Air Compressor Maintenance

I’ve noticed that my little 17 gallon/3 hp under the bench hotdog air compressor has been running for longer periods of time to fill the tank. I also noticed a nice sawdust/oil slurry forming on the tank where the pump sits.

It had been 5 years since I bought this second hand and completed the first service. I don’t have a way to track hours on the unit but with longer running fill times and an oil leak somewhere it seemed like time for a bit of maintenanceses . The oil change used AMSOIL Synthetic Compressor Oil (PCI) – in my case SAE 20 weight. as specified on the maintenance sticker.

Sears 919.721631 3hp, 17 gallon

Draining the oil is as simple as removing the two plugs – the horizontal one is the drain and the vertical plug on top is the fill plug and dip stick. The oil level should be at the top thread and 6 threads down is low.

I used 2 scrap 2×4’s under the wheel on the control panel side to tip the machine to drain out as much of the old oil as I could. Didn’t quite look like the ~500mL/16oz that should have been in there. That is why there was a nice coat of oil around the tank which was easy to wipe up and made a nice shine!

Put the drain plug in – I used sealant since I have a leak somewhere and the tapered drain plug screws in a long way before it snugs up in the threads.

Filling is a slow and precise process. The fill hole is pretty small so I didn’t use a funnel and you have to pour really slowly and methodically. The oil tube cannot handle too much flow so a half full bottle was really useful – decant to a different container if you’ve got a new bottle or keep rags close by.

I’ve got replacement air filters on order – that’s as easy as removing the plastic shroud and the metal cover and then R&R.

With the oil changed and the air filter swapped out the last maintenance task is to drain the tank often. I installed a 90 degree elbow, extension and ball valve to help with that and make it easy to do. I usually blast the air/water out after a lot of use, when the humidity or temperatures change a lot or if I want to scare the kids.

The manufacturing date on this unit is May 5th 1987. The previous one I had rusted out the tank even though the pump ran great. It’s a great unit for inflating tires, blow guns for air washing, nailers and smaller consumption pnumatic tools. This isn’t big enough for sprayers or larger air consumption tools but works great in a small garage.

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