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  1. #1
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    Default Aligning drive train.

    What's the best way to align the drive train? I searched the TECH archives, all I could find on the subject was this thread.
    http://www.chopcult.com/forum/showthread.php?t=47373 which didn't clarify anything for me.

    A little background: I had to repair the 4 speed in my 85 Softail, while I had everything torn apart I decided I would upgrade the brakes. I scored a 4 piston caliper off a 2000 FXR (I believe) which I had to modify the swingarm a little to use.(had to add a lug to anchor the caliper)

    Now I'm wondering how to best align everything. The method (if you can call it that) I was contemplating is to align the rear sprocket to the trans. sprocket, then to loosen the motor mount bolts and temporarily install the inner primary to align the motor to the trans. then snug what bolts I can access with the i.p. case installed then remove the i.p. case and finish snugging and torqueing
    all the motor mount bolts.

    That's the best way I can think of.
    Now what I am wondering is.... Is this the way to do it or am I completely off base.

    Thanks,
    Mark

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    The motor plate or inner primary will pretty much align the engine and tranny... Once they are torqued down you can remove the motor plate/primary and then you can use a string across the face of the trans sprocket and wheel sprocket with the chain removed to align the rear tire. I would only bother with this when initially setting up the bike with spacers, etc.

    You can also just eyeball the way the chain runs in the rear sprocket and adjust it until it runs centered in the rollers. Thats the easiest way

  3. #3

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    On a big twin, you start with the motor ALWAYS. Two of the holes in the motor case and the two corresponding holes in the frame are a close fit on the bolts and serve to position the motor in the frame. Everything else builds from that.

    So, install the motor, shim as necessary so that it sits squarely on the motor mounts, and torque it down.

    Then install the transmission with mounting plate, and torque the mounting plate bolts to the frame. Leave the transmission nuts loose.

    Install the inner primary to the motor, making sure it is not in a bind in any way, and torque the inner primary to motor screws.

    Snug the inner primary to transmission bolts or nuts to position the transmission. Torque the transmission nuts, and the primary to transmission fasteners.

    Now you are ready to deal with the rear wheel. If it's a stock H-D, the original wheel, sprocket, and axle spacers will put the wheel in the proper position. On a swingarm big twin, the rear wheel is NOT on the bike centerline. The rear wheel is always offset to the left, and the amount of offset varies depending on the model. You can put the wheel on centerline if you desire, by selecting axle spacers to do so. Then it is a matter of shimming the wheel sprocket to correct the chain line. And of course you have to keep the wheel square in the chassis while doing this. Lots of moving parts, so give it some thought as you go, so you don't end up chasing your tail.

    Jim

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    Thank you so much for the quick replies. After posting the original post I went back out to the shop and started checking on things.
    I put a straight edge on the rear sprocket. (stock wheel and spacers) and discovered that the rear sprocket was 1/8th of an inch too far to the left.(trans was pulled as far to the left as I could get it to go and there was still a .125 gap) I measured the axle bosses on the old caliper and the new one and discovered the boss on the new caliper was 1/8th wider than the old one, so I pulled it off and threw it on the mill/drill machine I have and shaved off an 1/8th. so that helped a bit.
    Rockman96 that's what I was thinking (the inner primary thing) I just wasn't sure which end to start. Jim, thanks for clearing that up.

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    Just a side note if it comes up, when you want to line the wheels up,2 8' flourescent bulbs make good straight edges.

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  7. #7
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    Here's what I ended up with doing what Jim wrote.

  8. #8
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    Quote Originally Posted by Dragstews View Post


    thats cheatin

  9. #9

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    No matter what the Factory sends out, the rear TIRE must be centered inline with the Back bone which should always be dead center of the frame. I always Center and then Align the Rear tire with back bone first then deal with spacing of the Trans. and motor using the Sprockets or Pullys.
    The motor mount holes are usually right on But sometimes you might need to enlarge the holes so as to find that sweet spot of Dead On Center of the 3 main components, the Rear Tire, Trans and motor.
    -- the ideal position of the motor after final Torgue is if you can "jiggle" the 4 bolts if you loosen one at a time.
    I personally think it is Not good to have the bolts "up-tight" against the frame holes.
    The glass light tubes are ok But I prefer the 1" x 8' Aluminum square tubing ( at most hardware stores ).
    If the rear fender is Off - raise rear end. Secure one end of each square tube firmly --but NOT so tight so as to bend them even the slightest -- against each side of the rear tire. Light rope from tube to tube through the spokes is usually good. The other end will lay down on the handle bars, be sure Nothing is restricting/pushing them in or out.
    Then you can carefully measure the inside of each tube to, lets say, the center of the neck post nut or whatever is stable/permanent. Adjust axle adjusters accordingly to find Center and Alignment.
    Once you have established Dead-Center/Alignment of the rear Tire Permanently mark or file or whatever Each Rear axle adjuster bolt so that you will always know how many flats to move each during future chain/belt adjustments.
    Last edited by frisco1rigid; 09-10-2021 at 4:54 PM.

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    I don't think the wheel must be centered relative to the chassis. Mine wasn't, and after investigating this I learned that it is common and apparently deliberate.

    The wheels do need to be running in the same plane, however. Squared to one another, or handling problems (or at least increased tire wear) may result.

    Example: The rear wheel shouldn't be trying to pull the end of the bike around because it isn't properly aligned. A "Dog Track" sort of situation like this is bad.

    I asked about this once, and there was quite a discussion about it. The great crash of 21 ate that thread, but all HD wheels are not centered in the chassis.

  11. #11
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    if you want a bike to handle & be safe the wheels must be inline & centered in the frame, Period !
    I have been building bikes of all sorts, from stock restorations to race bikes, but mainly Chops & Harleys for the past 45 odd years.
    & in that time I & all I know when building a bike, or working on one, will set the wheel & tyre central to the backbone of the frame,
    the odd exception I came across were off set so the chain didn't hit the tyre on a fat wheeled cartoon bike & he couldn't be bothered to do it properly, when you saw him ride from behind, 2/3rds of his body was off centre to the left to counter ballance the bike !! looked stupid at the least, dangerous at worse.
    I was once told that some BMW boxers had off set rear wheels to allow for the torque twist effect of the motor when opened up, but a BMW mechanic I was talking to said it wasn't so and as far as he knew never was,
    so not sure on that one, never haven worked on a BMW.

  12. #12
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    Thank you guys for all the help. Went to the coast this last weekend so I missed the last few posts until today.
    The last snap here is how everything lined up just following the instructions JBinNC gave me in post#3 so I guess I lucked out as the rear wheel looks pretty damn close to being on the center line as is.
    If I'm missing something chime in and educate me. Otherwise I'm thinking I'm ready to install the primary drive. I'll probably start that tomorrow unless I someone points out something I missed.
    Thanks again guys

    Mark

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