Anyone done the JIS to ISO headtube adjustment?

[slomo]

So i have one of those early 90's Rockhoppers that (it seems) Specialized decided to use all the weird sizes.....
73mm bottom bracket.
JIS heatset.

Although JIS headsets are still available, the variety is diminishing.

Ideally i would like a black headset with cartridge bearings - which would be so much easier if the headset were ISO.

Has anyone had the adaptation done?

My understanding is that this involves increasing the headtube ID by 0.2mm and reducing the crown race 'shoulder' by 0.4mm.

Any help greatly appreciated.

 

[lensmansteve]

I wanted to fit an FSA "The Pig" 1.125" headset to my '90 Reynolds 501 Raleigh Moonrun, and a modern Ritchey 1" to my '93 Clockwork. In both cases, I ground the cups down very carefully to achieve a nice fit. It was a fairly lengthy and tricky job, but worked out well. Crown races were ok without any reduction. My workshop is modestly equipped, and I didn't have suitable reamers- I might have been tempted to mod the frames otherwise, it would have been easier..

 

[slomo]

I am pondering whether adjusting the frame and forks is for the best in the long run.

I can fit an ISO headset with cartridge bearings - making maintenence much simpler.

I'll report back if i have the frame and forks adjusted.

 

[danson67]

I've not specifically made this change from JIS to ISO, but have the reaming and cutting tools to do it for my framebuilding and repairing work.
Headtube bore from 30.0 to 30.2mm with reamer, crown race from 27.0 to 26.4mm, roughed with lathe, then finish to size with cutter.

They are just the normal stuff for prepping a frame after building, so a decent local shop or builder should be able to do it, or you can send it to me. Not a big job, maybe 1/2 hour.

All the best,