Oversized Valve Guide

[1972_911T]

Why can I not find standard valve guides on pelican? when doing a rebuild is it nessessary to always use oversized? Also what part is oversized the external diameter? or is the internal bore thats smaller?

Steve

[Bill Verburg]

Not an expert here, but the process of removing the old guide, enlarges the hole in the head, hence the need for oversize guides, the inner hole is sized for the valve stem.

[TimT]

Removing the old valve guides doesnt usually require larger od guides. Partially drill out the old guide, finish removal by punching out the remains of the guide. Lube up the new guide and press in to place. Check clearance, ream if necessary.

The over sized guides are used when there is other damage to the heads, usually a result of bending valves etc.

[Bill Verburg]

This is from the 993 manual, but all of them have the same info

[TimT]

Im aware of the factory procedures. We have the complete set offactory manuals.

Years ago I was having my heads refurbed by one of the famous west coast machine shops, I asked them about oversized guides. They told my that usually they arent required unless the head has been damaged by bending/breaking valves, or damaged by poor removal techniques.

Chances are if you drill out the guide, and carefully remove it, you will find that you still have the 0.06-0.08 mm interference fit with regular guides per the manual..

Its convenient to measure furst, rather than spending time turning oversized guides down on a lathe. Chances are the normal sized guide will fit. BTDT

Pro machinists have lots of time saving tricks, and sometimes they share them, all you have to do is ask.