Mini Bike refurbish

[Dennis]

My neighbour's field was unmolested deep snow.  After all the melting and freezing, its firm enough to walk on.  Perfect for the balloon tired mini-bike.





Peace & Grease, Dennis

[Dennis]

With the snow mostly gone and replaced by mud, I thought it would be a good time to fix a couple problems with the mini bike.

My nephew hosted a mini bike race at his wedding in 2018.  Someone crashed my mini bike hard against a tree and bent the foot peg bracket and broke the weld.



Also I had a design flaw.  The kick stand spring was on the bottom.  This looked nice, but several times I bent the pin the spring was on, and lost my spring. 



I decided to pull it apart and fix both.

The foot peg was easy.  I quick grind and weld, followed by an anvil and big hammer.



I refabricated the spring parts to the top of the kickstand.



I just dropped the frame and forks at RCJ to get sand blasted.  I will just re-paint it, but I didn't want to spend an afternoon sanding off the old paint.

Peace & Grease, Dennis

[Dennis]

Almost a year ago I posted a thread about repairing some damage to my Mini Bike frame.

In the interim I did a bunch of fiberglass experiments with the idea I was going to make fenders.  With spring here, and my fiberglass skills still wanting, I decided to just put the Mini Bike back together without them.

The stock Princess Auto engine has a governor and an oil level shut off switch.  Both presented problems on the Mini Bike.  When riding along at full throttle, the governor did not just smoothly limit the top speed; it surged back and forth like rotating the throttle on and off.  Eventually it would settle into a steady rpm, but no right away.  The oil level shut off would kick in whenever going up a steep hill; worst time to have the engine suddenly shut off.

Opened up the side of the engine.



The governor is a plastic gear with steel weights that turn a shaft connected to a lever that is connected to the throttle linkage.  When the rpms go too high, the weights move and turn the shaft/lever and pull back the butterfly valve on the carburetor.  The plastic gear is held in place with a steel ring and there is no was to get at it.   Thanks to YouTube, the easiest removal is to destroy the plastic gear and pick out all of the leftovers.



Once removed, the hole in the case where the shaft was had to be filled.  I did not want a nut on the inside of the case that could come loose (if I just used and nut and bolt), so I tapped the case and screwed in a bold.



The oil level switch was easy; just unscrew and cut the wires. 

These Chines Honda clone engines are know for very loose valve lash.  I reduced from 3/1000th to 1/1000th cold.  When the engine expands the lash increases, so a tight lash is okay (many in the WWW have gone to zero cold).



With the governor lever gone I had to figure out how to have the throttle linkage actuate the butterfly valve.   A coat hanger and some pliers did the trick.



I needed a little more spring pressure to return the throttle to close.  Fortunately I had a leftover spring from the governor linkage.



Next up; paint and re-assembly.

Peace & Grease, Dennis

[Olafskii]

The best way to get old paint off without a sand blaster is 'aircraft' grade paint stripper.  Don't waste money on the 'safe' stuff sold at hardware stores--it doesn't work.  The aircraft stuff (like the product from POR15--sold at NAPA) contains methylene chloride.  Just don't get it on your skin and DO NOT USE METHYLENE CHLORIDE NEAR OPEN FLAME.  Open flame turns Methylene chloride into a blister agent (similar to mustard gas--very nasty and toxic).

Olaf