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Why would Cosworth take the time to produce pistons that small. They are a car engine specialist and their pistons are far larger. Casting on head has been soldered/welded on, you can see the crack where it doesn't meet the fin properly. The ONLY way you'd know if the engine has been modified is to open it up after buying it and by then it's too late, why no mention of a cam to allow these pistons to work properly???
I've never seen or heard of anything like that, doesn't mean it's not true though. I've seen a lot of stuff from that era in things from endurance racing where there was all sorts of weird and wonderful things going on but never seen any connection to cosworth. They've done alot of consultancy work for different companies over the years some of which will never be seen. They worked on things like MAE engine in mid sixties which was ford anglia based block but at 81mm bore it's way past having any piston commonality with the honda engine. It revved to 10,000 though and made up to 140bhp from 997cc though so pretty advanced in power terms.Their obvious specialist area though is twin cam sixteen valve heads which if it was like that then it would be very interesting. It doesn't appear from the outside to be anything different though, so as already said you'd have to strip it to see what's in there.I didn't understand Trigger the yz250 reference as I though yz was used on motocross range by yam. I had a yz250h, last of the aircooled engines. It'd be intriguing to get to the bottom of it though.