SOHC.co.uk Forums > CB750

Headstock dimensions please

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K2-K6:
Haven't got one readily available to give you accurate dimensions but, the one you have got maybe the original design solution.

If each yoke is located well to the bearings (seems to be so from the pics) then the only requirement is to pull the bearings into correct pre-load which the rod will do if of sufficient design spec (rods like this are used to hold buildings together and every bolt on the bike is essentially the same application). The fork legs will then keep the yokes in alignment, the tube is essentially redundant.

I'd guess that the headstock you have could be longer than standard so couldn't be adapted from a standard stem hence the solution that's used (odd but possible).

In front end damage the distortion usually happens on the legs just under the bottom yoke, the headstock of the frame itself and to the tube as it leaves the bottom yoke just inside the bearing race.

Can you get any info from another owner of this type of frame?

RupertB:
Good idea - I might try emailing Tony Foale himself. I'm good at missing the obvious!

Seamus:
These may help

http://cgi.ebay.co.uk/Honda-CB-750-CB750-SOHC-73-Bottom-Yoke-/270655844039?pt=UK_Motorcycle_Parts&hash=item3f04586ec7


http://cgi.ebay.co.uk/Honda-CB-750-SOHC-bottom-yoke-/370416018679?pt=UK_Motorcycle_Parts&hash=item563e83e4f7

RupertB:
Everyone massively helpful as usual - I emailed Tony Foale last night and got a reply this morning! Apparently the set up I have got is actually what he made - a tensioned rod between the bearings. Looks Heath Robinson but as suggested earlier in the thread there is every reason for it to work, and work it must have done judging by the success of the frames.

Tomorrow sees the head and barrels off to North West Enamellers for blasting to get presentable for fin repair...

K2-K6:
Aha! that makes for less work you need to do.

I've heard about Foale frames before but never actually seen one, it looks like he's pushed quite hard towards a light / strong solution and I guess that entails some more unconventional thinking to take a step outside what is standard.

It looks interesting, be good to see it when finished.

As a further extension to the original design logic it may have a specific torque requirement during assembly, in that taper roller bearings can and often do take a compressive load that maybe desirable as a form of damping to the rotation of the forks (i.e. a mild form of steering damper) if so, this would have to be set correctly prior to tightening the clamps around the fork legs. Be interesting to get an opinion from the designer for your benefit in re-assembly.

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