It has been interesting to look and compare photos of the 465/490 cylinder and porting to the later model engines.
I was thinking that these later motors could provide some guidance for future modifications of the old YZ's.
I mean, why not just copy the porting of the kx500 or cr500?
To see if this was reasonable I spent a little time collecting bore and stroke data from various big bore two strokes. If the stoke is the same as the YZ, then perhaps the port area and timing could be copied over as well... unfortunately, I found no other bike has the exact same stroke.
In any case, here is the table I made that lists the bore and stroke dimensions for the yz465/490 (in all oversizes) and the other big bore two stroke motocrossers. Dimensions are given in metric and english units. The bike with the closest stoke to the YZ at 82mm is the Maico 490 at 83mm.
There is one other interesting point from the table, that is, the standard yz490 piston is equivalent to an 8th oversize for a 465. Can those worn out 465 cylinders be saved by boring to 87mm?
Please let me know if anyone has tried this