Picked up a non-running coolster mountaintopz 3125r for dirt cheap for a Christmas present fir my son. Tore it apart, and it needs a piston and cylinder and new valves. I could buy direct from coolster, but im seeing full kits on Ebay and other places for half of what they want. Problem I'm having is figuring out the right parts.

from what I can tell, it's "supposed" to be a 125, but their parts on their sitel say 120, and the closest matches that I can find are all 110.

here are the figures I have:

Motor I'D plate says tzh157fmi
piston diameter measures 51.7mm
bore is 51.9mm
wrist pin is 12mm
Valve heads measure 22.9mm and 19.9

I found a cylinder kit that says it's a 52.4mm bore and a head that has 23 and 20mm valves, and everything else looks right.

am I on the right track?

 

There is something badly wrong, the 157 in the engine code stands for 1 cylinder, 57mm bore. Check the stroke and work out the capacity, my guess is it will be way less than 125cc. Either someone has previously fitted a smaller cylinder kit, or your engine was stamped up wrongly as a 125 at the engine factory. The Chinese do "mix and match" engine bores and strokes, but if stamped 157, it should be 57 (or more accurately 56.5mm bore).

 

The 57 in the engine number is supposed to mean 57mm bore but Chinese engines are sometimes mislabeled. For instance the supposed 250cc engine in my Taotao quad is labeled 171FMM so it should be a 71mm bore but I measured it at 63mm.

 

Did some more measuring- stroke is 48.8mm and the wrist pin is 12mm.

I'm coming up with about 105cc- but I noticed that the cylinder head is marked as 124cc.

Honestly, it doesnt make much difference to me. If it's actually a mislabeled 110, that's fine. I'm just stumped trying to figure out the parts I need to get it running.

I did find a thread buried in some forum that claims the TZH prefix says it's a Zongshen, dunno if that helps.

 

My guess would be that the factory ran out of 57mm bore pistons or cylinders and stuck a 52mm piston and cylinder on instead. Could have been done during a rebuild, but why go a smaller bore than standard? Either the 57mm or 52mm kits should fit, but I know you will be a bit wary of getting one that doesn't, as to further complicate things, a 57.8mm long stroke x 52mm bore engine is available that is described as a 125.

 

Yeah, after measuring everything I could find, I'm pretty sure it's a mislabeled 110. I though about getting the 57mm kit, but the wrist pin are different, so I'd have to change the rod and bearing for sure.

I have a 52mm cylinder kit and new head on order.

thanks for the help, is have never figured this out on my own.