What constitutes an "engine rebuild"?

Another question from a mechanical idiot:

What do people mean when they say that if you buy a Porsche with more than 100,000 miles on the clock it must have had an "enigine rebuild" or will need one soon? A 81SC (134,000 miles) I have just looked at had recepits for a "top end re-build". Is this enough or should I be looking for evidence of more work?

Thanks
James

To say a Porsche motor needs to be rebuilt at 100,000m is a predrawn conclusion. The motor you speak of can easily do twice the mileage on the stated odometer. It all depends on a lot of factors. Number one being the condition in which it was maintained. ie. oil changes, tune-ups. Even quality of gas. The climate the car was operated in. That is if a car is run alot in 100 deg plus without additional cooling its life will be shortened. The given motor. ie. 2.7,3.0,Turbo etc. I'm always a little weary of a motor that has a top end only rebuild without knowing the circumstances of why. Just make sure that the motor is checked out by a qualified mechanic. Even better find out who did the rebuild and give them a call. Bobby

Shouldn't require a rebuild quite that soon, but if the heads are removed, the dilivar studs stand a good chance of "fatal" damage in the future. A rebuild is exactly that. ALL parts must not just be within factory specs, but must be within ORIGINAL factory tolerance of a NEW engine. This usually means new pistons (not just rings and in the case of Porsche may require new cylinders as it is tough to match factory specs), valve guides (beware of worn stems because the valves are quite dear,) dilivar stud replacement, and everything else brought up to specs. The engine may have a reground crank or enhanced bore, but it should be stated as such and be as tight as the original specs or to your racing specs. Many shops advertise very reasonable "rebuilds" but few produce a real rebuilt engine. Most "rebuilds" are just glorified overhauls getting parts within acceptable "wear" tolerances. A few years back "rebuilt" batteries from various shops in L.A. were merely stripped from junkers and washed!! Some "rebuilt" trannies have merely been washed and if you are lucky got treated to some new seals. How do these guys get away with it? Any comments guys? Defense from those in the business?