How do I get this Syncros Cattlehead off my headtube?

[bikeworkshop]

Mallet sounds promising.

Also Aluminium expands much faster than steel, so some gentle heat will help, even boiling water.
Lacquer and paint are usually ok to 200⁰ if you want to get a blowtorch on it...
Oh, and the mallet!
I drop the forks into the bench vice with scrap cardboard to protect them, a wooden broomhandle is ok to a point - you need to bear in mind the equal and opposite reaction to any force, and what that might do to the paint!

 

[ishaw]

I'd try and secure the stem and use the forks (Luke) to try and break the corrosion that's holding it all solid.

 

[Bike Hoarder]

use the forks (Luke)

 

[Tootyred]

Try the mrs (or yours) hair drier.....you will need to be at it a while as the alluminium disperses the heat quick, but it will get considerably bigger (in engineering terms) than the steel.

 

[Bike Hoarder]

What about a freezing spray instead?

 

[Tootyred]

I would say a hot air paint stripper (which is a workshop staple for bearings etc) but they will take the paint and finish off!

If you dont watch it!

 

[Tootyred]

Its the wrong way round for freezing spray (unlike a seatpost trapped in a steel seat tube)....although it may still crack the bond a bit.

 

[bikeworkshop]

Its the wrong way round for freezing spray (unlike a seatpost trapped in a steel seat tube)....although it may still crack the bond a bit.

The idea is freezing spray into the tube to shrink the steel.
But...
the steel shrinks much more slowly than the aluminium expands
Freezing spray changes the temperature by maybe 40⁰, whereas a blowtorch or even heat gun will take it up 160⁰+++

I've got freezing spray in the workshop. It's safer in many ways than flame, but it's comparatively disappointing in its effects.