Jenny air compressor

7 years 8 months ago #1794 by danbaber
Jenny air compressor was created by danbaber
I almost bought a Jenny Air Compressor off a guy. I noticed some leaking oil. I then saw a crack in the end cover, apparently where the oil goes. It was missing the air filter and the dipstick for who knows how long and it's anybodys guess weather he ever drained the tank or not.

It is a AM780-HC4H, a 4 gallon hand carry. Everything seemed to run fine but it seemed pretty dang loud (loud enough that we could not talk over it).

I looked up parts and it needs about $40 worth of parts plus whatever oil it would need and any gaskets that I don't know about.

Questions:

Is it worth the $50 he was asking? It seemed pretty indestructible.
How loud are these supposed to be? It sounded pretty loud but it was missing the fan housing

What I'd be using it for is stuff around the house. Tires, small air tools, etc...
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7 years 8 months ago #1795 by MTR-Admin
Replied by MTR-Admin on topic Jenny air compressor
Thanks for the post!

Jenny air compressors are very solid units and go the distance, so bottom line...yes, I think it's worth the $50 asking price. These oil-bath direct-drive air compressors are some of the best out there.

As long as the motor is in good shape and the tank isn't rusted inside, it's a good buy. Hopefully the former owner drained the tanks regularly; if not then you could soon have a compromised tank and once it springs a leak, you can't really repair it with a weld.

These units are pretty loud, that's one caveat. It would be a bit quieter with the shroud installed, but it won't be a "quiet" running air compressor. You would need to construct a vented box around the unit to quiet it down effectively, which is an option.

I hope this helps, let me know if you have any additional questions and I'll do my best to answer!

- MTR
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7 years 8 months ago #1799 by danbaber
Replied by danbaber on topic Jenny air compressor
I don't suppose there is a way to know without an inspection camera? Maybe by tapping around on the tank or listening for loose debris if you roll it to the side? Maybe even opening the drain when it's partially charged?

I've included the picture of the end bell crack. My concern is with the fact that there is no oil, oil filter or dipstick in the thing. What exactly would I look for if this condition "ruined" the pump (or is the oil more for the motor?) It does seem extra loud to me and I understand that compressors are generally loud machines, but this one was loud enough that we could not talk over it without SHOUTING and it still was hard to make out what was being said...

That being said, I'm thinking that this brand is the slant 6 of the air compressor world. I just have never worked on one. I'm looking at the schematics and see that it runs like a single cylinder engine, only in reverse. I also see that a replacement crankshaft is $175... also, are these things fairly straight-forward to work on? ie: put everything back together and make sure the bolts are tight and no leaks, or will I need torque specs for each fastner?...

Anyways, I just don't want a 50 pound, hundred dollar door stop in a month.

Thanks for any help!
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7 years 8 months ago - 7 years 8 months ago #1801 by MTR-Admin
Replied by MTR-Admin on topic Jenny air compressor
Your supposition is right, the only way to really know would be to charge the tank with some air to 1) see if it holds air w/ no leaks and 2) drain the tank from the valve to see if you get very dirty (rusty) water coming out of the tank; if you don't and it holds air, the tank should be just fine.

The End Bell obviously needs to be replaced, once you replace the crankcase w/ the gasket/seal, oil breather/dipstick, clean out the crankcase and pour some good 30W compressor oil in, you should be good to go.

The unit should not be THAT loud, you're correct. Direct-drive units like this are typically loud, but it seems that because of either poor lubrication and possibly rattling of loose parts (I'd guess) it's running much louder than it should.

The oil is for pump lubrication only, and if this pump was ran low on oil for any extended period of time, it wouldn't "turn over" at all; the Conrod would be frozen onto the Crankshaft journal so the unit would just hum and stall (probably tripping your breaker). You want to make sure the Crank turns freely and that the Piston moves up and down in its cycle freely. Make sure the Piston Rings are not stuck in their grooves and that the gaps in the ring are staggered. Also, look for obvious gouging and deep scrapes in the cylinder wall.

There is no need to torque the fasteners down, Jenny doesn't give a torque spec for the fasteners on this unit.

Certainly make sure that all of the bolts that hold the Motor/Pump Assy onto the cradle/base are there and that they are tight. As long as the Motor/Pump is aligned onto the frame and it's bolted down tightly, you should be alright.

When you do this and install the new components and fill it up with compressor oil, I can't say to what degree it will quiet the unit down when running; it may or may not so if noise is a factor then you may want to pass on the unit.

These are pretty simple machines to work on, it is a bit like a single-cylinder gasoline engine running in reverse, but you don't have a lot of the components that an engine has so it's much easier to disassemble, install new components and reassemble.

BTW, you can view a full parts breakdown for this unit w/ a parts list on our site at the below link:

www.mastertoolrepair.com/direct-drive-ha...0-hc4h-p-659357.html

I hope I've given you some helpful information, certainly reply if you still have questions and I'll assist further if I can!

- MTR

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