jim beam > writes:

>that noise is not due to neglect. it's just a fact of life and to some
>extent, a function of the oil you're using. fortunately, a burnt valve
>is /no/ reflection on the wear status of the rest of the engine.

Well, that's what I was hoping at least. The biggest concern of mine is that a
new head, being perfectly sealed, will increase the load on the compression
rings causing them to fail sooner, or at least increase blowby (fouling the oil
more quickly and perhaps overloading the PCV system). But from what I've read,
this seems to apply to older ring types and not to "moly" rings that new cars
and especially Asian cars have been using, so this is nothing to worry about.
(I'd love a correction here.) If so, that would definitely be a good thing,
because most of these cars are also using OHC aluminum head designs which seem
to invite eventual head rebuilds or gasket jobs for various reasons.

Aside from that issue, I'll just be on the lookout for detonation both from
improved compression from the new valves, and from the unintended rise in
compression that comes from the head being milled down.

>i'd be scrupulous about cleanliness for the block. new rings and seals
>are debatable at this mileage, but if it was good before and was not
>burning oil, personally i'd leave them. rebuilds usually fail in 1/3 or
>less time than the original build. analysis shows this is almost always
>due to microscopic abrasive contamination left on the cylinder wall
>after re-honing. if you can avoid doing that [and you /must/ hone if
>you re-ring] you could continue to get good service from this engine.
>caveat: "conventional wisdom" is strip, hone, ring, etc. but the fact
>remains that rebuilds don't last and for the reasons i've stated. i
>would not follow my own advice in a shop environment because i cannot be
>"negligent" for following conventional practice, but if it were my own
>car, and i /knew/ the block was good, sure i'd leave it as is.

So the idea is, either buy a new or rebuilt short block from a professional
rebuilder with a warranty, or leave the rings alone?

How about bearings and seals? I seem to be under the impression that unless a
bearing spun, they should be safe to replace (with a factory sized replacement)
without a hot bath or crank job. Likewise seals, unless something catastrophic
happened to the part they are sealing, just to use emery cloth or very fine
sandpaper on any shaft burrs before installing the new seal.

Of course never having done any bottom end work, I'd prefer to have my head
screwed on straight and do it right the first time or to not do it at all.
That's an area where trial and error can get expensive and inconvenient, as one
error can pile on more problems very quickly.

Thanks.