Topic: '69 750 Rear Sprocket Fasteners

[Bob Wessner]

While I had the rear wheel off for a tire change, I noticed the nuts for the rear sprocket (4 of them and 2 tonged washers) were a bit banged up. According to the parts list, these are supposed to be 12mm, however, when I put a box wrench to the ones on my bike, they appear to be more like 19mm. Actually, given the task, 19mm seems more appropriate, but why the difference, can anyone shed any light on this. Thanks.

[Chris in Ramsey]

Hi Bob, 12mm is the bolt diameter, 19mm is the size of the bolt head/nut. Head and nut sizes can vary between manufacturers and applications. Different types of bolt heads and nuts will be different sizes from any "standard" and the "standard" has changed over the years.

[Bob Wessner]

Thanks Chris. After making that post, I vaguely recalled something from a generic motorcycle maint. book that the nut/wrench size is not how they are measured, so I went and double checked. The nut may be 19mm, but the bolt/stud to which it is fastened appears to be 12mm in diameter which is consistent with the explanation in the maint. book.

[Sam Green Racing]

Just pulled this from the bottom of page 900

Sam.

[Jonesy]

And now, the big burning, million dollar question....

WHY??

[Gordon]

Because he's awake at 2am and bored.