Just to be clear, I am not replacing the cast iron guides with bronze guides. The original cast iron guides are left in place. The worn original guide is corrected by drilling through with a pilot drill. You are only removing a small amount of metal but this corrects the guide for straightness. In other words, makes a nice round straight hole through the guide.
Once the original cast iron guide is corrected for straightness and slightly enlarged to accept the liner, the bronze alloy liner is installed. The liner is then reamed to fit the valve stem to provide sufficient clearance between the guide and valve stem. You want enough clearance for some amount of oil to lubricate the guides and valve stem. Once the liner is installed, reamed to size, the nice straight guide is the basis for the valve job. Everything pilots from the guide.
For me, the bronze liners do not require a lot of excessive oil for lubrication so between the bronze liners and the newer style Teflon seals, I can do a better job with oil control down the valve stem then what the little stock type O rings do (and those things fall apart abut 30 minutes after you install them) and thus keep excessive oil from the combustion chamber and tailpipe.
The cast iron guides, in my opinion, they need a bit more oil for cooling and lubrication. So if using a Teflon seal, the machinist has to make sure the clearance is not too tight, erroring on the wider side for the guide, stem and seal, just to make sure not too much oil, just right, to avoid excessive oil in the combustion chamber.
Many ways to tackle rebuilding a 848 head. Some good some not so good. This just happens to be how I do mine. Maybe my way is not so good, lol. Truth be told though, I zing my 235 and 261 motors pretty good and have done so for many many years, like 48, lol. So I stick to what works for me.
Last edited by Dragsix; 12/17/2025 5:13 PM.
