STM clutch issues

[supermoto]

I was hoping some of the other members here could discuss the recent issues that they have had with their STM clutches (chuckie108, FFRacing79).

Introduction:

I clubrace in the NorthWest and recently had my clutch go belly-up in the middle of a race (04 CRF450, completely stock except FMF pipe). Before I used this clutch the rear wheel chatter was horrible. I probably had about 6 races on the clutch. I purchased the clutch last year from Azionemoto (who used to be the North American importers) but now FMF is the North American importer of STM slipper clutches for dirt bikes. I have been trying to get some resolution through FMF since the beginning of August, but so far I have been unsuccessful. One issue is that all of Italy is on vacation throughout the summer. I have one of the older models (red anodized pressure plate) so it has been difficult to get a replacement, and so FMF is already starting to discuss the idea of me buying a new one at cost. The rep at FMF has been helpful so far.

My failure:

The base of the pressure plate (where the primary "spring" sits) on the STM clutch popped off like a tin can. To me this was clearly not an instance of normal wear and tear failure, but rather a manufacturer's defect. (my first time posting pictures, I hope this works)

My issue:

I love this clutch, and don't want to go back to the "old dog" regular job that all my loser friends use ? (you know who you are, "just push it down %$#&$@"). But I am concerned that the replacement pressure plate will fail again, and I am definitely not thrilled about buying a new one, even if it is at cost. I'm addicted to the damn thing and I feel like some sort of slipper clutch junkie.

Other TTers experiences:

I would really appreciate it if others would share their STM slipper clutch failures (bike model, what failed, etc...). To see if there are any commonalities. I'm not sure this would solve anything, but it would be interesting to put this data together. When I read that Henry's clutch went at the Colorado race I pretty much figured he was using an STM clutch, but wondered what went wrong. I see the advertisements for this clutch everywhere and the article in SMR was great, but I am concerned that lots of other club racers (such as myself) will drop the ~$1000, only to get screwed. I really think STM (or another company) really need to go back to the drawing table on this design.

One last thought: [make sure you say this next line with your best nerd impression, its easy for me because I am one] I wonder if the rate of failure is directly proportional to the power output of the bike. My stock bike lasted at least a few races, while it seems the other people on this board see it go almost every race.

Man this post is long, sorry.

-Art

[MotoGreg]

I heard that on Henry's bike the center nut came loose.

I guess that's why they changed them. I've installed an old style like yours with the red plate, and a couple of the newer updated styles, all in CRFs. There is more different than just that piece that you have broken. I don't know what parts exactly you'd have to get to have yours updated to the newer specs.

[TeamScream]

Man thats kinda crappy, I have the red plate style on mine, and have a few races on it plus a few track days and it still seems fine.

Maybe i should look into it, lemme know if you come across any more info Greg, what needs replacement to make it a newer spec upgrade.

[chuckie108]

I can't give you any feedback yet as our bike is sitting in a semi truck in Wisconsin with no way home. When I get the bike home and I tear into it, I'll let you know what I find. For now though it is all speculation as to what the problem is. The slipper might be totally fine, but when I get it all figured out, I'll post it here. ?

[smrscott]

I have been running the older style in two different bikes over the last year and half - no problems.

STM did give me an updated limiter washer to help keep the pressure plate from touching the outer case. The current clutch is different than the original. The springs are different and a few pieces have updated.

As for the nut spinning off - it is best to clean the threads and run a drop of red thread locking agent before you secure the nut. I run about 80lbs of torque on the nut. On the Yamaha clutch you can over tighten the nut and the clutch will not work and on the KTM you need to make sure you have the right clutch plates in the bike. I hear that it is best to take out the two thin outer plates on the KTM and replace them with standard plates. Just rumors- Call Dick Racing.

Just my two cents.

[MadMarche]

I have a '03 YZ450, and we put the STM clutch in my bike.("we" being myself and the lead mechanic from the local Yamaha shop who had installed a couple of these in other YZF's) We installed everything per the directions, and the damn thing doesn't work properly! No matter how much we tried to adjust the clutch cable, it still wouldn't correct the problem. While in neutral, I pull the clutch lever in completely, click the bike into gear, and BAMMMM the damn thing wants to lurch forward. The best that we could get it to do was only "drag" instead of "engage". We mic'd all the clutch plates, and everything is within tolerances. I have been too busy to pursue this issue, but this topic is giving me the chance. I talked to RAD at Copper Mountain, and he said that he had also heard of the problem before. Any ideas what I should do? ? I put the stock clutch back in for now and it works fine. I would like to get this sorted out, so I can at least use what I spent all my money on. Does anyone have a contact number for someone at FMF that handles technical questions for the STM clutches?

Thanks in advance....MADMarche

[supermoto]

Does anyone have a contact number for someone at FMF that handles technical questions for the STM clutches?

MadMarche,

The FMF phone number is 310-631-4363, and I have been told

that Dave Dye is their expert STM slipper clutch tech.

Apparently he used to be Chad Reed's mechanic and all

the team Yamaha bikes use the clutches. The problem is

that he is not in very often (apparently 1-2 days per week).

I have never actually spoken with him myself. This

information came from the tech that is handling my case.

motogreg, teamscream, chuckie, smrscott, and madmarche,

Thanks for your input so far. This is exactly the type of

dialog that I was hoping for. Even if the feedback is

positive or if the issues with the clutch are different than

mine I believe it is important to discuss. I just want to

be really clear that I am not bad-mouthing STM or FMF

(yet). I know the tech at FMF is trying, and I really do

like the clutch (when it is working). I think my biggest

problem is that I like the clutch too much and I don't

want to consider going back to the standard one. Maybe

the updated clutch is the way to go..........

Thanks for your input so far, keep it coming.

[MonsterJ]

I'll add my two cents, FWIW... I've never delt with STM slippers on CRFs, but I've delt with them plenty on Ducatis. I've installed quite a few and I even have one on one of my Monsters. I also have several other STM items on my bike. I've got nothing but praise for STM and thier products. I'd like to think you got a lemon and it's an isolated case. Just know it might take a short while to get some resolution. Italians take the month off and end up way behind when they get back.

[SFO]

Last year on Dougs bike the clutch worked perfect.

[grmracing]

we got alot of miles on ours, stm in a yz 450 have had it apart 4 times and mine shows none of the wear marks that are in your pic's.. works perfect. only thing we have differnt than most is a HINSON basket. I have installed a few of them for freinds and all of them have worked great. i know this does'nt help you any but its feed back. ?

[tillertracker]

In your last picture (of the spring), I see wear marks all the way down the fingers to the base of the fingers. Is this a trick of light? Is the photo of the outside of the spring (I think it is)? On my setup the only places the spring touches anything is around the edge on the inside and around the finger tips on the outside. That pressure plate looks burly enough, I can't imagine spring pressure alone broke it. Not being there to inspect makes it tough but I'm going with incorrect assembly, sorry. ?

[supermoto]

In your last picture (of the spring), I see wear marks all the way down the fingers to the base of the fingers. Is this a trick of light? Is the photo of the outside of the spring (I think it is)? On my setup the only places the spring touches anything is around the edge on the inside and around the finger tips on the outside. That pressure plate looks burly enough, I can't imagine spring pressure alone broke it. Not being there to inspect makes it tough but I'm going with incorrect assembly, sorry. ?

Tillertracker,

Sorry for the slow reply, I have been in Victoria (Canada)

racing for the past two days.

No reason to apologize for your comments. I am here to find

answers, not point fault at anyone but me.

Yes the wear marks you saw are really there, but the ones

going way down towards the outside of the fingers are very

mild (the anodizing is barely worn off). Thr majority of

the wear is on the inner portion (outer side of spring).

Where I do see a lot of wear is where the primary spring

sits in the pressure plate (where it broke). One thing I

was told by the gentleman I spoke with at Azionemoto was

that: 1.) I had gotten one of the very early models, 2.) a

steel ring had been added to the area where the primary

spring rests to prevent wear like I had.

It also appears (see post from smrscott above) that a

change was made to the limiter washer to help keep the

pressure plate from touching the outer case (which mine

was, see pictures). Either of the two updates made may

have prevented the pressure plate failure. Or it is

possible that I had installed the clutch incorrectly,

my only defense would be that the clutch had worked

flawlessly up until the moment it broke and that I can't

find any differences in how I had the clutch installed vs.

the directions (glorified schematic) supplied with the

clutch. I also compared my installation with the great

writeup in SMR (keep it coming Scott the mag is awesome).

I guess I feel that because the updates were not conveyed

to the people who bought the early models (ok, at least not

to me. others may have been), that I am due some

replacement parts free of charge. Maybe these changes are

all that is needed to prevent future problems. I just

don't want another DNF because of the clutch, and also

don't want to see it happen to anyone else (OK, unless

you are in front of me in a race, hah!).

A few questions for you tillertracker (for comparing spring

wear marks):

1.) what bike?

2.) which version of the clutch do you have (grey/red) and do you know if you have any of the updated parts?

3.) what type of riding and hom much time on the clutch?

My answer to question 3 would be about 6 races, but I also

have plenty of practice time at a kart track, MX track, and

indoor short track (clay oval and TT).

Thanks for you input tillertracker,

-Art

[tillertracker]

I have a CRF450 motor in a roadrace chassis. I must have the updated clutch because it's grey and has the steel shim that goes under the spring. I have around 15 hours on it now with no problems at all, I love it! I did notice that your anodizing has WAY more wear everywhere than mine. Mine has almost none.(better anodizing?) I didn't realize yours had no shim under the spring. That's just plain obvious, you can't have a sharp edge like that digging into aluminum, I see now why it failed. Glad I apologized before hand!