Roadmaster gets a motor

shop deals on amazon
Advertise with us
BOXKARS
Bike Wall
Rat Rod Bikes Bicycle Forum

Help Support Rat Rod Bikes Bicycle Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
hotfoot

hotfoot

Joined
Feb 20, 2009
Messages
325
Reaction score
1
Location
Bellingham WA
Rating - 0%
0   0   0
Picked this 80cc two stroke up off a fellow engineering student today, and it's going on the Roadmaster. Going to require a custom front motor mount, as the frame is pretty big, and I plan on making a gas tank for it that fits between the top bars behind the battery pack, and I'm probably going to have to make custom exhaust, since the motor sits so high in the frame to avoid hitting my large sprocket, the stock exhaust gets in the way of the pedals. I'm excited, to say the least! I'm thinking of using brake levers for both throttle and clutch, because I'd rather not have a twist throttle. Other than those few things, should be a pretty basic install.

Just a mock up. Building in a dorm room is fun!
DSCN0076.jpg


DSCN0077.jpg
 
Dude! My pal at work started building these...He's built 3 already! motorbicycling.com is THE place to go for info and to buy engines. Just an observation: most builds I've seen the engine is mounted to the front down tube...Be sure to check out Spooky Tooth's website...Good luck!!
 
I plan on making a custom front motor mount to mount it to the front of the frame too, without it there would be too much vibration. Plan on starting on the tank soon, probably make a cardboard mock up tonight. Anybody run these without a muffler? I run my older mini bikes without mufflers, sounds great and gives 'em just a little more power. I wouldn't just leave the exhaust port open, but just use a bent tube that dumps out below the bottom bracket so there would still be a little back pressure.

I just checked out motorbicycling.com and spooky tooth, good stuff!
 
bikeriderx said:
Dude! My pal at work started building these...He's built 3 already! motorbicycling.com is THE place to go for info and to buy engines. Just an observation: most builds I've seen the engine is mounted to the front down tube...Be sure to check out Spooky Tooth's website...Good luck!!
Click to expand...
The way it's mounted works great...I've built two and that is the best solution...in my humble opinion. :)
 
FOUND OBJECTS said:
bikeriderx said:
Dude! My pal at work started building these...He's built 3 already! motorbicycling.com is THE place to go for info and to buy engines. Just an observation: most builds I've seen the engine is mounted to the front down tube...Be sure to check out Spooky Tooth's website...Good luck!!
Click to expand...
The way it's mounted works great...I've built two and that is the best solution...in my humble opinion. :)
Click to expand...
Wait...duh, I mounted it to the seat post and the down tube...and that worked great. So it was held pretty tight on the bike. I had to custom fab a bracket that would actually work for the down tube to also be connected...other than that people stop you in the street and want to talk. So if your not social I'd pretend not to notice anybody around you 8)
 
Before this gets buried I thought I'd add some updates...

Lots of small fiddling to get this together, build is still going, just really slowly thanks to school. Lots of little problems have popped up like the cranks hitting the engine, still need to fab a front motor mount, and I need to redo my taillight because of the rear drive sprocket. I got the stock kit gas tank today, and I think I might use that for awhile since I really don't have time to make my own tank, though I did pick up some sheet metal and borrowed a brazing torch...

I'll try and post some photos in a few days.
 
I'm watching this thread because I think I'm going to build one too. Looks good so far. Will be interested in riding impressions too.
 
Im building a roadmaster also, got the sickbikeparts shifter kit for it and a nuvinci hub that will let me shift gears infinately should be a neat bike if i ever get it done. If you mount your engine in the front it will clear the sprocket and also you can run your exhaust that you have. If you take the end off the muffler and cut the tube coming up from it flush it will free up some power and its not to much louder,youll also want to richen it up 1 notch on carb . Ive built 2 and helped with 3 more and have a couple to do for others.
Picture102.jpg
Picture007.jpg
Picture069.jpg
user5892_pic1858_1223968208.jpg
 
Thanks for the tips, the rear wheel I'm running seems to have spokes about as thick as railroad ties so they should be fine. The only problem with my build and mounting the motor that far forward would be that I would need a heck of a lot more chain, and I really don't have much funds to buy some... I think the reason my cranks were hitting the engine were that the originals were twisted like a pretzel, I picked up some new old ones and they fit great.

I picked up a free 90's repop springer front end that has v-brakes on it and I've been thinking about running it because I figure I'm going to want more than just the coaster brake on this thing.

Plan for the next week: Mount bottom bracket, attach all chains, mount taillight under seat, take for test ride and test out the clutch and see if it turns over. Since it's a used motor the thing could be blown to heck, hopefully not though!

Here's as it sits now, the stock tank doesn't look too bad (okay, it does!), but will have to work for now. Sorry for the horrible photo quality.

DSCN0086-1.jpg
 
Updates, went home this weekend and managed to get some progress. Made a rear motor mount, straightened the cranks, and bent the muffler so it doesn't hit my front wheel anymore. I apologize for the lame sprocket, it's off a factory bike that I got from a friend who works at a bike shop. The huge sprocket I used to run on this thing wouldn't be very helpful for starting the motor...

So now, at a bare minimun, I need to hook up the stock gas tank and go! But I'm planning on doing some other tweaks too. Hope to have it running in a week.

DSCN0091.jpg


DSCN0092.jpg
 
She lives! Got it running today, fired up on the first try which I really didn't expect and just about sent me off the back of the bike as I was holding the handlebars with one hand and messing with the carb with the other while pedaling like mad. The carb needs a lot of tuning, and I need to work on my chain tensioner, and I need to fix where the chain is hitting the block, but at least the dang thing runs now!

I'll post a photo as it sits now tomorrow.
 
I highly recomend anyone who uses one of these to get/make a better chain tensioner, mine crapped out on me yesterday, which led to the chain falling off, getting caught between the drive sprocket and housing, and cracking the housing around the clutch. Thankfully I'm an automotive engineering student and I have the capabilities to weld aluminum (plus a bunch of people who want to ride this thing so they're willing to help). Not too big of a deal, but rather annoying. I've torn the whole thing down to the frame again to weld the engine up, and I will be making some sort of rubber motor mounts to help with vibration, and a shim on the rear drive sprocket to bump it out a bit and keep my drive chain from slapping on the balloon tires.

But for the few days I rode it, it's been fun as heck! It runs surprisingly well, and starts up really easy.
 

Latest posts

Back
Top