[tumamilhem]

Originally Posted by darrin

Head studs are the headless bolts that screw into the engine case and hold the cylinders and heads onto the case. They're fastened onto the heads under the valve covers, removing the valve covers can help disclose whether they're still intact. They break due to thermal cycling/etc. and when broken, require removal from the case and replacement.

Valve guides are sleeves in the head that the valve stems pass through -- they are there to both position the valve so that it can be actuated by the cam and to seal off the combustion chamber. As I understand it, porsche redesigned the valve guides for carreras (3.2 liter cars) and caused them to seal TOO well -- this prevented them from lubricating effectively and once overheated, they wear out prematurely, allowing the oil used to lubricate the cams/rockers/etc. in the heads to be sucked into the combustion chamber. Valve guide wear would show up as both excessive oil consumption (when mine were shot, I added a quart of oil at each fill-up) and as bad leak down in the affected cylinders. Although valve guides are cheap, they can only be addressed through an expensive top-end rebuild. Although the later 3.6 liter engines used in the 993 (and 964?) have hydraulic self-adjusting valves, prior 911 engines (including the 3.0 sc and 3.2 carrera engines) do not and require periodic manual adjustment of valve clearance)

PPI - pre-purchase inspection, given the age and relatively unique issues these cars present, generally a GREAT idea to have an independent mechanic (i.e. not the one who worked on the car for the previous owner and not a porsche dealer) that's familiar with the intricacies of a vintage air cooled 911 go over a prospective purchase to identify issues (like pulled head studs, valve guides, rust, etc.) that you might not be aware of. As with a home inspection, you'll need to pay for this, but the info gleaned may save you from buying an expensive basket case and/or give you leverage in your purchase price negotiation.

Thanks for your info!