I’ve had a few garage hours this afternoon and did some work on the nav I’m building from a box of bits. This mostly involved searching out the best front frame member to use.
what I wasn’t pleased to see on two of them was the beginnings of a crack that was only visible with the frame members off the bike and the paint removed. It’s rather an odd design as they are part welded and part brazed. I shall cut the cracks and mig weld them up. I may also weld the plate that the tank mount is attached to, in between the brazing. Given that 2 of my 3 spares are cracked , I’d check yours when you have the opportunity !
The crack is just above the frame top rail bolts and just at the end of the triangular gusset.
I've not seen a crack there before - when I next look in one of my lockups, I'll get back to you.
To be honest, yours does not look like a crack - its not jagged?
However, I have seen cracks before, lower down where the engine meets the frame. These are much more visible.
two of my 3 spares were cracked but I only saw it when I removed the paint. They are definitely cracks, I explored them with a file prior to welding them up!
You have an early Jubilee front frame member there. The top hole, opposite the tank mounting boss is provided for (don't know what but possibly the optional fairing or crash bar of early days). On the later models there is no third hole..
I can see the weld of the lock stop for Jubilee, near the third hole, not present on the Navigator.
I believe the cracks were soon seen in this model and Norton thickened up the steel pressing that encloses the cast steel headstock. Brazing would have been used to prevent overheating and cracking of the casting which I hope explains why a combination of welding (steel to steel) and brazing (steel to casting) has been used.
I would suggest you start with a Navigator front frame member if you have one. The head steady will be the correct one with holes at the right height for the taller Navigator engine.
Navigator frame member identified by two ears for mounting the head steady, rather than a bridge on Jubilee.
Have you got one?
I hope this will help others who might be trawling their stock of lightweight frame parts.
Thanks Peter, that’s interesting! I have two Navigator ones, one on the jubilee - which i haven’t inspected yet but is coming off along with its attached road holder forks and a spare one with a little crack in that I’ve welded up. I have a good jubilee one to fit to the Jub when I’ve finished putting a set of half decent forks together.
Mine are going to get a fairly easy life so I’m not too worried.