Bike Motor (moped) Build

This isn't very Jeep related, so the mods can move it if they want. It is a build though and I was afraid that it would expire from the off topic section before I finished it.

I decided to build a moped for some cheap fun transportation (Bad influence from Uncle Bill). The bike is an older Roadmaster that I found on Craigslist for $50. The important thing with these conversions is to find a good frame. Most new bikes will not work or are a pain to mount a motor in. These motors are made in China and are designed for the V frame type of bikes with skinny tubes like the ones I had as a kid. Modern bikes have fat tubes that are bent into all kinds of shapes and sizes. I almost just bought an old frame for $10 and then built the bike with all new parts. Another nice thing about older frames is that most of them are steel. You also have to be careful with aluminum frames. The mounting clamps can crush the tubes when you install them. I have also heard of the mounting clamps cutting the aluminum over time from vibration. You have to make or modify the clamps so that they have more surface area and spread the pressure out more evenly to prevent these problems. The motor that I chose is a 48cc two stroke and I spent a bit extra on an upgraded carburetor. My other big expense was the jack shaft kit. This allows you to drive the rear wheel from the existing pedal chain system instead of using the sprocket and chain that comes with the motor. It has two big advantages. First is that you can use your rear derailleur with the motor giving you gear options. The second is that the drive system that comes with the motor is on the cheap and cheesy side. The sprocket basically mounts to the spokes and has a tendency to bend spokes and throw the chain. The jack shaft kit is American made and is much better quality as well. The down side to it is that it costs just as much as the motor and it's kit.

http://gasbike.net/
http://www.sickbikeparts.com

So here is the bike as I found it on Craigslist. It needed some work. I removed the front derailleur system since all of that goes away with the jack shaft kit. So this ten speed is now a 5 speed.


When these pictures were taken I had replaced the skinny hard seat with a nice and comfy “fat boy” seat. The straight handle bars have been replaced with ones that are a bit wider and taller. All cables have been replaced. The rear derailleur has been replaced and tuned. The chain and grips area replaced. The shifter for the rear derailleur has been replaced with a twist shift style and moved to the left hand side to make room for the throttle. I added a rear rack and installed a dual break lever. The dual break lever allows you to control both breaks with the right hand so you can mount the clutch lever on the left side.




Here is the motor just sitting in the approximate location that it will mount in. As you can see, there is still plenty of room for the carburetor and spark plug wire.



This is the engine kit. It had some shipping damage, but nothing serious. They throw in some extra parts, which is a good thing since some of them were broken like the spark plug boot.


Yesterday I converted the pedal crank assembly from the cheap one piece bottom bracket to the nice three piece cartridge style. This is necessary for the jack shaft kit. I bought the conversion parts from sickbikeparts.com when I ordered the jack shaft kit. I am really impressed with the parts from these guys. The cage in the old crank bearings were broken so everything fell out onto the floor when I opened it up. I don't have any pictures of this step yet but I will try to get some later today. One thing that I didn't count on was that the old pedals don't fit in the new crank arms. I was able to “borrow” the pedals off of my wife's old mountain bike for now though.

Unfortunately, work is going to be busy this week so I won't have any more time to work on it after today until next weekend.

 

I understand why the dual brake lever concept but as a rider I don't like it. That means that you have to have both brakes adjusted perfectly to catch at about the same time.

Of course with old school U brakes it probably won't matter since they are not exactly known for their stopping power, you can grab them as hard as you want.

 

Ya, you have to squeeze pretty hard. The lever though does kind of compensate for the brakes not being perfectly timed. It has a swivel pull point that lets you take up the slack in the looser brake before engaging the tighter one. It's not perfect, but it sure helps.

 

Yeah those brakes are equivalent to the stock 9in drums on our Jeeps. Is the swivel pull point adjustable so you can maybe have the rear brake catch first or the front if you want?

 

Well the swivel point isn't adjustable, but there are individual adjustments on the lever for each brake. So yes, I can get one to start clamping before the other if I wanted.

 

nice progect. I have a motorized bike i made with an old jawa moped engine. Its freakin awesome. Its geared real low so i can climb anything with it. I go crazy places with it. And i just bought a used chinese kit for 20$ missing a few parts but cant beat the price. Im not sure what im going to build with it yet though. I dont think im going to put it on a bicycle . Might make a mini board track replica or somthing like that. Id also be a little afraid of that brake setup. Sometimes you really dont want the front brake because youll slide out. Just gotta be mindfull of what its doing i suppose

 

looks like a fun project!

 

This is the new crank set up that I put on yesterday. It is much nicer than the old one. You can also see the chain jump stop and bottom bracket for adjusting motor chain tension. The larger outside gear on the crank in driven by the motor. There is a new freewheel mounted between the crank and the sprockets. This lets you still pedal the bike with the engine off, but the engine can drive the sprockets faster than the pedals without the pedals swinging around like an egg beater.




Here are the parts of the old crank.


Today I got the main jack shaft bracket mounted to the motor. So far that has been the biggest pain yet in the project. They warn you in the instructions that it is tricky and that you may have to make some modifications due to the variance in these Chinese motors. I had to cut one of the mounting tabs off and weld it on in a slightly different location. At least it is a quality mount that is nice and thick so it is easy to get a good weld onto. Next weekend I will paint it and get some pictures.

I have been riding it around and getting used to the brakes and the feel of the shifter. I figure that I better be used to riding it just as a bike before I go taking off under motor power.

 

Well it is mounted and I have made a few runs with it, but it is not close to being done. The carb is far from being tuned. I can't use the throttle yet. It just bogs down if I do. So I have just been trying to get the idle adjusted. It want's to either race off or die. From what I read, this is an "upgraded" carb that has more power but is a pain to tune. A lot of guys switch them out with the older more basic type. I may just do that yet. While I am trying to tune it though I keep having other things come up that I have to mess with first. For instance my rear freewheel locked up on me while I was riding it and threw the chain. It was an old freewheel so that is no surprise, but it was still a pain in the butt and I had to make a trip into town to get it replaced. The latest is that the chain that came with the engine broke the master link and threw that chain. So I have to fix that yet before I can keep working on the carb. I put new pedals on it as well so my wife's old bike got it's pedals back. The new ones are wider so that is nice. I need a new kick stand and some mirrors. You can't hear cars behind you with the engine running.

Here it is all mounted up.


A close up of where I had to cut a mount off and re-weld it further up.


Here is the top rear mount. The bottom rear mount is the same. If you look close you can see that I have lost the key in the sprocket and it has spun on the shaft. I have to fix this too now.


This is the front mount.


I had to file a little around this bolt hole to make room for the chain since the jack shaft kit re-angles the chain a little. This is the master link that broke.


I also had to file down one of the water bottle mounts to make room for the front engine mount.

 

Nice project. That would be fun to tool around on.

 

youve got the master link clip on backwards. could be why it came part and broke last time

 

D'oh. (Slaps hand on forehead). Well I replaced the chain and used a chain breaker instead of a masterlink this time. The spun sprocket and shaft got doctored up and a new key. I forgot the loctite on the set screws last time. This time I made sure to use the loctite and I doubled up (piggy backed) on the set screws. Before all that though I measured the alignment of the sprockets and found them to be off by about half a tooth width on both sides of the bike. When I assembled it the first time I just used the shims that they said to in the instructions. This time I made my own shims to get everything in its proper place. Now it is much quieter and smoother. So next is the carb tuning. Right now it is idling too fast, but it flat out flies down the road and it shifts nice through the gears.

 

Status check...................

 

what no chrome poo pipe?


I need 1 more pic ,
how is the motor chain getting to the sprocket ?I can see it going down,but to where ?ours is run off the motor to the rear wheel hub .

 

Here is a picture of my feeble attempt at a motorized bicycle.



and a link to my build thread on Rat Rod Bicycles.

http://www.ratrodbikes.com/forum/viewtopic.php?f=54&t=41879&sid=fcbed9f5f8344a07073c7ffc524110cc

 

Pretty, cool, does it work well?

 

Thanks, as a mechanical novelty it does work well. Take off is smooth and it certainly looks dangerous when it is running. Nobody has taken up my offer for a ride, so I don't have any other opinions. It would be great for tooling around at a tractor show or fairgrounds at slow speeds on flat ground. With only the rear brake it stops reasonably, hooking up the front would be even better. My wife thinks it looks somewhat SteamPunk and I should play that up with copper and brass.
As a ride to work commuter, it is mostly a failure, somewhat rough riding and doesn't pull the hills the way I expected. The fatal flaw is the high speed of the primary jackshaft chain, flung all the lube off and burnt to a chrisp in less than 100 miles. Considering removing the modern Honda engine and installing an old school Briggs or Tecumseh. Wouldn't be street legal but might be more fun.
Time, effort, and money would have been better spent on the JEEP or my winter beater.

 

Got a buddy who is building these.





http://bigboycycles.com/