Has my air compressor died?

[Jonathan]

It looks like I just exceeded the duty cycle rating on my air compressor whilst running the router, since it overheated and the thermal cut-out activated. My fault for forgetting about that I suppose. Now it has cooled down I reset it and the motor wont start, the lights just dim and it buzzes. I've taken the cover off and I can spin the motor/compressor by hand but it's quite hard but does go all the way round.

The compressor is coupled to the motor shaft directly, so I can't tell if the problem is with the compressor or motor without further disassembly. It's the same as this one, just significantly older:

Airmaster Tiger Turbo 8/25 Air Compressor with air hose - Take a L@@K !! | eBay (http://www.ebay.co.uk/itm/Airmaster-Tiger-Turbo-8-25-Air-Compressor-with-air-hose-Take-a-L-K-/170923413246?pt=UK_Air_Tools_and_Compressors&hash=item27cbd44efe)

Looks like this is not an uncommon air compressor problem (http://woodworking.com/forum/showthread.php?14984-air-compressor-problem&)

Any ideas much appreciated - can't run the CNC router efficiently without it.

[irving2008]

Compressor can seize but since you can spin it it not likely to be that, tho as mentioned in the link, if its been overworked the cylinder sleeve can distort making it impossible for the motor to start under load ever if you can turn it by hand.

[m_c]

Is it still the same with all the air drained?
Have you tried checking/swapping the start capacitor?

[Jonathan]

I've just taken the cylinder housing bit off the top and found the problem. The piston slides smoothly in the cylinder, but the end of the connecting rod that attaches to the eccentric on the shaft is extremely tight, so the motor can rotate smoothly a very small distance now until the connecting rod touches the sides of the cylinder. The cylinder looks and feels nice and smooth, although to be honest I've nothing to compare it to so I don't really know. Presumably if I dismantle it further I should be able to make the bushing or whatever that is damaged?

[Jonathan]

Is it still the same with all the air drained?
Have you tried checking/swapping the start capacitor?

Yes it's at atmospheric pressure and I doubt it's a problem with the start capacitor given what I've just found, but I will check that if it still doesn't work.

Also I forgot to mention that inside the cylinder there is some black dusty goop. Could that be the remains of an O-ring? There are 3 springy metal rings on the piston. I should find a manual...

[irving2008]

Sound like it had seized and has buggered up the conrod and/or bushing... are you sure the conrod isn't bent?

[Jonathan]

are you sure the conrod isn't bent?

It doesn't look bent. I've got the cover on the end off now so I can get to the bushing, which is exceptionally tight/seized. Assuming I can get the con-rod off will it be a simple matter of boring the end of it out ever so slightly and putting it back together, or is there more to it? It doesn't look like I can get the bushing off to machine that since the parts seem to be press fitted. The con rod itself doesn't look difficult to copy...

[irving2008]

These low end compressors are all very similar (and most are made by the same company)...

This site gives some useful parts breakdowns: http://www.sipuk.co.uk/parts/1.%20Air%20Catalogue/Compressors/Airmate.htm The Airmate Nimbus 250 is probably very similar

[irving2008]

Its like the con rod bushing is an oilite press fit into the con rod, if its overheated and run dry it may have part welded itself or distorted, esp if its contacted the cylinder wall... May be fixable... but law of diminishing returns might start to apply...
You might find some info here: Air Compressor Parts by Manufacturer - Master Tool Repair (http://www.mastertoolrepair.com/air-compressor-parts-by-make-or-model-c-271.html)

ould also be very similar to the Clarke 250 Pather... http://www.clarkeservice.co.uk/manuals/compressors/panther25_50.pdf

At least one model on that site lists a conrod as a spare "in case you forgot to oil it and ran it dry"

[Jonathan]

It doesn't look like anything has contacted the cylinder wall that shouldn't have.
Thanks for the pointers... I'm back at University now so wont be able to look at it again until next week, meanwhile I'll read up on it. Even if I can only get it to work for a few months that should be long enough for a good one to come up on eBay. I wouldn't mind a bigger (or quieter) compressor, although that will probably cost more than the £25 this one did at my local car boot sale!