Raise the motor or wider crank

craigant

New Member
Aug 6, 2008
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Hi all, I am a first time poster from Australia and after reading this forum for a while I ordered the 70cc motor and today it arrive. My build will be on my old road bike, like a 20 years old steel famed Northern Star with 27inch wheels. I have learned a lot already from reading this forum and will be incorporating a lot of the tips and advice from other posts into my build. However I have a couple of questions that I really need some advice on.
First is if I set the motor as low as it will go in the frame the peddles hit the side of the motor. I am not sure if the best thing would be to raise the motor up the frame so the pedals pass under the motor or try and get a wider crankshaft. My first choice would be to raise the motor as it’s just easier and there is plenty of room to raise it. I am not sure if mounting it higher in the frame would be of a concern in regards to chain angle to sprocket issues. Also I don’t even know if wider crankshafts are available?
Also I pulled the clutch in and turned by hand the chain sprocket in the motor. I noticed that it was extremely hard to turn. Not binding or anything just tight. Do these loosen up with use or are they always that tight? Can these bikes be realistically ridden around with out the motor running?
I will post some pics when I get the build finished. Hope to hear some advice soon.
 

pedalpower

New Member
Aug 5, 2008
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Hi all, I am a first time poster from Australia and after reading this forum for a while I ordered the 70cc motor and today it arrive. My build will be on my old road bike, like a 20 years old steel famed Northern Star with 27inch wheels. I have learned a lot already from reading this forum and will be incorporating a lot of the tips and advice from other posts into my build. However I have a couple of questions that I really need some advice on.
First is if I set the motor as low as it will go in the frame the peddles hit the side of the motor. I am not sure if the best thing would be to raise the motor up the frame so the pedals pass under the motor or try and get a wider crankshaft. My first choice would be to raise the motor as it’s just easier and there is plenty of room to raise it. I am not sure if mounting it higher in the frame would be of a concern in regards to chain angle to sprocket issues. Also I don’t even know if wider crankshafts are available?
Also I pulled the clutch in and turned by hand the chain sprocket in the motor. I noticed that it was extremely hard to turn. Not binding or anything just tight. Do these loosen up with use or are they always that tight? Can these bikes be realistically ridden around with out the motor running?
I will post some pics when I get the build finished. Hope to hear some advice soon.
welcome.
Yeah, when I first installed the clutch and was adjusting it, the shaft turned pretty rough-it has loosend up-probably just everything getting mated properly-and probabaly a good sign in the beginning.

on the mounting, the engine should rise up some depending on what kind of mounting "damper" you use-metal to metal is just harsh.

the engine is 4.5 inches wide so a good older triple spindle should work. I assume you are capable of servicing the bottom bracket-a 134mm square tapered spindle should give you plenty of room if that is a possible solution. add 165 cranks and the engine mounts and the spindle. it might have to be a combination of any of these.

there's a front engine mount that brackets to the down tube and is kind of a spring like appearance that meets the front mount of the engine. I want to find one of those-that would raise up the engine some.

cheers.
jon

p.s. man, do you guys like to swim or what?
 

craigant

New Member
Aug 6, 2008
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Thanks for the advice, I can raise the engine up quite a bit as I can add a dummy tube on the down or seat tube to achive this and still get good mounting between engine and frame. Its just I am not sure how much it will effect the chain. The advice out ther is to have the top of the drive sprocket level with the top of the wheel sprocket.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
I would say that the angle of the engine to driven rear sprocket are not crucial as long as you get a straight run from one sprocket to the other.

At extreme angles you will find the chain may hit the bottom part of the case.
 

victoreperez

New Member
Jun 25, 2008
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I have change the angle in the same bike and like Bikeguy joe said it, it did not make any difference...just make sure you have as straight a line as posible from the engine to driving wheel.
 

craigant

New Member
Aug 6, 2008
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Thanks all, I will post some pics when its all done, Hope to get some fun riding done before the police tell me to pull the engine off.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
It's much easier to just use a wider crank & mount the engine the way it is supposed to be!!!
Don't start adding dummy tubes to your frame and all that other crazy stuff if you don't have to!
And definately DO NOT add mounting dampers!!! Mount the engine "metal to metal" the way it's supposed to be! mounting dampers can let the engine twist sideways in the frame!!!!! I've seen it happen!