Vibration Cure

[Deleted member 12676]

There's two main reasons why these engines vibrate so much. One is that the stock CDI fires way too advanced at any rpm above about 3000. Two is that the crank is not correctly balanced for the piston/wrist-pin. You can take the crank out and drill holes through the flywheels close to the conrod pivot point, or you can lighten the piston/wrist-pin. Standard wrist pins have a 5 or 6mm inner diameter. After I drilled some holes in my piston (which really is almost no change at all weight-wise since aluminum is so light) and had a machine shop drill out the pin to 7.5mm (and of course it had the Jaguar CDI to solve the timing problem) then the vibration was almost non-existent.
Here's the dimensions of the stock wrist pins:
48cc piston: 33mm x 10mm outer dia. x 5mm inner dia.
55cc piston: 37mm x 10mm OD x 6mm ID
60cc piston: 37mm x 10mm OD x 6mm ID

Treatland has a wrist pin that will work perfect for the 48cc because it has a 7.5mm inner diameter.
Yamaha QT50 33mm x 10mm x 7.5mm wrist pin $9
https://www.treatland.tv/OEM-yamaha-QT50-YT60-10mm-wrist-pin-p/piston-pin-163300.htm

I am waiting to hear back from pocketbikeparts.com on their wrist pins.

Treatland also has a wrist pin bearing of good quality that will fit any of these engine sizes for $8 which you should get while you're at it:
https://www.treatland.tv/olympia-needle-bearing-10-x-14-x-13-p/oly-needle-bearing-10x14x13.htm

If anyone wants to measure their 66cc engine wrist pin and report the dimensions to me then I will look to find a lighter wrist pin to use as a substitute.

 

[Fabian]

That's handy information to know Jaguar

 

[Deleted member 12676]

pocketbikeparts emailed me and said these wrist pins have a 7mm inner diameter which makes them lighter weight than the stock ones.
Generic 33mm x 10mm wrist pin $9 http://www.pocketbikeparts.com/Piston_Wrist_Pin_p/cgpr302445.htm
Generic 36mm x 10mm wrist pin & bearing $13 http://www.pocketbikeparts.com/Piston_Wrist_Pin_Bearing_and_Clips_10mm_p/pbpn10mm.htm
Generic 36mm x 10mm wrist pin $9 http://www.pocketbikeparts.com/Piston_Wrist_Pin_p/cgpr302446.htm

1mm shorter than stock (37mm) is completely OK in case you're wondering.

 

[Deleted member 12676]

Also, the vibration expends some engine power which slows things down. I just replaced the wrist pin (5.4mm hole) of my 60cc engine with the one I had drilled out to have a 7.5mm hole and got 2.1mph more top speed. A 2 stroke is all about harmony. Less harmony = less power.