Robert Thumper

GoldenMotor.com
Mr.B.

Mr.B.

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Oct 21, 2008
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About a year ago While passing through Madison Wisconsin I stopped at their Harbor Freight store.

They’re were closing out their Greyhound line of Honda GX200 clone (Thumper) engines and I picked one up for crazy cheap.

> $100

Since then several folks here have posted their successes with running these motors with the cylinder set up right.

So back in May even though I was still very involved in finishing my first built I decided to start another...


I wanted it to be everything my first “retro antique” build wasn’t...

Fast, inexpensive, easy to build, easy to ride, and much more modern looking.

I used a old Schwinn cantilever frame (Jaguar ?) a $10 flea market find.

Mountain bike forks, chain drive, and a centrifugal clutch, should make this a simple “Squirt & Go” project!

I decided to stretch the rear triangle and go for a “Bobber” style look.
 

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Mr.B.

Mr.B.

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Oct 21, 2008
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Last July Inspired by other builders here I nixed the C-clutch idea and ordered a CVT from Manufacturer's Supply...

http://www.mfgsupply.com/


In August I finally begin the frame fabrication by cutting the seat tube just above the bottom bracket and straightened the top wheel stays.

I filled the gaps with new tubes sleeved over black gas pipe.

This added nearly 5” of stretch to the rear triangle and will add a little rake the head tube.

I had to wait a few days for welding as I don’t own one :)

But I do have a arrangement with my Brother-in-law “Big J” who worked as a professional welder when he was younger and is always looking for a excuse use his nicely outfitted home shop.

With a chunk of black gas pipe I also lengthened the steerer tube from a inexpensive mountain bike fork to work with the Schwinn’s longer head tube.
 

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Mr.B.

Mr.B.

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Shorty after that welding session I won a brand new “Zoom” mountain bike suspension fork on Ebay.

It turned out to be much nicer that the one I was going to use for RT and at just $18.97 shipped a amazing bargain!

Another Ebay victory was a repop Schwinn retro “SSX” chainguard.

I’ve decided this will be a “Schwinn Bobber”


I did this quick mock up in September.

From the junk parts box a children's pedal tractor seat & a old Mercedes leaf spring as a possible seat support?

And a big fat 26 x 3.45 “BOA G” rear tire I had bought a while back.
 

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Mr.B.

Mr.B.

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I widened Robert Thumpers rears stays with a 2 x 4 and by careful pounding with a rubber mallet.

I left the right side a little wider for the chain and then had to file the drop out to get the tire to fit plump & square.
 

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Mr.B.

Mr.B.

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Oct 21, 2008
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Upper Mississippi River valley
In December Big J provided a little additional welding of some of my resent fab's:

A engine mount & Gusset, a mid century Indian style seat post & arm, and reinforcement to the rear stays.


I did another mock up with the newest progress...


Also some other recent stuff to report...

-I figured out a way to convert a 1-1/8” steerer tube to vintage american...

Simple: Cut the head off of a 7/8 grade 8 bolt, pound it about 3 inches into a vintage Schwinn steerer tube removed from its fork and weld.

Then cut the new fork’s s-tube off flush and tap the remaining hole 7/8”. Later I plan to add a shortened nut to the bottom of the bolt that extends 1/2 below the bottom crown.

-As you can see I’m also going to convert the fork into a triple tree with double bar clamps

-Built the rear wheel using a moped hub. A little research reveals that it is a Tomos brand and new replacement parts are easily found online.

A farm supply store provided the 48t sprocket simply drilled to bolt right to the old hub. Drilled some 1” lightening holes more for looks than for lightening.

I cut off the threaded side of a bicycle cluster hub and welded it to 48t sprocket, and added a BMX style single freewheel gear.

And 11G spokes of course!

-I’ll extend the CVT’s rear axle to run both chains on the right side of the bike.

-Bought a 3G Bike’s “Slickly G” 26 x 2.125 tire for a smaller front bobber look.

http://www.3gbikes.com/

I’m liking their tires, but I’m not crazy about the big logo’s and haven’t figured a way to remove them yet...
 

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MEASURE TWICE

MEASURE TWICE

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Jul 13, 2010
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I'm not sure I can remember using the work bench with a engine propped up next to the edge and a bike frame sweet spot (the triangle space between the tubes) right up close to the benches edge to figure does this work. That first picture in your thread is nice, I like it!

I did maybe a bit of over kill in the picture here, but I can say look no hands ma. There is also duct tape I've used at times to hold an engine in place to see what stuff would look like assembled:)

You have a nice project and looks like a good size power plant!

MT
 

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Mr.B.

Mr.B.

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Oct 21, 2008
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The seat pan is from a ancient children's pedal tractor, and it’s actually in pretty ruff shape.

I’m going to cover it in leather, and I’m thinking about hand tooling a design into it, but I’ve never tried that before so we’ll see...

-Kirk
 
C

curtisfox

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Dec 29, 2008
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Mr.B. said:
The seat pan is from a ancient children's pedal tractor, and it’s actually in pretty ruff shape.

I’m going to cover it in leather, and I’m thinking about hand tooling a design into it, but I’ve never tried that before so we’ll see...

-Kirk
Click to expand...
Awesome what are the springs from?.................Curt
 
Mr.B.

Mr.B.

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Oct 21, 2008
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Upper Mississippi River valley
The coil springs are from a antique Troxel saddle which had a broken frame, left over parts from my first build.

To make them work with this project I’ll have to make a longer “C” bolt.

I’ve abandoned the leaf spring support idea shown earlier...

-Kirk
 
Mr.B.

Mr.B.

Well-Known Member
Oct 21, 2008
1,329
559
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Upper Mississippi River valley
Yes, actually I’ve done a lot since my last post, the biggest remaining obstacle is finding a little time on my buddy’s lath.

I have been taking photos as I go and I do have some vacation time next week so I’ll update this thread and my blog soon!

Thanks,

-Kirk
 
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