New To Engines, and Bikes -- Planning a Build

Vanderbleek

New Member
Apr 20, 2011
3
0
0
TN
Hello everyone,

A friend recently showed me some "Derringer" bikes -- and from the sounds of it, a moped/motorized bike is what I need.

Currently my vehicle (a 1988 Cadillac) gets around 15MPG. As a college student, driving around the campus end of town gets costly, fast. Because of that, I've been looking into alternative means, but I can't warrant purchasing a motorcycle/scooter/new car. Enter the moped.

First, a note: I like building things myself. I'm an engineering student, and I enjoy planning, building, and troubleshooting. I have hardly any experience with gasoline engines, but I do know a bit about gears from working on robotics. I have seen the kits for $150 or so, but I don't want a 2 stroke, and I don't think they'd have enough torque for me -- I live in "Hill Country", Tennessee and so it needs to have fairly high torque.

What I'm looking for is:
4 Stroke Engine (I don't want to mess with adding oil to gas)
Relatively high torque
Cruising speed of 25-30mph
Ability to carry about 240lbs total (me, bike, engine, and backpack)
Cheapest I can get it -- this is a basic mode of transport around town, and more importantly something I can learn engine maintenance/tuning on.

What I've seen is the Harbor Freight 2.5HP 79cc 4 stroke -- this seems to be what I'm looking for. Cheap, about the power I need, and did I mention cheap? I wouldn't feel bad about tinkering with it, since I screw it up, a new one wouldn't break the bank.

To achieve a gear ration of 12:1 (Which should give me the speed I want, and the hill climb ability I need) I could run a 10T off the engine to a jackshaft with a 60T, then another 10T off the jackshaft to a 60T on the wheel, correct? The easiest way to do this would be to remove the pedals, I think, and replace them with a jackshaft, however that seems to be frowned upon. Another location could be chosen, I suppose.

I'm currently following leads on different bicycles, so unfortunately I don't have one to start with. I don't really want to pay more than $30 for one. I'm going to try to mount the engine inside the frame, for weight distribution, plus I want to add a rack and some saddle bags to the rear.

Lastly I have a question: does the HF 2.5 have a dynamo to power a headlamp off of? Mostly so other vehicles could see me, it can get a little foggy where I am.

Essentially, what I'm looking for is any suggestions/modifications to this plan, and, if everything looks to be in order, I would appreciate some suppliers/specific parts to consider.

I've been looking at the various threads involving the HF 2.5, about removing the oil sensor, and tuning it up -- lots of excellent information, and I have a pretty good idea what I have to do to get this bike built and working.

Eventually I'd like it to look like a Cafe bike, but form is more important than function, to start with.

--Vanderbleek
 

Vanderbleek

New Member
Apr 20, 2011
3
0
0
TN
That makes things even more affordable. I'm now thinking 10t to 36t, 10t to 36t. This will give me a larger ratio than twelve, but will cut down on the size/cost of the sprockets.

I also realized I probably need some kind of clutch, to allow me to actually stop...any suggestions?
 

Vanderbleek

New Member
Apr 20, 2011
3
0
0
TN
Ok, so:

Thanks cannonball, the Max Torque clutch seems like exactly what I need, for the clutch at least. Ideally my jackshaft would look something like

affordablegokarts: Jackshaft Assembly for 79cc HF Engine

I'm hesitant to order that one, though, since I still haven't found the bike and am not quite sure how the engine is going to be mounted. It can't be too hard to fabricate though right -- just a steel plate with holes drilled in it? Then I attach a shaft with spacers to get the sprockets to line up right, and off I go.

School's getting out, and people are going to be leaving campus, so hopefully I can snag a bike in the next week or two, and get to building.