Robert Thumper

Mr.B. · Feb 13, 2012

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.

Mr.B. · Feb 13, 2012

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.

Mr.B. · Feb 13, 2012

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.

Mr.B. · Feb 14, 2012

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.

Mr.B. · Feb 14, 2012

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...

bairdco · Feb 14, 2012

looking pretty cool so far...

use carb cleaner to clean the tire, then spray over the logos with black Plasti-Dip spray paint. lasts a long time and it blends in with the black tire perfectly.

http://www.plastidip.com/

harry76 · Feb 14, 2012

I like it!!!!!!!!!!

motorhedfred · Feb 14, 2012

I've had zero issues with ColorBond. It goes on and doesn't come off. The "Skid Mark" black color looks the same as a new rubber tire. Mask off the wheel, inflate the tire to open up the pores, spray the whole thing and you'll forget it ever had white letters.

http://www.colorbondtuner.com/

MHF

Mr.B. · Feb 15, 2012

Thanks for the tips!

I've tried paint stripper, heat, and steel wool with no success.

I never thought of paint...

-Kirk

Mr.B. · Feb 17, 2012

Here’s a better shot of the seat arm.

And the hefty gusset that replaces the top of the seat post.

-Kirk

MEASURE TWICE · Feb 17, 2012

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

Mr.B. · Feb 17, 2012

Goodness,

I think I have C-clamp envy...

"-)

-Kirk

curtisfox · Feb 18, 2012

Awesome build. You sure do have the awesome ideas.
What is the seat off of? Love them springs...........Curt

Mr.B. · Feb 18, 2012

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

curtisfox · Feb 18, 2012

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

Awesome what are the springs from?.................Curt

Mr.B. · Feb 18, 2012

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

silverbear · Mar 18, 2012

Just saw your thread, Kirk. Very cool bike and it should be a serious ride.
SB

motorhedfred · Jul 20, 2012

I was editing my thread subscriptions and found this. This bike is awesome....any progress ?

Mr.B. · Jul 20, 2012

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

motorhedfred · Jul 20, 2012

Just watched the Excaliber vid again on Youtube.....what a deep thump it has. Very nice build.

MHF

Robert Thumper

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