Engine Trouble Yd 100 clone blown up


New Member
Local time
5:24 AM
May 29, 2023
United kingdom - Edgware
Welp, its a relatively new engine (4 months) and the piston and cylinder are completely destroyed, I think there are shards in bottom end so will definitely take it apart. The culprit of this failure, believe it or not is the c washer from the throttle slide in the carby. I had recently taken it apart and lost it so I just fabbed one up from plastic cap but turns out it was hiding intake all along.

Engine ran well for about 15km after absorbing clip, and I pushed it hard with out knowing and didn't notice a thing. Engine was ran without airfilter BTW
I was wondering about options for cylinder, can I run an after market one from a saw or maybe a scooter?

If you look closely at the transfer ports you will see its edges (before the tunnel starts i.e on the skirt) rough (was wondering if its normal) and there appears to be a sort of filler in the corners of them however the angling of the ports look good i think

The piston has clear spots where you can see aluminium, i wonder if this is from the clip mashing up and down in cylinder

Anyway stud spacing is 50mm and crank is zmn100. Engine was purchased from Ali express for £65



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I would be worried about the connecting rod crank pin being roached. I'm sure with a failure like that, some metal made it thru the crank pin bearing.
Yes I think this is what I'm going to do, even though its pretty hard as a relatively new builder. Ms660 54mm with 12mm wrist pin seems like it should work, il order the cylinder and see if the geometry can be corrected via trimming the height and if not il just return it
The MS460 and 660 is a common build, I just didn't reccomemd it due to the difficulty. You will have to find a solution that isn't a bushing to get the wrist pin from 10mm to 12mm on your engine. The transfers just need to be filled. Most folks use JB weld. I don't believe either needs the height teimmed for the swap.
The most important part is the stroke length, if the stroke is too short then the piston won't clear the ports.
Get that bottome end cleaned out good, and the easiest conversion jug is the minarelli conversion

Unless I am mistaken. I thought most Minarelli builds were based on the 80cc bottom ends. I know there is a horizontal engine cylinder that has 49.5mm stud spacing that in theory could work with a YD, but it's the exception more than the rule.

Easiest "bolt on" conversion for a YD bottom end is going to be either an avenger 85 or phantom 85 top end, but both require a long rod with a 16mm small end for the 12mm needle bearing.