Display all headers To: ossamotorcycles@yahoogroups.com From: "woody_mar" Date: Wed, 01 Sep 2004 15:30:09 -0000 Subject: [ossamotorcycles] Re: 350 MAR bottom end... Reply-To: ossamotorcycles@yahoogroups.com   The 350/250 crankcases are the same but the 350 has the cylinder studs spaced wider apart so 250 cylinders won't fit 350 cases and vice-versa.   The 250/350 cranks take the same rod, pin and big end bearing kit However, the pin is positioned differently in each crank due to the different strokes of the two engines, so they aren't interchangeable. (discount the MK1 250 MAR in this as it has a different, smaller crank assembly from the others)   You could fit a 250 crank into a 350 engine but you'd have to put a 4mm spacer under the cylinder to lift it to re-align the port timing and take another 3 to 4mm off the top of the cylinder to get the compression back. That would give you a 280cc (approx) engine with the shorter stroke of the 250 and the larger bore of the 350 - basically an overbored 250, something that was done in the UK for some of the supported riders as the 350 was never that popular and there isn't enough meat in the liner to bore out the 250, so this was another means in the search for more power. Oh yes, and a reed valve too.       ------------------------ Yahoo! Groups Sponsor --------------------~--> Yahoo! Autos. Everything you need to know about buying or selling a car. FREE Quotes, 360° Tours, Research, Blue Book, Compare Vehicles, Buy Used http://us.click.yahoo.com/kEZsdA/bwnGAA/YiGOAA/fFPplB/TM --------------------------------------------------------------------~->     Yahoo! Groups Links   <*> To visit your group on the web, go to: http://groups.yahoo.com/group/ossamotorcycles/   <*> To unsubscribe from this group, send an email to: ossamotorcycles-unsubscribe@yahoogroups.com   <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/