Hi, does anyone know the differences between the two as i am after an o/s piston for a 247 montesa and as bultaco pistons are more common i was hoping they may be interchangeable without too much trouble,

Are the small end bearings the same size (piston pin same size ) and the same height. I can always more the ring pins if needed

Dave

Don't know about Mont/Bult piston similarities but there is someone selling Mont pistons on ebay UK at the moment, item number 120396701665 for what could be a 72.5mm Cota piston

72.50 may be standard size, can't remember but if it is it may be worth contacting him to see if he has others as he has a lot of Mont stuff to sell which is NOS, although you may need to give him the part number.

I got a 247 Wiseco piston from Jared Bates at Southwest Montesa in the US. It takes a different small end from the standard type but he can supply that too.

I was pretty sure they were different probably both made by mahle though?

Thanks woody, i have already contacted him but no o/s pistons as of yet, it was a bult piston he has that looks like it may fit but i'm not sure on wrist pin size and pin height etc.

O/S doesn't matter as it can be re-bored to size

Dave

Ive put a 238 bult piston in a mont 242(having put a steel liner in the barrel) and the the gudgin pin /little end bearings were the same.as was the skirt height.Just had to drill 2 holes to match the origional for the small transfer grooves in the back of the barrel.Given this i would think that a sherpa piston might fit a 247.might be worth giving the cota piston dimensions to Dave Renham to see if he could match a piston up?

Have you tried contacting Kevin Breedon? Seems to have a lot listed, never dealt with them though.

http://kevinbreedonracing.co.uk/products_pistons.asp

I know it's not what you're asking, but..........perhaps you could locate a standard sized new piston and have the cyl resleeved? Would cost some $$, but'll get you back on the trails......

Just a thought.

I did get a bultaco o/s piston and bored the barrel to suit and it runs fine

Dave