Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
WALTZ "LOANER" MINI BIKE BUILD
#1
Ok, so I've gotten a fair amount of positive feedback from the guys when I bring this puppy along to an event.

I certainly get a lot of appreciation shown and enjoyment demonstrated at Bakersfield when Josiah Rogers shows up.

He is a bit of a "favorite" of mine ever since I was able to outfit him with loaner gear at Prairie City some years ago when he was offered a ride in a single 820, but showed up in shorts - at which point grandpa Dan said, "See, I told you to wear long pants.  Too bad you can't take a ride..."  At which point I motioned Jo to visit me in my trailer, and in a few minutes he was fully outfitted with a black driving suit, black gloves, black head sock, black helmet and black neck brace.  The "man in black" was ready to hit the track - and took his balaclava home as a souvenir.

Since then I have offered Jo first dibs on the mini bike, which he apparently enjoys immensely.

Part of what vintage karting is all about is sucking in the young 'uns.....

So now on to the build story of the mini bike.

A little bit of background first, though.

The mini bike was actually put together as a gift for a dear friend of mine, Mike Kearns, who worked for me for 10 years, and was possibly the best employee I ever had.  He came to me as a "retreaded" carpenter who had torn up his rotator cuff and went back to school to learn CAD drafting.  Combined with his experience being a framer, a steam locomotive nut and a Harley Davidson afficianado, he had the perfect background to be an MEP (mechanical, electrical, and plumbing) designer/draftsman.  He did well at this, and created a whole new career for himself, which served him well as his final career.

So, one day he mentioned that he thought it would be cool to have a "Doodle Bug", which was an early verssion of a mini bike.

So, a few days before Christmas 2010 (as I recall), a box showed up on his front stoop.  He opened it and found a Bad Dog mini bike kit inside.  His next action was to call me and advise that I had mistakenly had an item of mine delivered to the wrong address - which notion I quickly squashed, explaining that it was not a mistake, and that I had an engine, gas tank, etc., that was all that was needed to complete the kit, and that we would finish the project together, once he assembled the roller that was in pieces on his porch.

Would it be that life would be so easy......

When we got together to finish the project we discovered that the mechanical caliper brake arrangement (using the sprocket as the disc) had the caliper mounted so high (obviously intended for an upright 4-cycle engine) that the chain arrangement for the NOS US Motors 580 was completely unworkable.

Some substantial work was needed, and time lapsed, and finally Mike gave up and re-gifted the the mini bike to me and abandoned the project.  I reluctantly accepted it back - but of course I was determined to finish it, and give it to him anyway - he just didn't know that.

As you will see, there were four basic modifications that needed to make this mini work, as follows:

1.  The gas tank needed a proper mounting.

2.  The 580 engine needed a "high-rise", angle mount to allow the chain to miss an original factory style exhaust.

3.  Further, a jackshaft was also needed to keep the chain from interfering with the exhaust - and the jackshaft needed to be adjustable because the rear axle was mounted behind the frame in a fixed position and could not be adjusted for chain tension.

4.  An Azusa combination drum brake and sprocket assembly was needed - but it had to be specially adapted to the modern one-piece spun aluminum rear wheel and modern axle with 3-bolt with bearing hub.  This part of the project was actually unnecessary as changing to an Azusa Tri-Star rear wheel would allow the combo sprocket/drum to bolt directly to the Tri-Stsr wheel, but that would spoil the modern spun wheel look.  I admit to being hard headed in this regard.  While it was unnecessary, it did end up being a pretty cool solution to the problem of mounting a sprocket/drum unit to  a modern spun wheel and hub assembly.

The photo below shows the "roller" mini bike as sold by Bad Dog.....


Attached Files Thumbnail(s)
   
Jim Waltz, West Sacramento, CA
Reply
#2
Gas tank mount.......

I found a cool old-school cylindrical tank with a cool cap.

The tank also came with a mounting bracket that was cut off of a lawn mower or some sort of machine.

I took a close look at the bracket, and realized that I could trim the asymmetrical bracket so as to make it symmetrical.

In addition, a couple of holes drilled in the bracket for its prior mounting method could be welded up by using a copper plate to back up the hole.  A welding trick I learned on line.  Worked beautifully.

Then, a small plate could be welded across the bottom of the top frame tubing, and the tank mounting bracket bolted to the plate welded to the frame.  In particular, the bracket was stamped such that it provided for the tank being mounted so that the tank was slightly tipped forward such that the cap was slightly elevated and the tank outlet being located at the bottom of the tank, and at the opposite and lower end of the tank from the fill cap.

The final installation had a neat, interesting and quite functional look to it - like it was made just for the dual, v-arranged top frame tubes.


Attached Files Thumbnail(s)
       
Jim Waltz, West Sacramento, CA
Reply
#3
The next major step was a high-rise, angle mount for the NOS 580 Bender engine.

I started my welding career many years ago with a buzz box welder when I was in high school with my Bird Engineering Wren mini bike.  It really wasn't much of a welder, and dimmed the lights in my parents house whenever I struck an arc.  I still don't understand how my parents put up with my stuff back then.

In recent years I had a Lincoln MIG welder, which I used to modify my current modern racing kart.

I gave up on MIG after I watched Michael Edick do a TIG repair on my buddy Tim's GK 800 at the Stockton kart track.  I became a TIG guy immediately after watching Michael.

The thing is, I had very little TIG experience, but dove in to do this mount as my first attempt at TIG welding.

Fortunately I had a couple of Power Bee mounts in kit form, ready for welding.

The end result was not a very pretty TIG welding job - but it was definitely strong.  My TIG welding these days is much, much better than this example.  I have always been a better grinder than a welder.


Attached Files Thumbnail(s)
           
Jim Waltz, West Sacramento, CA
Reply
#4
Next was the jackshaft.

Tricky, because it had to be adjustable.

In addition, I needed to weld a plate to the frame tubes behind the engine mount plate on which to mount the jackshaft.

Initially the mounting plate for the jackshaft assembly was attached with only two bolts through the frame plate.

The holes of course have a bit of clearance around them, and with the actual hundreds of pounds of force exerted by the chains, the assembly ended up skewed slightly on the frame plate, thereby missaligning the sprockets with the chain and creating slack in the chains.  I later added a couple more 1/4" bolts in front of the original 5/16" bolts shown, with the holes slightly offset so that as the chain from engine to jackshaft and jackshaft to sprocket want to twist the assembly, the bolts are set solidly against the frame plate to prevent this.  No problems now.


Attached Files Thumbnail(s)
   
Jim Waltz, West Sacramento, CA
Reply
#5
And fourth, adapting the Azusa drum/sprocket assembly to the modern axle and spun wheel hub assembly.

I'm afraid I really was a hardhead in this regard.

The key to the whole thing was to design and machine an adapter that would bolt to the modern hub, and also bolt to the drum/sprocket unit.  I had to "noodle" long and hard on this to come up with a way to do it.  The adapter plate itself was relatively straightforward, but adding an additional hub and figuring out how to get the two hubs solidly bolted to each other took quite a while to come up with.  Curiously, in writing this I'm listening to myself, and realizing by looking at my diagram that there was a way that I could have done this using only a single hub.  It would make the assembly easier too.  Rats!

My mini lathe (had to be a "mini" lathe since I was working on a "mini" bike, right?) came in quite handy here for machining the split hub (to shorten it and make room for a bearing), and for machining the T6 aluminum adapter plate.

This assembly has been beaten to death, and has not given a moment's trouble.  I do fear when Jo is fully grown, however..........


Attached Files Thumbnail(s)
               
Jim Waltz, West Sacramento, CA
Reply
#6
Then there is the finished machine........


Attached Files Thumbnail(s)
       
Jim Waltz, West Sacramento, CA
Reply
#7
And this post will provide a link to the delivery videos when we surprised my buddy Mike by tricking him into visiting my karting buddy Timmy at a Starbucks near Mike's home and Timmy's work.

Since it was a gift, the deal was that if he ever got tired of it or didn't need it any more he'd give it back to me.  Until then, it was his to do what he wished with it.  Paint it, modify it, crash it - anything but sell it.

Well about 4 years after he took possession, he let me know that he wasn't riding it and neither were his kids, so it was time to hand it back over.  And that's how it ended up appearing at our vintage events.

Now I just gotta figure out where to upload the videos and how to link them to this spot.

Any help, please?
Jim Waltz, West Sacramento, CA
Reply
#8
Next steps will be including stuff like the following:

1.  Reversing the sprockets on the jackshaft, so the mini bike will accelerate from a standstill better (though with a bit lower top speed of course).

2.  Changing out the intake manifold to a "V" type for a bit more grunt (though this may involve messing with the carb arrangement - the engine mount plate is way forward - 4 cycle frame design again).

3.  Mounting up fenders.  I have some nice pebble-grain black plastic fenders that will not detract from appearance, but will keep the bike a bit cleaner.

4.  Some sort of frame finish.  Possibly something simple like SharkHide.

5.  A loop of fuel line from the outlet fitting up and over the top of the tank to act as a sight gauge.  It's dang hard to fill this tank without overflowing it.  I have done this on all my vintage karts, and it works really slick.

Long term may see the engine and jackshaft plate cut free and moved rearward, and a V700 installed - just like on my mini bike in high school.  Could even be a 5 Port, as I drove one of those in high school as well.  Hmmmmm..., may need an open exhaust at that point........
Jim Waltz, West Sacramento, CA
Reply
#9
(07-29-2017, 11:03 PM)Jim Waltz Wrote: Now I just gotta figure out where to upload the videos and how to link them to this spot.

Any help, please?

Best way I have found to upload and share videos is to use YouTube and upload them there and then use the video function of the forum and use the link from YouTube. We would host videos here, but the demands of video on the website are just too much.
Reply
#10
So, how do you upload to You Tube?
Jim Waltz, West Sacramento, CA
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)