How to hook up your motor and use fat rear tire [ Coaster brake Arm Mod ]

Discussion in 'Frame Mounted Engines' started by Blaze, Jan 18, 2007.

  1. Blaze

    Blaze Guest

    Hooking up your bike and you want to keep that fat tire on the back? There are a few things you have to do to get your chains to clear your back tire.

    Here is how you can hook your bike up to run with a fat tire on the back, and still keep the coaster brake. I had to sort this out because I couldn't fit a calliper brake over the fat tire and I really didn't want to spend all the money on a whole new set of chopper forks with disk brakes attached.

    You're going to need to put an extra rubber ring under the rear sprocket to push the chain out from the fat tire, and make sure the sprocket is flipped so that the teeth are offset away from the wheel.

    I don't have photos for how to hook up the motor end, but I might take some and post them later. Basically, you take the pinion off the motor, flip it around with a couple washers under it, and make sure to use red loctite when you put it back together or it will fall apart in no time. You also might have to put a washer or two under the pinion cover to keep the sprocket from rubbing on it when you put it back together. Make sure the top right washer doesn't rub the chain. Grind it down a bit if it does.

    Now you may need to clear the inside of the frame. Add an extra nut to the rear axle on the inside of the frame on the motor chain side to push the frame apart a little, and you should be ready to go.

    The chains will be pretty close to the tire on each side, so make sure you adjust the wheel position with the bike straight up and down, not leaning to the side on it's kickstand. If the wheel is rubbing on one of the chains, you can just point it left or right a little. It's not going to be noticeable if the tire isn't perfectly aligned and it dog-tracks just a little. If you want to get super cool, you could "dish" the rim by tightening the spokes on just one side or the other, which would offset the wheel to the side of the tightened spokes while keeping the wheel perfectly in line with the frame. I wouldn't bother with dishing it myself, but it is an option.

    If you're still having a hard time getting both chains to clear the wheel, add a washer or two to the crank on the inside of the pedal-drive sprocket. This will push the pedal-drive chain out just a bit and it will give you more room to adjust the tire away from the motor-drive chain if you need to.

    Here is the fabrication of the extended brake arm:
    Note that as this brake arm is currently designed, you will need to put a washer againt the outside of it. I will probably grind the opening to a round shape where a nut will fit into the brake arm opening and rest against the outer washer that was welded into it.

    I am a Dremel grinding FOOL!!!!
    Last edited by a moderator: Nov 23, 2007

  2. Blaze

    Blaze Guest

    Here it is installed. It's been working really well for quite a while now. I love knowing that the next time I have to replace brake parts, I won't have to get everything welded again.

  3. srdavo

    srdavo Active Member

    coaster brake arm mod

    good info.
  4. Sockmonkey

    Sockmonkey Guest

    Man, that's a lot simpler then the way I was thinking of going (machined part)!

    Thanks for the tip, I will have the welder make one up when he makes the motor mount.

    I keep thinking I need to learn how to weld!
  5. Gimmick

    Gimmick Guest

    re: the coaster brake arm. I just put mine in a vice and beat it with a brass hammer into a shape that cleared the bolts.
  6. azbill

    azbill Active Member

    this modification is meant to clear fat tires
    blaze's switchblade has 3" wide rear tires
    same as my old deviate
    takes a pretty big bend to clear that !
  7. Sockmonkey

    Sockmonkey Guest

    I understand the concept of "Pounding the brake arm into submission":lol:, but fear that the bend/grinding needed, in the specific case of the bike I am doing, might weaken the arm to where it could fail.

    Also, being a bit lazy I would rather have the arm mod welded up then spend a couple of hours grinding away at the arm and sprocket.
  8. LiamSckhot

    LiamSckhot Guest

    Like your axle adjuster tensioner for the drop-outs .Would like to know of a source for the little gem's .I have been bending my arms not so easy.Nice job.
  9. gone_fishin

    gone_fishin Guest

    exactly...davo bumped this up because it's another good option and someone was wondering, but the "basics" of using a coaster brake are well-covered:
  10. davidsis

    davidsis Guest

    Something left out

    You forgot a photo of the big old fat tire. Lets see how fat and juicy we can get the tires.
  11. smitty

    smitty Guest

    Brake arm modification

    I was waiting until I needed to remove my rear wheel so I could photograph my brake arm modification.(I did my install before I knew about this GREAT forum or I would have taken progress pics.) Any way today I pulled my rear wheel to adjust the bearings, and while I was at it, I took photos.

    To make a long story short, I'll say that is is nice having a metal cutting band saw and a MIG welder.

    All I did was cut the brake arm off so that the axle end fit inside the (opened) hole in the motor sprocket, over lapped it and welded it back together.Oh yeah I also counter sunk the bolt holes in the sprocket.

    Ratz! Well I tried several times to post photos but it wouldn't work.
  12. danhill

    danhill New Member

    I love this site, no matter what problem I run into there seems to be a perfect fix already posted :D
  13. f4lloutdiablo

    f4lloutdiablo New Member

    I also went with this method... it was very easy and worked well