5:1 Transmission FWD Project

You might be able to use a front freewheel crank with an extra sprocket to accept power from the motor. If a frame mount will make the combined drive train easier, maybe one of those HuaSheng 4stroke expando mounts could be made to work.

You're really smart using derailleurs instead of geared hubs. I think geared hubs are a weak point that's a pain to fix, and a good derailleur is trouble free and strong. The geared hubs are only really a packaging advantage and the shifting when sitting still. I think if I ever do a mountain bike it'll be running through Shimano derailleurs, maybe a 4 stroke so I can get away with some trails if its quiet like a generator unit. I think for a practical non-toy bike this is THE way to go for reliability. I haven't tried running the hubs on a jackshaft at higher revs to reduce the loading, something I'd like to try but I doubt it is more reliable than a derailleur. Hubs aren't the best for shock loading too, something a regular bike doesn't have a problem with. The new rapid shifters work so well its amazing.

I'm interested in seeing how it turns out. If that little motor has mounting points on the bottom you might consider in-framing it because I think all you'd have to do is drill some bolt holes in the HS mount. Then the chain for the motor to cranks would be really short.

That's good to know about the freewheel cranks. I imagine its scary having those things come loose if they really go bad. That's the only lousy thing about freewheel, pawls. For a cheap single speed the BMX ACS crossfire is a strong setup, I put that on my Mongoose BMX as a kid because I kept breaking pawls because my friends and I would race.

I'm interested in strong freewheels and cassettes, it would be nice to not worry about it. I totally agree on the benefits of freewheel on a MB, I like the freewheel on my electric bike going downhill, because you can keep revving past redline with the electric motor and get really high top speed over the flat ground speed. Or you can chill and use absolutely no power except to bump it out of a couple corners on the way down. With the little gas motor you won't be over-zinging it, but freewheel is more efficient. Freewheel on a low powered electric bike is actually so efficient that it actually surpasses the gains you can get with regenerative braking, so it works for little gas engines too.

I think the only time you wouldn't really want it is if you needed the engine braking because you live in a really hilly area and you've got a 4 stroke, or you have a shifting motor that needs the direct link to synchronize properly. The disc and drum brakes are so good these days, plus if this keeps the low rpm stock centrifugal clutches with hook springs from breaking then it makes them as reliable as the motors they go on!

I hear you on keeping it simple, then you get to go out an ride on your free time instead of preparing to ride.

Can you hook it up without a spring tensioner? My dirt bike flung chains on bumpy trails until I tightened up the tensioner significantly to counter the weight of the chain bouncing around. On my motard wheels I was able to get the chain length right so that I could eliminate the tensioner, and that worked most efficiently of all the setups.

lowracer said:

I installed the engine out back yesterday & took it for a few test drives.
For some reason (which I think I figured out), the chain got thrown on 3 seperate test drives. After each test drive I fine tuned the chain line & tensioner but due to the suspension movement, the chain gets out of alignment & flies off.
I'm glad I didnt damage anything, but on one occasion, I bent a 1/4" bolt.
I have since scrapped the chain drive & gone back to trusty ole Friction drive.
Maybe on a non suspension bike this would work better.
-lowracer-

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How about an old derailleur as a chain tensioner?

Chris
AKA: BigBlue

doh! I hate breaking bolts. If you have any spare change at all, get some grade 5 or grade 8 nuts/bolts/washer sets for your mounts.

I also recommend some KMC510 bmx chain, or any other BMX chain with 'anti-drop' inner plates. They are basically just super tall innners, with extra thick outers. After the first 20 or 50 miles, you should have the finish/honed bits worn off, and be able to achieve a longer-lasting tension on the run.

Dude, use them. If you get rid of tensioners and just get the chain tensioned at a fixed relation, it won't skip off if it's a single speed. Ever since I tensioned the **** out of my dirt bike tensioner it hasn't skipped off once. If I had adjustable dropouts or a 1/2 link (crap I forgot to order one in my big monster order darnit!) I could get rid of the roller bearing tensioner and prolly pick up a mph and a mile of range. Spring tensioners are a waste of energy, a properly tensioned chain will almost float and makes just enough contact with the sprockets to drive. As long as your rear mount is rigid enough for a fixed relationship you should be okay. Another thing you can do is use smaller chain which is definitely strong enough but has less inertia so it will want to skip on bumps less, like some 8mm or #25 chain, the 25 stuff is incredibly strong as long as your chain line is withing a huge ballpark, it's amazing stuff. Mine accelerates me on my 100 lb bike at a car rate and goes trail riding no sweat.

Lol, that's what I'm trying to avoid too because the pile of boxes keeps getting bigger, not to mention I have the same thing going on with auto parts as well! One click shopping

Wide cranks?

ooh nice motor, congrats

that's the same gearbox i used i really like it