My compressor uses a 7 hp, 3450 rpm, 240V single phase motor. It is intermittent use in that it doesn't run continuously for long periods of time.  I understand in principle that imbalance  of voltage causes higher amperage which causes higher heat.  So I've started checking the voltage to the shop while I source another motor.  FYI..The lines to the panel box are 10 feet long and the wire is oversized as well.  I don't have a lot of experience here.  What more can I do to protect these motors?   

how is the motor cooled?  you may want to not only make sure its clear for cooling air flow, but additional air for cooling may be needed, I installed a 750 Hp motor that had 2 aditional 20Hp motors just for the cooling fans operation, one located on each end

Not sure what compressor you own but it needs a loading type clutch so the motor can get up to speed. Starting under full load is hard on the whole circuit.

However, it sounds like a power problem to me. I would recommend you have a licensed electrician look at it.

I don't know the set up but the rpm seems awful fast, especially when you consider that most compressor applications have a large pulley on the head and a small one the motor? I would check with the compressor head manufacturer. Often in the cut and thrust of operations an incorrect  part is inadvertently fitted and the next guy just fits what was there etc.  

I wonder if part of your problem may be in your location.  "2nd hottest place in US behind Death Valley"   Is your area dusty as well?

Everywhere down here in the desert Southwest is dusty hahahaha!

I second looking at the cylinder unloader, if it has one, the motor should be allowed to get up to speed before loading.

Summers down here are brutal with triple digits every day for 3 months. If it is outside it is cooking the motor during the day when you consider the infrared added to the motor rise. Car fenders easily hit 177° F. Hot air being compressed and made even hotter is probably also taking a toll on the compressor head.

I suggest a mechanical power hammer as not only the solution to your issue but to lower your power costs as well. 

My compressor uses a 7 hp, 3450 rpm, 240V single phase motor.

This sounds like a big box store compressor to me...... they are notoriously underpowered and not made to last. What brand/model is it?

I'd suggest the biggest problems are probably, in no particular order, a hot climate, possibly a problem with the unloader, and single phase.

 

If there is any way you can realistically get 3-phase to it, it will greatly increase reliability. 3-phase motors can generate a decent amount of starting torque where single-phase have to have life made easy for them simply in order to get started.

 

Religiously change the pastille in your non-return valve every year (maybe more if you are somewhere hot; I'm in England and change them annually) and check that the unloader on the bottom of the pressure switch spits out air when it switches off, but at no other time. The idea behind these 2 components is that the NRV stops tank pressure getting back to the pump head and the unloader dumps what was there when the pump last ran.  This lets the pump get a revolution or so in before the pressure builds between the pump head and the NRV and lets it get somewhere near to full speed before starting to do real work. If the pastille goes brittle, it stops sealing, pressure bleeds back to the pump and it has to start against a load.

Have you ever put an amp meter on it while it is running under full load? After charging the tank does the motor seem warm or is it HOT to the touch?

has anyone altered the settings to get a higher pressure?

changed pulley size?

changed motor speed or size from original?

good quality motor or cheap one?

how is the motor cooled?  you may want to not only make sure its clear for cooling air flow, but additional air for cooling may be needed, I installed a 750 Hp motor that had 2 aditional 20Hp motors just for the cooling fans operation, one located on each end

A 750 hp motor? What kind of Compressor is that Steve?

This was for a machine that crushes Cars and School Busses.  One like it was on the History channel not to long ago.  Insert whole, and out comes pieces less than 2 inches, even the engine block gets chewed up, was fun installing in the blizzard that week, the point is that motors need to be kept cool or they burn out

Ah Yes,  I saw that, That thing was scary!   And your right heat will kill a motor and he's in Yuma Az too much heat