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Pinned FZR R6R rear shock conversion

Discussion in 'Yamaha 250cc In-Line 4's' started by ruckusman, Jul 3, 2016.

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  1. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Check with Craig on what he got. Not sure exactly what it was.


    Sent from my iPhone using Tapatalk Pro
     
    Andych, Apr 12, 2018
    #81
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I was the Service Manua Supplement for the 3LN3 FZR250R
    I'm part way through translating it
    '
    20180323_201458.jpg
     
    my67xr, Apr 12, 2018
    #82
  3. Joker

    Joker See "about me" for contact details. Contributing Member

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    I just asked on facebook (track junkies) and picked a good one up for $160 posted as the guy had a spare. Wreckers were quoting me $350-400 which frankly is a joke to me. I've bought whole bikes for that.

    And... as I'm going to JP if you want manuals sent somewhere and can wait a few weeks...
     
    Joker, Apr 12, 2018
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  4. Dropdead53

    Dropdead53 Active Member

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    Hey guys, I recently bought a 2008 R6 rear shock off gumtree, only 8000kms old (apparently) for $200 delivered. I’m fitting it to my 3LN3, thought I would post some pictures of the shock and the mods to the brackets etc in the interest of sharing knowledge. I haven’t quite finished the conversion yet but will post anymore relevant info or pictures as I go. I still need to make spacers for the top mount and also will need to modify the chain guard slightly.
    -the new shock
    7E465CB6-DCEC-4BEB-AD89-062D30D61424.jpeg
    -the new and old shock
    D668E983-5DC8-412A-9EAD-143FEB70DF8E.jpeg
    -rough fit up and marking of the bracket for mods.
    432590E3-EF83-4489-A2DC-8F3236440A9D.jpeg

    -this is what the battery tray support bracket looks like after being modified to suit the shock.still feels pretty solid considering the amount of metal I cut off it.
    FBABC631-C94F-4D23-B404-CF5256AE7F22.jpeg 6777D206-6A82-4BA5-9771-14AA162705FD.jpeg
     
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    Dropdead53, Nov 2, 2018
    #84
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    ruckusman, Nov 2, 2018
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  6. Dropdead53

    Dropdead53 Active Member

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    Lol yeah I have read it, my dog bones are stamped “2KT” and are roughly 140mm hole centres. So after I’ve finished the conversion in theory the bike should sit approx 20mm lower with the standard dog bones fitted?
     
    Dropdead53, Nov 2, 2018
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  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Check with @my67xr on what his were to start with - I shortened mine over the 140mm -> 132mm formula, going to 128mm for memory, which raised the back and neutralised the steering, prior to that at slow speed it would want to spiral down into a corner which took reverse pressure on the bars to prevent - lane splits in traffic a treat

    I measured the trail recently and with no load it is now 23.7 degrees for memory, which is fine as I'm converting to ZXR25 front end which has less offset in the triples putting it back to just over 24 degrees IIRC - I have notes and calculations somewhere
     
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    ruckusman, Nov 2, 2018
    #87
  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    One other option would be to measure the ride height with the OEM shock, remove and then prop the back with a piece of timber or something at that precise height and measure the length the dogbones should be, I chose to sharpen the steering instead
     
    ruckusman, Nov 2, 2018
    #88
  9. Dropdead53

    Dropdead53 Active Member

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    Are there many down sides to the bike being lower in the rear?
    Obviously it affects steering geometry but can this be countered by lowering the front abit? What is the ideal spec/degrees for the trail angle for a road bike?

    Also by turning the big nut on top of the spring (with a c spanner that I don’t have) does that change the ride height or just the stiffness on the spring??
     
    Dropdead53, Nov 3, 2018
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  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Nov 3, 2018
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  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I used the standard dogbones on my 3LN3, i raised the forks so they stuck out 13mm in the tripples (since found out this is the standard height for the 3LN3)
    I'm very happy with the R6 shock conversion.
    I cant really tell the rear is a touch lower.
     
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    my67xr, Nov 3, 2018
    #91
  12. amdeleon11

    amdeleon11 Active Member

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    just wondering if anyone knows the dimensions of the 2kr rear shock mounting holes? thanks.
     
    amdeleon11, Mar 24, 2021
    #92
  13. Mike Green

    Mike Green Well-Known Member Premium Member

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    Thought anyone looking at this topic might be interested in replies to my post on FB, see image below.
    upload_2024-1-2_8-33-45.png
     
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    Mike Green, Jan 2, 2024
    #93
  14. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    WOW you found the right tree to shake.
    Well done!
     
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    ruckusman, Jan 2, 2024
    #94
  15. Mike Green

    Mike Green Well-Known Member Premium Member

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    I've been checking weights, spring rates, and linkage ratio. I'm not sure what it all means yet but it is quite interesting how the linkage ratio ramps up quickly from fully extended over the first 5mm of wheel travel and then increases a small amount over the rest of the travel, see the attached image. The final ratio measured at 90mm of wheel travel was 2.46:1. The first column, turns, is the turns of a nut on a piece of 8X1.25 threaded rod used to lift the wheel. I also made a tool to bolt in to replace the shock which I attached my digital calipers to which measured the amount the shock would be compressed as the wheel was lifted. The results tie up with what I feel. The initial travel is very soft but firms up quickly. In my opinion the R6 spring is way too hard. The stock FZR spring may also be too hard. I think a spring rate needs to be chosen for the middle area of the stroke where the ratio is approx. 2.60:1. I'm sure there's more to it, but with my son on the MB100 powered bike the weight on the rear wheel is 80kg. 80X2.6=208kg on the shock spring. With an 8kg/mm spring it would compress only 26mm. With a 7kg/mm spring it would compress 29.7mm. With a 6kg/mm spring it would compress 34.66mm, and with a 5kg/mm spring it will compress 41.6mm which is getting close to mid travel. If installed with say 5mm of preload the 5kg/mm spring would be compressed as if by 25kg and the travel would be decreased by a similar amount for any particular load, theoretically. I have 5kg/mm and 7kg/mm springs which could be used. They both need to be shortened and adaptors made so I'll give them a try. Probably the 7kg spring first.
    upload_2024-1-9_21-44-52.png
     
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    Mike Green, Jan 9, 2024
    #95
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I have the Ohlins shock for the fake CBR250RR, you know the single cylinder pile of ****. Dimensionally it is identical to the Fizzer shock. I don't have the bike yet so it lives in the hope chest.
     
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    maelstrom, Jan 9, 2024
    #96
  17. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Have you got a link for the Ohlins unit for the fake 250RR? I think my 3LN6 would like one, one day :)
     
    Linkin, Jan 9, 2024
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  18. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    upload_2024-1-10_7-34-14.jpeg
     
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    maelstrom, Jan 10, 2024
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  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I cannot recall the precise recommendation(s) of front/rear sag as per Dave Moss for street/track, I think it is front: 35mm street/30mm track, rear : 30mm street/25mm track OR thereabouts.

    Interesting and very worthwhile method to make sense of it all, seeing it visually like that in a chart - the travel at the wheel correlating with the travel at the shock and the linkage ratio all factored it - I like it!

    Out of interest - the MB100 powered bike is obviously very light.

    How did you get to the 80KG weight over the rear wheel?
    By weighing the bike front/rear weight distribution at the wheel then adding 50% of your son's weight?

    The 7KG/mm spring with some preload does look to be ballpark for static sag with rider aboard.
     
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    ruckusman, Jan 10, 2024
    #99
  20. Mike Green

    Mike Green Well-Known Member Premium Member

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    My son sat on the bike with the back wheel on a block of wood. We rolled it off the wood onto scales. He was in the normal riding position and I supported the bike tryng not to add or subtract from the measured weight. Yeah, 25mm(25%) rear sag with the rider, or less with a really light bike. I have retrieved a spring from the bin and am in the process of making a jig so I can shorten it for practice before getting into a good spring. I'm going to try for close to 0 preload on the minimum preload setting. The standard R6 spring has about 10mm preload on minimum
     
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    • Nice Work Nice Work x 1
    Mike Green, Jan 10, 2024
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