Mark VII drive belt.

[zenman]

Is the Mark VII drive belt the same as a Mark V?

Do I believe the FUD on ebay that shopsmith's belts are too narrow.

This shopsmith has been a pain to change speed, turning the dial was always hard and in many cases the dial would change on it's own, you can feel the tension in the demon that wants to turn it to the highest speed.

Last night my Mark VII stops working. The motor was good, but the sheaths for both pulleys were separated out and the belt was danging between on both ends of the pulleys.

So I had to reset the cam and everything and now the bottom sheaths are locked onto the belt at the outer most position and the sheaths on the top pulley cannot come together at all. The Mark VII is locked at a million RPMs.

My understanding of the process of speed control and that the cam pushes and pulls the wedged pulley sheaths on the top pulley. As the conical pulleys are pushed together they create a larger diameter in the overall pulley of the top two part pulley system.

By increasing the diameter of the top pulley, the v of the belt adds more tension to the conical pulley on the motor pulley set pulling the belt closer to the axle separating the two sheaths of the split conical pulley of the motor, thus changing the gearing ratio. Thus the spring of the motor end keeps the conical pulley sheaths/sides together.


This drive belt is slotted.

Has it been the wrong belt for all these years?

What holds the sheaths apart on the bottom, motor pulley system, and what causes then to stay together other than the spring?


To replace the belt, Do I have to unscrew to motor from the bottom housing?

[beeg]

WHICH mark vii are ya talking about? I assume the older one. WHEN was the last time ya oiled it?

[zenman]

Old one.

About every 8 hours of use, I oil with sewing machine oil.

The bearing for the follower on the inner sheave was also, not smooth.

I have another Mark VII (old one). and will swap out some things. Just never fidgeted with the pullies before.

[zenman]

Gonna answer my own question.

Just replaced the belt with the belt from a broken Marv VII head that I had in storage. Same part number as the current Mark V.

The bottom sheaves were in need or serious lubrication. been using sewing machine oil, but not good enough, but a synth high speed lube in there.


The bearing on the follower on the top inside sheave was bad, so replaced the sheave from the other unit. Used a bearing press to press out the bearing but cracked the sleave. Will have to put another sleave around that, but might have to rebalance. 7/8" ID diameter aluminum tube and metal lathe. and a VXB bearing.


Even on the good sheave, the bearing was not smooth.


replaced the speed adjust assembly from the other one as well, I think the spring loaded buttons which lock the speed were in need of replacement. I also used a different speed knob.

Seems like it is running well now. It pays to save the pieces from a $50 Craigslist Mark VII.

[JPG]

Is the Mark VII drive belt the same as a Mark V? YES 'motor belt also]

Do I believe the FUD on ebay that shopsmith's belts are too narrow.FUD??

This shopsmith has been a pain to change speed, turning the dial was always hard and in many cases the dial would change on it's own, you can feel the tension in the demon that wants to turn it to the highest speed."NORMAL"

Last night my Mark VII stops working. The motor was good, but the sheaths for both pulleys were separated out and the belt was danging between on both ends of the pulleys. 'LOWER SHEAVE STICKING'

So I had to reset the cam and everything and now the bottom sheaths are locked onto the belt at the outer most position and the sheaths on the top pulley cannot come together at all. The Mark VII is locked at a million RPMs.

My understanding of the process of speed control and that the cam pushes and pulls the wedged pulley sheaths on the top pulley. As the conical pulleys are pushed together they create a larger diameter in the overall pulley of the top two part pulley system. THE CAM ONLY PUSHES

By increasing the diameter of the top pulley, the v of the belt adds more tension to the conical pulley on the motor pulley set pulling the belt closer to the axle separating the two sheaths of the split conical pulley of the motor, thus changing the gearing ratio. Thus the spring of the motor end keeps the conical pulley sheaths/sides together. YEP!


This drive belt is slotted. COGGED????

Has it been the wrong belt for all these years? NO - IIUC WHAT YOU SAID

What holds the sheaths apart on the bottom, motor pulley system,THE BELT and what causes then to stay together other than the spring?THAT IS ALL


To replace the belt, Do I have to unscrew to motor from the bottom housing? NO

I realize ya already got er running, but I wanted to answer all those ??(and ask a couple).

[JPG]

Gonna answer my own question.

Just replaced the belt with the belt from a broken Marv VII head that I had in storage. Same part number as the current Mark V.

The bottom sheaves were in need or serious lubrication. been using sewing machine oil, but not good enough, but a synth high speed lube in there. GOTTA WONDER IF DONE 'PROPERLY'(OIL GETTING TO WHERE IT NEEDS TO GET)


The bearing on the follower on the top inside sheave was bad, so replaced the sheave from the other unit. Used a bearing press to press out the bearing but cracked the sleave. Will have to put another sleave around that, but might have to rebalance. 7/8" ID diameter aluminum tube and metal lathe. and a VXB bearing. KEY DETAIL!!!! Make another sleeve for the other control sheave and put it over the hub prior to pressing the old bearing out to prevent(no guarantees) breakout.


Even on the good sheave, the bearing was not smooth.


replaced the speed adjust assembly from the other one as well, I think the spring loaded buttons which lock the speed were in need of replacement. I also used a different speed knob. THEY NEED TO BE FREE TO MOVE

Seems like it is running well now. It pays to save the pieces from a $50 Craigslist Mark VII.

I am amazed at how easily the MVII speed control dial turns when all is assembled properly(and how difficult when not!).

Keep the control sheave bearing well lubricated(when oiling the control sheave[the shaft and hub INSIDE]). Tis overheating that bearing that causes the plastic cam melt down[gets holes]

[e.friedl]

There was an earlier thread that addressed part of your problem, the speed wanting to increase. The follower for the cam, that is the wrap around fork, can be installed one of two ways. One way is wrong and it causes the system to want to move to high speed. The one time I had mine apart I must have gotten it right by blind luck. It was after that I found the thread. So try looking for that.
Ed

[zenman]

Thanks,

Yeah I saw that thread. I had this problem before with this unit. Now everything is replaced but the motor. Everything is cleaned and lubed on the top pully, inside and out.

I am getting really good at removing the speed control.

anyways, I used it for a bit tonight and the demon is worse. Everything great at 800 rpm.

Now it goes from 1200 to 5400 in 3 seconds without resistance. The speed dial spins out of control.

I reversed the follower and the same.

The speed adjuster dial seems fit tight against the head and it was from a working unit.

Now I am wondering if the spring on the motor sheaves is too strong.

It's actually dangerous now.

Any idea on some adjustments,

[billmayo]

Gonna answer my own question.

Just replaced the belt with the belt from a broken Marv VII head that I had in storage. Same part number as the current Mark V.

The bottom sheaves were in need or serious lubrication. been using sewing machine oil, but not good enough, but a synth high speed lube in there.


The bearing on the follower on the top inside sheave was bad, so replaced the sheave from the other unit. Used a bearing press to press out the bearing but cracked the sleave. Will have to put another sleave around that, but might have to rebalance. 7/8" ID diameter aluminum tube and metal lathe. and a VXB bearing.


Even on the good sheave, the bearing was not smooth.


replaced the speed adjust assembly from the other one as well, I think the spring loaded buttons which lock the speed were in need of replacement. I also used a different speed knob.

Seems like it is running well now. It pays to save the pieces from a $50 Craigslist Mark VII.

You can use the control sheave and bearing from the Mark V by using the Mark VII cam follower in place of the button. I have been machining the control sheave cylinder bearing depth another .08"-.09" so I have material to stake the bearing. I had a couple of bearings come out even with LocTite before I begin machining this depth. Contact me if you need a control sheave machined for the deeper bearing depth. Thanks.

[JPG]

Springs do not get stronger with age, so too much pressures is unlikely.

Are both detents engaging the dial correctly?

Is the surface of the detents or dial worn?

Are the dial stops correctly adjusted? One is a high speed limit.

Relevance starts at # 13 and finishes at # 19.

https://forum.shopsmith.com/viewtopic.php?p=137245#post137245

Not sure why you are experiencing the advancing speed, perhaps that thread will help expose a cause.