Primary Belt Height- How to adjust on shift out

02ViperMody44

02ViperMody44

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Hello all,
What is the biggest factor in getting the belt height in the primary closest to the top? Mine would almost be near an inch away from the top of the sheeves upon shift out.(marked w/ a marker) Is it the twist in the secondary or secondary spring tension that controls this? Can I assume that if it is wound too tight or tension too much, it won't allow the primary spring's force to enable the sheeves to stay closed long enough to make the belt ride up into the sheeves. Also, if you are running a small lug track (.7"), would spinning instead of "hooking up", make this happen too? Plan on going to an 1.25" ripsaw this season. I have a piped 136" Viper w/ 8 tooth drivers. All springs are new-ish, WWW primary and Hauk Green in secondary. Would like to fix this issue for this season. Thanks in advance.
 
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Somebody please correct me if i am wrong, but i think the stock yamaha clutch doesnt really shift out all the way. I remember reading somewhere that the belt will stay like an inch below the top of the sheve @ full shift.
 
stock viper/srx clutch will shift the belt to about 1/4" from the top when every thing is set up properly and the engine has the horsepower to pull the current clutch and gearing combo.
 
What about a NON-stock clutch? I have 8DN-20's w/ about 51gr of total weight(if I remember). A WWW primary spring. Should I be looking at less twist on the secondary to allow the primary to move up. I am just trying to get a handle on this clutching question. Maybe a weaker spring in the secondary. It is the Hauck green painted spring. I don't know if it is equal to a green Yamaha spring. If anybody knows that answer please chime in. Just trying to get some efficiency out of my clutch set-up. My understanding is that w/o the belt rising fully up, than it is kind of like running in a lower gear, and you lose out on top end speed. I have SLP tripples and 1.86 gearing(8 inch drivers). Does gearing play some factor in this too, as I think I may want to change my gearing to a lower numerical value. It is a 136" track. Thanks
 
I used a Hauck green a few years back and I was told by Pat Hauck that their green spring is "similar" to the Yamaha green secondary spring.

A few comments:
-a stock Yamaha primary clutch is mechanically incapable of running a stock belt to the very top of the sheaves as it is machined to only close up enough to bring the belt to approx 1/2" from the top of the clutch[you can check this by removing all the weights + spring from the clutch then pushing it closed, if you measure the distance between the sheave faces you will see that the distance is wider then the belt] this is why some companies offered "overdrive" sheaves to allow the cluth to run the belt to the top

-gearing has huge effect on how high the belt will ride in the primary clutch. Most factory sleds are geared for approx 10% higher speed then the sled is capable of running. The higher the gearing the lower the belt will be in the clutch so obviously the lower the gearing the higher the belt will run.

- when you raise the RPM of an engine by adding pipes ect you have effectively geared the sled up so some times you have to gear the sled down to better match the power band to the sleds capabilities.
ex: Stock Viper RPM: 8500
Piped Viper RPM: 9200
In this example you have raised the RPM + speed capability by 8%, since the sled was already factory over geared by 10% you obviously have a way over geared sled that will never be able to fully shift out and bring the belt to the top of the primary. In this situation I would reduce my gearing by at least as much as the RPM % raised to get a better balanced setup.

If a sled was geared 1.86:1 and then 8 tooth drivers were added you have effectively lowered the gearing by 11% to 2.09:1 , so the belt should want to ride higher in the primary then it did before [even with an RPM shift raise]

Hope this helps:
Bob
 
YAMMIEGOD3:16 said:
BOB, GREAT INFO. WITH THIS ALL SAID, THAN WHY DOSE,NT HAUCK SELL HIS OVER DRIVE SHEAVE LIKE HOT CAKES. 3;16 (yammie tony)
Click to expand...

In my opinion, in certain applications the overdrive sheaves work pretty well[some trail applications], but they have their downside.

Clutch effeciency is at is optimum right around the 1:1 ratio[that means the diameter the belt is turning at is the same in the primary + secondary clutch just like equal tooth gears with a chain]

When you overdrive the system the belt speed starts to increase and the resulting friction, heat ect starts to scrub off efficiency and consequently robbing horse power...not good for radar runs ect.

SkiDoo, back in the day, ran pretty big overdrive ratios, heavy weights and springs and they were getting outrun on top speeds, on the trail and in Radar runs, by less horsepower smaller engined Polaris sleds that were running P85 clutches at a max shift of 1:1 with relatively light springs and weights. [These same SkiDoos could hold their own in a Drag Race.]

Its the old story...no such thing as "one size fits all"...each setup must be talored for the specific use/application

Bob
 
-gearing has huge effect on how high the belt will ride in the primary clutch. Most factory sleds are geared for approx 10% higher speed then the sled is capable of running. The higher the gearing the lower the belt will be in the clutch so obviously the lower the gearing the higher the belt will run.

- when you raise the RPM of an engine by adding pipes ect you have effectively geared the sled up so some times you have to gear the sled down to better match the power band to the sleds capabilities.
ex: Stock Viper RPM: 8500
Piped Viper RPM: 9200
In this example you have raised the RPM + speed capability by 8%, since the sled was already factory over geared by 10% you obviously have a way over geared sled that will never be able to fully shift out and bring the belt to the top of the primary. In this situation I would reduce my gearing by at least as much as the RPM % raised to get a better balanced setup.

If a sled was geared 1.86:1 and then 8 tooth drivers were added you have effectively lowered the gearing by 11% to 2.09:1 , so the belt should want to ride higher in the primary then it did before [even with an RPM shift raise]

Hope this helps:
Bob[/QUOTE]

Bob Thanks for the info.
I have a 1.86 gearing taking into effect the 8 tooth drivers(38/23 gears). I used to have it geared numerically higher, and it really limited the top end speed. I was running like a 1.96(including 8 tooth) and top end was not there. Did not look for where the belt height was when running that gearing. I was thinking of going to a 38/24 for a 1.78 gearing(including 8 tooth). Not running in the mountains, trail riding and lakes only. IF I understand what you are saying though, is to get the belt height higher in the primary, I need to go back up w/ the gearing to a higher numerically ratio. Is that correct? I don't really want to go that way, so to avoid that route, to keep sled speeds up, can adjustments to the secondary spring control the primary belt height?
 
I FOUND THE BAD STRESS CRACKS IN BOTH MY SHEAVES ON MY 95 VMAX 4 800 GRASS DRAG SLED. I MEAN CHANGE THESE OUT OR THEY WILL BLOW. I BOUGHT A BRAND NEW YAMAHA MOVEABLE. DEALER HAD ONE IN STOCK AND GAVE ME GOOD PRICE. HE THAN GAVE ME PRICE ON YAMAHA FIXED, WHICH WAS TO BE ORDERED. I WAS ABLE TO BUY A HAUCK OVER DRIVE BRAND NEW FIXED FOR LESS THAN THE YAMAHA. I WENT WITH THE HAUCK. 1. PRICE, 2 FOR ONLY DRAG RACING THIS SLED 500 f.t. MY THINKING OF CORSE IS TO BE ABLE TO GEAR DOWN MORE FOR BETTER ACCELRATION IN 60 f.t. AND STILL MAINTAIN GREAT E.T. AND SPEED. FIGURED IT WAS WORTH A TRY. 3:16 (yammie tony)
 
02ViperMody44 said:
I have a 1.86 gearing taking into effect the 8 tooth drivers(38/23 gears). I used to have it geared numerically higher, and it really limited the top end speed. I was running like a 1.96(including 8 tooth) and top end was not there. Did not look for where the belt height was when running that gearing. I was thinking of going to a 38/24 for a 1.78 gearing(including 8 tooth). Not running in the mountains, trail riding and lakes only. IF I understand what you are saying though, is to get the belt height higher in the primary, I need to go back up w/ the gearing to a higher numerically ratio. Is that correct? I don't really want to go that way, so to avoid that route, to keep sled speeds up, can adjustments to the secondary spring control the primary belt height?
Click to expand...

I don't think you have a gearing issue...I suspect you are running the SLP piped Viper around 8600-8800 RPM...if so with 1.86:1 final gear ratio you are geared for approx 100mph at a 1:1 shift ratio. I would think your sled if set up properly would easily be able to run over that speed on hard pack.

Most people, including me, will tell you that big speed numbers are in the secondary clutch setup, but the weight/spring combo/profile in the primary obviously has a huge influence as well. If your engine is in proper tune and the sled is in top mechanical shape I would start looking at the clutch setup/combination for lost speed.

The clutching gurus can steer you better in this area as nowadays I run adjustable weights[heavy hitters] in my primary and a Team roller secondary.

JM.02c

As an afterthought...our stock Yamahas already do over drive a little beyond 1:1...I have never sat down and figured it out but I think its at least 5%.
 
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You were right on in regards to the RPM range. I believe I am achieving 8700rpms. The engine was completely rebuilt last year, NEW welded crank, new pistons,rings, Opti-cool gasket, peak performance heads. Skid all gone through-bushings, oversize wheels in the rear. If I go to a lower numerically gear ratio, 1.78, would that push my belt higher or lower? Helix 50/42.
 
02ViperMody44 said:
You were right on in regards to the RPM range. I believe I am achieving 8700rpms. The engine was completely rebuilt last year, NEW welded crank, new pistons,rings, Opti-cool gasket, peak performance heads. Skid all gone through-bushings, oversize wheels in the rear. If I go to a lower numerically gear ratio, 1.78, would that push my belt higher or lower? Helix 50/42.
Click to expand...

I.78 : 1 is higher gearing then 1.86 : 1... so changing to 1.78 :1 would move your belt lower in your primary for the same speed all other things remaining equal.

What kind of GPS speeds are you getting now?

Where the belt sits in the primary is not that critical as long as its approaching the max height it is capable of running at. A properly geared trail sled should not normally shift out completely but have some reserve.

If you want to "explore" your shift out belt height, keep gearing down[higher numbers] until the sled finally starts to over rev at the end of the longest straight stretch you would normally run wide open, then gear up slightly, thats how I used to set up my drag sleds for 660' but my trail sleds are geared higher then that.
 
Bob
I did do some "duking" on ice, I believe it was roughtly 500' that was cleared out. I seem to remember to be approaching my target max RPM at the end of the run. I guess w/ that I should probably go to a gearing it higher(lower numerically), for better drivability in the mid and upper speeds, instead of maxing out too soon.

In you opinion, does the secondary wrap/spring tension effect the belt setting lower in the primary?
 
When you wack the throttle open from a dead stop, or any other time for that matter, the engine RPM should hit and hold your target[shift] RPM[8700] almost immediately. and stay at the shift RPM right thru to its max top end. If your sled takes 500 feet to reach the RPM your clutching is way off.

Yes...spring tension and wrap will effect where the belt rides as it will either prevent it from upshifting or allow it to upshift too quickly.

I also think 1.86:1 is pretty darn close to optimum gearing for your application, I would leave it alone until I sorted out the clutching.

I would suggest you pick up Olev Aaens clutching handbook as it is the "Bible" on understanding clutching and all its variables...definately educational and worth every penny!

Bob
 
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I thank you for the instructions. I shall pick up a copy of the book.

I may have misrepresented, what I meant about the 500' runs. It wil initially shoot up to 8500ish and then climb till I'm about 8700ish going through the traps. I've never GPS'd the speed though.

I'll read the book, and than plan from there. Thanks for the insights.
 
while your book buying, take a look at cutlers' clutch book. written in more laymans terms and you wont need a slide rule or dictionary as you would with aaens. i use both books, as neither is expressely written for yamaha clutching, but all the principals will apply, and each makes for some good cross referencing and throne sitting.
 
02ViperMody44 said:
I thank you for the instructions. I shall pick up a copy of the book.

I may have misrepresented, what I meant about the 500' runs. It wil initially shoot up to 8500ish and then climb till I'm about 8700ish going through the traps. I've never GPS'd the speed though.

I'll read the book, and than plan from there. Thanks for the insights.
Click to expand...

You are not far off then on your clutching set up, a slightly different primary spring should bring you right into the slot. A little more pretension with the same final tension.

As a side note:
I would recommend staying with all Yamaha springs on both clutches as you can compare + change spring rates to fine tune your set up.
Works for Me!
Bob
 
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