Tweaking the 2017+ Sherco/Scorpa Diaphragm Clutch

Discussion in 'Trials' started by motobene, Aug 16, 2017.

  1. motobene

    motobene Motoing for 46 years

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    This thread has been renamed to reflect the evolving subject of this thread. As usual, the more updated/evolved info is later on in the thread.

    At first I was only interested in the minor differences between the 250/300 and 125 clutches, but then I realized I could capture a good portion of the info on this new and VERY good clutch from early 2017 production then into later 2017 production. The 2018 production bikes will have the factory's small tweaks from 2017 plus one or more other small changes.

    The vast majority of you will like your clutches as they come. A few might want to tweak them because like me you are technogeeks. This info is for you, or the just plain curious.


    This thread is a continuation of a previous thread:

    http://advrider.com/index.php?threads/the-2017-sherco-scorpa-clutch-a-big-change.1176484/

    The 2017 Sherco-Scorpa clutch is fantastic! It's Sherco's version of the diaphragm-spring-type clutches the majority number of manufacturers now have: GasGas, Ossa, JTG, TRS, Vertigo, and now Sherco-Scorpa.

    If you adore your clutch just ride your bike and enjoy it. If you have any desire to tweak your clutch behavior, and you are technically competent to do so, here is some helpful info.

    The only repeat complaint I've heard about the new clutch regards lever pull force. Some think it a bit high. For example, me. I adore the clutches on both my 2017 Sherco Factory 125 and 250. The 125 I like a little better, however, because the lever pull is easier, as in very similar to the clutch in the Stu Preston-modified 2014 GasGas Replica 300 I had.

    I wanted the same feel for my Factory 250, and achieved it. If you wish to do the same for your Sherco-Scorpa, 2017 and later, there are two parts you can buy from RYP or your local Sherco-Scorpa dealer. These are discounted heavily by RYP to not dissuade riders from achieving their clutch behavior preferences.

    Precharge or Preload Ring
    A Sherco exclusive. This part sits between the spring and pressure plate, and comes in two versions:

    6351 (1.2mm thick - more preload)
    6680 (1.0mm thick - less preload)

    For you non-metric folk that's a thickness difference of only 0.008" FYI, my Factory 125 and 250 both have the 1.0, thinner 6680 ring. Measure yours to see which one you have before ordering a stiffer or softer option.

    Spring Retainer Plates
    There are potentially four versions under two part numbers.

    Part Number 6899, More Preload:
    - earliest production version, no additional material removed from the step cut

    - current production version, less preload than early production

    Part Number 6343, Less Preload:
    - earliest production version

    - current production version, less preload than early production

    For practical purposes ignore early or late production and order by part numbers.

    My two bikes came with the current production 6899 on the 250 and the current production 6343 on the 125.

    Here's how I measured mine:



    Considering the two spring retainer plate and two preload ring options, you have a bandwidth of 0.46mm (.018") of preload to play with to tweak the clutch.

    Compared to whatever configuration you have:
    Less preload will lower lever force noticeably and reduce engagement speed slightly. More preload will increase lever force noticeably and quicken engagement slightly.

    More photos, vids, and background discussion:




    The 250's clutch being actuated by the clutch lever. The video starts with the lever pulled in, then out, in, out:



    Because of the lever plates, diaphragm clutch pressure plates move very little, much less than conventional clutches, but the much smaller slave cylinders make the lever plate tips move a lot. Put an older, larger slave cylinder on the new clutch and it will hardly disengage.

    The single diaphragm (Belleville) spring requires very little preload to achieve a high clamping force. The force ramps up quickly. The system is very spring-preload sensitive, with very small changes in preload have a big effects.

    In my hand is a spring retainer plate turned edge-on so you can see the step cut and the back side:



    The glint on the step cut is from the oxide being removed by the secondary operation by Sherco to take more material off to reduce preload overt he original design.

    Given the reduced preload on the 250, I have had zero issues with clutch slip in any gear and under heavy loads with the softest configuration. The softest configuration is probably fine for most 300 riders too. Always keep in mind bike individuality.
    In the bell curve of manufacturing variability your individual bike could have softer or stiffer lever pull depending on how all the normal parts tolerance variances sum up.

    Take care with the ten T20 Torx-socket stainless M4 flat-head cap screws. Progressively tighten them until true full bottoming, which can be hard to feel due to the spring being preloaded. Never impact them tight (OK to impact when loosening). Don't over tighten them by hand or they will get stuck.

    The new clutch has oil volume spec of 700cc, more than before. If you run the old go-to spec of 450cc, the clutch can shudder while gently slipping it at low RPM. Use only a light purpose formulated gear lube like Maxima MTL 75. Thicker oils or oils lacking clutch additives can make diaphragm clutches drag.
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  2. Bronco638

    Bronco638 Nobody Home

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    Chris, could you remind us as to when Sherco went to this clutch design? I'm pretty sure my '14 ST 3.0 doesn't have this clutch design, right? Thanks.
    #2
  3. motobene

    motobene Motoing for 46 years

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    2017, and there are two versions, early and later production. The only change was cutting the deeper steps later.

    Also the Factory models came with the older-style AJP master cylinder. Don't know why as the pistons are the same as what's in the BrakTec master cylinder.
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  4. motobene

    motobene Motoing for 46 years

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    The helical coils springs Sherco clutch was very good.

    I rode an X-RIDE and a recent 2006 trials version with excellent clutches, meaning light lever pull and no lurching, quick engagement.

    My 2016 clutch and many later Sherco clutches are too fast engaging (for the majority of riders). These can be slowed down with the 4-springs clutch mod, or shimming under the springs washers to reduce springs preload, and use of slightly thicker Maxima MTL 80 can help too.

    My only complaint regarding my 2017 250 clutch has been slightly high lever pull than I prefer, but that is now solved.
    #4
  5. motobene

    motobene Motoing for 46 years

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    I revised the first post above extensively based on new info. Please re read it if you read the original.
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  6. heffergm

    heffergm Long timer

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    Dear Sherco,
    Welcome to a modern trials bike clutch design. We expect an engine re-design to follow so you don't have to do this funky retro-fit setup in the future ;)

    Signed,
    Your buds: TRS, Vertigo, GasGas
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  7. motobene

    motobene Motoing for 46 years

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    Sorry heff, I don't get the drive-by dig.

    GasGas led. All but two have come around 8+ years later.

    And what's funky about a diaphragm clutch in the 2012+ cases? For funky try the gaggle of fiber and metal plates thicknesses on the GasGas clutch.

    On the Sherco, having no slave cylinder in the way of direct access to the clutch, and being the only diaphragm clutch you can directly view working is a first.
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  8. motobene

    motobene Motoing for 46 years

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    A detail. The packs of shims shown in the data photo above and mentioned in my mega RYP Techpub (earlier version) I used to investigate preload differences. Fitting shims takes a lot of skill and is not something recommended. Too easy to drop a hardened shim down in the cases. Don't do it! :amazon The two versions of Sherco parts I listed are cheap and the best way to tweak clutch behavior.
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  9. motobene

    motobene Motoing for 46 years

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    OK, so here's what I know so far, and this may change as I learn more.

    Sherco has, like GasGas did in 2005, evolved away from the stiffer, faster-hitting clutch preferred by a minority of high-skill riders. When you buy a Sherco-Scorpa today, you will get a softer lever pull. So things are already very good, and only geeksters like me will care about the minor nuances.

    Part number error in the following for the stiffer spring retainer plate. I will correct and upgrade this graphic in a follow-on post.



    My Factory 125, inspection date March, and my Factory 250, inspection date April, both have 1.0mm 'precharge' rings. The 125 has the spring retainer ring with the least spring preload (which I prefer for my 250 as well), and the 250 has the spring retainer ring with the middle of three spring preload mounts.

    The majority of tweaking, then, is in a stiffer direction which only a very might wish to do. But a number of you, like me, might like the 125 spring retainer plate in your 250 and 300.
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  10. Norman Foley

    Norman Foley Devotee of the Husqvarna

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    With summer temps, my arthritic hand doesn't mind the lever pull at all on my '17 125. I thought it was pretty stiff when I got the bike, but that was in winter and we were riding in sub freezing weather. It will be interesting to see how it feels, as we get into colder weather again.....
    #10
  11. Harry Potter

    Harry Potter Been here awhile

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    So Sherco is advertising a much improved clutch for 2018, is this a working out of the bugs in the all new 2017 clutch or yearly advertising hype?
    #11
  12. lineaway

    lineaway Long timer

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    Both.
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  13. Buschog

    Buschog Been here awhile

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    <Forest Gump voice>

    And that's all I have to say about thaaat.

    </Forest Gump voice>
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  14. lineaway

    lineaway Long timer

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    Usually when a transmission is overfilled it has an effect on how a wet clutch works. Was there any changes on clutch feel going from 450cc to 700cc?
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  15. motobene

    motobene Motoing for 46 years

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    'Much improved' for 2018 is marketing bullshit. 'Improved' apparently doesn't inspire enough.

    It's already improved in 2017 with small changes like backing off on spring preload.

    I'm really enjoying the 125 spring retainer plate on the 250.

    Lineaway, your last comment is not appreciated.
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  16. Gordy

    Gordy SUPPORTER

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    One of the main reasons that I instantly liked my 2017 300 was the clutch. It just simply works for me exactly like I want it to. I "think" it has the original harder pull but not sure and I haven't had the desire to tear it apart to measure since I like it as is.
    Still running 450 cc of oil but will up that this week with a change and see what (if anything) that does.

    Good onya Chris for experimenting and detailing how the various mods are all working for those that desire or could use lighter lever pull. :thumb
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  17. motobene

    motobene Motoing for 46 years

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    Thanks, Gordy!

    Your bike is early production with more preload. This is assumed of course because what factories put into bikes can itself vary. Got a few parts being checked out and a need to ship a few bikes? They know the part will do no harm, so in it may go.

    But your clutch being sweet may just be from bike individuality. Your whole bike including tge clutch is sweet! (I rode and tweaked on this bike). I wouldn't change a thing about the clutch!

    Diaphragm clutches are very sensitive to spring preload. The amount of preload is determined by the fine specifics of the manufacturing of many clutch components like clutch hub, basket, all the plates, and even the spring itself. A felt difference in lever pull can be noticed with dinky changes in preload - we're talking two or three human hair diameters!

    Preload amount of an individual bike will fall somewhere on a bell curve. Some clutches with the same parts by part number will be stiffer than others.

    Clutch tweaking, should anyone have both the sensitivity to and need for, is best looked at as a from-to endeavor, just like jetting. Going only by formulas or one specific spec for all bikes may be psychlogically comforting, but it misses details that can matter in some cases, a lot.

    You know your bike so you know the from. Good and adequate tech info helps with the decisions on where to go to, should you feel the urge to tweak.
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  18. motobene

    motobene Motoing for 46 years

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    I had RYP check my table. They loved it but found one part number error. SO use the table here instead of the one above. It's better anyway in flow and educational content. Shown is an Excel document saved as jpegs in two parts:





    What other minor changes there will be for early production 2018? Grain of salt regarding marketing statements like 'much improved clutch.' More like slightly improved....

    The clutch started out as an excellent unit and all they've done is play a bit with settings and minor parts. Sherco could surprise me with several tweaks in 2018, but I doubt it. Ryan reported the factory guys were messing with the throw-out bearing part. I'll find out with RYP when the `18s come in what exactly is different.

    I talked with Cabestany who said his `17s clutch engagement was less fast than his `16's with very heavy springs. Those top guys like their stiff-fast clutches, which may explain why Sherco started (mistakenly) out in 2017 with a clutch more aimed at the Pro riders instead of the vast majority. GasGas made that same error in 2002 to around 2004, then fit a lighter spring. A few of you may be gluttons for a stiff clutch lever to be a Pro. The table will show you how to get there. Most of us want a less stiff lever. Sherco obliged, and you can go further with the 125 spring retainer plate as I have. Thankfully the clutch stiff has very high thrust capacity and hit speed, without lurching, no matter how much preload you choose to have. Engagement sweetness is why diaphragm-spring clutches can be superior with respect to at least some of the long running six helical coil springs clutches.

    They are rumored to use the AJP master cylinder (versus Braktec) that showed up on later production on the Factory models. It may be a cost issue as the older design is probably less expensive. Otherwise both are based on interchangeable 9.5mm pistons and seals. I have AJPs on my two Factory bikes. I'd not care a bit if they were Braktecs.

    With the Braktecs you have lots of lever options to change the pivot-to-push-pin distance. This will affect lever pull. This thread concentrates on the clutch itself.
    #18
  19. laser17

    laser17 Long timer

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    MB - GG went to a light Belville washer style clutch spring in 2006.

    Thanks for the Sherco info! :clap
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  20. lineaway

    lineaway Long timer

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    An American had the first light spring..
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