Duccout wrote:I got that info from a book called 'Ducati Tuning' by Steven Eke, who used it to explain that heads should not be heated prior to removing valve guides. Just shows that you cannot believe what is written in books!
I just looked for the info online.
* All references I found say that phosphor bronze expands more than aluminium.* - Wrong
The above sentence was a dumb mistake: I meant Aluminium expands more than phosphor bronze, as I said earlier in this thread.
Ducati may not be unique in offering oversized guides but it did make me wonder why they would, until I read their suggested method for guide replacement. Hondas evidently don't normally need O/S guides.
Heating the head sufficiently and cooling the drift, as well as applying a lubricant to the guide, both when removing a guide from the head and when inserting a guide into the guide bore will help prevent the galling of the guide bore. Galling or the removal of metal from the valve guide hole bore, the metal removed being attached to the valve guide, means that the valve guide can be unstable in the bore hole and doesn't transmit heat away from the valve stem efficiently. So, the valve doesn't seal against its seat and also can overheat and sieze in the guide in the worst case scenario. 
