Old Mountain Bike BTR

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anota

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Jul 2, 2012
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Narragansett
I just bought this 'vintage' 26"Mongoose Hill Topper for $50. I like how the top bar is straight to I can put a BTR style tank on it without it cocked on an angle. I ripped all gears off-

My plan:

I want to stretch top bar 6 inches and put a deep U in the lower bar. I am looking to see if I could go buy a mig welder or should I commission someone to Tig weld it for me. I'd reinforce where the cuts were made with a 8" tubing insert in the tubes where the outer tubing comes into contact. I ideally want to drop a stripped 4 stroke in it but I have no clue how to do 4 strokes that dont come as kits. If not ill just have mounts welded and put a 66cc 2 stroke straight up with that whole fake engine casing deal that fills the U.

Bike picks are of before then after. The first one is my ideal look. I like the style of this 1919 Indian Powerplus
 

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anota

New Member
Jul 2, 2012
106
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Narragansett
I think it is too. Saw you can weld it to mild steel. Has anyone done that because I really want to stretch and drop the frame
 
wret

wret

Active Member
Feb 24, 2014
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Maryland
Yes you can MIG weld mild and chrome-moly steel. Expect to do a lot of grinding and re-welding. You will probably find it easier and cleaner to replace the whole bar rather than cutting and splicing.

Here's the template I used before getting started:

 

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anota

New Member
Jul 2, 2012
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Narragansett
Thanks for the advice. Will a gasless mig do the job? I was thinking of stretching the top bar directly in the center and putting an long inner tube inside the top bar maybe 12". Thoughts? Im just nervous about cutting welds and replacing entire top bar because that multiple welds to do. The welds look extremely strong and trust worthy everywhere.

Thats a killer ride. Exactly the look i want! Ill be using that! What should I go for? 2 stroke or 4 stroke
 
wret

wret

Active Member
Feb 24, 2014
355
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Maryland
You have probably noticed that the top bar on a board track bike isn't straight. Also, if you add a second bar below the top bar, you will have little room left for your motor.

I have a cheap MIG welder with no gas hookup (flux core) that I have on occasion stuck pieces of metal together with. For my build, I had the use of a nice Lincoln welder with argon bottle. I am VERY inexperienced and it took a lot of welding, grinding, inspecting, re-welding but in the end I am confident that it is a strong frame.

Your choice of motor depends on your goals. For me, I envision riding legally on the street, not on the shoulder and not holding up traffic. A decent sized four stroke was the only choice.
 
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anota

New Member
Jul 2, 2012
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Narragansett
Ive been following your build and really love it... I was going to drop an old fire extinguisher under the top bar and drop the lower bar deep so there would be tons of clearance but I really like the look of yours. Im just nervous about skrewing the connections on the ends of the pipes.

How did you go about bending the pipes because I have no available pipe bending equipment? How long is the straight pipe from the seat post to the fork?
 
wret

wret

Active Member
Feb 24, 2014
355
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Maryland
The pic above is laid out in 1 x 1 inch grid. You can see, if you count the squares, that the straight piece is about 26 inches.

I used this same picture to draw a full scale layout on masonite board. I also used that image to cut and paste various motor profiles so I could be sure of the fit before I purchased one. If I had to do it again I would use thicker plywood, allowing more stable mounting of support blocks and clamps.

You will definitely need a bending tool. I used a HF pipe bender.

 

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anota

New Member
Jul 2, 2012
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Narragansett
Hey I really appreciate that wret. Moving mountains for my plans. if your willing I have one more questions haha. What size tubing did you use??
 
wret

wret

Active Member
Feb 24, 2014
355
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Maryland
I used 12 gauge 1-1/8 chrome-moly. Overkill maybe but at least I know it won't be a weak point.
 
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greaser_monkey_87

New Member
Mar 30, 2014
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USA
With a drop loop frame, you will definitely need to fabricate mounts for a 2 stroke engine, but a 4 stroke should fit nicely. After going to all that trouble to fabricate such a nice frame, I'd put a larger 4 stroke in it personally. Just my personal opinion.
 
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