Headset iso or jis

My 70s/80s Dawes kingpin refurb is in need of a kickstart. ( Haven't checked the year on the hub yet)

I stalled at the headset previously.

Bought a mpart headset but the cups were too small for the frame. I could easily push them in by hand.

Can you tell from that what headset I need?
Iirc @brokenbetty had a unexpected headset sizing on hers

Edit:
I'm using an mpart headset. Sjs suggests cups are 30.0mm I need iso cups.
Thank s

Easiest way is to borrow or buy an electronic calliper. If you’re near SE24 or shoreditch you can borrow mine.

Yeah, mine turned out to be JIS. At least I assume it was JIS since ISO was a wee bit too small.

ISO and JIS cups are pretty much the same size but the crown race isn't. So my tip is fit the crown race first. I did not do this and only found out I had the wrong size after I'd pressed the cups in.

https://www.lfgss.com/conversations/2746­45/?offset=25#comment12588082

https://sheldonbrown.com/headsets.html#s­ize

(I also have an electronic calliper in N15 if that's closer. I think you are/used to be in the area?)

I have a crack team of Kingpin enthusiasts now if you want me to ask them?

hi james, the jis/iso should only be a (noticeable) issue with the crown race. 1" cups are pretty much universal in my experience.
was there a headset on the frame when you got it? possibly headtube flare. callipers are best tool to know for sure, as others have mentioned. hope that helps

Just looked at it again.

I've modded folders before using a 1" threadless headset loaded with the of topnut.

The mpart headset cups push on with almost no resistance by hand.

I bought the headset on here I think it originally shipped with both crown races. I'm not so bothered about the crown race as I could use a split race?

The cups are the issue I think. Not sure the 0.2mm extra an ISO cup might give will be enough to hold it.

I could jbweld the cups i have in place I suppose. It's only an old Dawes kingpin but I'd rather do it properly. I may still have the original cups. Guess it's possible I flared the headtube removing them.

@brokenbetty thanks the hub is stamped 86-4

a flared head tube usually happens as a result of riding with a loose, or ill fitted, headset for a long period. i've had good results using metal epoxy with headcups, i'd recommend that route :-)
i think 'split' races can only be used with sealed bearing units bit im happy to be told otherwise

A bit late but I've had 2 old steel bikes that had this problem after removing the original headset cups (flared headtube after removing). Not really sure why but they were both bikes that were not cared for and sitting in a garage for 20 years+
See if the original cups fit or if they're too loose now too. If the head tube is really flared you can use a shim on the new cups, that's what I did and never had any problems.

Cool thanks