new project, how to mount it, and what transmission should I use?

Toby woodman

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I have a 98cc 2.5 hp engine, I'm looking at mounting it on a bike, I have already figured out how to control the throttle with a cable, and I have taken the fuel tank off to make the engine smaller. It is too wide to fit in the bike frame, so I'm looking at a rear rack. I can weld but the bike has no rack mounting points. can anyone suggest some mounting and transmission types that would fit this engine. it has a 5/8 shaft. I am trying to stay away from centrifugal clutches because they are rough, and the cheap ones use bushings that wear out quickly. the rack that I made to fit the bike in the pictures is too wobbly, however i want to use this bike as it is a good mountain bike with suspension and hydraulic brakes. Thanks.
 

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That's a nice bike Toby. Too bad the engine won't fit in the frame. It's not a good idea to drill holes in the frame because it make is easy for a stress fracture to start from there. Would you be opposed to welding on your frame?
How about a close up shot of the rear wheel including only the seat post and rack. That way we can see other possible anchor points.
 
yeah, the bike was a great deal at only 25 pounds, or about 30 something dollars. I don't have the ability to welt aluminium but it can try and get some more photos later
 
A lot of us will tell you that putting this much power on an aluminum frame might not be such a good idea, especially with the center of gravity being so high. Nevertheless, any anchor points will have to be bolted on with no modification to the aluminum frame. If your rear axle is not long enough to accomidate another 3/16 inch flange on each side and still get the nut all the way on I would replace it with a high quality one that is extra long. This would become the primary anchor point for your rack and all necessary bracing would be weded to the upright attached here.

To anchor the front of the rack, the only thing I can see would be to use one of those CNC machined clamps that go around your seat tube. ( measure the O.D. of your seat tube for us ) They have two holes that are intended for the motor to bolt to. Use these holes to attach the front of your rack. I remember someone here posting pictures of what I'm trying to explain. Maybe that person will show you again. Anyway, do not use a muffler clamp ! It does not have enough surface area contacting the seat tube, which I feel is important to help stablize the front anchor point seeing it is only a single point of contact.

The amount of additional bracing will need to be determined after you start the mock up assembly. Do this test with the motor in place. BTW........did you pedal your bike around with the motor on the rack. I am just curious as to how top heavy it felt being that far off the ground. I have never ridden a bike with this configuration Toby. This is just my personal opinion on how I would approach this build. I'm sure others might have better ideas to share.

One other thing. If you plan to relocate your fuel tank to the top bar you will need to install some kind of fuel pump, I'm sure. Best wishes going forward.
 
the motor is fairly light, at under 20 lbs, most bike racks are suitable for at least 50 lbs of capacity. so I expect it would feel fine althought I have not tested it with the engine, I strapped a bag of concrete to the back and went for a pedal, and once I was above about 8mph it felt almost no different to a normal bike, i suspect due to the giroscopic action of the wheels. I have taken the fuel tank off and I think that with the bike seat up, the motor will fit nicely under the seat. I've started a new thread about the transmission because i want to use a large belt sheave. thanks for the help.
 
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