Quote:
Originally Posted by DJMOJO
id still toss the old one. i guess you dont get my point eather, i get what your saying, and on say, a pulley bearing i totaly get and understand your point. its something that is easily accesable, and if they pulley is still up to spec and has no signs of wear then why replace it. if im tearing down an engine for a rebuild id much rather use a master rebuild kit and not have to worry about specing every single piece. just replace it and get it over with.
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Even with new parts you should still be specing them prior to install. At no point in the rebuild process should you not be specing any part in a high tolerance location (all bearings and seals). So again, beyond a false sense of security, extra work, extra money, there is no benefit (can those really be called a benefit?) to replacing an in-spec part for a new in-spec part. If an old in-spec part does eventually fail in the engine, it's not going to be because the part was old/tired and broke from fatigue, it will occur--more likely from an out of spec, improperly installed, or catastrophic failure from a pre-ignition event. All of which would cause the same exact failure of a new part in the same way.
Now that being said, some parts are better off being replaced even if they're still in spec: Apex seals, if they're of the old 3 piece kind, can easily be upgraded to the newer 2 piece without much issue or head ache. In spec 2 piece so long as you remember which rotor they came from and which apex they came from on that rotor can easily be used for the rebuild if there's enough life in them. If however the apex seals are getting closer to the wear limit (6.5mm~7mm) One should think about replacing them with new because failure of those seals will occur sooner than a new (8mm) apex seal (for further clarification look at the ash content of oils thread in the general tech section). Apex seals are wear parts.
When it comes to bearings however there is absolutely no benefit to replacing the old with the new, unless of course you're stepping up to a 3 window, or race bearing. This is because there is supposed to be no actual contact between the eccentric shaft and the bearing, as well as the rotor bearing should make no actual contact with the eccentric shaft. The journal bearings use the principle of shear to keep wear from occurring, and as such the oil will play a much bigger role in the life of those parts than the actual time in the engine of the part.
So, if I still don't get it. Please explain it to me where the benefit comes from replacing old-in-spec parts with new-in-spec parts?