A week or so ago I advised I'd ordered a socket to fit the cush drive nut in order to compare tightness between torquing up the nut or using a hammer and drift. Well, the socket arrived today, so I set about making the comparison.
First I tried tightening the nut just a fraction more (already done up previously with a punch). At 140ftlbs I stopped, as the socket kept slipping off the nut. Still no movement. I'd add that I'd locked the flywheel via a 1/2" stud through the 'sump' and into a balance hole, to circumvent the cam messing with the figures. So I'd guess the nut was at least 140ftlbs.
Secondly, I backed the nut off to discover how much torque was required to bring it back to just touching the sleeve - c. 20ftlbs.
Lastly, I measured the cam overlap at full extension (no spring fitted) - 5/16", confirming that even with a broken spring, one still has drive (assuming correct parts fitted).
But here's the pinch - engineering wisdom states that there is little correlation between torque and 'tightness' or compressive force generated by a bolt or nut. Apparently assumed tightness, even taking account of thread pitch and lubrication, can vary by 50% or more, which is why many critical fastenings these days are set by yield as opposed to torque. For my own part, even after almost sixty years of bike ownership, I've never had a problem with doing such nuts up with a drift, so shall continue to do so. By the feel of the hammer one can tell when it's 'there'.
