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what would you automatically replace?

I'm thinking things like the timing chain (assuming you have one) because it seems prudent (cost effective) to heave the old one...

What else gets the closest scrutiny?

This is assuming a normal engine that's tired, not one that has come to a bizarre end.

I've read that new engines may come with new, space age one or two molecule deep lubricants that are applied at birth. Can that be done on a rebuild?

Definitely rings, timing chain (as you said), and other parts that have worn to well beyond the mid-point of their measurement/ tolerance specs. Especially bearings (oil pressure limitations)and valve guides (leak down). And oil pump must be in spec of course.

Camshaft wear (pitting especially) can't be tolerated and valves that have thinned due to many re-facings likewise.

I'm sure opinions vary regarding re-boring and other major work but my opinion is measure carefully and make a decision based not only on wear but also on 1) how rapidly the engine has worn during past use, and 2) how much you are willing to spend!

If you've done many miles and engine wear has been minimal then why re-bore etc at the mid-point tolerances when you may get many more miles with just a set of rings and regular oil changes? (That's my philosophy, not being wealthy!)

I'm sure that for some, anything other than 'new spec / minimal tolerance' is not acceptable. But if a new valve guide causes a valve to jam then a bit of wear in the original guide would probably have prevented that situation, at the cost of a bit of extra oil being used.

Regarding assembly lubricants I think a spray of Molybdenum Disulphide on every moving surface is a good idea - even necessary. Adding a slip agent (oil modifier) to oil is a good idea as well - unless you are 'running in' a re-bored block, in which case you don't want a slip agent during the running-in period.

Pat, it depends entirely on what you find on disassembly, inspection and measurement of all the components and critical tolerances, and on how much you want "new engine" performance and longevity and how much you're willing to spend to get that. I don't know what the composition is of the specialized assembly lubes but that's what I'd use.

I would probably have the cylinder head checked for warpage and have it resurfaced if necessary . It is relatively inexpensive and removing the head is pretty simple.

Quote:

Of course. Guys in the club discuss it from time to time and the answers are usually different and predominantly frugal. Therein lies the problem as far as I can see.

Let me rephrase the question: what would you do, and on a scale of 1-10, 10 being the ultimate overhaul, how would you rank what you would do?

Put another way, what's cheap and what's prudent?

Owen Dyneto has answered your question already.

Quote; " Put another way, what's cheap and what's
prudent?"

You need to add "and whats NOT neccesary" to that statement.

Pat, let me put it this way. Unless the engine has had something catastrophic happen to it, the chances are that by the time something needs attention (like valves, bearings, rings, pistons, etc), the chances are that everything will need attention.

My recommendation is to avoid unnecessary machineing and/or excessive machining such as cylinder boring, valve seat grinding, crank grinding.
Those prosesses can often be necessary and sometimes NOT. Aa good example is grinding a crank to maximum undersize when only the next incremental undersize is needed or simply polished with some crocus cloth to "clean it up".

As was said, it kinda depends on what you find while it's apart. I went through and overhauled my wife's Triumph engine when we got it, and ended up only needing to replace the piston rings, crank bearings, timing chain, and gaskets. We had to turn the crank, but everything else still looked good.

If you're going to take the block apart anyway, that'd pretty much be the minimum I would do, although having the crank turned may not be necessary (and I wouldn't do it if it's still mirror shiny and good).

Here's the before and after on the engine:

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