The following instructions explain how to install a helicoil in the exhaust studs of a 65cc Metrakit.
You can buy Helicoil kits from many auto parts stores for about $30.
On the Metra65, the studs aren’t threaded into the cylinder. If you have a broken stud that’s threaded in, it might be better to try to unscrew it before you decide to drill it out.
First, prep. I’ve drilled and helicoiled exhaust studs without removing the cylinder. You can drain all the fluids, flip the moped upside down, turn the flywheel so the piston blocks the exhaust port, and stuff a paper towel in the exhaust port to keep the metal chips out.
This cylinder already had metal shavings from the ports, so I wasn’t too worried about a few more.
Gather up some tools. You’ll also need a tap handle.
Cut the studs off so they are sticking out a little past flush if possible.
Grind down the studs so they are flush, but try not to damage the flange.
Use a punch or something to punch a dent dead smack in the center of the stud. As close as you can get it.
You’ll want to drill a pilot hole in the center of the stud, and a Dremel tool with a 1/8” bit is easier to control than a cordless drill.
Drill the pilot hole, and make sure that it is dead centered, and perpendicular to the flange. If the pilot hole is not perpendicular, your stud won’t be when you finish. Use some oil. Clean the chips out of the hole.
For an M6×1.00 helicoil, the final drill size is 1/4”. Step up the size in small increments. You probably won’t get the pilot hole dead center, and the old stud that’s in there is surrounded by aluminum. If you go straight to 1/4” without steping up in small increments, the drill will walk. Stepping up in increments will allow you to drill out as much steel as possible before the drill bit touches aluminum.
When the drill size is big enough that it hits the aluminum, there should be very little steel left to push the drill away from where you want to drill.
Tap the holes. Use some oil. Clean the chips out of the hole.
The M6×1.00 Helicoil kit came with a pre-winder.
Put the Heli-coil in the pre-winder and crank it until it starts to come out.
Line it up with the tapped hole, and start to screw it in. Once it starts to thread into the hole, gently pull up on the pre-winder as you continue to turn the tap handle.
When the Helicoil is almost all the way in, if you’re pulling up on the pre-winder, the Helicoil will release from the pre-winder.
Keep turning the tap handle until the Helicoil is 1/2 to 1 turn past flush, then turn the tap handle backwards to get it out. You can snap the tang off with a tiny screw driver or something. Put the blade against the tang, and hit the handle sharply with a hammer or whatever you have laying around. Then you just turn the cylinder upside-down and shake it, and the tang should come out.
One good thing about Helicoils is that if you’re just going to use regular bolts instead of studs, at least now you’ll be threading steel into steel, whereas if you just tapped into the aluminum, you’d chew up the threads if you took out the bolt and put it back in repeatedly.
If you’re using studs, jam two nuts together.
Thread the stud in as far as you need, and then hold the bottom nut with an open-end wrench, and remove the top nut with another wrench.
I put locktite on everything, and I don’t know if it does anything useful on an exhaust flange, but I put it on there anyway. So that’s it.