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Thread: swap front ends from GS550T to GS650L - any concerns?

  1. #1
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    Default swap front ends from GS550T to GS650L - any concerns?

    I currently have two GS projects, an '81 GS550T and an '83 GS650L, which I have not yet heard run, it's still early in the project.

    I'm thinking about swapping the front wheel, forks, triple trees, and headlight brackets. If all goes well with the 650 I intend to keep that one and sell the 550. The forks from the 550 are in better shape and I like the traditional forks rather than offset "L" forks.

    I assume the steering column dimensions and bearings are all the same.

    Are there any gotchas to this swap, other than ending up with two bastardized bikes?
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

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    The yokes (triple trees) on the L forks have less of a front/back offset than the standard ones.
    This brings the yokes back into collision with the front of the fuel tank, which is why L tanks are set back a bit or have a recess at the front.

    However, none of that matters if you measure the distance from the bottom of the bottom yoke to the wheel spindle (and assuming the wheels are the same size, and the rake is the same on both frames) and if it's the same bike-to-bike, then proceed to swap the entire yokes + legs over.
    That's assuming the yoke bearing sizes are the same - x-check the bearing part numbers. Even if they're different it's easy enough to get around that.
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  3. #3
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    Quote Originally Posted by Grimly View Post
    The yokes (triple trees) on the L forks have less of a front/back offset than the standard ones.
    This brings the yokes back into collision with the front of the fuel tank, which is why L tanks are set back a bit or have a recess at the front.

    However, none of that matters if you measure the distance from the bottom of the bottom yoke to the wheel spindle (and assuming the wheels are the same size, and the rake is the same on both frames) and if it's the same bike-to-bike, then proceed to swap the entire yokes + legs over.
    That's assuming the yoke bearing sizes are the same - x-check the bearing part numbers. Even if they're different it's easy enough to get around that.
    Thanks. I hadn't considered clearance between the T tank and L forks, but will check that. Should be fine the other way around, T forks on L tank.
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

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    The 550 tank might be back far enough to stay away from the 650L forks, but since you are not keeping the bike, it will be low on your priority list.

    Is there anything wrong with the 650 forks? Functionally, the two are the same. Rake, trail, wheelbase are all virtually the same, so handling won't change. Either way, be sure to change the seals and oil. While you are in there, it would also make sense to change the springs. Sonic springs are highly-recommended here.
    Last edited by phydeauxmutt; 12-06-2021 at 08:01 AM.

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    Quote Originally Posted by phydeauxmutt View Post
    The 550 tank might be back far enough to stay away from the 650L forks, but since you are not keeping the bike, it will be low on your priority list.

    Is there anything wrong with the 650 forks? Functionally, the two are the same. Rake, trail, wheelbase are all virtually the same, so handling won't change. Either way, be sure to change the seals and oil. While you are in there, it would also make sense to change the springs. Sonic springs are highly-recommended here.
    It's mainly three things, two of which are cosmetic:
    1. The 650 forks have some rust spots that may have damaged the sliders in areas that will go past the seals. I haven't spent enough time with them yet to know if it is fixable.
    2. I've already polished the forks lowers on the 550T, so they look nicer.
    3. I prefer the look of straight forks rather than offset,
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

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    Quote Originally Posted by phydeauxmutt View Post
    The 550 tank might be back far enough to stay away from the 650L forks, but since you are not keeping the bike, it will be low on your priority list.
    yep, sure enough the mounting rubbers for the 650L tank are >1" further back in the frame than those for the 550T tank. That section of the frame is the same for both bikes and you can see where they have two sets of positioning holes for the various tank/fork options.

    The forks probably would bang and dent the tank. It's relatively undented, so I'll come up with a different solution.

    The left fork slider on the 650L does have pitting in the areas that will contact the seal, so I'll look for new forks tubes.
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

  7. #7
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    Drill & tap the stops on the triple tree & screw a bolt in there to make them bigger. Add washers until it no longer hits tank... Obviously you lose some steering lock doing this.

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    Quote Originally Posted by salty_monk View Post
    Drill & tap the stops on the triple tree & screw a bolt in there to make them bigger. Add washers until it no longer hits tank... Obviously you lose some steering lock doing this.
    Thanks. I'll add that technique to the list of options.
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

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