Hello , I'm hoping to get some information regarding my CRM250 , I have what I believe is the MK2 however I live in South Africa and spares are unobtainable I'm in the process of totally restoring the bike and I managed to find what might be the only other one in the country so I bought it to use as spares , the two bikes seem identical however upon removing the cylinder from each engine I found one has a 66mm bore and the other a 72mm bore , finding a piston and rings for the better condition 72mm bore seems impossible and I can't seem to find any info on the bike with a 72mm bore . Is there anyone out there who might be able to enlighten me as to why I might have a 72mm ?

The cylinder has been overbored in the past. Heres a link to a company with all sizes im not sure on availability you would need to contact them
http://www.forged-pistons.co.uk/webshop ... iston-kit/

Overboring to 72mm would require some serious work and making a bespoke liner. Maximum piston size for a CRM is 68mm I took mine out to 68.5 or 68.25 (can't remember) and that required a special racing piston. If you bore out more than ~70mm you have no liner in places.

You should be able to get the 66mm bore rebored and use a TRX 250 piston as in the FAQs ................

Thank you for the response guys much appreciated, so obviously someone has done some work to this cylinder , I must say it looks absolutely factory which is why I thought it was, I will have to move forward on my project using the standard cylinder that I have , one last question if anyone can offer advice. The standard cylinder I have looks to be in great condition however there is one very small vertical scratch about 20mm in length just above the exhaust port I can hardly feel it , I know this is not ideal but getting re nickeled is not an option for me , I'd like to know if the bike will run like this ?
you guys talk about boring , but as far as I understand the crm has the nickel plated liner and if I was to bore this I would need to have it nickel plated again (not an option for me)
Please excuse my ignorance with regards to these things but that's why I'm on this forum

Mk2 crms dont have nickel plated barrels its just a case of getting it rebored which is much cheaper.

Shane please read the FAQs before you ask questions. If they don't answer your need at least you will be better informed to ask a more pertinent question. - viewtopic.php?f=20&t=5267

I shall do that , thank you once again for your responses I've actually never joined a forum before so I'm unaware of the appropriate protocol

Okay I have read the FAQ's and have gleaned quite a bit but before I purchase a piston and prepare for a rebore I would just like to confirm something , I intend to use the TRX piston as suggested in the FAQ my bore is currently the standard 66mm , what size TRX piston would I need ? would it be a 66.25mm ?