Comet 780 advice

[superpro56]

http://forums.bajasae.net/forum/uplo...SAECatalog.pdf

Page 8 has the table to roller/spring engagement table for the 780 primary.

[Notsoezgo]

Originally Posted by superpro56

http://forums.bajasae.net/forum/uplo...SAECatalog.pdf

Page 8 has the table to roller/spring engagement table for the 780 primary.

Thank you

[sho305]

If you can adjust the spring preload in the secondary you can reduce it to lower rpm a little, it will respond slower and at lower rpm. If you have a BB you may want to try it as they like lower rpm with all the extra torque they have.

For primary heavier weight is lower rpm and lighter spring is lower rpm, but each can affect it differently. The preload of the spring (force at rest) more will cause higher engagement. So a weaker spring may engage lower or not, may shift lower rpm. Heavier weight may do same however one may do it at engagement and the other at top end or likely some combination of both. That is when its nice to know what other people did or know good setups to start with. In theory heavy weights will lower top rpm more likely, but springs can too. In theory the weights should be more powerful at top rpm.

[Notsoezgo]

Originally Posted by sho305

If you can adjust the spring preload in the secondary you can reduce it to lower rpm a little, it will respond slower and at lower rpm. If you have a BB you may want to try it as they like lower rpm with all the extra torque they have.

For primary heavier weight is lower rpm and lighter spring is lower rpm, but each can affect it differently. The preload of the spring (force at rest) more will cause higher engagement. So a weaker spring may engage lower or not, may shift lower rpm. Heavier weight may do same however one may do it at engagement and the other at top end or likely some combination of both. That is when its nice to know what other people did or know good setups to start with. In theory heavy weights will lower top rpm more likely, but springs can too. In theory the weights should be more powerful at top rpm.

Thank you that helps with my understanding of theses cvt`s

[sho305]

Well here is more if you are trying to tune a clutch and figure out what you need to change.

Basically the weights fly outward as rpm increases and push the sheaves together causing a 'higher gearing' of the belt. The spring(s) pull the weights back in so it returns to lower gearing at lower speeds. At middle rpm they settle on a balance between the two causing the sheaves to be in some mid shift position. Changing the weights, or changing the spring to have more force at rest (engagement/low speeds) or at full compression (top end shift) will change how the clutch reacts at a given rpm. Usually the weights are set for max rpm this is the rpm it holds when on the floor and clutch is not fully shifted yet. The weights usually have the most effect here and springs tend to not change max rpm that much. The spring is more for engagement changes, low speed shift rpm and part throttle shift, or to fine tune to the weights you are using.

The secondary mostly follows the primary and just keeps tension on the belt so it does not slip, except for one thing it reacts to torque. This will cause the rpm to rise under load such as going up a hill, and rpm to be lower under light conditions such as a steady speed on a smooth surface. The torque of the belt will push the ramps up to resist the primary upshift and set a 'lower gear' than would otherwise be running, like when you floor the gas this should happen. More tension (bigger spring or longer/etc) or preload (where you wind the spring in a different hole during assembly) will bias the secondary to run more rpm and or be more reactive to load and raise rpm more when you gas on it. With a larger engine you need less of this so setting the spring (if you can adjust it as some do not) with less preload or tension usually works better, which in a GC is often the stock setting or close. The smaller stock engine you want it higher with larger tires or to tow because its torque peak is at higher rpm and you don't have much torque to work with. If you preload the spring way tight it will act like you have it on the floor all the time, so even at part throttle rpm will stay at maximum. Also takes more gas and makes more noise. Its usually good to have this slightly higher than stock for offroad use of a cart because little more rpm also gives you more fan cooling of the engine and better performance especially with larger tires or HS gears. Again with a BB engine its not working as hard and torque is lower and stronger so its not as important. If you don't run offroad or work the cart then you can run less or often stock settings are the best.

I run a 94c that uses pucks instead of weights, the pucks slide up the cover to push the sheave in. Its an old design that works but sliding is not as smooth an action as roller bearings in newer clutches. The difference to the 780 is those all use a single central spring. If you get a larger diameter wire spring it shifts higher rpm, longer spring will raise engagement (because it has to use up that much spring before the sheave goes in more or less). The springs are rated in initial and compressed values to tell you if it changes things more at low or high shift. The 780 uses 3 small springs I believe that act on each weight. So you can't really change the length of them you just need the right one. They stopped using them on sleds I think because with more high performance 2 strokes coming out back then that need to engage at much higher rpm you can just drop a longer spring in a single spring clutch or shim the spring some. The 780 work nice on GC because even my clone with a cam and rod and all that still can engage only a little higher than stock and runs fine that way. The 780 is nice smooth clutch and proven, it works well for lawn engines.

[Notsoezgo]

Originally Posted by sho305

Well here is more if you are trying to tune a clutch and figure out what you need to change.

Basically the weights fly outward as rpm increases and push the sheaves together causing a 'higher gearing' of the belt. The spring(s) pull the weights back in so it returns to lower gearing at lower speeds. At middle rpm they settle on a balance between the two causing the sheaves to be in some mid shift position. Changing the weights, or changing the spring to have more force at rest (engagement/low speeds) or at full compression (top end shift) will change how the clutch reacts at a given rpm. Usually the weights are set for max rpm this is the rpm it holds when on the floor and clutch is not fully shifted yet. The weights usually have the most effect here and springs tend to not change max rpm that much. The spring is more for engagement changes, low speed shift rpm and part throttle shift, or to fine tune to the weights you are using.

The secondary mostly follows the primary and just keeps tension on the belt so it does not slip, except for one thing it reacts to torque. This will cause the rpm to rise under load such as going up a hill, and rpm to be lower under light conditions such as a steady speed on a smooth surface. The torque of the belt will push the ramps up to resist the primary upshift and set a 'lower gear' than would otherwise be running, like when you floor the gas this should happen. More tension (bigger spring or longer/etc) or preload (where you wind the spring in a different hole during assembly) will bias the secondary to run more rpm and or be more reactive to load and raise rpm more when you gas on it. With a larger engine you need less of this so setting the spring (if you can adjust it as some do not) with less preload or tension usually works better, which in a GC is often the stock setting or close. The smaller stock engine you want it higher with larger tires or to tow because its torque peak is at higher rpm and you don't have much torque to work with. If you preload the spring way tight it will act like you have it on the floor all the time, so even at part throttle rpm will stay at maximum. Also takes more gas and makes more noise. Its usually good to have this slightly higher than stock for offroad use of a cart because little more rpm also gives you more fan cooling of the engine and better performance especially with larger tires or HS gears. Again with a BB engine its not working as hard and torque is lower and stronger so its not as important. If you don't run offroad or work the cart then you can run less or often stock settings are the best.

I run a 94c that uses pucks instead of weights, the pucks slide up the cover to push the sheave in. Its an old design that works but sliding is not as smooth an action as roller bearings in newer clutches. The difference to the 780 is those all use a single central spring. If you get a larger diameter wire spring it shifts higher rpm, longer spring will raise engagement (because it has to use up that much spring before the sheave goes in more or less). The springs are rated in initial and compressed values to tell you if it changes things more at low or high shift. The 780 uses 3 small springs I believe that act on each weight. So you can't really change the length of them you just need the right one. They stopped using them on sleds I think because with more high performance 2 strokes coming out back then that need to engage at much higher rpm you can just drop a longer spring in a single spring clutch or shim the spring some. The 780 work nice on GC because even my clone with a cam and rod and all that still can engage only a little higher than stock and runs fine that way. The 780 is nice smooth clutch and proven, it works well for lawn engines.

Thank you for the detailed explanation of the clutches operation. I will do some work with my secondary and see the effect