125cc cylinder replacement kits...

Ottomic · 11-10-2022, 04:25 PM

I've got a couple projects (three pit bikes and one cart) with 125cc engines and I'm looking to just replace the cylinder and piston altogether.

One in the cart is a bit rubbed off, but reads "152FMI" and I'm guessing that the 52.4mm kit from amazon should be just fine, yeah?

The pit bikes are

154FMI
FH157FMI (two have this mark and are identical looking with "qiye" marked casings)

I've read a bit here that the two digits in the middle (52, 54, 57) should be the bore diameter, but I'm not seeing any 57mm bore kits. Am I just zoning out and completely missing them?

I'm guessing the stroke length would be different between these engines in order to give the same "125cc" displacement between the different sized bores, so the wrong kit could lead to headache or a piston crashing into the head.

I've had great success doing such swaps on 110's, 70's, and 50's, but wanted to tackle these bigger bikes.

Any help, advice, links in the right direction/previously discussed threads would be much appreciated!

Ottomic · 11-23-2022, 05:15 PM

Anyone have any input available on such things? Perhaps links to the info already discussed in other threads that I've missed?

Thanks either way.

dirtbkr188 · 11-23-2022, 10:15 PM

You cannot take the engine numbers at their face value when it comes to the Chinese engines. The engine makers take great liberties when listing an accurate bore and/or stroke size.
The only positive way to know what size bore and stroke you have is to remove the head, and then measure the stroke and bore size with digital vernier calipers.

Ottomic · 11-29-2022, 06:00 PM

Good to know! Just got a big shop put up so I can just tear these open and measure instead of hoping the right parts are already in the mail. :P

culcune · 12-01-2022, 03:03 AM

Quote:

Originally Posted by Ottomic

I've got a couple projects (three pit bikes and one cart) with 125cc engines and I'm looking to just replace the cylinder and piston altogether.

One in the cart is a bit rubbed off, but reads "152FMI" and I'm guessing that the 52.4mm kit from amazon should be just fine, yeah?

Any help, advice, links in the right direction/previously discussed threads would be much appreciated!

This little Honda DAX replica bike from Icebear uses a Loncin branded LC152FMI engine as seen in the specs. http://www.icebearatv.com/product/pbz125-2 Not sure if this info points you in any kind of 'right' direction...

11-10-2022, 04:25 PM	#1
Ottomic Join Date: Nov 2022 Posts: 3	125cc cylinder replacement kits... I've got a couple projects (three pit bikes and one cart) with 125cc engines and I'm looking to just replace the cylinder and piston altogether. One in the cart is a bit rubbed off, but reads "152FMI" and I'm guessing that the 52.4mm kit from amazon should be just fine, yeah? The pit bikes are 154FMI FH157FMI (two have this mark and are identical looking with "qiye" marked casings) I've read a bit here that the two digits in the middle (52, 54, 57) should be the bore diameter, but I'm not seeing any 57mm bore kits. Am I just zoning out and completely missing them? I'm guessing the stroke length would be different between these engines in order to give the same "125cc" displacement between the different sized bores, so the wrong kit could lead to headache or a piston crashing into the head. I've had great success doing such swaps on 110's, 70's, and 50's, but wanted to tackle these bigger bikes. Any help, advice, links in the right direction/previously discussed threads would be much appreciated!
	0

11-23-2022, 05:15 PM	#2
Ottomic Join Date: Nov 2022 Posts: 3	Anyone have any input available on such things? Perhaps links to the info already discussed in other threads that I've missed? Thanks either way.
	0

11-23-2022, 10:15 PM	#3
dirtbkr188 Join Date: Aug 2009 Posts: 498	You cannot take the engine numbers at their face value when it comes to the Chinese engines. The engine makers take great liberties when listing an accurate bore and/or stroke size. The only positive way to know what size bore and stroke you have is to remove the head, and then measure the stroke and bore size with digital vernier calipers.
	1

11-29-2022, 06:00 PM	#4
Ottomic Join Date: Nov 2022 Posts: 3	Good to know! Just got a big shop put up so I can just tear these open and measure instead of hoping the right parts are already in the mail. :P
	0