how to measure "head" and bottom bracket

[emilmh]

Hi Guys,

I'm building a 1988 Centurion Signet road bike into a single speed and want to overhaul/replace the head cups/bearings, and the bottom bracket. The condition of the original is pretty good, except there is some chipping in the chrome on the head cup/nut things and some cracked parts in the bottom bracket spline thing. I will be buying parts online because im on a strict budget, so i cant simply compare the two side by side.

My questions.
1/ How do i know what size cup/nuts washers etc i need for the "head" section (where the forks and stem go through)? I've heard a bit about 1" heads? Where is this measurement taken from?

2/ How do i know what size bottom bracket i need? How do i measure this?

Given the age of the bike and that japanese road bikes of this age seem to be quite similar i am hoping the wise users of this forum will be able to let me know!

Thanks,
Emil

[Uncle Grumpy]

For that model, headset would be 1" threaded (provided you are using the original fork).

Bottom bracket would be English thread, but not sure of the BB axle length. If you're going to set it up as a single speed then the axle length would depend on the cranks and chainline you wish to run. What cranks are you going to run?

Grumps

[emilmh]

For that model, headset would be 1" threaded (provided you are using the original fork).

Bottom bracket would be English thread, but not sure of the BB axle length. If you're going to set it up as a single speed then the axle length would depend on the cranks and chainline you wish to run. What cranks are you going to run?

Grumps

Thanks for your reply.
Yes i will use the original threaded forks. I was suspecting it was a 1" but wanted some confirmation.

The cranks im using are sugino 175mm i think. I'll have to re check. The cranks and chainline are already "set up"/sorted, i merely want to replace the existing bottom bracket with a new one of the same size. As i was browsing some cranks online, i saw that they came in different sizes, so thought that if i knew how to measure mine, it would make it easy to know what size replacement to get

Thanks again.

[Uncle Grumpy]

Yeah cool, just measure the BB axle then once you get it out of the bike to make sure you get the right one.

Actually, before doing that, set up your rear wheel with your sprocket on it, and run a chain to your crank to check the chin is running straight. Then you'll know whether you need to go narrower or wider with your axle. Do be careful though if you think you need to go narrower, that you have enough space to ensure the crank arm doesn't hit the chainstays.

Grumps