Mismatched Threaded Headset: Acceptable?
 

I have a track frame with a Dura-Ace HP-7410 headset installed with an undrilled track fork which has a 27.0mm crown race.

I have a Tange track fork drilled for a rim brake which I wish to install into the aforementioned frame, though it has a 26.4 crown race.

I have a Hatta Vesta headset which has the appropriate fittings for a 26.4mm crown race.

My idea is to leave the upper section of the HP-7410 installed, yet remove the lower race from the frame, install the lower Vesta interface into the frame, bang on the Vesta crown race to the drilled fork, and tighten it all up...

Is there a potential problem which I am neglecting to foresee?

Thanks so much for any help and advice—the gratitude is overflowing and the appreciation blooms like the flowers in spring :)

Edit: I should add that the reason I am trying to work this out is that it is my hope to use this frame with both its original fork and the drilled fork interchangeably... I love riding brakeless keirin frames on sunny days, but I have a special opportunity here to create a foul-weather track bike with brakes and would love to make it as easy as possible to switch between frontends as the season permits. (The HP-7410 has a sealed-bearing design and the Hatta Vesta uses a rubber o-ring to seal the bearing interface from water ingress.)

well, your tires could spontaneously explode upon turning. it's all i can think of.... :foo:

Interesting, makes perfect sense to me. If the stack height works out, should be good.

Tires?

Sometimes these replies baffle me so much that I just wish I could delete my entire question and remove myself from the equation... I have obviously not made myself clear and have no idea how to make myself clearer.

(I often wish there was a giant brush that would just eliminate my entire history when trying to interact with these forums... It feels like such an embarrassment. It is a wonder why I even try.)

Thanks for this... It makes sense to me, though perhaps there was a devil in the details which a knowledgable wrench would catch. The stack height will be fine, indeed I have already anticipated adding a few millimeters of spacers to accommodate the new fork per my measurements.

i was just making a joke, man :) wasn't meant to be malicious or anything. i was sincerely hoping you'd get a chuckle. sorry

I am using mismatched top and bottom cups on a Fuji Ace. It has the proper specs and works like it was built to work that way. The only way you can even tell is with close inspection, the lower cup is older with more outer wear. The replacement I had on hand was with a 27mm crown race and I needed 26.4. So I used the bottom cup and crown race from the original.

The least bothersome way to accomplish this is to use the same make/model crown race on both forks, and a matching lower pressed cup on the frame. Shimano, Hatta, and Tange all offer headsets with either JIS 27.0 crown races or ISO 26.4mm crown races; often these are available separately. A Dura Ace 7410 ISO crown race on your Tange fork would be an easy fix, as you wouldn't have to worry about stack height issues, crown race/cup compatibility, etc. Otherwise, a Tange or Hatta headset with both types of crown race is also a possibility, although you need to take care that the stack height is reasonably similar. You could just replace the lower stack (sometimes that can minimize stack height concerns) and leave the Dura Ace upper stack. I'd probably replace the whole thing, if stack height allows.

Sometimes, mixing different make/model cup and cone doesn't work well, particularly with headsets that have seals, as the OP says he has. In the case of a mismatch, you'd need to replace the entire lower stack (crown race and lower pressed cup) with a matching set.

The way I read it, Ethet is using all Dura-ace parts for the upper, and all Hatta Vesta parts for the lower.