Rol-Air knocking when it's running...

by scottw
(Eugene Oregon)

Electric, belt drive,1.5HP motor, Twin cylinders(pistons), 2 air tanks.

Received used Rol-Air compressor had not been well maintained. Oil level was low. Drained oil added fresh, replaced air cleaner filter, pulled flywheel, motor pully, belt guard then generally cleaned up.

Motor seems fine. Compressor seems to compress air but there is a slight "knock" sound, from the head and cylinder area, at a particular moment of the cycle. This isn't a particularly loud or harsh noise, not metal on metal impacting.

I have been reluctant to run for very long with noise like that.

The owners manual suggest a loose belt or flywheel but they are off right now. Manual general maintainance suggests you re-torque various bolts including-the head, cylinder, connecting rod, bearing carrier and flywheel. Some of these i can get to others not so easy unless there is a service panel in the bottom of the crank case!(may be worth making one!) I will check those i can access.

What is the likely cause of the knock how is the diagnosis determined?

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Bill says....

OK, ScottW, maybe lets put this into perspective. You have a compressor that you obtained used, and when new, might have been worth under $200.

At certain pressure point or cycle you hear a knocking when the air compressor is running.

Does the air compressor still generate air? Does the air compressor run the tank pressure up to cut out and then stop? Are you using the air to do the work you want? How much money have you spent overall, and how much time do you want to spend trying to "fix" your air compressor?

A tear-down might, and I emphasize might, locate the impact point or loose component that may be causing the knocking. It is impossible to diagnose from afar, and my be impossible to diagnose on tear-down.

If this were me, and knowing how much I had invested in buying the compressor, and recognizing that I fill my days with other "stuff", I maybe wouldn't want to spend a lot of time on fixing a compressor, and just use it up?

My .02 worth, of course.

Cheers,

Bill