Normally there should be no problem of grounding the frame of the motors, check for continuity between motor power and frame.
Also for a semi-commercial machine, especially in this application, I would seriously consider a linear supply for motor control particularly.
Is the control for the machine mainly hard-wired devices? i.e., no electronic control?
The wiring looks messy and can affect the operation, do you have a decent schematic of the control? (should be the first thing in line).!

Yes, Sir, no electronic control. just hardwired with some DPDTs and push-hold on/off buttons. i'll upload circuit diagram after few hours as i reach office.

 

You may need to disassemble the Motors to find how they are Grounded.
This would also be a good time to insure that the Gear-Box has plenty
of high-quality Molybdenum-Disufied-Grease,
because it's not unusual for the manufacturer to
scrimp on the quantity of Grease in the Gear-Box.

The Rotisserie-Motor should probably have a thin Aluminum-Shield to
block some of the radiant-heat from the Grill.

It will also be running for long periods of time, so it's probably a good
idea to run it at less than ~10-Volts to keep the heat-production down.

Do not use the Slow-Speed-Wire unless it has
a greater Resistance measurement to Ground than the High-Speed-Wire.
Windshield-Wiper-Motors sometimes have very strange Winding-configurations,
they don't always follow the "standard" way of doing things.
.
.
.

Sure Sir, i'll set voltage to 10v

 

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What do You think the 3rd Wire goes to ?
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.
.

What 3rd wire are you even talking about? If you meant "wiring" of the motor that is what you should have said, instead of "winding". Winding has to do with the internal parts of a motor, and a PMDC motor only has one winding,the ones on the armature.
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.
.
.
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.

 

What 3rd wire are you even talking about? If you meant "wiring" of the motor that is what you should have said, instead of "winding". Winding has to do with the internal parts of a motor, and a PMDC motor only has one winding,the ones on the armature.

.
Read the Thread from the beginning.
There are many different configurations used in Wiper-Motors,
and we don't know anything about the Motors that the TS is using,
only that it has 3-Wires,
so at this point,
everyone can only speculate as to the best use of the information at hand.

Wiper-Motors may also have Switches or Commutators built into the Gear-Box.
.
.
.

 

Most wiper motor mechanisms for a while now, translate the continuous rotary motion to oscillation by means of a crank mechanism.
IOW, they rotate one direction.

 

Most wiper motor mechanisms for a while now, translate the continuous rotary motion to oscillation by means of a crank mechanism.
IOW, they rotate one direction.

.
The Switches or Commutator are usually for "Parking" in the correct position.
.
.
.

 

You may need to disassemble the Motors to find how they are Grounded.
This would also be a good time to insure that the Gear-Box has plenty
of high-quality Molybdenum-Disufied-Grease,
because it's not unusual for the manufacturer to
scrimp on the quantity of Grease in the Gear-Box.

The Rotisserie-Motor should probably have a thin Aluminum-Shield to
block some of the radiant-heat from the Grill.

It will also be running for long periods of time, so it's probably a good
idea to run it at less than ~10-Volts to keep the heat-production down.

Do not use the Slow-Speed-Wire unless it has
a greater Resistance measurement to Ground than the High-Speed-Wire.
Windshield-Wiper-Motors sometimes have very strange Winding-configurations,
they don't always follow the "standard" way of doing things.
.
.
.

Respected Sir, i did the same as you said and Your Highness, Motors ran for many hours without heating even with Good load on them. It was so Surprising !!! Many Many Thanks.

Here are photos, video links of final Machine, Sir

manufacturing:

lift:

Demonstration:

Many Thanks

 

All Respected Sirs,

Thanks you all Sooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo Much