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Runaway speed

#250137 by Plaiter208 » Thu Jul 12, 2018 5:57 pm

Ok, I FINALLY had time last night to finish the rebuild on my Mark VII powerhead (replaced all bearings, idler shaft and speed control sheave - the 6 shaped part). I started off at low speed but it immediately tried to runaway to high speed. As long as I held the speed control dial, it would maintain speed and would go up and down with ease but if I let go, it would take itself to full speed.

Everything appears to be lined up properly. Did I get the idler adjusted too tight? Is it something else?

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Re: Runaway speed

#250149 by JPG » Thu Jul 12, 2018 11:43 pm

The two spring loaded detent 'thingies'(bullet nose shaped) have lost some tension with age.

The 'notches' on the back of the speed dial can get their edges mashed.

Are you sure the cam follower(the part with the two pins on each side) is installed correctly(it is easily reversed).

Is the speed control dial tight to the shaft?(both in/out and 'wobble')

Idler????

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╔═══╗
╟JPG ╢
╚═══╝

Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

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Re: Runaway speed

#250203 by Plaiter208 » Sat Jul 14, 2018 2:51 pm

JPG wrote:The two spring loaded detent 'thingies'(bullet nose shaped) have lost some tension with age.

The 'notches' on the back of the speed dial can get their edges mashed.

Are you sure the cam follower(the part with the two pins on each side) is installed correctly(it is easily reversed).

Is the speed control dial tight to the shaft?(both in/out and 'wobble')

Idler????


So do I need to tighten up the spring loaded detent thing on the sheaves for the motor?

The notches in the speed dial are clean and smooth. I cleaned them when I put everything back together.

The cam follower is on the right way and the speed control dial is tight to the shaft and to the power head.

The only thing I can think is that I have the idler adjusted too high and it’s making the belt “too small” so it tries to pull itself into high speed in order to relieve the tension.

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Re: Runaway speed

#250207 by JPG » Sat Jul 14, 2018 3:29 pm

Plaiter208 wrote:
JPG wrote:The two spring loaded detent 'thingies'(bullet nose shaped) have lost some tension with age.

The 'notches' on the back of the speed dial can get their edges mashed.

Are you sure the cam follower(the part with the two pins on each side) is installed correctly(it is easily reversed).

Is the speed control dial tight to the shaft?(both in/out and 'wobble')

Idler????


So do I need to tighten up the spring loaded detent thing on the sheaves for the motor? That will not help

The notches in the speed dial are clean and smooth. I cleaned them when I put everything back together.

The cam follower is on the right way and the speed control dial is tight to the shaft and to the power head.

The only thing I can think is that I have the idler adjusted too high and it’s making the belt “too small” so it tries to pull itself into high speed in order to relieve the tension. That is not likely


The tension spring on the motor shaft is necessary for the floating sheave the do it's job. The tension provides sufficient closing force on the floating sheave to prevent the motor belt slipping. If it is indeed forcing the belt to the inside of the idler pulley, it is performing as it should.



The control sheave(the movable sheave the control cam moves) pushes against the cam follower while the belt tension is providing that force. That force tends to cause the cam to rotate(towards fast). Only the detent pins and the dial notches provide resistance to the cam rotating.

The position of the notches relative to the detent pins is critical. The detents(both of them) must be perpendicular to the notches(the dial must be parallel to the headstock surface(for reference). The dial must be close to the headstock surface(the detent springs more compressed)._

The detent springs and the dial notches are places where too much lubrication will work against proper operation. I am not suggesting NO lubrication, but too slippery will cause your problem.

Time has likely decreased the force of the detents and created a tendency to 'auto increase speed'.

When you push in on the dial, will it move towards the headstock? If so a shim washer between the dial and the retaining ring MAY help. That will increase detent force.

I had a similar issue with my MVII which was corrected by a less worn dial and shaft. The dial was wobbly on the shaft.

BTW what motor belt are you using? OEM? If not, what?

---

╔═══╗
╟JPG ╢
╚═══╝

Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10E(SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange

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