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1930's Curtis Compressor Rebuild


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  #1  
Old 04-16-2010, 07:25:27 PM
dawfun dawfun is offline
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Question 1930's Curtis Compressor Rebuild

I recently bought an old Curtis compressor (1937 vintage, I believe), and am in the process of cleaning it up. It was in service at a local repair shop from about 1938 up until last January, and the thing has about an inch of crud all over it that I'm cleaning off.

When I got around to the back side, and pulled the big fly-wheel, there was a lot of dampness around the crank shaft. Cleaned some of that up, and I could see that there was air sucking (and blowing) in and out around the shaft when I turned it by hand. I've never taken one of these apart, but I did find some good patent illustrations which show how the crank shaft is lubricated but I do not see how the shaft is sealed.

The crank shaft itself has no play in it that I can detect, and the whole thing turns over nice and smooth. It's got clean oil in it, too.

So I've got a couple of questions for you guys:
  • Is it normal for these compressors to leak around the crank shaft?
  • Does it take a seal, and if so, where could I get one? Can I make one? (My shaft is 1 3/8" diameter.)
  • Is there a rebuild kit available for this beast?
  • It looks like it would be easy to put a new seal in there, but is anyone aware of any tricks/quirks?
  • What qualifies as "good cylinder oil" these days?

Here's a picture of the plate attached to the front of the compressor:



And here's a picture of the whole thing:



Any help you guys can provide would be sincerely appreciated.

JC
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Old 04-16-2010, 10:39:41 PM
GADavis GADavis is offline
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Default Re: 1930's Curtis Compressor Rebuild

J.C. I have a 2cyl 2 stage 1938 model Curtis that looks almost like yours except for the fact it is 2 stage where yours is a single stage. Mine was mounted on a riveted seam tank and had a flat belt pulley on it when I bought it used in the mid 70's It needed a cylinder head gasket, so I made one out of some 1/8" asbestos sheet packing and it has run ever since then. I took the flywheel off and machined 2 grooves in it to run the more modern "A" sized V-belts. I use a 1-1/2 hp capacitor start 220 volt 1 ph motor on it and have it turning at 950 rpms and it produces around 6 cfm of air. The flywheel originally had a centrifugal unloader, but it was missing when i got it and a capacitor start motor starts it off well because i have an in line check valve at the new 60 gallon tank i mounted it on. It could turn a little faster, but it supplies most of my needs except for running an air powered cut off wheel and i just give it a moment to catch it's breath and go again since I don't use the cut off tool often. About 5 years ago Curtis was still in business because I looked up a website for them and e-mailed them my serial number and information and they told me mine was built in 1938. They might be able to tell you something about the oil seal. Mine has a breather hole on the front of the crank case behind the flywheel and i keep it clean. If that vent were to stop up I suspect that the piston movement in the crankcase would blow oil out because the air is displaced on the down stroke of the piston, and it has to go somewhere..

As for oil, I have used 15-40 wt. engine oil in mine since the 70's and change it about once per year. The instruction telling you to "remove the cover and clean it out", were for non detergent oil which did not hold the crud in suspension and it would build up in the crankcase bottom. Mine has valve chatter on the high pressure side for a brief moment befor it cuts off with the pressure switch. I took them out once and polished the stainless steel disc and the seat with fine valve grinding compound and it almost stopped it. I think it needs new valve springs now but it is not that bad, I. will get them one day probably when it quits. It sits there merrily chugging along and then when I hear the valve chatter a few times I know the tank is full without even looking at the gauge.

I don't see an air filter/silencer on yours anywhere. I took a 6 cylinder Ford oil bath unit and weled an pipe thread adapter into the throat of it so i could screw it onto the intake pipe of mine and ditched the old foil type thing on mine and now it runs very quite. I have it in the front corner of my 50x35 shop and is not very loud. it just sits there chugging merrily along then all of a sudden it chatters a time or two and kicks off till needed again. It has been a very dependable unit and the heavy cast iron construction will likely out last me. The cooling fan is cast into the spokes of the flywheel and when I got it the air flow was being sucked over it, I reversed the direction of rotation so that the air blows over it and it stays cooler now. I could not ask for a better unit than it. If I was doing a lot of production work it would not keep up I know, but it is in my personal (hobby grade) shop now and as long as it keeps my 1/2" impact and my Binks #7 paint spray gun going i am pleased. Gene Davis Tennille, Ga.
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Old 05-14-2010, 02:44:04 PM
gil393 gil393 is offline
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Default Re: 1930's Curtis Compressor Rebuild

I, too, have a recently acquired Curtis compressor that is going into service.

I am curious if anybody knows what the black canister between the cylinder head output and the tank, in the photo above, does?

I have two of them on my compressor with some sort of safety valve between them. They don't seem to be removeable, or serviceable.

Thanks,
Greg
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Old 10-31-2018, 11:17:18 AM
perpetualmotionrus perpetualmotionrus is offline
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Old 10-31-2018, 11:44:50 AM
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Old 10-31-2018, 11:45:16 AM
I like oldstuff I like oldstuff is offline
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Default Re: 1930's Curtis Compressor Rebuild

You just did.
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Old 11-04-2018, 12:25:18 AM
cobbadog cobbadog is offline
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Default Re: 1930's Curtis Compressor Rebuild

I just found this thread and although it is an oldie I am now curious as to what that small black canister is between the pump and the motor as well.
Any clues?
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Old 11-04-2018, 09:46:39 AM
ronm ronm is online now
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Default Re: 1930's Curtis Compressor Rebuild

Probably an accumulator that serves as sort of an unloader, delays the pressure buildup until the motor gets up to speed before it has to overcome the tank pressure. Primitive, but it probably worked...
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Old 11-20-2018, 10:21:34 PM
dkamp dkamp is offline
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Default Re: 1930's Curtis Compressor Rebuild

Ron is 100% dead-on- that small cannister exists between the cylinder's head valve and a check valve at the tank. When the compressor stops, the head valve will leak down a little bit, eventually bringing the outlet (and that chamber) down to atmospheric pressure. When the motor starts, it takes about ten or twelve strokes before pressure is high enough to pose any load to the motor.

The original motor was PROBABLY a repulsion-start unit (rather than capacitors). It would have been capable of a fair amount of starting torque, but this little chamber gave it about 50-60 motor revolutions before facing full load.

As for crank seals, most of these old compressors didn't have much of a crank seal... oftentimes, the seal was just a little piece of rope in a groove... and there was an oil drainback passage at the bottom. Frequently, the crank's oil dipper would fling oil up onto the cylinder wall, as it drained down, it would fall into a trough that flowed over to the center of the bearing journal, through a hole, and the bearing or bushing would frequently have a line across the top, and an X-groove on the bottom leading down that drain-back passage, so that oil would WANT to flow back to the sump.

The airflow you're noticing, is simply because the piston is displacing air on it's backside, just like it does on it's top. There SHOULD be a breather cap up high, sometimes on the oil fill... If you hear airflow back through the crankcase breather when the pump is idle, that means two things- that your head's check valve is not unloading properly, and that your piston rings are a bit worn..
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