Norton Exhaust Port Repair

B+Bogus said:

My machinist used to do this for the Lancashire Constabulary bikes back in the day.
Nowadays he makes a bronze insert to return to spec.
I think the real villain of the piece is balanced exhaust systems and shorter thread engagement.
I've never seen an earlier 750 head requiring remedial work, and conversely, every 850 head I've had has needed to be repaired

Click to expand...

Probably doesn't happen as much on a 750
But it does happen

Oversized thread necessitate the making of one off rose nuts and I cannot see that being any easier or cheaper than making and inserting a threaded insert.

But moreover, cutting and using an oversize thread isn’t a long term fix IMO, how many times can you do it before you run out of material ?!

An insert can be re fitted countless times without ‘eroding’ the head. That said, it is unlikely to need doing often as the bronze material usually used is far harder wearing than the base aluminium.

So all in all, IMHO I cannot see how cutting bigger threads and making bigger rose nuts is in any way better than a quality insert job.

baz said:

Probably doesn't happen as much on a 750
But it does happen

Click to expand...

It's worth remembering that late 750s had balanced pipes too Correction - no they didn't!

Fast Eddie said:

So all in all, IMHO I cannot see how cutting bigger threads and making bigger rose nuts is in any way better than a quality insert job.

Click to expand...

Couldn't agree more!
I suspect the only 'advantage', and why plod bikes were done like this, was faster turnaround for reduced fleet downtime.

B+Bogus said:

It's worth remembering that late 750s had balanced pipes too

Click to expand...

Eh, what.

L.A.B. said:

Eh, what.

Click to expand...

Yup - I'm wrong again!