Mount engine behind rear tire

Discussion in 'Performance Mods' started by Pyrotechnic, Oct 27, 2009.

  1. Pyrotechnic

    Pyrotechnic New Member

    I have an old 24" aluminum frame mountain bike I want to motorize. The engine I have is a Tecumseh 2.5HP 127CC motor. Don't know the weight but it's aluminum and not very heavy.

    I was considering putting the motor all the way in the rear behind the tire. The reason is, I feel that whatever mounting apparatus I used would be lighter and more rigid than having it over the top of the rear tire. Also, it would allow the drive chain to follow a short and simple path. It's going to need 2 stages of gear reducion, and the mounting points for could be integrated into the mounting rack.

    My concern is that the bike will be unbalanced and wheelie prone. I know I can slide the seat forward on the rails a touch, and I can shift my weight foward if necessary. I know it's going to be easier to do wheelies, but as long as it's not unreasonable then I can live with it.

    Has anyone ever done this before ?

  2. BikeMan

    BikeMan Member

    I'm not sure if the engine would affect balance or not but you could always put some weight up front.I dont think it would take much if it was needed.Its funny cause I was asking on another site if the sprocket and chain would work ok since the sprocket and chain relation is opposite.The members thought it would work ok.This so happens to be my dream set-up for the next build.I'm taking a Yuba Mundo cargo bike and mounting a 6.5hp honda clone engine at the rear behind tire. Reason for the rear mount is so I have all the cargo area open for cargo.

    Hey Pyro if you end up doing the project please let us/me know how it worked out.Hopes for the best!
  3. srdavo

    srdavo Active Member

    build some wheelie bars, into your mounting rack & go for it!! :evilgrin:
  4. Pyrotechnic

    Pyrotechnic New Member

    Well I think I found my forum. All the others seem to deal with those kits, this one seems to be more about built from scratch stuff.

    Right now I'm just collecting parts and planning. The project should be under way during christmas break. I don't think it will need any ballast weight. If anything I'll just try to look cool popping wheelies all the time. :D

    The HF 6.5 was my initial impulse for it's raw power, but I was concerned about weight. Thinking about it now, any ballast weight I added to front would be more than made up for by the power of the engine. Maybe if the little 2.5 Tecumseh gives up...
  5. BikeMan

    BikeMan Member

    Pyro, depending on how far you want to take this I think the solution for the possible weight/control/balancing possible problems is to simply add a vertical bar/pipe on a wheel.Also this would allow for any weight engine up to a 6.5hp.What I mean is you buy a mini bike engine mounting plate(real cheap) put that on a vertical bar/pipe,down to a wheel.The total weight would be on this rather than on your bike.Not sure about bicycle wheel/tires but a 6" mini bike rim/tire would work great.Of course you would still run your chain to your bikes rear wheel/sprocket.

    Attached Files:

  6. WhizBangAndy

    WhizBangAndy Member

    Sounds like a reasonably fresh take on these! Good Luck with the build!:D