If you own a moped, sooner or later you're going to need to work on it. Trust me on this one... Once in a while you may need to remove the flywheel or clutch. This can be tricky to do because as you try to remove the nut, the motor will want to spin. How does one stop the motor from turning, you ask?

Piston stop!

I'll show you how to use it.

I made it at Techshop. The have a work bay where you can work on your car, motorcycle, moped... whatever! There are 3 of them around the SF Bay Area, so it's pretty convenient. There's others around the country and they have lots of tools and workshops. Wood, Metal, Fabrics, Electronics and more. It's rad. 

Check it out here:       

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Step 1: Krusty Bike

Picture of Krusty Bike
   So, this is the victim. It's a 1977ish Sachs moped. Adorable, isn't it? Believe it or not, this bike needs some work done to it. Clutch work. Apparently, Sachs motors have notoriously crappy clutches. If you have an impact driver, the job would be easy, but you don't, do you? Didn't think so. That's why you're reading this Instructable about using a piston stop. But it's okay. That's how we roll in the shire. Let's move on, shall we...

Step 2: Follow duh Wire...

Picture of Follow duh Wire...
   You're going to need to remove the spark plug. "But where is duh spark plug" you ask? Just follow your nose... to the wire that leads to the spark plug. It's typically the 7mm wire that runs to the front of the motor. Still lost? Take out your calipers and start measuring the wires and find one that's 7mm. What's that you say, you only have dial calipers that use the Imperial measurement system and not metric? Fret not, it should read 0.2756 inches. Aren't I a sweetheart! Anyways, pull the "boot" off from the sparkplug.
dorkpunch2 years ago
Very cool tool if you need to hold the engine in one spot. One other suggestion if you need to just lock to motor to undo a flywheel nut, just rotate the piston down to the bottom, take the sparkplug out, and stuff a bunch of rope down the hole. Then just turn the nut until the piston hits the rope, locks the motor, and viola- the nut is loose.
JoeBeau2 years ago
I'd like to know more about making that piston stop. I have a Columbia Commuter with a 70cc athena kit and D crank that i'm working on. Something i have done with great success as a piston stop is some thin, synthetic rope pushed into the sparkplug hole so it fills the cylinder. Cushions the piston nicely and is effective (and cheap)
A_G2 years ago
thats a good way to knock a hole in the piston, id use a wooden dowel or something softer, and piston head is actually thinner than you think it is, and if that flywheel nut is stuck on there, you could knock a hole in your piston. then your screwed
rimar20002 years ago
Clever idea!
l8nite2 years ago
Wait, I thought this instructable was about making a piston stop not on how to use one we don't yet know how to make ! Humorous "ible" Ty 4 posting