My 1988 Craftsman DeVilbiss Air Compressor Is Making strange clunking noise?

by Daniel Shortt

(Travis AFB, CA)

I recently bought a 1988 model Craftsman air compressor made by DeVilbiss. It has a 3 hp electric motor and a 20 gallon horizontal tank.

Overall the compressor looks to be in great shape for it’s age.

I have done small upgrades to the plumbing on it and just made it look more presentable.

The only concern I have is when it is building pressure at around 40 psi maybe and about 60 psi again it makes a loud clanking or rattling sound. I have tried feeling all over the compressor as it runs and can’t find where the problem could be coming from.

At all other PSI-s it runs quiet and smooth and it also builds pressure quickly and easily.

The noise is a pretty loud and distinguished sound. Am I OK to keep using it like this and what are my possible troubleshooting steps?

I have changed the oil since buying it also. Any ideas?  Thanks.

Clunking Noise From Air Compressor Could Mean Loose Belt

Response by Bill

Typically, Daniel, clunking or clanking noises can be cause by a too loose belt, belt misalignment, mounting bolts loose, and then into the heavy stuff, perhaps a bearing issue inside the pump.

I cannot hear the noise, nor can I see the compressor as I can find no image of it. Perhaps you might upload a photo or two?

If all mounting bolts are tight, if the belt is correctly tensioned and aligned, and there is no impact of visible moving parts on stationary components, then, I’m going to have to go with a bearing issue.

That will mean a tear down of the pump, unfortunately.

Follow up

by: Daniel Shortt

I have checked everything that was mentioned.

I have taken apart and re-assembled the whole assembly other than the actual compressor itself. I will probably take it apart and have a look inside the compressor this weekend, what should I be looking for?

Would you say it is the bearings on the connecting rods? Also, I can provide pictures of the compressor if it helps.

Wear Marks Could Indicate Worn Bearings

Response by Bill

Difficult to be certain. Wear marks, sloppy bearings….

Yes, please upload photos.

Why is my air compressor all of a sudden making a loud knocking noise?

By peter

(greene, ny 13778)

Oil level is good, just recently changed, in a heated garage?

It could be a mechanical issue in your pump

Response by Bill

Hello Peter. I get asked this question periodically, and really, since I cannot see the air compressor running, or hear it while it is making this noise, you don’t identify the compressor or the model, so I really don’t know how to answer the questions.

If the motor is still mounted securely to the mounting plate, and the pump is too, then either it would be a mechanical issue in the pump, or the motor shaft rotating and hitting.

It might be a loose centrifugal switch inside the motor cap, for example.

Can you not isolate the knocking to a specific compressor part or area and add a comment with that information and the make and model?

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