What do we see here?

[deltarider]

Thanks Bryan.

[K2-K6]

Cheers Nigel. Well that looks to be a busted idea, shame but that's sometimes the way things go. I'll have to either buy new ones or plate the old ones after a good polish up to get rid of the pitting etc.

Yes Ken, it's these and the conrod bolts that appear to be running the closest to their design limitations out of all of them, and so difficult to make alternative.

Polishing would certainly take them in the right direction though, removing production marks that are sticking out (without removing base material bulk) will improve them in regard to ultimate stress capabilities and a good move with the polishing skills you have used on other parts. If you've a spare to experiment on that would give you good insight as to how they come out.

Plating though, no. It's another process that can cause problems with load performance so I'd stay away from that as a finish.

[Oddjob]

Are they not zinc plated initially Nigel? I'd have said yes or they'd rust for fun. By plating I meant zinc not chrome. I wouldn't of course use acid dip to clean them.

[K2-K6]

They've not looked it to me, certainly that could be wrong on my part though.

They do look as if they've been rolled to form the waisted section though, which will always improve the corrosion resistance on steel from compressing the outer layers and giving less voids for corrosion to establish.

Manufacturing when quenched is usually in oil too (possibly whale oil then) because it controls the cooling rate, establishing the desired grain structure.  When the hot steel is plunged into oil it immediately heats the oil next to it's surface with this effect partially stalling the cool down phase, with this rate critical in how the grains in the steel propogate to make the steel come to it's target tensile specification.  Too fast and it heads more brittle, too slow and it stays more malleable. So the goldilocks quench is just right 

The oil stage also adds some resistance to corrosion too.

[Trigger]

They can be plated BZP but, there are two parts on a SOHC that can't be pickled, Head studs and carb butterfly. The studs have to be in good condition to plate. Here is a picture on this page of plated studs >>>
http://www.sohc.co.uk/index.php/topic,20419.150.html

[deltarider]

Still in the process of learning... I've dimensioned a bolt similar to the one in the pic, only 35mm, so I can add a nut on the end. Question: is it crucial to have the shoulder part of the bolt on the outside of the bike or does it not matter much?

[Trigger]

No need for a nut, there is one welded to the shock mount 

[deltarider]

Not on the Koni's. They have only thread in the hole (one). The thread of one is suspect (either the clevis or the bolt, I still have to find out). Before I start anything, I realise I have two options for reassembly.
a) Have the threaded hole of the clevis on the outside and so the shoulder part of the bolt on the inside of the bike or b) vice versa which is how Honda assembled it.
This matters for eventual removal in the future.
a) implies removal of only the rearwheel, where as
b) means you'll have to remove the exhausts (original) to be able to get the bolts out.
Option b is clearly not my favourite. That's why I'd like to know if it matters much, whether the shoulder part of the bolt, which ofcourse needs to go through the unthreaded hole of the clevis, is on the outside like Honda had it, or just as well can be on the inside of the bike.
I realise this may seem a futile detail, but I hope to learn more on non standard fasteners.
This post (45 minutes!) has stressed my handling of English, but I hope I've made it clear.
Addition: I still find it odd, Honda did not chose the shoulder part of the bolt to be longer. The inside of the bushing is plain. Not only you don't need a thread there, but in theory the bolt's thread could gnaw on the metal in the bush.