MVII motor belt length

nothungry3 · Post by **nothungry3** » Tue Feb 04, 2014 9:55 pm

I think I now know the reason for the different rear face of the eccentric. It allows different positioning(in/out) of the idler shaft etc. Not sure(yet) of when/why to use the 'alternate positions'.

I tried both faces on my Mark VII. The result was to change the speed cam/follower alignment. The low side of the eccentric face, at 1/8" poly v belt deflection, resulted in the follower nosed up on one edge of the cam and the high side jammed it up against the other side. The happy medium, with the follower centered on the cam, resulted in a loose poly v belt. I am confused about this design.

JPG · Post by **JPG** » Wed Feb 05, 2014 1:30 am

nothungry3 wrote:I think I now know the reason for the different rear face of the eccentric. It allows different positioning(in/out) of the idler shaft etc. Not sure(yet) of when/why to use the 'alternate positions'.

I tried both faces on my Mark VII. The result was to change the speed cam/follower alignment. The low side of the eccentric face, at 1/8" poly v belt deflection, resulted in the follower nosed up on one edge of the cam and the high side jammed it up against the other side. The happy medium, with the follower centered on the cam, resulted in a loose poly v belt. I am confused about this design.

The MVII eccentric has the added result you described(cam follower varies from side to side). The rear face will have no effect upon that.

The extreme positions are when the eccentric is at a 9 or 3 o'clock position. Rotation past either towards 12 o'clock will increase follower clearance to the cam sides.

I now believe the absence of a firm stop for the floating sheave is to prevent the belt squeeze that occurs when lowering speed to be felt at the control dial. The floating sheave is free to move back so the belt is not actually squeezed. The poly-v belt then must bring things back to equilibrium by pulling the floating sheave back to 'normal' position.

A centered position would be at 6 or 12 o'clock. 6 o'clock would be the slack position, and 12 o'clock the tightest.

Watching this beast on the bench with the cover off is gonna be interesting and hopefully educational!:)

JPG · Post by **JPG** » Wed Feb 05, 2014 7:04 am

nothungry3 wrote:I think I now know the reason for the different rear face of the eccentric. It allows different positioning(in/out) of the idler shaft etc. Not sure(yet) of when/why to use the 'alternate positions'.

I tried both faces on my Mark VII. The result was to change the speed cam/follower alignment. The low side of the eccentric face, at 1/8" poly v belt deflection, resulted in the follower nosed up on one edge of the cam and the high side jammed it up against the other side. The happy medium, with the follower centered on the cam, resulted in a loose poly v belt. I am confused about this design.

The MVII eccentric has the added result you described(cam follower varies from side to side). The rear face will have no effect upon that.

The extreme positions are when the eccentric is at a 9 or 3 o'clock position. Rotation past either towards 12 o'clock will increase follower clearance to the cam sides.

I now believe the absence of a firm stop for the floating sheave is to prevent the belt squeeze that occurs when lowering speed to be felt at the control dial. The floating sheave is free to move back so the belt is not actually squeezed. The poly-v belt then must bring things back to equilibrium by pulling the floating sheave back to 'normal' position.

A centered position would be at 6 or 12 o'clock. 6 o'clock would be the slack position, and 12 o'clock the tightest.

Watching this beast on the bench with the cover off is gonna be interesting and hopefully educational!:)

nothungry3 · Post by **nothungry3** » Thu Feb 13, 2014 10:17 pm

JPG40504 wrote:The MVII eccentric has the added result you described(cam follower varies from side to side). The rear face will have no effect upon that.

The extreme positions are when the eccentric is at a 9 or 3 o'clock position. Rotation past either towards 12 o'clock will increase follower clearance to the cam sides.

I now believe the absence of a firm stop for the floating sheave is to prevent the belt squeeze that occurs when lowering speed to be felt at the control dial. The floating sheave is free to move back so the belt is not actually squeezed. The poly-v belt then must bring things back to equilibrium by pulling the floating sheave back to 'normal' position.

A centered position would be at 6 or 12 o'clock. 6 o'clock would be the slack position, and 12 o'clock the tightest.

Watching this beast on the bench with the cover off is gonna be interesting and hopefully educational!:)

What is the rear face?

JPG · Post by **JPG** » Thu Feb 13, 2014 11:34 pm

nothungry3 wrote:What is the rear face?

The rear face is the 'end' that is visible and that the retention screw and washer rest against. i.e. the end with the screwdriver slot in it.

See last pix this post http://www.shopsmith.net/forums/showpost.htm?p=139693&postcount=18

Note it is not flat.

zenman · Post by **zenman** » Mon May 19, 2014 2:09 pm

Any luck finding a good belt for the Mark VII from Autozone??

I have two Mark VII that I need a belt or two for.

One came with a Shopsmith belt, the other without a belt.

I bought a belt from bandsaw belt warehouse (on Ebay for $20) for the Mark VII and it was a good 2 inches shorter than the belt that was on the working MArk VII. That belt barely reaches the axis of the two sheaves and definitely can not shift. I think it is too short.

The shopsmith belt I have is 31" on the outside. That one is 29", outside.

JPG · Post by **JPG** » Mon May 19, 2014 2:26 pm

zenman wrote:Any luck finding a good belt for the Mark VII from Autozone??

I have two Mark VII that I need a belt or two for.

One came with a Shopsmith belt, the other without a belt.

I bought a belt from bandsaw belt warehouse (on Ebay for $20) for the Mark VII and it was a good 2 inches shorter than the belt that was on the working MArk VII. That belt barely reaches the axis of the two sheaves and definitely can not shift. I think it is too short.

The shopsmith belt I have is 31" on the outside. That one is 29", outside.

17295 is what I currently believe is the correct length.

http://www.autozone.com/autozone/parts/_/N-8gcul?itemIdentifier=66425_0_0_

Unfortunately I think this product line is being closed out.

I think 29 1/2 is correct since the idler shaft - motor shaft spacing is 2" further apart than the M5/V.

One caveat, I am still struggling to get this beast correct. Internal parts are not all as they were when they left the factory. So the jury is still out, but I do feel confident re the belt length.

zenman · Post by **zenman** » Mon May 19, 2014 3:17 pm

Do you think my belt is wrong??? at 31""

Gates equiv is

87019295 9295 9295 AUTO V-BELT XL

$18 at o'reilly.

JPG · Post by **JPG** » Mon May 19, 2014 4:35 pm

zenman wrote:Do you think my belt is wrong??? at 31""

Gates equiv is

87019295 9295 9295 AUTO V-BELT XL

$18 at o'reilly.

Possibly. A long belt will result in faster speeds and possibly reduced range.

At least that is what I have concluded.

db5 · Post by **db5** » Mon May 19, 2014 6:23 pm

zenman wrote:Do you think my belt is wrong??? at 31""

Gates equiv is

87019295 9295 9295 AUTO V-BELT XL

$18 at o'reilly.

Tried this about 3 years ago when I couldn't find one the right length. It didn't work to my satisfaction and I returned it. I finally found the correct length at ACE Hardware; they were closing out some VERY old stock. I don't know the width but it just worked ok. Probably narrower than the original.

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MVII motor belt length

Any work on a MArk VII belt