Assuming the Zeda 100 has a 10mm rod, you need a way to run 52mm (12mm wrist pin) piston. If you do, you're options are
1) Buy a 12mm pin crank that has the stroke you need
2) Use bushings and washers inside the piston to run a 10mm wrist pin, which would allow you to run a 10mm needle bearing on the conrod
3) Something I would never suggest to do before the other two, but people will run a 12mm wrist pin and instead of a needle bearing, they'll use a bushing instead. I am not a fan of this at all.
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Photo #1 - This is a 372xp piston with a 10x12x10 bushing. Look to the left, notice how the bushing is sticking out? You want it to be flush. Otherwise the bearing cage is going to ram into it.
Photo #2 - This is a 10x12x8 bushing. It is flush with the piston and will not contact the bearing. I had to look hard for bushings 8mm in length, most common size is 10x12x10
Photo #2 - 372xp piston with a 10x12x8 bushing. It fills the entire piston where the wrist pin is and doesn't contact the bearing cage
You cannot only use bushings and wrist pin. You need a wrist pin 3mm shorter than the original one. My 372xp wrist pin was 36mm, so I needed 33mm. I couldn't just use another 10mm x 36mm wrist pin.
Without washers circlip is not securing the wrist pin or even touching it, only the ear/tail is. The wrist pin is 10mm OD and the circlip is for 12mm. You need to put a washer on each side because the piston circlip will touch it entirely.
The M6 washers are 12mm OD and 1.5mm thick
(click this for the link)
Photo #4 - MS460 piston with 10mm bushings. The only part of the circlip touching the wrist pin is the ear/tail which is not safe
Photo #5 - Using an M6 washer, it fits perfect over the wrist pin as the washer is a 12mm OD.
Photo #6 - Now with a 33mm wrist pin, and a 1.5mm thick washer on each side, it equals to 36mm which is the original length of the 372xp wrist pin, and the piston circlip is contacting it entirely making it safe.
I made the mistake of buying M6 washers in a kit but they were 1mm thick. You need to find the length of your wrist pin first. For example, if it's 40mm long, then finding one that is 38mm may be easier than 37mm. You need to find out the original length first because then you'll know how thick you need your washers to be. For my 10mm x 36mm wrist pin, it was easy to find a 33mm wrist pin instead of a 34mm in length pin, therefor I went with 1.5mm washers.
If I were you, I would ditch the P85 piston, get an Ms460 piston and run a piston port setup. I see many failures on the piston skirt where the window is, this is mostly due to saw pistons being thin anyways and the window affecting the integrity of it. Yes I know there are plenty of people who have had no problems, however the amount of people who's pistons explode right at the window can't be ignored. I've never heard of an exploding piston on a YD100 or a 66cc. P85 is good, just some serious flaws that can't be denied.