Headset Fit Advice - 91 Roberts White Spider II

[7Speed]

I am a very average mechanic and need some advice on fitting a 1” threaded headset to a Roberts White Spider. I am a headset fitting virgin and it all looks a bit intimidating.

I picked up a 1" HP-M900 Headset but it seems this came in a few different cup sizes. It was described as "English" which I thought meant ISO standard thread. The frame head tube internal diameter comes up as 29.9mm when I measure it. The headset cups outside diameter come up as just over 30mm - around 30.2mm. The 0.3mm difference seems like quite a bit. The same headset also comes in a version with a 30.0mm outside cup diameter. I have the tools etc to press the bearing cups but really don't want to damage the frame. Is the 0.3mm nothing to worry about and essentially needed for a good fit? Any advice welcome.

7Speed

 

[FluffyChicken]

Normally you would have 30.2 for the 1" headset on an MTB, it could be your internal reading or you need a special 30.0 cup headset.
The frames steel, it'll be the cups that go if anything ?

What's your crown race diameter (just another variable to worry about with 1" headsets ;-))

Stick Roberts W S in the title, as owners/builder may jump on the frame knowledge.
My personal advice for most people building bikes would be.
ohh it's a bit stiff, whack it a bit harder (hammer and wood method), probably the method used by everyone at home circa late 80s or them pesky Oranges.



Older headsets (loose ball XT/DX M73x & M65x )





M900


Then most up to date spec (this is 199 cartridge XT/LX

 

[7Speed]

Thanks for the advice @FluffyChicken. I will take a few more measurements and worry a bit more

 

[7Speed]

Sooo…more measuring suggests I have a HP-M900 1” headset with 30.2 cups and 26.4mm crown race - @FluffyChicken thank you for telling me to measure the crown race.

The frame is definitely 30.0mm head tube. Original fork which has a very short a-c which limits tyre choice has a CR seat of 26.4mm. I have two alternative 1” forks - a P2 and a Dave Yates that have a-c of 390mm - both with crown race seat of 27.0mm.

Essentially I need a 30.0mm cup, 27.00 crown race 1” headset if I want to be able to run some bigger tyres. Anyone think I am wrong or that there is more margin for error than I am allowing?

I had no idea a headset would be so complicated. Thinking of going threadless given I would have to significantly extend threads on the new forks - feels simpler or Am I opening up another can of worms?

Also - if anyone wants a 1” HP-M900 NOS headset with 30.2mm cup and 26.4mm crown race I have one available at a good price…

 

[hamster]

The cup is an interference fit, so it should be bigger than the head tube it fits into. Have you measured the head tube for ovality?
Remember that a vernier is known in engineering circles as a 'very-near'.

I would just get on with it and press it in.

 

[7Speed]

Thanks @hamster - saw the same recommendation on 30 vs 30.2 cups from Sheldon Brown and @FluffyChicken said the same as you. My issue is now the crown race - which is a 26.4 vs the JIS 27.0 I think I need. Will find a way…seems I can got it wrong is many ways.

 

[7Speed]

Any thoughts on machining the fork crown race seat? Not certain how feasible this is, but it’s just 0.6mm…or machining the crown race from 26.4 to 27.0mm

 

[ishaw]

If the cups fit, isn't the simplest option to find a crown race in the correct size? The rest of the headset should be the same regardless of the race. I'm sure there are people on here that may have a spare, even some who have one for the same, but opposite reasons you have?