RS 125 > CR 125

[Munchkin]

I have an RS 125 engine in a Micro Sprint I just bought. The local track rules don'nt allow the RS. I have a ported CR cylinder and head. Will the CR cylinder work on the RS bottom end? What do I need to look for if it will fit? Any help or advise will be appreciated. Thanks!

 

[tzr8cr]

1 make sure the bottom of the cyl doesn't interfere with the crank.
2 if id doesn't intefere check your squish to make sure the piston doesn't hit the head and you have.030 clearense
you might have to use the rs head with the rs piston or vise versa cr with cr
what year rs motor ? what year cr?
i believe the rs 98-present is a 54 stroke x 54 bore make sure they are the same
i think the only difference might be the porting and head volume

 

[Munchkin]

Thanks for the rply TZ. The RS is a "94, I think the CR cylinder is a "96 but to be honest, I don't know for sure. I guess I could sell the RS, and just buy a CR, but I thought if the bottom end is the same, I could just swap the top end...Anybody ever done this???

 

[tzr8cr]

yes it's been done the problem with the 94 is a longer stroke than the cr i beleive. i know that it's been done but you have to notch out the cases where the shorter stoke cylinder takes place of the longer stroke one.also i'm pretty the notching of the cases is due to the skirting on the piston and such because of a shorter con rod for the shorter cyclinder. this was a common upgrade for the 94 -97 tzs kevin murray had a kit to convert to the 98-newer square bore but you had to send him the cases for the necesary cutting and such. put the rs motor for sale on www.usgpru.net then buy a cr motor probably your easiest way. let me know if you want to sell and i could check around for you. might be able to get a resonable amount for that year motor. the site i gave you would probabbly be best though.

 

[MXFastGuy]

The karting guys on the forums over at ekartingnews.com can tell you everything you ever wanted to know about the CR/RS125 motor, and LOTS more!