Don's garage: 1979 Puch Maxi CRF50 Engine Swap

This Maxi is actually a pretty nice example. I rode it around,
got bored, and sold it.

I know the story:

You bought yourself a Puch Maxi or some other piece of shit moped at a dude's garage sale - the engine is all locked up, but you still want to ride it! So you go surfing on the internet and come across all sort of bullshit web pages selling uber expensive parts that are "new old stock" for a 40 year old moped.

Then you sign up on some shady moped forum and start reading about putting nuts and bolts in the gas tank (frame) in order to knock the rust loose, and what fuel mix to run.

You start wrenching on it and soon realize that for what you'll have in it, you could have bought yourself a brand new Metro, Ruckus, or Sachs MadAss. But what you will really end up with is a 40 year old bike with a high-strung, delicate, European 2 stroke ready to grenade or lock up at any moment.

I know because I've been there.

There's no point. Ditch that Puch motor and install one from a 4 stroke Chinese (or Japanese) Honda CRF50 clone!

Here's a 72cc pit bike I picked up at a yard sale for 250 bucks.
Looks like the dude also had some sweet mud tires up for grabs.

You can find the entire CRF cheap used, or buy yourself just the complete engine from Ebay.

Some special tools you'll need:
Welder - Wire feed seems to work okay for me. In Don's Garage, I don't use gas with my welder, just flux core wire. A cheap ass stick welder will work also, but may be sloppier.

Angle Grinder - Make sure you have cutoff wheels, a grinding wheel, and a wire wheel is really helpful.

Balls and Commitment - You're potentially destroying your Maxi frame if you fuck up.

Some supplies to get your hands on:

Chain - I don't remember what size chain it will take, but I do remember that it's the same pitch for the CRF front sprocket, just with wider links for the Puch rear sprocket. You should be able to find it at a place like Northern Tool.
Balls and Commitment - If you're really going to do this, you can't be a fucking pussy.

Get Started

First up, you'll need to dismantle the Puch. This means draining the fuel and removing that piece of shit engine from the frame. You'll also have to remove the pedal assembly. This just takes a couple of hours to do if you're a normal person, and about 15 minutes if you're a Spartan.

I notched the shit out of the frame to make this 72cc motor fit.
Just take your time and don't be a fucking pussy.

Frame Cutting

Clearance the Puch frame around where the CRF engine will mount. You'll have to make room for the upper part of the motor. Use your angle grinder and balls for this. Please wear safety glasses.

In this picture you can see an engine mount peeking out from
behind the exhaust.

Engine Mounting

Fab up some mounts for the new motor. I used the mounts that were welded to the CRF frame. Just cut them off, bolt them to the motor, put the motor in place, and weld to the Maxi frame. Make sure you check your chain line (twice). This is really critical. You'r re-powered Puch moped will go about 55 miles per hour, you don't want to throw the chain.

Chain

Get your chain and make it the right length. You don't need a fancy go-to-meeting chain tool. Grab your grinder and grind off the rivet heads, and you can take the chain apart. Use a master link to reinstall.

Controls

The CRF50 throttle cable should reach. You might have to extend the kill switch wires.