Originally Posted by
sreynolds1977
There is some damage to the headset bearing races on this bike and so I would like to replace them. The problem is that no one seems to know if it has a JIS or ISO headset. I'm on an extended tour, so taking the headset apart to measure everything would be a pain, plus I would have to buy a dial caliper.
Well, if you're planning to replace it you're going to have to remove it at some point, right? May as well be now. And you can get a cheap, but functional vernier caliper for $3 at Harbor Freight:
6" Utility Caliper
Also, how would I determine what "stack height" this bikes headset has?
You measure the thickness of the cups and races (with the bearings in place, and excluding the flanges that insert into the frame) and add that to the thickness of the locknut and any washers or spacers.
But if you're replacing your current headset, the more important measure is how much stack your frame and fork can accommodate. Remove all the cups and races from the frame (remember, you're planning on replacing them anyway), put the fork through the head tube so the crown race seat (where the crown race would sit, if it were still installed) snug against the lower edge of the head tube, then measure how far the steer tube extends above the top of the head tube. That measure is the tallest stack height your bike can use. You can use a shorter headset and simply add washers or spacers to take up the slack.
When I had the headset apart to investigate the looseness in it last week I wrote down and photographed the parts and the numbers on them. It is a 1" by 24 TPI Tange Seiki Levin NL500 threaded headset. There are a couple of Tange NL500 headsets for sale on eBay, but one has a JIS crown race and the other an ISO, so it appears that the NL500 was made in different sizes. I've called Harris cyclery and they don't know what size I should get either.
No, I'm afraid you're going to have to measure your crown race seat as most Tange headset are available in both ISO and JIS dimensions. Otherwise, you can simply buy a headset with an ISO crown race, and if it turns out to be the wrong size, take the fork to your LBS and have them mill the race seat to ISO spec. It's not a big job and shouldn't cost much.