CB750 cam on advance/retard mechanism

[PHILIP2908]

Hello everybody.
Just looking at billdn’s problems with setting ignition timing; a comment by my fellow Gloucestershire resident, Bryan, forced me to look at my 750 (still fighting me after 5 years – it WILL be on the road this summer).
It relates to the 22mm nut on the end of the crank and how you should not use this to turn the engine over whilst the plugs are in.
A previous owner seems to have done this and I noticed that the nut wiggles gently around gently, scribing an oval pattern, noticeable even when turning over on the starter. Still runs though.
I seem to remember that the cam & advance/retard plate and cam sits on a 6mm screw thread which is drilled into the end of the crank and mine is obviously bent which will upset the points gap.
Two questions;
1.   How can I replace the threaded portion emanating from the right-hand crank end? Is it screwed in? Please don’t tell me I have to take the crank out !
2.   Could this problem be solved by installing an electronic ignition system such as the one from Dave Silver or Hondaman?
Any advice appreciated. TIA.
Regards,
Phil

[AshimotoK0]

https://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_250_55&products_id=2877


Original part is 30231-300-010 + 'O' ring


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[JezzaPeach]

I have noticed something similar on my CB500/4, as the large end nut has a small securing bolt in the middle and when this is tightened up it goes slightly off centre. The large one has a graze on one edge suggesting that being dropped caused the cam spindle to bend minutely in relation to the base plate. It is so slight it hasn’t affected the timing or gap significantly and is only really evidenced by the small centre bolt head drifting about 1mm off centre only when fully tightened.
I found a nice very clean assembly online and will replace with that next time I need to adjust the points. (which have kept their settings well)

[PHILIP2908]

Thanks for the info on the Yamiya part; but how do I take the 'old' one out?
- Locking 2 M6 nuts together and winding it out?
- And what is the 'O' ring for? Is it screwed into the crankshaft oil feed?
I still think that electronic ignition would be a better resolution. Thoughts?
Cheers,
Phil

[K2-K6]

Yes to how can you remove, two nuts etc.

Designed to be sacrificial in the event of a crash so that it doesn't trash the crank, they are quite soft and not heat treated to make them spring type metallurgy.

You'll need one whatever ignition system you use as they all have a rotor of varying design fitted to that shaft.

If you remove the advance and retard mech along with points plate,  then you can spin the motor and mark the error to just gently bend it back to rotate straight again.  It can't even be far out else you'd experience much more problems getting the points to work.

The DS ignition I think may use the points (or they used to sell one like that) with many others using the original A&R mech too. All of the full electronic systems will need at least competent alignment from that stud.