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Boring a Tapered headtube bottom flange to taper?

5K views 51 replies 22 participants last post by  mtnbikej 
#1 ·
So my bike looks like it has a tapered headtube - so I went and bought an upgrade fork than has a tapered steerer.

Taking a closer look at the headtube, there appears to be a flange on the bottom to fit a 44mm headset bottom cap - which I find rather strange.

I am aware that there are headsets available for 44mm to 1.5" tapered steerer - but I would rather not fit a traditional headset since this will further lift the front of the bike (the upgrade fork is longer already, I wanted to change the geometry a little on purpose)

So the question is - can I machine out the flange without destroying the frame?

Here is kinda what the headtube looks like
Line Parallel


The bike is a Scott Spark 29er Team, 2012

Should the headtube be butted, or is it usually just straight tube?
Knowing that the resulting ID of the headtube may differ to standard, a custom bottom cup may be required, which I am ok with.
 
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#42 ·
Just knock out the bottom cup and put in new cup for a tapered steerer. No need to bore the frame. The bottom cup that is currently in your frame is designed to adapt a tapered steering tube to a straight steerer. You just need a Cane Creek ZS56 lower headset and crown race.
 
#43 ·
No, that is not what he needs, if he got a ZS56 (ZS stands for zero stack) he would need a HT designed for a fully internal cup to run a 1.5" steerer, which this isn't, what he needs is the EC44 lower cup or the EC49 depends on how it's currently bored.
Just knock out the bottom cup and put in new cup for a tapered steerer. No need to bore the frame. The bottom cup that is currently in your frame is designed to adapt a tapered steering tube to a straight steerer. You just need a Cane Creek ZS56 lower headset and crown race.
 
#44 ·
If you have the ability and experience to machine the headtube, you should be able to best answer this by yourself taking a few simple measurements. If you can't make this call by yourself, then you shouldn't be attempting it.

I modified a carbon road frame from an english threaded bottom bracket, to PF30 on a milling machine, and it works perfectly fine. No different than a factory designed frame. It didn't require multiple internet opinions.
It's either possible or it isn't. A dial caliper doesn't lie. :)
 
#45 ·
Correct you are!
Posted this hoping that someone else had done something simular, and now I have the answer.
Also wanted to find out if there are considerations or assumptions which I was forgetting, which there were none, although I will certainly be taking more time for this operarion on the mill.

Will order a 54mm zs bottom cup today, and bore sometime next week - I will post the results here, accepting that there are risks, and treating this as an experimental hack
 
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