Added Flywheel Weight - Modern 250s

Discussion in 'Trials' started by motobene, Mar 27, 2018.

  1. motobene

    motobene Motoing for 46 years

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    I've really enjoyed the total inertia of my Sherco 250s without added flywheel weights. On the 300s no question. I add weight, but on the 250s I have been skeptical the last two years.

    As part of thinking about nationals prep I thought why not get the S3 weight for the Sherco? It's easy enough to take off for an altitude event and put on for low altitude or slick conditions, increasing flexibility for varying conditions.

    Test results were a little unexpected (read on...)

    I fit S3 FW-SH-12 "Flywheel Weight inertie Sherco 2012" to my Hidria flywheel. Here are the two parts being clear spray lacquered:

    IMG_20180327_083208.jpg

    I found the two black oxide coated steel M6 dodads for the two M6 flat head cap screws were not a press fit into the flywheel holes, so I bonded them in with aluminum epoxy. That way they will not back into the stator when I remove the weight without removing the flywheel. Lots of delicate stuff here:

    IMG_20180327_083020.jpg

    Here are the dodads in place on the inside:

    IMG_20180327_083323.jpg

    Riding the bike, I expected the throttle response to be noticeably delayed coming on and going off. Oddly, that was barely noticeable and I reprogrammed to the slight change in timing inside if a minute.

    The 250 Sherco is perky without added flywheel weight, and with added flywheel weight is still perky.

    Adding to total inertia has been a positive change, as in the bike is a little more controlled in the rough. A gnarly rocky uphill line by the house requires lifting and placing the front wheel in a series of floater turns. I had more difficulty cleaning it before the change.

    Another positive has been that dumping power into the clutch does not require as much precision, increasing confidence.

    So there it is. I was wrong in my assumptions. ...Regarding added flywheel weight and 250s, at least the Sherco-Scorpa 250s.

    You can have too much total inertia (think stock TY350), but that is definitely not the case with the S3 weight on Sherco-Scorpa.

    Not sure yet about keeping the weight on above 5,000 feet, but otherwise, yes, it's definitely a keeper.

    What are your experiences adding weight -or not - to your 250s?
    #1
  2. PMK

    PMK Been here awhile

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    My riding buddy installed a Jitsie version onto his 17 250 factory. Unfortunately he got sick and has not yet ridden it yet. Actually, we opted out of heading to Tenn last weekend as he was feeling that crappy. Pretty certain the flywheel weight will be good for him.
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  3. dmay

    dmay Been here awhile

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    Being the lamest rider in our Southern Indiana Trials Team that bought 2016 and up Sherco 250s I was a early adopter of the weight,Where it helped me was when doing roll ups I could get off the throttle a smidge earlier and keep the front end under control. If I was a bit tired sometimes I would get behind the bike and feel like I was hanging on rather than being in control. Other benefits seems to be a velvet smooth bottom end and less fatigue throughout the day. SoupBill and our dealer in Indy rode mine and added flywheels to their 250s also. I had a 2011 250 prior to my 2016 and never felt the need for a weight,even after adding a 2014 exhaust to it. Possibly due to still having a Dellorto carb?

    edit-my inserts fit my flywheel tight enough to have to be pressed in,but I would put the bolts back in with washers if I wanted to remove the weight, however,I have never wished for a quicker response after installing.
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  4. PMK

    PMK Been here awhile

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    Curious about these added weights. With the two holes plugged with bolts securing the weight, are you using an impact gun to tighten the flywheel not and skipping the torque wrench?
    #4
  5. motobene

    motobene Motoing for 46 years

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    Yes. I've not used a flywheel holder and the holder hole(s) since my 1974 Penton. I don't think the holes on the moderns are for that anyway. They are for flywheel weight dodads.

    I punch the crank end and nut to record the factory nut torque setting (which is overkill). I remove the nut with an impact wrench. I also use impact on flywheel puller inside screw to break loose the flywheel. The factory assembles dry, so impact helps pop the flywheel loose on the shaft taper.

    On reassembly, I grease the shaft and threads. No Locktite. I use an impact driver and stop nut rotation roughly 20 to 30 degrees shy of the factory torque setting, depending on resistance to impacts with the wrench at a low setting.
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  6. motobene

    motobene Motoing for 46 years

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    Good feedback dmay, thanks!
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  7. irishgb

    irishgb Adventurer

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    How much extra weight are you adding ??
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  8. Sting32

    Sting32 Trials Evangelist

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    How much weight are/did you add? we want to know....:lurk
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  9. PMK

    PMK Been here awhile

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    I know my friend did not weigh the disc. It is a Jitsie part with the spacer to move the side cover outboard. If they list the weight, I will post it.
    #9
  10. alpineboard

    alpineboard Been here awhile

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    you can estimate the weight by finding the volume, steel is approx. 180 pounds per cubic foot. or 1728 cu inch. If yall forget to weigh it.
    #10
  11. lineaway

    lineaway Long timer

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    It is very little in effect because of how the weight is dispersed. If it was just an outside ring, it would really make a difference. But weight is weight.
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  12. 2whlrcr

    2whlrcr gooligan

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    I'm putting on weight, does that count?
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  13. motobene

    motobene Motoing for 46 years

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    On the weight was inked something like 0,62kg, but that isn't the correct way to look at inertia. It's really about how far the distribution of weight is slinging around the rotational axis. A small weight zipping around way out there has more inertia than a block of lead extruded longways near the rotational axis. The unit is weird, like inches to the 4th power.

    Just go with what you get from Jitse or S3.
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  14. irishgb

    irishgb Adventurer

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    Thanks for the weight I understand the inertia , was just wanting to compare it to the clutch side weight on the Beta which is 0.72Kg
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  15. Sting32

    Sting32 Trials Evangelist

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    I just wanted to know weight because the Vertigo has 2 different weights you can add, and someone says so and so uses the light one, and soneone else used the heavier one, I got to ride heavier one a few times now. I wish we had one for the TRS, but I will just have to weight for one I guess, lol.
    #15
  16. utopia

    utopia Adventurer

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    Steel weighs 490 lbs/cubic ft
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  17. alpineboard

    alpineboard Been here awhile

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    oops, sorry, was thinking granite. yes 490
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  18. MATTY

    MATTY BORDER RAIDER

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    A casual observation on the weights quoted here 0.62 kilograms on the end is a lot more than I used on my homemade weight on a 200cc Minsk RTX, my flywheel weight band came in at 2490 grains which is under 6 ounces.
    The difference that made to bottom end running and response was significant.
    I arrived at the final weight by trial and error the bands started life approximately 3580 grains and I kept turning them 2 millimetre at a time which by my rough calculations equated two about three quarters of an ounce Steel waiting 7.8grams per cc.
    The Minsk run better at the 2500 grain area I felt performance with heavier weights the throttle response was impaired and once it got below 2500 again response was not noticeably better but the lo but the low speed shuddering was evident. The first band which weighed in at 1910 grains that's after grinding off loss so I estimate it to have been around 2000 grains sweated on the flywheel, was not as responsive it shuddered more low down and throttle response was no better off my test bank bottom than the 2500 grain band and as such that was the one I went with.
    All pretty farmyard engineering I agree but I did not know any other way I could do it and I know for sure it has significantly improved this particular engine.
    #18
  19. lineaway

    lineaway Long timer

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    You made a band around the flywheel?
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  20. motobene

    motobene Motoing for 46 years

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    If there are two weights available and you have a 300, I'd go for the most-added-inertia option if your 300 is a fire breather when stock.

    We had this issue on GasGas 125 to 225 conversions. The heaviest available weight out of UK only made those conversions sweet. With the other option available in US for example, made these bikes still spool up too quickly.

    The 250s have the same crank and flywheel as 300s, but given the smaller displacement don't need the maximum added inertia, just some more added.
    #20
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