August 17, 201115 yr Starting to restore my 172 montesa and was always told it was a 123 bored out to 156.Have got a 123 engine for spares and the 172 has a longer con rod and heavier fly wheels. abit more than a bigger bore me thinks.
August 23, 201115 yr Top parts are completely different and you are right about the longer conrod. The bottom bits? Don't know. Could be same as the 123. To tell you the truth have never compared them but it would not surprise me if a lot of the parts are the same. I have a couple of 348's and 247's and a lot of the parts are exactly the same. Good luck with the restoration. Just in case, if you can find another 172 motor, buy it mate and make sure that the kick starter shaft is OK. They where prone to breaking and finding another one are as rare as rocking horse poo. You probably know this but I am going to tell you anyway. The 172 stands for the weight of the bike, 172 pounds. I really have no idea of cc capacity but I would guess you are right in saying about 156cc.
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