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Wordman's Build (with questions, answers, and suggestions)

Discussion in 'The Garage' started by Wordman, Jul 21, 2019.

  1. Wordman

    Wordman XS650 Addict

    Correct, the stock Triumph crank is a 360°. The Triumph doesn't have the central bearing though, so it also has a crank "whip" factor (the crank flexes in the middle like a jumprope. Going with a 76° crank, while a lot more expensive for a Triumph, does even more to quell the vibration.
  2. Raymond

    Raymond XS650 rider & fettler XS650.com Supporter Top Contributor

    Interesting - I've never seen a 76° crank for a Triumph. That flexing of the crank was always seen as putting a limit on the revs. Does the offset crank allow a higher rev limit?
    Jim likes this.
  3. Wordman

    Wordman XS650 Addict

    Triumph always had a pretty high rev limit, they just felt like they might come apart (and sometimes did) when you approached it. In racing, the offset "billet" crank would allow you to stay at the limit longer and with fewer chances of turning the thing into a grenade, I would think. As I am going with a stroker crank and a much larger bore (840cc), I plan on staying with 9:1 (at most) compression and fairly "soft" cams so I won't have to rev the snot out of it to hit the highway now and again. The whole exercise is to build a strong and reliable Triumph.
  4. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    I see that the 76° crank doesn't have that insidious "sludge trap".
    Good filtration recommended...
    Wordman and gggGary like this.
  5. Wordman

    Wordman XS650 Addict

    I've been running an external filter for years. The sludge trap was a good idea in the 30s and 40s, but with the advent of detergent oils, a good filter is a far better solution.
    TwoManyXS1Bs, Jim and Raymond like this.
  6. Wordman

    Wordman XS650 Addict

    I'll be running a belt drive primary on the Triumph. I like the MAP belt drive, but the Bob Newby is my favorite. 008273_-_bob_newby_racing_-_belt_drive_and_clutch_for_triumph_unit_750_c.c._t140_tr7-1_720x.jpg

    The only issue is, the Newby doesn't have a cush-drive (the cush is in the clutch assembly on a Triumph).

    Well, XS650 tech to the rescue! Just received a nice TX500 rear hub and brake plate. The TX wheel is drilled exactly the same as the XS, so I can use the XS flanged aluminum wheel.

    s-l1600 - 2020-10-28T142823.273.jpg

    And since I already run an XS650 front wheel... Yes!
    Raymond and Jim like this.
  7. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi Ray,
    76º is the nearest the XS650 crankshaft splines will get you to the 90º offset that works best.
    The offset reduces vibration which makes for a nicer ride.
  8. Wordman

    Wordman XS650 Addict

    Actually, the XS is usually done a 277° (83°) offset because of the splines.

    76° is what Phil Irving suggested for parallel twins (though this is based on rod length as well, and so is not definite).
    Jim likes this.

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