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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:                 www.techshop.ws

word!

Step 1: 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...

   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.

Step 3: Grab a Wrench...

   We start by removing the spark plug from the cylinder head. there are a few different sizes of spark plugs out there, but 99.832% of mopeds use the 21mm type. At least I think it's 21mm. I forget. Anyways, put the socket onto the socket wrench, then onto the spark plug. Righty tighty, lefty loosie is a good rule of thumb.... unless it's a reverse thread. But spark plugs aren't a reverse thread. EVER! I'm pretty sure. So, yeah. Remove that naughty spark plug.

Step 4: Fancy Tools!

   Here it is, the piston stop. Yes, yes... I've used this picture twice. Stock footage is what we call it in the industry. The FILM industry, not the industry you were thinking of. Let's stay focused here, okay? anyways, This is a homemade piston stop. It was constructed out of a bolt, an old spark plug and a nut. That's a whole different Instructable yet to be Instructabled. Now, lead the piston stop into the hole where the spark plug came out from. You may need to turn the flywheel a bit, thereby moving the position of the piston down a bit to allow clearance. Tighten the piston stop down by hand finger tight. Snug.

   Once the piston stop is in place, turn the flywheel in the direction that you will be wrenching until the piston makes contact with the piston stop. And there you have it. You are now ready to start working on and cursing at your moped-super bike.

Have fun!
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.
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)
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
Clever idea!
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

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