Bicycle Mechanics - Quick question about crown race diameter

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cmdr
06-25-07, 09:01 AM
Before I order a new headset for my 84 trek 500, I just wanted to make sure of the size that I need. Does anyone know if it takes an ISO or JIS standard? I don't want to take off the current headset until I have the new one. Thanks.

well biked
06-25-07, 09:11 AM
It should be ISO, but it is possible the crown race ID is 27.0, although I'd guess 26.4. If you go ahead and order an ISO headset with a 26.4mm crown race and it turns out that the crown race seat on the fork is 27.0 ID, you should be able to find a bike shop that can mill the 27.0mm crown race seat down to 26.4mm with a tool Park makes for this. As far as the headtube diameter, that will be sized for ISO headsets-
vpiuva
06-25-07, 11:21 AM
My '84 Trek 760 is ISO, but the 500 uses a Tange fork and a Tange MA-60 headset. Harris sells it as a JIS headset, but does it come as an ISO version? (http://harriscyclery.net/itemdetails.cfm?ID=1628) Call them and find out.

tuz
06-25-07, 11:32 AM
As far as the headtube diameter, that will be sized for ISO headsets Most probably. Even if not, the difference between JIS and ISO on the headtube is 0.1mm so it's pratically interchangable.

For the fork race the difference is much bigger (0.6mm) so you should be able to tell by measuring it with a cheapo caliper. If you can put your bike aside the time the new headset comes, remove the crown race (srewdriver + hammer) and measure.
well biked
06-25-07, 12:35 PM
Most probably. Even if not, the difference between JIS and ISO on the headtube is 0.1mm so it's pratically interchangable.

"Practically" being the key word. There's variation even between one ISO headtube and another. In putting JIS cups into an ISO headtube, especially if the headtube is nearer the large end of the ISO spec, you lose the proper "interference fit." Headtube ID for ISO and JIS can be as much as .3mm difference, and still be within spec. The cups are .2mm difference. I don't like doing stuff like that, especially if it can be easily avoided-
well biked
06-25-07, 01:21 PM
My '84 Trek 760 is ISO, but the 500 uses a Tange fork and a Tange MA-60 headset. Harris sells it as a JIS headset, but does it come as an ISO version? (http://harriscyclery.net/itemdetails.cfm?ID=1628) Call them and find out.

Yeah, they've got the Tange MA-60 headset in the ISO size:

http://harriscyclery.net/itemdetails.cfm?ID=1629