I snaged this from another forum (tachometer readings):
RE: Ys 45 2-stroke - 8/26/2007 8:07:43 PM
sydc
Posts: 21
Joined: 5/1/2006
From: Skirlaugh, UNITED KINGDOM
Status: offline Hi Wood489,
I have recently converted a YS91st to aero, I believe that the 91st is a bored out 80st and should have the same output shaft threads. Here are the part numbers I used to convert the 91st with the output shaft thread of 8x1mm.
Drive washer YS part number F9323
Drive washer retainer YS Part number F9324
Reach through prop nut Tru-Turn part number TT-0813-A, (these prop nuts are designed to take the Tru-Turn alloy spinners).
Hope this helps,
Regards, SydC.
(in reply to wood489
Unquote
Would it be cheaper? I dont know, but folks are doing it. It may work for smaller engines too but you need to do your parts research here:
http://www.webra-austria.at/motor.php?lang=EN