How do you know when it is time for a rebuild?

On a related matter, I am thinking about having a go at re-building an engine myself. For those with experience at this, what parts of the build should I (read someone who has no real knowledge of these things and will be going step by step through the book as I go) leave up to a professional?

All thoughts and advice greatly appreciated.

well if you have no knowledge then I would have the bottom end essembled by an engine builder, then do the top end yourself.

Bottom end= everything in the crankcase including the flywheel.
Top end=pistons,heads and then completion of the motor.

How do you know if it needs a rebuild ? When it DIES !!

Or just before it dies and uses 1 litre of oil every 1000km.Buy a Bentley manual your gunna need it.

All the bearing machining and selection.

ie give your case to a machineist and get them to line bore and thrust cut it and give it back with a matching set of bearings.

All the head work - - valves, guides etc.

Setting the end float is a pain too. But once the bottom end is together you can get this done in a shop.

well i say if the engine is not needed, eg just a spare or something, just get all the machining done and dot he rest. if its for your daily driver that is a different matter.

Mate has a few old 1500 engines, we are going to strip and rebuild it, for some club motokahan cars, so if it dies no big problem, juts rebuild it again, and its the best way to learn!!!!

Yeah, its not my daily driver, I would be doing it more for the learning experience3 than anything, and knowing me, wouldn't be doing it really quickly either.
I've got a 1500 that was running a bit average when I took it out of the car, so I just thought I'd have a go and keep it as a spare.
So what are the bits I can re-use and what do I have to buy new?

The parts that are worn out,so you need a manual to get the specs and measuring gear to see whether there within spec or not.