Motor Replacement on Mark V

bassman41 · Post by **bassman41** » Mon Jan 11, 2010 3:42 pm

I'm sure this question has been asked before. The motor hums and turns slowly or not at all. It seems to be temperature related. Warming the motor with a hair dryer helps. The motor is not bound up and turns freely by hand. I suspect a bad capacitor in the motor. Any suggestions on how to remove the motor?

dusty · Post by **dusty** » Mon Jan 11, 2010 3:59 pm

Before you remove the motor, I would suggest that you first remove the motor drive belt. Then, with the belt removed, turn the Mark V on to check if the motor will run with no mechanical load.

If the motor starts now, without hesitation, I would suspect trouble elsewhere.

If the motor still just hums, you may need a start capacitor. This is reportedly a very rare occurrence.

wa2crk · Post by **wa2crk** » Mon Jan 11, 2010 4:25 pm

Hi;
I agree with Dusty that a bad start capacitor is a rare occurrence but not unheard of. Check your Shopsmith manual for "sluggish startup" and you will find that SS recommends that the shop be brought up to at least 55 degrees if you start the machine and it is slow to respond.
If you remove the belt and start the motor and it seems normal it may or may eliminate the start cap as the culprit although it is a good indicator.
Capacitors are notorious for changing value and the value of the start capacitor is determined by the engineers when they design the motor.Look at it this way; if you have a start cap that is marked 450 MFD (microfarads) in the motor that capacity is required to start the motor under normal loads and other circumstances. If the cap loses value and is now only 250 Mfd then you only have half of the kick to start the motor. This may work under no load conditions but may cause a problem under the load of a sawblade or the band saw. Im my opinion the reason that SS wants you to turn the speed down to low when stopping the machine is to reduce the "kick" required to restart the machine. Starting in the faster speeds is like trying to move away from a traffic light in high gear instead in first gear.
Make sure that the motor shaft turns very freely when the belt is removed and when you reassemble stuff and you still have a problem then it is time for a trip to an electric motor shop with the motor and they can determine if the capacitor is the problem.
One additional note: a capacitor is like a bucket, it has capacity and it stores electrical energy the same as a bucket will store water. If you have half of the original capacity then you only have half of the energy to to start.
Bill

dusty · Post by **dusty** » Mon Jan 11, 2010 4:29 pm

But do not get a bigger bucket. If anything, get a "full bucket".

JPG · Post by **JPG** » Mon Jan 11, 2010 4:41 pm

[quote="wa2crk"]Hi]

Interesting analogies!

I would be thinking the start switch has dust in it.

bassman41 · Post by **bassman41** » Mon Jan 11, 2010 4:42 pm

Gentlemen, I thank you greatly. I will follow your advice, which sounds good to me. No point in replacing something if it ain't broken. I'll make sure to see if the motor runs under a no load condition. Thanks again.

dusty · Post by **dusty** » Mon Jan 11, 2010 6:48 pm

So much to read and so little time.

http://www.sawdustmaking.com/ELECTRIC%20MOTORS/electricmotors.html

This reference discusses direction of rotation too.

billmayo · Post by **billmayo** » Mon Jan 11, 2010 7:37 pm

bassman41 wrote:I'm sure this question has been asked before. The motor hums and turns slowly or not at all. It seems to be temperature related. Warming the motor with a hair dryer helps. The motor is not bound up and turns freely by hand. I suspect a bad capacitor in the motor. Any suggestions on how to remove the motor?

Before disassembling anything, I normally remove the belt cover and tie it to the tie bar. Put the Shopsmith in the drill press position. Using a rubber hammer, I tap/bang on the motor pan a few times and use compressed air to blow out any sawdust in the motor pan. Then try the motor.

I have not found a bad capacitor in 7 years so I still have the capacitors I ordered when I started. It is always the centrifugal switch contact points that have sawdust on them causing them to be non-conducting. The sawdust may have burnt onto the points causing them to stay open. A nail file does an excellant job of cleaning these points if they are not too destroyed. Contact me if more detailed information is needed.

wa2crk · Post by **wa2crk** » Tue Jan 12, 2010 8:52 am

JP and Bill Mayo;
You're right about the centrifugal switch. If dirt prevents the switch from resetting when the motor is turned off it will cause the same symptom.
Bill

dusty · Post by **dusty** » Tue Jan 12, 2010 10:09 am

billmayo wrote:Before disassembling anything, I normally remove the belt cover and tie it to the tie bar. Put the Shopsmith in the drill press position. Using a rubber hammer, I tap/bang on the motor pan a few times and use compressed air to blow out any sawdust in the motor pan. Then try the motor.

I have not found a bad capacitor in 7 years so I still have the capacitors I ordered when I started. It is always the centrifugal switch contact points that have sawdust on them causing them to be non-conducting. The sawdust may have burnt onto the points causing them to stay open. A nail file does an excellant job of cleaning these points if they are not too destroyed. Contact me if more detailed information is needed.

FWIW, having dirty contacts on the start switch has the exact same effect as having no/bad start capacitor. The dirty/defective contacts serve to disconnect the start capacitor from the motor.

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