A friend of mine recently bought a '98 WR 400. Here's what we found: it got hot, and burned the piston/cylinder (see pix) Whilst searching for options, I came across a TT post here that alluded to using a 426 jug, a 450 piston, and the stock 400 bottom end and head. We're kicking options around and reading as much of the material on here that we can. If we're asking redundant questions, we do apologize...we've searched for these and not found answers! Here's the original inspirational post: http://www.thumpertalk.com/topic/935821-400-to-426-conversion-the-easy-way/ - Can the 400 jug be bored out to 426 (we think that's 95mm or so, right?) safely, without over-thinning the cylinder walls? We've heard of them being bored out to 97mm and that seems extreme. Is it better to just buy the 426 jug and be safe? What's the max a 400 should be bored out to? - What's the correct piston-to-cylinder-wall clearance? (If we bored out the 400 and used a 450 piston?) - What's the deck height differences on the stock 400 setup vs the 450 piston/426 jug setup? - What's the final static compression ratio with the 426 jug and 450 piston? - What years of 426 jug and 450 piston will work? (thinking ebay parts maybe...maybe). - What kind of power increase/delivery should be expected from the bump up to 426cc? Because of the original post, we feel that an OEM Yam 426 jug and an OEM Yam 450 piston will not need extra calculations and theorizing...it will just need assembly, not figuring. On the other hand, it's tempting to bore out the 400 cyl to save a few bucks, but then we need very exact data for the boring and then matching the piston, etc. Anything else we haven't thought of? Pix of the damage prompting the rebuild thank you all!