MVII motor belt length

[BuckeyeDennis]

Yes it is. Link type belts are not reversible. Note line #3 in the installation instructions from Fenner Drives:
Installation
1. Turn belt with tabs to the inside before installing.
2. Determine direction of drive rotation.
3. Belt must travel following the belt direction arrow (&#10142]
4. Fit belt in nearest groove of smaller pulley.
5. Roll belt onto larger pulley, turning the drive slowly. Belt may seem very tight; this is ok;
DO NOT JOG MOTOR.
6. Check to see all tabs are still in their correct position and are not twisted out of alignment.
7. For multiple belt drives, work belt from groove to groove. On particularly wide drives, it may be easier to install half the belts from the inboard side and half from the outboard.

Thanks for the education, Mike. I'm usually diligent about reading instructions, and so thought that perhaps I had just forgotten that detail. But one of my recent Power Station pics shows that my two belts are not even oriented in the same direction. I haven't noticed any problems though.

So now I'm curious as to why the belt direction does matter.

[BuckeyeDennis]

Thanks for the education, Mike. I'm usually diligent about reading instructions, and so thought that perhaps I had just forgotten that detail. But one of my recent Power Station pics shows that my two belts are not even oriented in the same direction. I haven't noticed any problems though.

So now I'm curious as to why the belt direction does matter.

Well, here is one guy's opinion, over at this link.

[ATTACH]25099[/ATTACH]

[JPG]

Well it has been an 'interesting' path that I have been on for way too long.

First I now am confident the proper length is 30 1/2" for the motor belt.

As for a setup method, the first step is to adjust the speed control dial to 700(minimum setting). At this setting the idler pulley needs to be about 1/2" between sheaves at the periphery. An outside measurement would be 3/4" as the sheaves are 1/8" thick there.

Both the control sheave and the floating sheave traverse over a 1" range in opposite directions. So at max speed, the motor pulley should be 1/2" between sheaves also.

The belt width will affect the actual speeds attained.

Since the belt I have is barely 1/2" wide(one cannot believe specs from v-belt purveyors nor manufacturers) the speed is also affected. The belt will ride closer to the center of the idler pulley, and further out on the motor pulley resulting in faster quill shaft speed. At max speed the belt rides further out on the motor pulley.(sticks out beyond the periphery)

To compensate for the thinner belt at 700, I moved the eccentric in thus causing the speed control cam to close the idler pulley further so the belt will ride closer to the periphery. This is dicey since this also causes the belt to ride closer to the center of the motor pulley(potential grabbing of the belt by the vanes). That still results in faster than 700 rpm, but it becomes closer.

I am confident that a proper width belt(17/32"? 9/16?) would result in correct speeds. I have not been successful coming up with a work around for the narrow belt nor a source for a wider belt that includes future availability. I am using a 'duralast' cogged belt(17305) from auto zone, but think the cogged belt is a detriment as it is more easily snagged by the pulley vanes.

This experience has explained why a badly worn belt(down to near 3/8" width) on the Goldie caused it to run faster than normal' a few years back(original belt!!!!!).

So it appears I will not get proper speed(damn that tach!!!!) with available belts. I will run it with the eccentric slightly(1/8" to 3/16") inset. Will probably add a bushing(washer) to move the pulley and install the eccentric normally. The speeds with a new belt are about 850 to 5500 rpm. Without a tach I would likely have been satisfied(ignorance is bliss!:D).

Things learned(finally) from this. Most is also applicable to the Mark5/V.

A narrow belt will cause an upward shift in the speed range.

A short belt will also.

Either will be more likely to get jammed in the motor pulley.

A short belt is likely to get jammed in the idler pulley.

Internally cogged belts create vibration when running close to the inside ends of the sheave vanes(to the point of jamming).


Changing belts on a Mark VII is not as easy as on a Mark 5/V.


I am going to see if a 'top cog' belt from advance behaves differently.

[zenman]

Grainger has dayton v belts all lengths including 31 in. The a, ax, and L5 series has a half inch top width and 5/16 bottom close to 3/8 inch I might have measured on the original belt. Not cogged. Around 10 bucks.

[JPG]

Grainger has dayton v belts all lengths including 31 in. The a, ax, and L5 series has a half inch top width and 5/16 bottom close to 3/8 inch I might have measured on the original belt. Not cogged. Around 10 bucks.

If I have learned anything from this it is that the belt length is critical to obtain correct speed range. And 30 1/2" is the correct length. If I cannot get one of proper width as well(1/2" is too narrow), I may attempt adding spacers to raise the motor slightly. However since only one side rests on the bottom of the motor pan, and there is precious little room to raise it, that may not be possible. I did raise a M5 motor 1/4" so as to use a 26" belt, but there was more room there and all 4 screws attached to the bottom of the motor pan.

And I am very frustrated by repetitively reading about belt widths that in reality are narrower than specs.

Tomorrow I pick up a dayco top cog belt (30 1/2") and will try that. Next attempt(if needed) will be an SPA775 metric belt. 775 mm is close to 30.5" and the profile is non-cogged with a thicker depth(13mm wide x 10mm deep). That extra depth will help prevent belt jamming in the vanes at extreme speed settings. Again I be trusting specs. I hope the metric belts are more faithful to the specs.

[rcplaneguy]

Does this chart help at all?
http://www.lebo.ca/en/beltid.pdf

[JPG]

Does this chart help at all?
http://www.lebo.ca/en/beltid.pdf

YES THANK YOU!!!!

I need to point out that the profiles shown for v belts are the crowned shape that were the cause of great consternation, anguish and dissatisfaction a while back. IIRC those belts were Gates and were a terrible 'substitute'.

Again if one could only depend upon this info as accurately describing the reality of what they are. Nominal dimensions seem to be no longer the production target, but rather the low side of tolerances has taken their place.

i.e. 1/2" +- 1/16 tolerance becomes a target of 7/16" plus little, minus nothing. Minimizes material costs. :(:(:(:(:(:(

Asinine IMHO, but saves production $$$$.

[JPG]

Hookay! Got a 'top cog' 30.5" belt from Advance Auto. It is the most successful one yet. Still only 1/2" across the top.

It will go from even with the outer edge of the idler pulley at '700' to even with the outer edge of the motor pulley at max.

The eccentric needed to be inset about 3/16" to obtain that. A wider belt would eliminate the need for that

Am having problems with my tach, but it 'sounds' correct.

These old parts are noisey, but at least the belt question is answered.

There is no doubt in my mind that the original belts were 30 1/2" and were the same as Mark 5/V belts at slightly OVER 1/2" in width.

The sloppy sheaves still tend to get grabby at the extreme speed settings but less so than with the other belts. Again a wider belt would relieve that.

So I will now proceed to shuffle parts to try and quiet things down.

Gotta figger out why my CNC produced cam 'wobbles'. I fear the 'reference' plastic cam may have been warped. May need to rebore/add bushing to the shaft hole.

Both the 'as received' movable sheaves need repairing(welding the hub damage).

Fortunately the floating sheave appears to be identical to a Mark 5/V.

The idler sheave differs due to the pulley width(13 ribs), but a mark 5/V sheave would work with a narrower Mark 5/V belt with the sheave positioned correctly on the shaft by using bushing washers as spacers. The main shaft pulley is adjustable along the shaft axis.

[rcplaneguy]

The cam is not square on it's shaft?
Congrats on finding a belt, even though it may not be "perfect".
Progress!

[JPG]

The cam is not square on it's shaft?
Congrats on finding a belt, even though it may not be "perfect".
Progress!

The cam outer edges move in/out(along the shaft axis) as the shaft is rotated. Causes interference between the rim of the cam and the cam follower.