Cannondale Si bung or similar might help?
http://www.tritoncycles.co.uk/components-c9/headsets-c79/cannondale-headset-comp-23-6id-expander-assembly-p15464/s44906?utm_source=google&utm_medium=cpc&utm_term=cannondale-headset-comp-23-6id-expander-assembly-kp017&utm_campaign=product%2Blisting%2Bads&gclid=CIPNh5CCpc0CFQo6GwodSYsKlg
@Acliff started
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Cannondale Si bung or similar might help?
http://www.tritoncycles.co.uk/components-c9/headsets-c79/cannondale-headset-comp-23-6id-expander-assembly-p15464/s44906?utm_source=google&utm_medium=cpc&utm_term=cannondale-headset-comp-23-6id-expander-assembly-kp017&utm_campaign=product%2Blisting%2Bads&gclid=CIPNh5CCpc0CFQo6GwodSYsKlg