Secondary spring wrap

[iam_canadian22]

Can somebody explain to me what they mean by that and what should it be stock on a 141 mtx?

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[PeeWee86]

Great question. When I bought my first Yamaha I had no idea what people meant by 3/3 wrap and how that was different from a 6/1 wrap. To make things even more confusing Yamaha's documentation doesn't use wrap a number instead it referred to degrees of pretension.

Each spring hole number represents 10° of torsional rotation on the driven clutch spring. One side has the numbers 0, 3, 6, and 9. The other side has 1, 2, and 3. Add the two numbers together and multiply by 10 to get the number of degrees of torsional pretension. So a 3/3 wrap is 60° and a 6/1 wrap is 70°.

Most Yamaha's that are set up for low elevations from the factory will use a 3/3 or a 6/1 wrap. The Viper MTX comes from the factory with a 3/1 wrap and a shallow 37° helix. It is set up for 10,000 feet of elevation. More spring pretension will give you have a quicker backshift but it will create more friction within the driven clutch. A steeper helix angle will load the motor harder on upshift but will require more spring pretension to prevent slipping.

If you are riding a Viper MTX at lower elevations, especially if you are doing some trail riding with it, you should have a steeper cam angle than the stock 37°. Yamaha recommends a 43° cam for lower elevations. I don't believe they make multi angle cams. I prefer a 45/39 or a 46/40 depending on the amount of on trail versus off trail riding you do. The multi angle cam will prevent an initial over rev condition right off the line. With the steeper cam angle I would prefer at least 50° of pretension. Turbocharged vipers have different cam angle requirements.

I have started working on some notes for a low elevation MTX clutching and gearing thread. I'll try to get it posted sometime soon.

 

[iam_canadian22]

Thank you very much, im at just above sea level. I do some trail ridding with it but more off trail. Havent experienced any over rev, that would be noticeable anyways. It doesn't seem to hold rpm in either deeper or sticky snow.

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[PeeWee86]

If you are at sea level and you are not over revving then you must no longer have the stock MTX clutch calibrations. Let me know what you have in place currently. Bogging in deep snow suggests to me that you need better back shifting. Increasing the driven clutch pretension will help. Then if you start to overrev you will need to add more weight to the clutch arms. Yamaha doesn’t make any rivits heavier than 4.5 g but they are available from other sources.

Before I put the 1st mile on my viper I switched to the 8DN belt. There’s plenty of information on here that suggests that the factory belt gives inconsistent clutching.

 

[iam_canadian22]

If you are at sea level and you are not over revving then you must no longer have the stock MTX clutch calibrations. Let me know what you have in place currently. Bogging in deep snow suggests to me that you need better back shifting. Increasing the driven clutch pretension will help. Then if you start to overrev you will need to add more weight to the clutch arms. Yamaha doesn’t make any rivits heavier than 4.5 g but they are available from other sources.

Before I put the 1st mile on my viper I switched to the 8DN belt. There’s plenty of information on here that suggests that the factory belt gives inconsistent clutching.

I will check later in the week what my setup is. Machining is required for the 8DN belt correct?

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[PeeWee86]

I have had Ulmer Racing machine my clutch, but machining is not required to run the 8dn belt. Because it is slightly longer you will have to just the belt deflection. This is done but adding an additional washer to the three small bolts on the backside of the driven clutch. They are available in .5mm and 1mm thicknesses from Yamaha. Adding theses washers should not be confused with adding three washers underneath the cam to prevent spring binding. I’ve seen some posts on this forum that suggest some people are confusing the two.

On a sidenote: If you do want to space out the cam, which I recommend trying, using the oval washers from a toilet flange Bolt kit will give you the correct shape to support the entire surface area as opposed to using a standard round washer. (See photo) These washers are usually a usually made of stainless steel. This is for use with a factory Yamaha cam. Many aftermarket cams have already have been properly clearanced.

 

[iam_canadian22]

View attachment 137153
I have had Ulmer Racing machine my clutch, but machining is not required to run the 8dn belt. Because it is slightly longer you will have to just the belt deflection. This is done but adding an additional washer to the three small bolts on the backside of the driven clutch. They are available in .5mm and 1mm thicknesses from Yamaha. Adding theses washers should not be confused with adding three washers underneath the cam to prevent spring binding. I’ve seen some posts on this forum that suggest some people are confusing the two.

On a sidenote: If you do want to space out the cam, which I recommend trying, using the oval washers from a toilet flange Bolt kit will give you the correct shape to support the entire surface area as opposed to using a standard round washer. (See photo) These washers are usually a usually made of stainless steel. This is for use with a factory Yamaha cam. Many aftermarket cams have already have been properly clearanced.

Is there a way to tell if ive been experiencing bind?

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[PeeWee86]

All SR Vipers with a factory Yamaha cam will experience spring bind unless you drive like my wife -never past half throttle or faster than 60mph. LOL. The telltale sign is that the paint will start wearing off of the driven clutch spring.

I am also of the belief belief that all viper MTX’s should be geared slightly taller if they are being used at lower elevations. There is more available horsepower when you’re down at a lower elevation. This will help the spring binding issue. The Viper BTX uses the same 21/49 gearing but uses eight tooth drivers. The other option for a low-cost gear change is to switch to 22/48. This combination will work with the original 90p chain. In the US new eight tooth drive sprockets or purchasing both gears each cost about $80. Eight tooth sprocket’s will throw off the calibration of the speedometer and will not fit with a 3 inch lug track.

 

[iam_canadian22]

Sorry took longer then anticipated to look at, how do i know helix angle? Only marking on mine is 8bv31. Spring wrap appears to be 3-1 so im gonna assume i have the 37* helix.

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[PeeWee86]

I googled “8bv31” and I believe that the cam you have is a straight 43°. This makes sense if it was a dealer set up elevation calibration. I believe the factory sea level calibration for a Viper MTX uses this cam, a 3/1 wrap, 4.5g rivets in both cam arm holes, and primary spring that is softer than the original GGG. I cannot remember the exact off the top of my head.

While it apparently is successful in holding the engine rpm in the correct range, it is recipe for poor back shifting clutches. Yamaha doesn’t make a clutch arm rivet heavier than 4.5g and because of that limitation they are compensating by running less than ideal spring tension in both clutches.

I would start by switching to a 3/3 wrap and adding shims under the cam like I suggested above. Give it a try like that first. I would expect that you will now over rev. To bring the rpm’s back down remove the 4.5 g rivet from the tip of the clutch arm and replace it with a heavier one in the 5.5-6g range. MPI and Hauck sell heavy rivets. I made my own from a button head bolt and nut. I believe it was a 6 mm bolt. Mine are 5.9g. If you don’t have a gram scale you can pick one up for less than $15 at Harbor Freight tools. I have one of their scales and I also have one that cost me nearly $200. They both work equally well.

I use a pink-green-pink primary spring. This one has a similar engagement RPM and about 150 RPM higher on top end than the original factory green-green-green spring.

 

[iam_canadian22]

Thank you very much for all the help

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