classic motorcycle forum

Yes, they're well worth having. As for being "not ideal" you can buy a kit to fit a filter in the feed to the engine but it's much more pricey than the standard return-line kit.
I'm happy with the return-line jobbie.

Thanks for your reply - when I say 'not ideal' I was only referring to a few comments I had read on other sites - not that I'm any sort of authority on the subject!  

For final precise sizing after fitting the bush my personal preference is to hone rather than ream. I find honing to be more precise and gives a better finish than reaming.
Also, on the gloom and doom side, how much wear is there on the mainshaft? Usually, if a bronze bush is worn to that extent the underlying shaft is badly worn also. There isn't much point renovating one without the other.
Again, I have refurbished mainshafts using an electroless nickel system. This is not electroplating but instead uses a chemical bath where the plating medium can be precisely controlled so a very accurate repair can be made that is ready to fit as soon as the job is removed from the bath.
A sweet gearbox is a thing of joy. I appreciate why you want to get it right.
Good luck,

There is actually a section of the main shaft that is worn - at the cog end of the pictured gear, directly under the cog. When I measure the area with a digital vernier it appears to be worn about .006" undersize to the rest of the shaft - I fully expected it would need replacing at some point, and wasn't sure if a repair was even a possibility. I was hoping that replacing the bushes might buy me some time!  :-/
The gear box always worked fine last time I rode the bike - never had any noticeable problems at all. The main reason I took the box out was to replace the drive side oil seal - and at that point I decided to take the clusters out and check / replace the bearings at the same time - I'm only an amateur 'mechanic', and was hoping to get it back on the road quickly!  :-[
So where is it possible to get the main shaft repaired? And what sort of cost are we talking about?

Thanks!

Thanks for your reply, 52t-bird  

Now you mention the direction of the spiral inside the bush, I'm wondering if the one already fitted is correct or not?!
 - The gear would be spinning clockwise, (as viewed from the angle in the picture) but the spiral appears as though it would be driving oil back towards the camera rather along the shaft towards the clutch end of the mainshaft - So am I right in thinking it's already the wrong way round??

Thanks again.

Although it would be this version manual  http://sackheads.org/~caseyc/triumph/reference/99-0983.pdf

-for a '76 ('73-'78) model

 Well done for finding that - I only stumbled on that link today - didn't realise there was loads of other manuals!!