A Rupp story

A

atom4488

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Its an XS 650 site, but this falls into the "other brands" category. Moderators, tell me to cease and desist if this thread is inappropriate for this site.

Many moons ago when I bought my son's first bike (a Yamaha PW 50), I got a Rupp minibike sorta rolling chassis thrown into the deal. Thoroughly trashed, but still straight and in many ways largely complete. I needed a small-scale project with fab work, so decided to have a go at doing a Rupp restomod. Looks like this, with some new rear shocks of dubious origin on it:

011 (2).jpg

Then there was this B&S 5 hp engine floating around the shop. It got a full rebuild with a new piston/rings, new guides and valves, a ported block including "shaving the eyebrows", a heavily-milled cylinder head (on the lathe) and a Mikuni knock-off carb on a custom-made stainless intake manifold. Looks like this:

009 (2).jpgIMG_20210320_131958053.jpg

The engine runs very well on a test stand; lots of compression and very responsive.

More installments to follow if it amuses the readership here.
 
atom4488 said:
Its an XS 650 site, but this falls into the "other brands" category. Moderators, tell me to cease and desist if this thread is inappropriate for this site.

Many moons ago when I bought my son's first bike (a Yamaha PW 50), I got a Rupp minibike sorta rolling chassis thrown into the deal. Thoroughly trashed, but still straight and in many ways largely complete. I needed a small-scale project with fab work, so decided to have a go at doing a Rupp restomod. Looks like this, with some new rear shocks of dubious origin on it:

View attachment 247440

Then there was this B&S 5 hp engine floating around the shop. It got a full rebuild with a new piston/rings, new guides and valves, a ported block including "shaving the eyebrows", a heavily-milled cylinder head (on the lathe) and a Mikuni knock-off carb on a custom-made stainless intake manifold. Looks like this:

View attachment 247442View attachment 247444

The engine runs very well on a test stand; lots of compression and very responsive.

More installments to follow if it amuses the readership here.
Click to expand...
 
Jim said:
Yes please! :geek:
We're an XS650 forum, but we ain't all snooty an' high an' mighty and all that. ;)
Build threads are entertaining. Don't matter the subject.
Click to expand...
Thanks for the +ve response Jim. I'll carry on then.
Kevin Werner said:
Is that the stock swingarm or did you build it?
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Hey Kevin, that's a stock Rupp swingarm. It has been sandblasted and primed, making it look different from the rest of the frame.
 
atom4488 said:
Thanks for the +ve response Jim. I'll carry on then.

Hey Kevin, that's a stock Rupp swingarm. It has been sandblasted and primed, making it look different from the rest of the frame.
Click to expand...
As a kid I played with B&S 3hp on a go kart. I did exhaust tuning by adding an 8 inch pipe between the exhaust port and the muffler. Underside chrome so it looked cool. Then, I removed the governor so that puppy could really spin. That crank whips around enough that the flywheel side oil seal takes quite a beating. When the seal goes, the points would get oiled. I got pretty good at tearing those down to clean the points and tap in a fresh seal.
 
Carrying on with the Rupp story...

So one of the things missing from the bike when I got it was the exhaust system. As the powerplant was now going to be a B&S rather than the original Tecumseh, a custom exhaust was needed. Started with the pipe itself which has a number of subtle bends in various directions:
013.jpg

I wanted to try my hand at making a muffler. This is the anatomy of the muffler and the finished product:
015.jpg023.jpg

Time for a mock-up of the bike and a detail shot of the front sprocket guard as a work-in-process:
004 (4).jpg002 (5).jpg

The front wheel visible above is a custom center between original Rupp rim halves. The Rupp forks and stem are excessively crude (the stem is a large carriage bolt that is a very sloppy fit in the stem bearings and the forks have springs but no damping) and will get replaced. We'll do that next time.
 
Another installment...

As mentioned last time, one of the less attractive features of the Rupp frame is the use of a giant-size carriage bolt and low-precision flanged bearings as a steering stem / stem bearings. With new bearings and a properly tightened stem bolt, there is still an alarming amount of slop. Not a problem per-se on a minibike, but it offended my mechanical sensitivities. The forks are also very primitive, being two telescopic tubes inside one another with a nylon sleeve and an internal spring. No brakes on the front wheel either.

An opportunity presented itself in the form of a Chinese pitbike front-end, that has proper hydraulic forks, triple trees with bar riser mounts, a hydraulic disc brake and conical stem bearings! So the stem tube from the pitbike chassis was grafted onto the Rupp frame backed by an appropriate gusset:
001 (3).jpg
This now allowed the installation of the full pitbike front end. This pic also shows the hand-formed fender fresh off the planishing hammer:
001 (6).jpg
Next up there was a need to improve the pegs, as the originals are not spring-loaded and have sloppy mounts. These bits were fabbed-up and welded on to the existing peg mount cross tube:
029.jpg024.jpg
Need to speed up this build as there are too many other projects in the pipeline!
 
My brother and I would drool over mini bikes saying, "This one has to be the fastest! It has a 5hp motor!!!"

Will be watching this with a lot of memories being brought back.
 
GaryInVA said:
My brother and I would drool over mini bikes saying, "This one has to be the fastest! It has a 5hp motor!!!"

Will be watching this with a lot of memories being brought back.
Click to expand...
We were so poor that I only saw one minibike in my part of town as a kid. The thought of having one never crossed my mind.
 
46th Georgia said:
We were so poor that I only saw one minibike in my part of town as a kid. The thought of having one never crossed my mind.
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For me, it was not a question of so poor, there just weren't any around. In my time and town, there was an abandoned clay pit and brickworks where we all rode whatever we had; most of us had stripped-down bicycles, some of the older kids had stripped-down Honda S90's and the real cool kids had older Jawa or CZ motocrossers. There was a BSA 250 or two and maybe even a 441 Victor. We're talking late 60's.
 
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