MVII motor belt length

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JPG
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MVII motor belt length

Post by JPG »

This thread addresses the proper length of the motor belt for the Mark VII as well as later additional problems. At first confusion reigned. So it behooves me to say up front(here) that the correct length is 30.5".

WELL,since posting that, I have acquired a 'new old stock' Mark VII motor belt (507490). It appears to be 29.5". Have not tried it out, but I needed to mention that!!!


Got out today with intention of putting the Mark VII headstock through final assembly.

Set speed control to fast, slipped the motor pan up to the headstock and surprise!!!! There is no way to get the belt onto the motor pulley unless it is about an inch or so longer.

So anybody else encountered this, or is my head in the dark on a sunny day?

The parts list has an entirely different parts number set from my Mark 5 info, so no clues there.

I measured the idler shaft to motor shaft distance, but have not yet had a chance to measure a M5/V. Gotta go fer a spell. Shall return this evening.



HELP!:)

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Last edited by JPG on Sat Apr 22, 2017 1:14 pm, edited 1 time in total.
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Post by JPG »

After getting back home, I measured the idler shaft to motor shaft distance on a M5.

M5 ≈ 7 1/4"
MVII ≈ 9 3/8"

Soooo it appears the MVII requires a motor belt that is 2" longer!

25.5 + 2 = 27.5" - so I will get a 27" belt and try again.


Duhhhh! Pulley spacing 2" greater implies a belt 4" longer.

Also MV belt is 26 1/2" so 30 1/2" is de one!!!!<<<<<Measuring stretched belts is unreliable. I now believe the Mark 5/V belts are 25.5". (Guess I was right the first time!!!! :D )
Last edited by JPG on Sat Apr 22, 2017 1:17 pm, edited 1 time in total.
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E[/size](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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Post by nothungry3 »

If you measured the sheave center spacing to be 2 inches longer, I believe you want a 29 1/2 inch belt. If you make the belt 2 inches longer on one side, the other side will be to short.
FYI, I put a 29 1/2 inch Dayco segmented (grooves cut on the od for flexibility) belt on my Mark VII, but it slapped at low speed and tore up the way tube rack gears. I suggest a standard belt.
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Post by JPG »

nothungry3 wrote:If you measured the sheave center spacing to be 2 inches longer, I believe you want a 29 1/2 inch belt. If you make the belt 2 inches longer on one side, the other side will be to short.
FYI, I put a 29 1/2 inch Dayco segmented (grooves cut on the od for flexibility) belt on my Mark VII, but it slapped at low speed and tore up the way tube rack gears. I suggest a standard belt.
Yer Correct! My bad!

I will try a 29" belt. There is no way a 25.5" belt will work. Getting a belt with proper width is crucial. I have a 'new' Dayco top cog 17250 that is less than 1/2" wide. It is supposed to be .53".


If the auto zone online info is correct, a 'duralast' belt is $1.99 and in stock locally. We shall see if that is for real. I doubt that.

Thanks for the 'correction'!:cool:
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E[/size](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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Post by nothungry3 »

Please let me know how the 29 inch belt works out. I put at 30 inch belt on mine (not 29 1/2) and I'm not using the full cam profile. I have about 20 degrees left at max speed.
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17/32" belts are less that 1/2"??????? etc.

Post by JPG »

nothungry3 wrote:Please let me know how the 29 inch belt works out. I put at 30 inch belt on mine (not 29 1/2) and I'm not using the full cam profile. I have about 20 degrees left at max speed.

That makes sense! The floating sheave bottoming out/belt reaching the periphery.

Went by Auto Zone to look at belts. After diving into the online sites last night I was hoping my previous experience with 17/32" belts actually being .480 width was just a fluke.

Alas that was wishful thinking.

I went to my neighborhood location knowing they did not stock a 29" belt.

There 26" belt was 'skinny'.

So it seems my 29" belt will be the size of the hour(tomorrow). Not sure I will swap the belt until a less 'wintry mix' day.

IIUC I need to disconnect the cam shaft from the knob to get the follower off the cam and then the belts slipped over the cam follower. May need to remove the motor pan/headstock casting screw to allow belt to slip between the pan front and the pulley. Think I will be separating the motor pan and casting(again).

A bit more cumbersome than a M5/V.;)
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E[/size](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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Post by JPG »

Picked up a 29" and 29.5" belt and tried them. The 29" is too short. The 29.5" is close to 'correct'. I will try a 30" tomorrow.

One thing that surprised me was the idler sheave positioning on the idler shaft. It is free to slide on the shaft, and is only 'restrained' by bumping against the eccentric etc. There is supposed to be a retaining ring there. I did not notice it today.

I had to move the eccentric 'in' 1/8" to make the 29" belt almost work(the idler pulley opened too much with the outer surface of the eccentric flush with the outside of the idler shaft bore. Bear in mind, this also moves the poly-v pulley relative to the main shaft pulley. Unlike the Mark 5/V, all of the grooves are used(the belt is wider and equal to the pulley width. There are two different surfaces on the eccentric, so two different positions are possible.

The poly-v belt I have is a Mark VII belt of unknown history(wear/stretching) and requires the eccentric be rotated about 100 degrees. The direction determines which outer surface can butt against the 'stop' screw/washer above the bore. This affects the motor belt positioning on the pulleys slightly.

I did not try the 29.5" belt with the eccentric 'flush', but will before trying a 30" belt.

One thing this has taught me is that as Nick has said, "a lotta stuff going on with the speed control". Consider, only one thing sets the speed(position of the control sheave). Everything else responds/adjusts to it until equilibrium is restored. Belt length/width affects all that stuff also!

My 'definition' of correct, is when the ,motor belt is near the outer periphery of the motor pulley at max speed (5200) and near the top of the idler pulley when at minimum speed(700). Numbers are the dial calibrations at the limits of the control knob. After achieving that, then the tach will come out to 'verify' things.

What a difference a couple of days make!:D

I am not comfortable with my 'understanding' of today's 'trials'. Some things reacted the opposite of what was intuitive to me. Too damn many things interacting!!! Tain't simple Magee!;) The excess freedom of the idler sheave(it ain't 'fixed') was unexpected. Not sure I like the idler sheave butting up against the bearing either. I may 'add' a spacer.

The pulley does not float!!!! It bears against the retaining ring in front of the bearing/eccentric.
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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'/ 10
E[/size](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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Post by billmayo »

[quote="JPG40504"]Picked up a 29" and 29.5" belt and tried them. The 29" is too short. The 29.5" is close to 'correct'. I will try a 30" tomorrow.

One thing that surprised me was the idler sheave positioning on the idler shaft. It is free to slide on the shaft, and is only 'restrained' by bumping against the eccentric etc. There is supposed to be a retaining ring there. I did not notice it today.

I had to move the eccentric 'in' 1/8" to make the 29" belt almost work(the idler pulley opened too much with the outer surface of the eccentric flush with the outside of the idler shaft bore. Bear in mind, this also moves the poly-v pulley relative to the main shaft pulley. Unlike the Mark 5/V, all of the grooves are used(the belt is wider and equal to the pulley width. There are two different surfaces on the eccentric, so two different positions are possible.

The poly-v belt I have is a Mark VII belt of unknown history(wear/stretching) and requires the eccentric be rotated about 100 degrees. The direction determines which outer surface can butt against the 'stop' screw/washer above the bore. This affects the motor belt positioning on the pulleys slightly.

I did not try the 29.5" belt with the eccentric 'flush', but will before trying a 30" belt.

One thing this has taught me is that as Nick has said, "a lotta stuff going on with the speed control". Consider, only one thing sets the speed(position of the control sheave). Everything else responds/adjusts to it until equilibrium is restored. Belt length/width affects all that stuff also!

My 'definition' of correct, is when the ,motor belt is near the outer periphery of the motor pulley at max speed (5200) and near the top of the idler pulley when at minimum speed(700). Numbers are the dial calibrations at the limits of the control knob. After achieving that, then the tach will come out to 'verify' things.

What a difference a couple of days make!:D

I am not comfortable with my 'understanding' of today's 'trials'. Some things reacted the opposite of what was intuitive to me. Too damn many things interacting!!! Tain't simple Magee!]

I replaced a badly damaged Mark VII Control Sheave with a Mark V Control Sheave this week. I found the Mark VII Control Sheave bearing has a 6mm ID vs 7mm for the Mark V. I used a washer to space the Control Sheave bearing away from the Mark VII yoke so I had room to stake the bearing after installing the bearing. I drill the yoke and all the Mark V buttons with a drill bit that removes about 1/3 of the material in the yoke/button shaft so I can use a small nail set to expand the yoke/button shaft to hold the bearing very tight. I do use LocTite along with staking and expanding the shaft to hold the bearing. I found expanding the shaft to fit the bearing has worked well for me for many years as the shaft does not always extend pass the end of the bearing on some yokes/buttons. I admit I tried 3 different Mark V Control Sheaves before I found one where the vanes lined up even between the Mark VII Idler Sheave vanes. I did machine the Control Sheave bearing depth another .030" deeper so I could stake the bearing. I did my hillbilly tighten of the Idler Sheave on the Idler shaft. I nicked the key a couple places that is under the Idler Sheave and used pliers to put a couple ridges on the Idler shaft where the Idler Sheave fits. I used a pipe spacer to drive the Idler Sheave onto the Idler shaft up to the fixed snap ring and it is a really tight fit now. It will take a lot to move it again. There was no ring or retaining clip to hold the Idler Sheave on the Idler shaft for the Mark VII. First time I have done this modification.
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Post by JPG »

billmayo wrote:I replaced a badly damaged Mark VII Control Sheave with a Mark V Control Sheave this week. I found the Mark VII Control Sheave bearing has a 6mm ID vs 7mm for the Mark V. I used a washer to space the Control Sheave bearing away from the Mark VII yoke so I had room to stake the bearing after installing the bearing. I drill the yoke and all the Mark V buttons with a drill bit that removes about 1/3 of the material in the yoke/button shaft so I can use a small nail set to expand the yoke/button shaft to hold the bearing very tight. I do use LocTite along with staking and expanding the shaft to hold the bearing. I found expanding the shaft to fit the bearing has worked well for me for many years as the shaft does not always extend pass the end of the bearing on some yokes/buttons. I admit I tried 3 different Mark V Control Sheaves before I found one where the vanes lined up even between the Mark VII Idler Sheave vanes. I did machine the Control Sheave bearing depth another .030" deeper so I could stake the bearing. I did my hillbilly tighten of the Idler Sheave on the Idler shaft. I nicked the key a couple places that is under the Idler Sheave and used pliers to put a couple ridges on the Idler shaft where the Idler Sheave fits. I used a pipe spacer to drive the Idler Sheave onto the Idler shaft up to the fixed snap ring and it is a really tight fit now. It will take a lot to move it again. There was no ring or retaining clip to hold the Idler Sheave on the Idler shaft for the Mark VII. First time I have done this modification.

I looked at a MVII idler shaft and idler pulley spare that I have last night, and the shaft had a c-clip(the snap ring you mentioned). I now assume that clip is intended to retain the bearing, but it also provides a limit for the idler sheave as well. The clip is not shown on the MVII exploded parts drawing since it apparently is part of the eccentric/bearing 'assembly'.

I figger belt pressure will keep the sheave there and all that hillbilly rigging is not needed.(JMHO;)) The secret here is getting the motor belt correct so the belt never drops too low into the idler sheave(the 29" belt was so far down that the internal belt cogs were bumping against the internal end of the vanes).

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'.

The poly-v pulley alignment is affected by this. The speed range is affected by this(wholesale shift in rpm due to idler puller flange spacing).

The belt size is really critical here. I am 'delighted' that 1/2" incremental belt lengths are available.(that and the phenomenon that three belts cost less than $7 total!!!). Adding to the 'issue' is the 17/32 belts are actually about 15/32 across the wide top. They may run in a v-pulley like a 'wider' belt, but not in these sheaved pulleys. The internal cogs may be a detriment. Once I zero in on length, I will try a 'commercial grade' standard v-belt(4Lxxx).

Thanks for the insight! As always good stuff!:cool:
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Post by JPG »

Verified the c-clip is on the main shaft.

Tried a 30" belt.

Noticed the positioning of the pulley on the main shaft.

Noticed the pulley has a history of both all the way forward, and all the way to the back.

Noticed the Poly V belt will auto align if things are free to let it happen.

Verified the idler sheave is correct part.(13 ribs).

Still did not like the belt not reaching the outside of the pulley at slow speed setting.

So this has evolved into more than a belt size puzzle.

Back to the shop for further sleuthing out how it is supposed to be.



Keep the faith, I shall resume after I am satisfied with my 'understanding'.



At this point any information is relevant and helpful.
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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'/ 10
E[/size](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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