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.
 
Last edited:
robs ss said:
Yes - my bad - you're correct about the chain type - but the point about the disastrous placement of the primary chain is still relevant!
Cheers
Click to expand...
When they made them they did not plan for them to be around over fifty years later. But I agree that the chains on a sohc honda are its weak links. The primary chains and cam chains are probably the biggest failure points when racing a honda 750.
 
Another exhaust port repair shipping off to
Ventura California. For the movie industry
 

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Make a pair of threaded stubs to fit recut threads in the ports and screw them in against seating gaskets. Then modify the starts of the pipes to make slip joints. Weld a tab on each pipe to accommodate the end of a spring. If Nortons were Japanese, the exhaust pipes would already be mounted that way.
'A job worth doing is worth doing well'.
The motor in my Seeley 850 is rigidly mounted, I still make provision for movement where the pipes fit the head.
 
acotrel said:
Make a pair of threaded stubs to fit recut threads in the ports and screw them in against seating gaskets. Then modify the starts of the pipes to make slip joints. Weld a tab on each pipe to accommodate the end of a spring. If Nortons were Japanese, the exhaust pipes would already be mounted that way.
'A job worth doing is worth doing well'.
The motor in my Seeley 850 is rigidly mounted, I still make provision for movement where the pipes fit the head.
Click to expand...
 
jseng1 said:
Why doesn't someone just machine new threads and provide a larger diameter exhaust nut?
Click to expand...
I have a set of oversize rose nuts lying around.
They are profesionnaly made, so there must be more of them.
They came from England, but I don't know who made them.

Norton Exhaust Port Repair
 
The job Dan did on my 750 several years ago. Good work, fast turn around, and still working fine.
Norton Exhaust Port Repair
 
ludwig said:
I have a set of oversize rose nuts lying around.
They are profesionnaly made, so there must be more of them.
They came from England, but I don't know who made them.

Norton Exhaust Port Repair
Click to expand...
My 74 850 came to me with oversize, left-hand threaded unobtainium roses. When started to self release, Dan was able to fit his sleeves and returned to standard thrwad size/direction roses.
 

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