from the intake valve into the cylinder. The discharge was through a check valve that was positioned over the relieved area.

The cam was still there to support the oil slinger, but I removed both tappets. The original spring on the intake valve was replaced with one just strong enough to close the valve. The exhaust valve is covered by the new cylinder head.

I probably left too much space in the relieved area and port for the check valve. I can only get about 60psi, but it's hard to expect more from a 1/3HP motor. I set the pressure switch to 40psi to ease the strain on the motor, and that's enough to meet my needs.

I haven't had to do anything to other than replace the hose and power cord in 43 years, so I'm calling it a success.

kbertoson
12-02-2010, 04:48 PM
Indeed your homemade compressor is a success. Now to see if any of the present crop of oil free compressors are in use after the same amount of time. My money is on your compressor.

mike os
12-02-2010, 04:57 PM
my oilfree is getting on for 10-11years now..... of occasional hard use:rolleyes:

vpt
12-02-2010, 06:53 PM
My oilfree has been good to me for 7 years untill this summer when it broke a rod due to a loose flywheel. I welded the rod back together cleaned and reset the flywheel and loctited the set screws, has been fine ever since.

I would like to have a quieter compressor or move this one outside. I have lots of different motors around and always wanted to try and make a compressor out of one.

A.K. Boomer
12-02-2010, 08:33 PM
There was a company that made kits to convert VW engines into a compressor. They were based in North or South Carolina.

That's the first thing I thought of was the old volks, keep the front two opposed for power and turn the rear two opposed for compressing -- pretty extensive teardown to do things right and lots of mods to heads and pistons but the engine/comp. would have a good balance.


Also years ago when spark plugs were more accessible they sold a spark plug replacement to put into a cylinder and use for emergency air for tires. Did see it used once sometime during the 1960's. He aired up a flat tire.

I also heard of that years ago and immediately wrote it off due to (back then) not wanting to inject a gasoline mixture into a rubber tire/tube as that's what the compression stroke would be filled with... (due to having a carb)

Nowadays you could pull the fuel injector wire off the injector and at least get just air...

A.K. Boomer
12-02-2010, 08:38 PM
And in keeping with the original topic I would think the seal is made of some kind of teflon --- delrin AF might have a fighting chance but UHMW? forget about it - it wont take the heat...

J. R. Williams
12-02-2010, 08:45 PM
Many years ago there was a kit to make a standard Ford flat head V8 into a four cylinder compressor with a four cylinder drive. One bank was the engine and the other was the compressor. I do not recall the name of the conversion.
JRW

bruto
12-03-2010, 10:17 AM
That's the first thing I thought of was the old volks, keep the front two opposed for power and turn the rear two opposed for compressing -- pretty extensive teardown to do things right and lots of mods to heads and pistons but the engine/comp. would have a good balance.



I also heard of that years ago and immediately wrote it off due to (back then) not wanting to inject a gasoline mixture into a rubber tire/tube as that's what the compression stroke would be filled with... (due to having a carb)

Nowadays you could pull the fuel injector wire off the injector and at least get just air...I thought that too when I first saw one, but they did not push out intake air. They used the compression to operate a little piston of their own. They actually worked pretty well if you had easy access to the plugs, and an engine that tolerated running a cylinder short. Back when I was a teenager and could have used a really cheap inflator, unfortunately I was driving old Peugeots with hemi heads, and no way to fit one.

Alan Smith
12-03-2010, 12:19 PM
On a similar note I can recall using a portable milking outfit in the 70s where the vacuum was draw as above by screwing an adaptor, with appropriate one way valve, into the spark plug hole of an engine. Seemed to work well.

A.K. Boomer
12-03-2010, 08:47 PM
I thought that too when I first saw one, but they did not push out intake air. They used the compression to operate a little piston of their own. They actually worked pretty well if you had easy access to the plugs, and an engine that tolerated running a cylinder short. Back when I was a teenager and could have used a really cheap inflator, unfortunately I was driving old Peugeots with hemi heads, and no way to fit one.


Hmmm, don't remember that far back but if there was a couple of different systems the one you mention makes much more sense --- Just so its used sparingly as to much running would still build up fuel in that cylinder and run the piston and rings on diluted oil...

jdunmyer
12-04-2010, 08:43 PM
Many years ago there was a kit to make a standard Ford flat head V8 into a four cylinder compressor with a four cylinder drive. One bank was the engine and the other was the compressor. I do not recall the name of the conversion.

Just a couple of years ago, there was a commercial construction compressor at the scrapyard that was made from an OHV Ford V8. One bank was compressor, the other was engine.
I think Schramm made compressors like this, but I don't remember if the above unit was made by them.

mike4
12-05-2010, 06:54 PM
Toss the camshaft, fab new cylinder head using an intake and an exhaust (compressed air) port. Use two 0.006 feeler gages, each to cover two 3/8 inch holes, and held with loctited screw mounted in the center. One pair for air intake, other pair for compression port.

New head to provide actual max compression, as top compressor pressure output is governed by the 'clearance' volume, ie. compression ratio.

Stock valves should be below finished deck height of the block surface. We checked for good sealing of the stock intake/exhaust valves, sealed with locktite, then covered over with J and B weld, to remove every last bit of compression volume.

Compressor still running after 12 years, slow but quiet with an air filter of sorts. Max pressure about 105 psi.

--G
Why did you change so much ,all that i have ever done for any converted single cylinder petrol engine was to put a solid plug in the sparkplug hole amd remove the electricals, exhaust and carb , then fit an aircleaner directly to the inlet port.
Make an adapter for the exhaust port to a standard pipe fitting ,the only internal thing was to make sure that the inlet and exhoust valves sealed properly , after this a two valve was fitted to the exhaust adapter to make startup under pressure a little easier, this is opened to the atmosphere when starting and then closed when the drive engine is running allowing compressed air to go to the tank which was usually made of heavy walled 6 inch dia pipe which also served as a base .

T hese old things were fine for years until we became more sophisticated, I may make on as a project soon just to compare its output to the commercial unit which has servers me for about twenty years now.

Michael

franco
12-06-2010, 10:01 AM
That's the first thing I thought of was the old volks, keep the front two opposed for power and turn the rear two opposed for compressing -- pretty extensive teardown to do things right and lots of mods to heads and pistons but the engine/comp. would have a good balance.


Boomer,

We used to use these for light railway track maintence. Two cylinders on one side supplied the power, and the two on the other side were fitted with a special compressor head.

As a matter of interest we also had Ingersoll Rand radial portable compressors built specially for this application. They looked like a 6 cylinder radial aircraft engine mounted with the crankshaft vertcial, and had alternate compressor and power cylinders.

franco