Puch Tomos Motocross Build Story: Chapter 1

Chapter 1:

The Ups and Downs 

  
I built a motocross bike with a Tomos Sprint frame as the base coupled with various Puch parts.  The inspiration came one day when I stumbled upon a European maxicross build by #therealribens and his crew #ejowpuchacademy, and #banana.  They used a Puch Maxi frame as their base and converted into a motocross bike that they took off road and raced around a dirt track.  Their bikes looked super cool and looked super fun to ride.

I initially set out to build this bike for my sons and niece to tear around on her uncle's farm.  It supposed to be a cheap build using all the left over parts I had.  But as you will see, it turned out to be anything but cheap.  #mopedluau build to the scope creep degree. 

The build story begin with a rusty barn find at my cousins house:

Barnyard Tomos Sprint rusting in the rain at my cousins house for over 10 years.

Reach the Moped Luau garage only because the television show Hawaii Five-O wanted to use it as a prop in one of their episodes.  Made a hundred bucks for a days shoot for that rust bucket.

I even had to rig up a uni strut shock so it could even roll prior to its TV time.

Sat in the rain at my house for an additional 4 years before I decided to do something with it.  At one point I was going to give it away or throw it away.

Stripped it and got rid of most of the Tomos parts.

Bought some generic KTM pit bike seat and plastic panels from Ebay.

Went to town on hacking the rear fender off and various tabs that was no longer needed.

Mocked up the seat and new plastic fender to just where I wanted it.

Fabbed up some metal scrap pieces I had for the frame work.

Cut and grind until I got it to a level of "good enough".

Good enough.

Laid down some welds.  Can't take all the credit for the weld up.  My buddy Josh (#i_be_alaka_i) cleaned up my mess.

Heavy duty butt framing.

Good Enough

Fit up all the plastic panels and magnum fork.  Shout out to John #inspireoahu for the freebie fork.

John also hooked me up with a Puch engine mount.  I decided to go with Puch Powa since I was most familiar with the engine and I had more parts for it lying around.

Cut off the Tomos mounts and tacked up the Puch mounts.

Getting there.

Mock up with fork and plastic panels.  Cut off the forks light brackets in the process.

I might have sat on it at this point and busted one of the tacks.

Josh helped me with the final welds for the engine mount and swing arm mount.  I reused the Tomos swing arm mount.

Josh also reinforced the engine mount by welding in some filler braces.  Gave it a mean solid look.

Now it was time to tackle the swing arm.  I used 2x3 box steel.  In hind site, I could of gone with something smaller like 1x2.  These 2x3s were heavy.  I ordered them on Amazon!  Yup Amazon free shipping to your door.

Cross brace fit up.

Drilled the holes and tacked up for fit up.

Side profile

Welded end plates for the chain tension-er.  Full mock up with gear and shock.  Gear and shock bought from #treatland.

Mock up with both shocks.  Used the leftover box steel as the bottom shock mounts on the swing arm.

I think I sat on it again at this point.

Looking good.

Mock up with handle bar.

Project status check.

Now it was time for the motor.  I decided to use my kickstart E50 I had lying around.  I was going to build this motocross bike's power plant similar to a Puch Magnum X pit bike.  I also had the Magnum bore with L-ring too.

First:  Tear down.  I had this sitting in the garage for years.

Karate Kick!!

Clutch.

Photo for record for reassemble.

Clutch.

Bell.  Record photo.

Disassembled.  Time to clean.

Light cleaning with engine degreaser was in order.

Time to mod the clutch.

Initial clutch shoe weight.

Shaved off over 10g per shoe with just drilling holes.  Didn't want to go too crazy with any cuts.

Reassembled clutch.

Kickstart springs with 1.5 turns out from flush.

Magnum bore.  Old school port work still holding up.  Didn't have to do anything to it.

Back in the day, these ports were going at least +55mph.

Ports done back then without Dremels!!

Use of pure ingenuity to make you go fast.

50cc is all you needed.

This was hand filed down back in the day.

And the trusty 50cc L-Ring piston.

Transfer matched the case.

Didn't want to go crazy just in case I had other plans for this kickstart motor in the future.

Fit up complete.

Cases clean inside....

....and out.

Had my sandblaster open so I gave the combustion chamber a brush blast to help with fuel atomization.

Changed out the bearings and seals.

Fits like a glove.

Time to marry the halves together.

Transmission assembly begin.

Clutch in.

Plate in.

Kickstart cover on.

Added some fuel boost ports.  Don't ask me why.

Wrinkle finished the cylinder and head.

Scraped the fins for a nice look.

Side view.

Mounted the tires (without tubes...long story) onto the bike.  This is the first time as a rolling chassis.  Sat on it and was surprisingly nice and springy.

Starting to look like a motocross bike.

Motor mounted.

Chain fit up.  Was holding my breath that it cleared.

Used a 21mm Dellorto carb I had lying around.

Gutted Magnum pipe.

Final fit up with reversed bracket.

Mounted the pegs.  Used the Tomos mounts and welded extension pieces to each end.  But I found out quickly that the kickstarter would hit the pegs no matter where I tried fitting them up.  I figured this final location gave the kickstarter enough travel to start the motor.  Will shall see if this decision pays off....

Other side no problem.

Top view of the pegs.

Kickstand mounted.  Had to do a lot of bending to make it clear the swing arms and chain.

Coil and fuel valve on.

Fuel line and cables on.

Ready for its first start!!

STOOOOOPPPPPP!!!!  ONE STEP FORWARD... TWO GIANT STEPS BACK!!!!  EPIC FAILURE on my part.  First, off the kickstarter didn't have enough throw to turn the motor over.  So I had to crank it with a power drill.  After a whole day of trying to start it, i scratched the motor portion of the project.  It was either an air leak in the case, too big of a carb, or the magnum bore and piston was damaged.  Either way, I reached my wits end after a days worth of trying.  I decided to scrap the motor and go a different direction.  This is when the scope creep started.  I figured I had the 21mm Dellorto carb.  Why not bring the cylinder size up to the carb instead of buying a smaller carb and going down to the 50cc Magnum bore.  Yeah makes total sense.  Right?  In other words, JUST SLAP A KIT ON IT!!

Check out Chapter 2 of this build on how it turned out.