Need help asap pleas convert 90cc baja to 125cc

[Blasterbrian]

Can i convert my 90 cc baja to 125 cc by switching cylinder, head and crank, cracked cases on 125 motors look the exact same are all bottem ends the same please help i have 50cc bottem end too all look identical i can change crank and head and cylinder

 

[Blasterbrian]

Anyone know ?

 

[motodevo]

Depends on the 125. Some run the smaller stud spacing like the 50/70/90/110 whilst the others run the larger stud spacing. So if the studs for the cylinder/head are spaced the same it should all swap into the 90cc cases. May just need to clearance the cases if theres anything like case webbing that interferes with the longer stroke crank. Make sure to use the oil pump from the 125 and make sure the outlet size that exits the cases under the cylinder (to feed top end) is the same size, if not drill it out to match. Also the opening where the the skirt of the barrel fits into the cases may need to be opened up too if its too small, doesn't need to be precise, can be done a dremil or similar

 

[Blasterbrian]

This is great info is there anything else i will need to know do i need to swap the cranshafts, or is 90cc 110 and 125 all same stroke?

 

[motodevo]

Most 90cc china motors use the70cc bore with a 110cc crank(bore and stroke of 47x49.5) where a 110cc has a 52mm bore (52x49.5). Assuming the 125 has a 54mm bore (about as big as will fit between stock stud spacing) you will only get around 113cc. You need 54x54 to get 124cc.

 

[Blasterbrian]

Okay thank you i realized after pulling my head and cylinder that i think the only problem is the timing chain guide in cylinder broke and the timing chain tensioner under fly wheel may be broke or missing how do i get fly wheel off

 

[motodevo]

You need a puller, if its kick start only it will be a 27mm reverse thread puller, if it has leccy start there are 2 different sizes so you need to work out which one you need. All can be had for less than 20 bucks off ebay and the like