Motor Has No Torque, What is Up?

geopicker · Post by **geopicker** » Thu Nov 27, 2008 10:33 am

All,

I just bought a very used Shopsmith Marv VII. I think it is about a 1963. All the mechanical parts work freely but the motor is a bit fishy. I have verified that all bearings in the mechanical part of the Shopsmith work freely. But when the motor is all connected to the unit it turns but does not seem to have any torque. It turns slowly for a bit if you give it a turn then stops in a minute and clicks until you turn it off. At this point the motor is hot. When the motor is out of the unit it turns really fast. I have taken the motor apart and do not see any obvious problems.

So, What could be the problem? Is it the motor? Should I have it looked at or just replaced?

Many Questions,

Mike

8iowa · Post by **8iowa** » Thu Nov 27, 2008 10:55 am

I don't have a MK VII, but I understand that the motor is reversable, probably having two starting windings. It would seem that one or both of the start windings are not being energized, giving the motor very little torque with which to come up to speed.

There may also be a starting capacitor, which could be bad. Fortunately, this is an induction motor and almost any capable electric motor shop can fix your problem.

dusty · Post by **dusty** » Thu Nov 27, 2008 11:12 am

No, don't replace the motor yet unless you have money to burn.

Low torgue at startup is often the result of a defective start capacitor. I know nothing about this particular motor but if it has a start capacitor I would begin by checking that.

If you have no electrical skills take it to a motor shop and have it tested.

The startup capacitor operates, typically, only as the motor comes up to a predetermined speed. Once that rate of rotation has been achieved, a centifical switch opens to disconnect the startup capacitor.

Don't keep trying to get it started without a fix having been employed. To do so could result in heat damage (open winding).

beeg · Post by **beeg** » Thu Nov 27, 2008 11:16 am

Have you cleaned and lubed the mk7?

mikemarkvii · Post by **mikemarkvii** » Thu Nov 27, 2008 3:55 pm

hi mike;
welcome to the forum and congrats on buying a m7, which is imho a step up from the m5 500.
the first thing i would do is disconnect all belts and test the motor only. if in fact the motor is at fault, take it to a good motor shop. have it checked out, new cap if needed, new bearings [likely needed], install a 12 gauge elec cord[buy an extension cord and cut the end off]
next check all connections to the switch, as i had one that was a bit loose and would at times arc.
and of course, lube and wax everything, even to the point of disassemblying, and cleaning everything you are comfortable with. if you are ok with bicycle maintance, a shopsmith is not much harder.
goodluck, i think you will be happy with your machine, i know i am with mine.

feel free to send to pm if you need to.

mike

geopicker · Post by **geopicker** » Fri Nov 28, 2008 10:50 am

Guys, Thanks for the tips. I think I will take it into a shop and have it looked at. Maybe it is the capacitor. I have taken the motor all apart and do not see anything else odd or burnt.

Just so I know, what is the cost of a replacement motor?

Mike

beeg · Post by **beeg** » Fri Nov 28, 2008 11:29 am

geopicker wrote:Just so I know, what is the cost of a replacement motor?

Mike

ABOUT $300.00. Last time the shop told them to buy the OEM.

billmayo · Post by **billmayo** » Fri Nov 28, 2008 6:00 pm

All the Mark VIIs I have serviced had bad switches. The start windings are connected through the switch (not to the input power) and was not making contact. I replaced the Mark VII switches with an ON/OFF switch and a FORWARD/REVERSE switch which took care of each problem. One of the forum guys named Gary furnished me with the wiring hookup which helped me solved my Mark VII problems. I have the wiring hookup that Gary gave me if anyone needs it.

avace007 · Post by **avace007** » Fri Dec 05, 2008 1:14 am

Hi,

I have a Mark V with similar symptoms. I have been told to look at the armature contacts in the motor (where the brushes contact the spindle). The unit has been sitting for over 10 years since its last heavy use. Any suggstions?

Thanks!

billmayo · Post by **billmayo** » Fri Dec 05, 2008 1:19 pm

There is no brushes in any Shopsmith headstock motor. Along with a capacitor, there is a centrifugal switch with contact points that cuts out the start windings once the motor starts to come up to speed. Sawdust and crud often cause these contact points to burn and either stick together or not make contact. Any thin file or emery cloth can be used to clean and polish these contact points. This normally is what causes a motor to hum and not turn. I have not found a bad motor capacitor yet.

The Mark VII motor has external connections for the start windings that are switched to reverse the motor. These connections must be connected correctly to start the Mark VII motor.

I have found a few motors where sawdust and crud seems to suck the oil from the fromt motor bearing causing it to become very difficult to turn. Removing the drive belt and turning the sheaves will check this possiblity.

Have you checked that if either belt might be slipping? Sawdust and crud on the motor shaft can prevent the floating sheave and spring from transmitting full motion to the drive belt. Loose tension for the upper belt can have the same problem. I remove the motor belt from the motor sheaves and operate the motor without the drive belt connected. I have been known to use a wooden hammer handle to put pressure on the floating sheave to see if I can slow or stall the motor but this is not recommended as it can be dangerous to your health.