STM Primary Clutch Setups

[spacehog21]

What are the turbo guys using for 4 post primary STM clutch setups?

I have used a lot of setups on this clutch from mild to wild and was wondering what everyone has found to be the best balanced setup for mountians?

Last ride I used a 460 finish rate spring.

The supertips take quite a bit of weight in the heel to grab the belt down low on my setup.

If too much weight is in the middle of the arm then it takes more time to get to the topend.

Putting even four grams on the tips causes the arms to rotate backwards and stick in the clutch not allowing shiftout or engagement if there is not enough weight in the heel to overcome this shift.

Running light weights in the tip causes the belt to slip under max load.

I also tried 2 other 1200 turbo clutch setups that are working for others and they are not even close to what I am looking for.

Lots of different setups hold the power in the mid to high 7s for rpm but I am looking to bump it up to 8200 while keeping quick revs and operating at a very low engagement rpm as well.

My sled is a 1200 turbo but any STM 4 arm setup on a turbo sled would be useful information.

 

[187POW]

stm clutch

have you had any luck with stm set up....im running same clutch on 1200 with 18lbs of boost and burning up belts....im also looking for info...thanks

 

[Rotax_Kid]

What are the turbo guys using for 4 post primary STM clutch setups?

I have used a lot of setups on this clutch from mild to wild and was wondering what everyone has found to be the best balanced setup for mountians?

Last ride I used a 460 finish rate spring.

The supertips take quite a bit of weight in the heel to grab the belt down low on my setup.

If too much weight is in the middle of the arm then it takes more time to get to the topend.

Putting even four grams on the tips causes the arms to rotate backwards and stick in the clutch not allowing shiftout or engagement if there is not enough weight in the heel to overcome this shift.

Running light weights in the tip causes the belt to slip under max load.

I also tried 2 other 1200 turbo clutch setups that are working for others and they are not even close to what I am looking for.

Lots of different setups hold the power in the mid to high 7s for rpm but I am looking to bump it up to 8200 while keeping quick revs and operating at a very low engagement rpm as well.

My sled is a 1200 turbo but any STM 4 arm setup on a turbo sled would be useful information.

Get in touch with a fella named Burrhead on Dootalk or give the guy who owns Turbo Addicition down East a call. I've ridden Burrhead's machine and it's clutched spot on IMO. I know how ended up grinding supertips for best response.

Run the 1200 even a bit higher at 8300..I like clutching it to just hit the rev limiter on a full throttle pinch and then back off slightly. Seems to run best at higher RPM.

 

[jvb]

I went through quite a few belts for a while too with this clutch. When i sold the sled i finally had it working pretty good i cant remember what spring i had but i thought i had a yami spring (blue-pink blue maybe not sure) I had almost if not all tongstons in the heels and then gram or two in the mids and then 4g or so in the tips. My clutch was always pretty hot though.

 

[gus bohne]

I use the rage 8 on 2 and a 4 on the other.
I also have 2 using JBR billet tra's..
Email me directly .

gus.bohne@comcast.net
I will shoot you pics of the setups and breakdowns..

fussy clutch till you understand there is only ONE way to use it or it slips like crazy..

 

[spacehog21]

I believe Burrheads sled is a short track setup for trail riding.

When I first set mine up I looked at what he had for a setup.

I have been riding the steep and deep at about 20-22 PSI and my clutch is working flawlessly when it comes to holding the belt and belt heat.

I can do consecutive pulls, open the side panel and hold my hand on the primary. I does not ever get to hot to hold a hand on.

Burrheads method of shaving weight off of the arms thus reducing arm weight will not help squeeze the belt at high load, on high boost, in deep snow and powering a long track.


After many different setups I have found how the STM clutch reacts when adding weight along the supertips.


Like Gus said this clutch is extremely fussy and must be perfectly balanced between a number of functions to work well.

My setup:

I have found that my setup will not engage at a low 3500 rpm unless I put dual tungstens in the base and keep my belt adjusted tight so the track barely moves on a stand at idle.

Also the tip cannot be loaded down with more than 3 or 4 grams or it will reverse in the clutch and stick against the outside not even engaging. This happens if the sled is tilted toward the clutch side at an angle and not running.


As far as weights, I now have supertips with 11 grams in each base, 2 in the mids and 3 in the tips. This comes out to 16 grams of added weight for 1 single arm.

I believe the primary spring I am now running is a Doo pink 250/460.

This setup is quick reving and responsive similar to a race sled setup with a higher engagement than a stock 1200.

It may not be for everyone but works very well in the trees when on and off the throttle.

With this stiff of a spring the rpm climbs rapidly before the sled has moved very far thus shifting it into the powerband quickly.

Stays at about 8200-8300 in climbs

 

[jvb]

what are you running your sencondary? Thats sounds close to the same as what i had with my stm.

 

[spacehog21]

I run a stock secondary clutch with turbo hi torque rollers and a much stiffer purple AC EPI secondary spring. I also have in it a Q50 helix which helps tremendously with throttle control and backshift.

With the steep helix the sled is easy to handle and it also loads up the engine well.

Stock secondary spring is a 58/98

AC spring is a 86/148


Before the stiffer spring there was major belt slippage even at 10 psi in the secondary.

I also wound the spring 90 degrees - grips the belt very nicely now



Shimming is also needed for the spider in the primary to drop the engagement rpm.

Every 30 thousandths drops the rpm about 400 rpm but be careful to leave at least 60 thousandths of metal at the end of the roller/ramp contact area at full shiftout so your clutch does not come apart



Also, on my application, shims are needed in the secondary to force the secondary clutch to stop short of full shift.

This method is used primarily in high hp drag racing sleds but is helpful with my setup. By doing this you can stop the primary from shifting completely out and allowing the 2 sheaves to bash against one another.

Higher gearing also helps to alleviate the problem by loading up the engine more but there is a balance point. To high of gearing adds more stress and belt heat to the drive system.