Just so you will know - the same technology of two sets of sheaves -one driven -one reacting, gave the start to the snowmobile industry. At one time I had a 1957 Ski-Doo by Bombadier (Canada) The big difference is snowmobiles dont have a dial in speed control - just a throttle.solicitr wrote:All these relationships are linear- as the belt seeks a new circumference all the movement is first-order proportional, so that the (lower) floating sheave necessarily moves exactly the same distance as the control sheave, and therefore the 'effective center' or drive belt centerline moves together (at half the rate of the sheaves' movement) on both shafts, remaining in vertical alignment throughout.
Clever, clever man, that Dr Goldschmidt!
Now I just have to turn all this into numbers....
Fan sheave set screw
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Octogenarian's have an earned right to be a curmudgeon.
Chuck in Lancaster, CA
Chuck in Lancaster, CA
OK, SS experts, I need some brainstorming here. Ridiculous as it sounds, I may have a nonstandard fan sheave (off a Mark VII, perhaps? The previous owner had one). According to Dave at SS tech support, the thichness of the sheave hub (= depth of the hole) is 7/16".
Mine is 11/16"- a quarter-inch thicker.
This is the same as the measurement from the back to the plane of the rim (the part you don't want touching the fan housing)- .680 and .686 by my calipers.
Now, get this. .680 plus .019 (inner bearing race) is .699. The distance from the motor plate to the fan plate is .739; add 1/8 (.125) clearance and you get .864.
The spacer thickness ought to be the difference between the two. Well, .864-.699 is .165: i.e. just about exactly 1/4" (.245) shorter than the spec spacer of .410!
So...why the *&%*&! is my fan sheave a quarter-inch too deep?
Mine is 11/16"- a quarter-inch thicker.
This is the same as the measurement from the back to the plane of the rim (the part you don't want touching the fan housing)- .680 and .686 by my calipers.
Now, get this. .680 plus .019 (inner bearing race) is .699. The distance from the motor plate to the fan plate is .739; add 1/8 (.125) clearance and you get .864.
The spacer thickness ought to be the difference between the two. Well, .864-.699 is .165: i.e. just about exactly 1/4" (.245) shorter than the spec spacer of .410!
So...why the *&%*&! is my fan sheave a quarter-inch too deep?
Bill
Richmond, Virginia
Richmond, Virginia
Bill - This is a wild guess - and I may not even know what I'm talking about:
Is there a chance the two sheaves have been reversed?
Seems as though I can remember (maybe just fantasizing) the sheave on the inside had a recess on the back, like a counter bore, where the spacer fit. I can't remember if both bottom sheaves had keyways, but it stands to reason they do. If this doesn't work, take a look at the upper sheaves to see if one of them belongs on the motor shaft.
Is there a chance the two sheaves have been reversed?
Seems as though I can remember (maybe just fantasizing) the sheave on the inside had a recess on the back, like a counter bore, where the spacer fit. I can't remember if both bottom sheaves had keyways, but it stands to reason they do. If this doesn't work, take a look at the upper sheaves to see if one of them belongs on the motor shaft.
Octogenarian's have an earned right to be a curmudgeon.
Chuck in Lancaster, CA
Chuck in Lancaster, CA
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Ed in Tampa
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charlese wrote:Just so you will know - the same technology of two sets of sheaves -one driven -one reacting, gave the start to the snowmobile industry. At one time I had a 1957 Ski-Doo by Bombadier (Canada) The big difference is snowmobiles dont have a dial in speed control - just a throttle.
Chuck
I believe the same technology is used in the Auto industry, in CVT transmissions. I'm not sure all CVT transmission function this way but for the one I saw a diagram for it did. Instead of a rubber belt they used a steel link belt/chain. I believe the diagram was for Saturn or Honda.
The one in the diagram functioned just like those in a snowmobile, as engine speed increase the sheaved was moved to increase diameter which caused the output sheaved to reduce and increase rpm which increased speed. As the engine speed decreased the sheave moved away making the diameter smaller with caused the output shaft to increase and the vehicle speed got slower but with more torque.
I didn't think it would last but the article says they have tested for 100's of thousands of miles and it worked
Ed
There's an animated illustration of a Reeves-type CVT (ie the Shopsmith system) here:
http://auto.howstuffworks.com/cvt2.htm
It's worth observing that this arrangement preserves power throughout the speed range, unlike the cheaper sort of electronic variable speed (as in a drill), which just bleeds off voltage.
http://auto.howstuffworks.com/cvt2.htm
It's worth observing that this arrangement preserves power throughout the speed range, unlike the cheaper sort of electronic variable speed (as in a drill), which just bleeds off voltage.
Bill
Richmond, Virginia
Richmond, Virginia
Dear Nick:
Thanks so much to you and Jan for helping me out with my oddball fan sheave. I don't know where the darn thing came from and probably never will; the better part of valor, plus its wobble, persuaded me to replace it with a new spec sheave.
Could it conceivably have come off a Sawsmith? That together with the MkV and MkVII are the only products from Magna/SS I'm aware of ever to use this speed control system. Unless it's from a clone.
Thanks so much to you and Jan for helping me out with my oddball fan sheave. I don't know where the darn thing came from and probably never will; the better part of valor, plus its wobble, persuaded me to replace it with a new spec sheave.
Could it conceivably have come off a Sawsmith? That together with the MkV and MkVII are the only products from Magna/SS I'm aware of ever to use this speed control system. Unless it's from a clone.
Bill
Richmond, Virginia
Richmond, Virginia