Can't change motor speed

[entropy]

I recently inherited a Mark V which works wonderfully, but I am unable to change the speed. I know that you do not change it without the motor running. The dial does turn but the speed does not change. Before I open it up can you tell me what is the most likely problem and what I should look for. Thanks

[JPG]

Is it running slow or fast?

A stuck control sheave is a likely candidate.

A disconnected quadrant gear(porkchop) is likely as well.(allows the gear to move without the control sheave restricting it)

A pix taken through the access hole will be informative.

[entropy]

Thanks for the quick reply. I think that it is a stuck control sheave, all thought I don't know the terminology. When it is on the slow setting the arm touches the shaft in the center of the pulley. When it is on fast the shaft says where it was when the arm swings away. I took some photo but I do not know how to attach them, sorry.

[JPG]

That verifies it!

Time for penetrating oil and some difficult sheave removal.

[everettdavis]

Is the clip broken off that pulls the sheave back? It is likely if the sheave is frozen and the arm moves.

Equally, if it broke off without the sheave being frozen, the result is the same.

Everett

Pork Chop.jpg (13.98 KiB) Viewed 1916 times

[entropy]

Thanks to both of you! The clip is gone. The shaft that the clip goes to spins freely but I can't pull it outward. If I use penetrating oil where do I put it? Howard

[wa2crk]

Entropy
If you look at JPG's photo you can see the oil hole in the sheave. Put an ample amount of oil in there. You can't over oil it. Because the clip is missing I will assume that the small bearing in the end of the sheave is also bad. Comes from a lack of proper oiling for a long time. Definitely fixable.
Bill V

[everettdavis]

Thanks to both of you! The clip is gone. The shaft that the clip goes to spins freely but I can't pull it outward. If I use penetrating oil where do I put it? Howard

Do you see the oil hole? Put it there.

Also remove the belt cover end and check the motor sheave with the spring.

It too likely needs attention, but the hole is under the spring next to the sheave. You have to have the sheave in (spring most relaxed) to pry it back.

Best bet would be unplug it, take the belt off the motor by hand as you rotate it over the motor sheave and see if you can freely move it as well.

There are posts on how to remove the spring which is way longer than one first believes if you need to do that. It has to be compressed and held secure during the retainer removal, then gently un-tensioned. Most folks have their favorite way to do it.

Jacob Anderson publishes about 30 free YouTube videos that really will get you some good foundational info. Pick the ones on how things should look, and the ones on disassembly to see what makes sense for you.

https://jacobs-repairshop.com/youtube-videos/

Everett

[JPG]

For the record!

The wire clip is not there to 'pull' the control sheave.

It is there to hold the center 'button' so it does not rotate with the control sheave(the reason for the bearing in the first place).

The force to 'open' the idler pulley is provided by the belt and motor pulley. The spring maintains tension against the floating sheave which closes that pulley causing the belt to push the control sheave thus opening the idler pulley.

It IS possible that the floating pulley is also stuck which caused the clip to be pulled off. The clip(and pin) may be in the bottom of the motor pan.

P.S. That ain't 'JPG's' pix. Looks far too good to be mine!!!

[everettdavis]

You are right and I totally understand the purpose of the clip and the bearing, yet if one has the belt off and rotates the speed control in and out, without it, the control sheave would stay in.

Without the rotation of the belt and geometry of the sheaves (hopefully moving) due to the large spring on the motor idler sheave pushing it inward and allows the motor sheave set to come together, aided by the motor running and turning the belt.

If one cranks on the speed control without the motor running, it still does exert some pull, even though below the motor sheave spring is pushing the idler sheave toward the fan sheave.

If the control sheave is really stuck it is the pull from the quadrant (pork chop) moving away that actually tears the clip off the button / bearing assembly as it attempts to move the control sheave, sending it to the bottom of the headstock.