Re: A raft of engine rebuild Q's

["Vee Dubb" <Scirious@hotmail.com>]

Knife-edging the crank means machining off any non-critical material from
the crank and leaving a relatively sharp edge where the counterweights on
the crank used to be.  The "knife-edge" cuts through the oil reservoir
better and reduces viscous drag on the crank as it passes through and
reduces foaming of the oil.  Removing or reducing the counterbalances on the
crank can leave it unbalanced, which will accelerate fatigue of the
crankshaft (usually not a problem) and accelerate wear of the crankshaft
main bearings.  The engine will rev faster.  Because of the accelerated wear
problems, I would only suggest doing this if you have already done
everything else to lighten the rotational mass (i.e. machined ALL extra
material off of the flywheel).  Either of these will lead to slightly more
driveline vibration, so have good motor mounts on the car.  For my 16v, I
would consider knifing the crank pretty far down the list of performance
mods just because of the longevity issues it raises.

Micropolishing reduces surface imperfections that could otherwise lead to
cracks.  I don't know how routine or practical this is, so ask around.

The idea behind putting 3angles on a valve is essentially to retain a good
sealing surface with the first two angles, and then to knock the sharp edge
off of the circumference of the valve with the third angle.  Any sharp edge
left on any part creates a place with lots of surface area and little
volume.  Heat can enter along the ample surface, but can't diffuse quickly
through the volume toward the cooler center of the valve (or piston or
whatever).  So the edge is called a heat concentrator, and the temperature
of the metal there will be higher than in the rest of the surfaces.  High
heat concentration zones can cause detonation of the fuel, or more
specifically, pre-detonation, a.k.a. knock.  To reduce knock in an engine,
eliminate the sharp edges in the cylinder by polishing the cylinder head
(you can do this yourself, just like porting / polishing the intake), and
cutting that edge off the valves with a 3-angle valve job.  These steps
aren't really necessary unless you are raising the compression ratio.  16v's
use 10:1 compression with premium fuel and have the same 2-angle valves and
cast combustion chamber surface as your engine will have.  Don't worry about
these things unless you excede this 10:1, or wish to use lower grade fuel.

I've seen hand-lapping done, but I don't know why it's done.  My first
impression would be that it basically can clean up the valves nicely, but
you won't be able to change the angle (i.e. add a third angle) by this
means.  Lapping is basically polishing.  The tools to do this are pretty
basic, so at least check to see how much they would cost to do it yourself.

Reusing valves and springs is relatively safe.  Having them magnafulxed
would be nice, otherwise just inspect them well.  If the valves are all
straight, and if they show no pits from corrosions or burns, you can
probably re-use them.

I'd replace all bearings (cam, crank, and rod).  That's kind of the point of
an engine rebuild, isn't it?

Also, Deck height check should be dirt cheap and a usefull measurement
towards checking compression ratio.  It's not really important unless you
are planing/decking the head for higher compression.  Magnafluxing is a must
(yes, to check for cracks).  No sense in investing in a bad block.  Honing
the cylinder walls should also be cheap, and very do-it-yourselfable.  Some
Autozone/PepBoys type shops will rent a cylinder hone.  Ask them how to use
it, or ask the list.  Basic idea is to run the hone up and down in the
cylinder to create a spiral up and down the walls with a 45° incline to it
to provide a smoother surface than machining provides.  The sprial pattern
helps oil distribution along the cylinder walls.

Basically, similar to other's suggestions, I'd do "everything" to the block,
including magnafluxing, thorough cleaning (don't know about the freeze plugs
on this engine in particular), new bearings, and honing.  Re-boring the
cylinders will require new pistons, and it doesn't sound like you are up for
that.  Shouldn't need to be done unless the walls of the cylinder are
scratched for some reason, or if you just get bad compression (i.e. bad
"dry" compression test, but good "wet" compression test).  Start with those
basics.  Lap the valves and seats to get them nice and clean, and polish the
inside of the combustion chamber if you are bored and have something to do
it with.  Don't chew up the valve seats while trying to polish the chamber.

A tap will work as a thread chaser.  I don't know if anyone sells something
other than a tap to do this, but I'm sure someone will take your money for
something by that name if you ask them.  Don't know what taps you would
need, but if you have the bolts that will go in the holes you can measure
them easily enough.  Metric bolts only have one tap size for a given bolt
diameter.  That's the diameter of the bolt, not the head of the bolt, but
the two are related.  If you have no other way to measure it, go to Home
Depot and buy a micrometer to measure the diameter.  Or you can borrow the
micrometer out of the package there in the store (I'll admit to doing this
only because I already own a micrometer).  You will probably find that it
costs more to buy the tap set than it does to pay someone to chase the
threads, so consider whether you would ever use the taps again (bearing in
mind that much of our world isn't metric (unfortunately)).

Freeze plugs are made to let the water in the engine block expand when it
freezes, pushing the plugs out instead of breaking the block.  Galley plugs
are actually orifices (plugs with holes) that regulate the flow of oil in
various passages.  Otherwise either plug could just be sealing up a hole
that was needed to make a passage.  Don't know about removing them for
cleaning.

Don't know about the paint first hand, but it's an iron block, so I would
assume it should be painted.  High heat engine paint is available at auto
supply stores (in lots of nifty colors if you are so inclined).  A definate
do-it-yourself thing.

Any responses are welcome.  I'm no expert.

Sincerley;

Brian Haygood

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