i was changing the valve seals on my heads ( out of the car) and as i was prying the seal off, the vavle guide just broke off!

could the valve guides be replaced? or do i have to buy a new head???

 

The guides are cast iron and are pressed into the head , to repair your head you'll have to remove the head from the engine so as when the new guide is fitted, the valve seat & valve itself will need to be ground ( recut ) so as everything is nice & concentric once again.
"No you don't have to purchase an new head."
Don't stress it's <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> not a big job for your local engine machinist.
Hope this helps