Roadmaster Mountain Bike (Walmart) build

[Foeller32]

I just finished my first build. I picked up a cheap Roadmaster mountain bike from Walmart ($74), and bought a 2-stroke engine kit from thatsdax. I had to make a couple slight modifications (received a few VERY helpful pointers from threads on here of others who have build the same bike), so I thought I would detail everything here in case anyone else is trying the same build.

Modifications:
1. I had to replace the front mounting studs with longer bolts, since the frame tubing is taller than normal. Bolts worked better than longer studs or threaded rod would have, since I was able to manipulate the motor into place, then put the bolts in.

2. I had to grind a couple small notches in the frame for the front mounting bolts. The frame was just a hair too wide for the bolts to fit, one on either side of it. One I ground a couple notches in the frame, everything just barely fit. I also had to elongate the holes in the saddle part of the front motor mount, since the bolts were still pushed outward slightly by the frame.

3. I had to add a 45 degree 1/2" copper street elbow to the intake in order for the carb to clear the frame. I read a couple people on here say that they soldered the elbow on, so I got out my plumbing tools and started soldering - or should I say, TRIED to solder. It wouldn't work. Came back here to read some more and saw somebody who said they SILVER soldered their elbow on. Cost me $16 for a little tube of silver solder, and another $7 for a flux to work with it, but it worked like a charm! I had no idea that it was possible to solder steel and copper together - guess I learned something new! I also had to put a couple turns of electrical tape around the new elbow to make the carburetor fit snugly. I also painted the whole thing silver to match.

4. I had to bend the exhaust pipe slightly. At least, I think I bent it slightly. The left crank just barely rubbed on the muffler, but before it was completely tightened down. We clamped the pipe in a vise - hard enough to dent the pipe, even with wood blocks - and pulled on it pretty hard. I'm still not sure that we bent it, though. ThatsDax claims that the pipes are easy to bend. He's dead on with everything else I've heard from him, but there is no way that these pipes are easy to bend. I guess the right way would have been to forget about the nice chinese chrome, get out the oxy/acetylene torch, and bend it right. If I had to do it again, I would just grind a tiny bit off the very corner of the left crank arm. I just barely rubbed, and it would have been easy to take a little bit off the corner of the arm without hurting anything.

5. I had to bend the chain tensioner mount a little bit. Actually think I may have messed it up at first by not having it straight. Not really sure - I though I had it straight, but the chain jumped up on the edge of the tensioner wheel the first two times I tried to start it. Actually twisted the plastic wheel cockeyed on the bearing that it rides on. I straightened things out again, and hopefully things will stay put now. NOTE: Make sure that they tensioner wheel is straight in line with the chain, and also not tilted to the side. I'll be ordering a new tensioner from thatsdax, just to make sure it doesn't take a dump on me 20 miles from home.

Five things to work around - not bad for a $74 bike from walmart.

Thank you to all those who have shared their knowledge here on the forum. I had a thousand questions answered before I ever asked them.

 

[Cabinfever1977]

I did my first build with a roadmaster,those frames are a tight fit.
I also modified my frame to get the engine to fit.
But i ended up getting a cruiser bike to move the engine to.
The funny part is im using the roadmaster wheels,tires and handle bars on my cruiser bike.

If i had to do it again i would have just kept using the roadmaster and not bought a cruiser,i could have used the $100 for something else,like upgrades.

My roadmaster bike i bought used like new for $20.

 

[Foeller32]

I did my first build with a roadmaster,those frames are a tight fit.
I also modified my frame to get the engine to fit.
But i ended up getting a cruiser bike to move the engine to.
The funny part is im using the roadmaster wheels,tires and handle bars on my cruiser bike.

If i had to do it again i would have just kept using the roadmaster and not bought a cruiser,i could have used the $100 for something else.

I just wanted to start with a cheap bike - make my mistakes on that one before I start messing with the one I ride every day. Now I know what to expect from these engines. I'm guessing that I can probably sell this pretty easily for what I have in it - around $250. Then I'm even and can start over fresh.

 

[Toadmund]

3. I had to add a 45 degree 1/2" copper street elbow to the intake in order for the carb to clear the frame. I read a couple people on here say that they soldered the elbow on, so I got out my plumbing tools and started soldering - or should I say, TRIED to solder. It wouldn't work. Came back here to read some more and saw somebody who said they SILVER soldered their elbow on. Cost me $16 for a little tube of silver solder, and another $7 for a flux to work with it, but it worked like a charm! I had no idea that it was possible to solder steel and copper together - guess I learned something new! I also had to put a couple turns of electrical tape around the new elbow to make the carburetor fit snugly. I also painted the whole thing silver to match.

This is what I have been searching for for the past couple of days!

I sized up my carb and a 90 Degree piece of copper pipe elbow,

sure the OD of the straight copper piece to connect it fits into the (failed strike through)

The ID is less, but still bigger than the venturi? outlet from the carb.
What a mess of a post! (getting more coffee).....

Summary, I have the silver solder, a propane torch, flux, copper pipe pieces, sandpaper, the skilz and the motivation which got started without me.

I am doing this.

I could buy an offset intake from a vendor but they are like 4 inches long and are made to clear any bike frame universally and is not specifically built custom per individual bike.

Anyone else done this?

 

[Cabinfever1977]

I have and used jb weld,it didnt hold up very long,im sure the welding is alot better.
if i had to do it again i would have just bought a offset pipe and trimmed it to fit.
but its always more fun to custom make it yourself.

 

[dbscrapper]

I just finished my first build. I picked up a cheap Roadmaster mountain bike from Walmart ($74), and bought a 2-stroke engine kit from thatsdax. I had to make a couple slight modifications (received a few VERY helpful pointers from threads on here of others who have build the same bike), so I thought I would detail everything here in case anyone else is trying the same build.

Modifications:
1. I had to replace the front mounting studs with longer bolts, since the frame tubing is taller than normal. Bolts worked better than longer studs or threaded rod would have, since I was able to manipulate the motor into place, then put the bolts in.

2. I had to grind a couple small notches in the frame for the front mounting bolts. The frame was just a hair too wide for the bolts to fit, one on either side of it. One I ground a couple notches in the frame, everything just barely fit. I also had to elongate the holes in the saddle part of the front motor mount, since the bolts were still pushed outward slightly by the frame.

3. I had to add a 45 degree 1/2" copper street elbow to the intake in order for the carb to clear the frame. I read a couple people on here say that they soldered the elbow on, so I got out my plumbing tools and started soldering - or should I say, TRIED to solder. It wouldn't work. Came back here to read some more and saw somebody who said they SILVER soldered their elbow on. Cost me $16 for a little tube of silver solder, and another $7 for a flux to work with it, but it worked like a charm! I had no idea that it was possible to solder steel and copper together - guess I learned something new! I also had to put a couple turns of electrical tape around the new elbow to make the carburetor fit snugly. I also painted the whole thing silver to match.

4. I had to bend the exhaust pipe slightly. At least, I think I bent it slightly. The left crank just barely rubbed on the muffler, but before it was completely tightened down. We clamped the pipe in a vise - hard enough to dent the pipe, even with wood blocks - and pulled on it pretty hard. I'm still not sure that we bent it, though. ThatsDax claims that the pipes are easy to bend. He's dead on with everything else I've heard from him, but there is no way that these pipes are easy to bend. I guess the right way would have been to forget about the nice chinese chrome, get out the oxy/acetylene torch, and bend it right. If I had to do it again, I would just grind a tiny bit off the very corner of the left crank arm. I just barely rubbed, and it would have been easy to take a little bit off the corner of the arm without hurting anything.

5. I had to bend the chain tensioner mount a little bit. Actually think I may have messed it up at first by not having it straight. Not really sure - I though I had it straight, but the chain jumped up on the edge of the tensioner wheel the first two times I tried to start it. Actually twisted the plastic wheel cockeyed on the bearing that it rides on. I straightened things out again, and hopefully things will stay put now. NOTE: Make sure that they tensioner wheel is straight in line with the chain, and also not tilted to the side. I'll be ordering a new tensioner from thatsdax, just to make sure it doesn't take a dump on me 20 miles from home.

Five things to work around - not bad for a $74 bike from walmart.

Thank you to all those who have shared their knowledge here on the forum. I had a thousand questions answered before I ever asked them.

The bigger spring from the clutch cable should on the other side of the post and the smaller one were it is now.

dbscrapper

 

[alienboy366]

whoa cool. I too have a walmart roadmaster. except my carb is flat and level. Did you recently get that bike? it has a better color scheme than the one i recently got.

 

[burnt_toast]

That looks pretty nice for a budget build roadmaster, props

 

[darkness]

im in a bit of a pickle.
I recently bought a roadmaster and even with an angled spark plug i cant get the engine to fit. Ill see if i can work around the tight frame.
but it seems like i wont be able to make it happen
Looks like you got a tight fit there. i dont want to alter anything cause i think i want to return it. but its such a nice and cheap bike.

 

[darkness]

how far is it from the bottom of the frame to the top (inside the tubes) at the back where the seat post tube is? (sorry for the unofficial terms)
i really want this bike to work.

 

[darkness]

also, did the sprocket fit on the stock roadmaster wheel alright? or is it a different back wheel?

 

[happycheapskate]

There are very short intake tubes made of billet aluminum, for about $20, WITH o-ring and slot for it. They will put the carb right next to the engine, and bolt right on. Manic Mechanic makes it.
I think thatsdax.com, Pistonbikes, and bikeberry have them.

If you want to do the 90* bend with the copper part, get some 5 min. Epoxy by loctite ($3-5, comes in instant mix syringe). Epoxy the pipe in the stock manifold, and let it cure in sunlight for 2 or 3 days. It will hold up to heat and fuel. I built a manifold that way, for a briggs tiller.
You can also build up a layer on the extension, cure it, and sand it round, for the carb to fit like stock. Or cut a shim from a piece of bicycle tube to wrap it , meeting end-to-end, just barely cramming into the carb. Got to be better than electrical tape. When that tape gets wet or hot, the carb will fly off.

I have and used jb weld,it didnt hold up very long,im sure the welding is alot better.
if i had to do it again i would have just bought a offset pipe and trimmed it to fit.
but its always more fun to custom make it yourself.

 

[happycheapskate]

Another option for moving the carb: get another $10 stock manifold or the copper part, some rubber hose and clamps, and hack off the mounting tab on one. Connect them with hoses, then brace your carb somehow, like with the stock bolt holes, zip ties, hose clamp, wire, etc.

If you use the 5 min epoxy to connect the copper elbow into the carb, you're fixed up good, then just replace the hose in a year or so when it starts corroding. (If it's not fuel grade hose, it might eventually become defective.)

This is some powerful stuff! It won't immediately burn you like super-glue, and is WAYYYYYYYY stronger when it cures. But if you get any on you, get it off fast with spray-pam and a rag, or it will get HOT. Sets in less than 5 minutes, cures in 1 day.

http://cn1.kaboodle.com/img/b/0/0/1...nce-quick-set-epoxy-clear.jpg?v=1302442214000

 

[Acraze]

I have the loctite stuff and its stronger than the jb weld

 

[Toadmund]

Here is the results of my Carb-fit mod:
I used silver solder, it was not airtight, you can only re-apply solder only up to a point, couldn't completely seal it, but it was very strong, could not twist it. I used JB weld on it as extra insurance.
I also had to solder on a piece of copper pipe slit up the middle and stretched out a bit to the end of the elbow to make a better fit in the carb, then sealed it with 'permatex grey' gasket sealer/maker.

When I mean solder, I mean with a propane torch, not a soldering gun!