VW Engine Talk -- What Year is Best?

None of them.

The alloy used in the VW crankcase has proven to be susceptible to age-
hardening and the cracks which follow. It took about thirty years (!)
for that fact to become evident but tests went back and confirmed that
the crankcase, which is a magnesium-aluminum alloy, became more
brittle with age. So in 1971 Volkswagen changed the alloy, increasing
the ratio of aluminum. Which helped. But after 36 years that's the
best they can say; the age-hardening is not as BAD as it was with the
earlier alloy. The 'new' alloy, which is at least 35 years old as I
write this, still shows a propensity to become more brittle with age.
As for cracking, the jury is still out.

Which isn't a problem with a professionally built engine. Because you
always start with a NEW crankcase, which are still available from
Mexico and Brazil.

The best part of the joke is that a NEW crankcase usually turns out to
cost LESS in the long run than trying to re-work an old crankcase.

Why? Well, there's a lot of reasons, some people put more emphasis on
one than another, which can get you into a race to see who can type
the fastest :-) But most of the problems stem from the DESIGN of the
VW engine, in that it only has three main bearings. There's a fourth
bearing on the crankshaft but it was only added to off-set the
asymmetrical load of the dynamo & blower and should be addressed more
as an accessory item than an engine item. Engine bearings are the
three which support the crankshaft and have two connecting rods
between each of them. The thrust bearing is located on the flanges of
the #1 main bearing, immediately adjacent to the flywheel. The #2
main bearing is in the center of the crankcase and unlike most flat
fours, it has the same bearing area as the other two. (Corvair or
Subaru provide good examples of how flat engines are usually
designed.) The #3 main is adjacent to the last pair of con-rods.
Then comes the cam gear and a scroll-gear for driving the distributor,
THEN another bearing, this one only 40mm in diameter where all of the
others are 55mm.

One of the reasons a new crankcase usually costs less is because the
youngest USED crankcase is so old. Old crankcase, the center-main has
been pounded out by the asymmetrical load of the 'boxer' design. That
asymmetry appears in the bearing shells for the center-main as well as
in the WEB supporting the shells. Bottom line is that a used engine
with 20 or more years of service is going to require an align-bore.

Align-boring is a basic chore in automotive machining and VW provides
a range of over/under sized bearings, plus the thrust flanges. One
rainy afternoon I worked out how many bearing-sizes they offered: 127,
although not from Volkswagen. They put the limit for over-size main
bearings at half a millimeter -0.50mm for the OD of the inserts. They
did the same with their crankshafts, putting the limit for UNDER-sizes
at half a mil, meaning you could have a center-main that spec'd plus
50 for the OD and minus 50 for the ID, plus you could have two ranges
for your thrust flange. And since you have STD-STD as your starting
size, so you're already up to a dozen sizes and you haven't even SEEN
what some of the after-market bearing-makers will sell you: Oversizes
as large a one and a half millimeter!! And ditto for under-sizes on
your crankshafts!

No reputable builder will use that sort of stuff of course. But the
kid will have no trouble finding someone who will. Of course, you
gotta ask yourself if that Someone is a competent automotive
machinist? Because in most cases the answer is 'no.' It's some kind
with a portable cutter-bar who will argue that his dune-buggies run
just as good as all those other dune-buggies... mebbe even better,
with his chin sticking out to about... here. So... howz they do in an
airplane? you ask. And the answer(s) can keep you smiling for a
while.

So let's leave the align-boring aside for a minute. In fact, lets
assume your engine doesn't even NEED an align-bore. (Miracles HAVE
happened, you know..:-)

So now what you need is to open up the spigot-bores for the cast iron
cylinder barrels. You got four jugs so you'll need to open up four new
holes. Ideally, you'll do it on a milling machine using a cutter
that's been 'proofed' on earlier work to show that it cuts a true
circle with square sides, meaning the sides of the hole are
perpendicular to the deck of the crankcase... which may need to be re-
cut due to 30 years of shuffling by the cast iron jugs. Such
shuffling is normal, by the way. It's an artifact of the thermal
coefficient of cast iron as compared to non-ferrous metals such as the
aluminum in the heads and the magnesium in the crankcase. Every time
you start the engine it under-goes a 'heat-cycle.' It is those heat
cycles that cause the relative motion between the barrels and the
crankcase. And between the heads and the barrels. And of course,
after enough of those heat-cycles the tension in the head-stays (most
kids call them 'studs') tends to relax, which is why Volkswagen tells
you to re-set the torque of the head-stays periodically. And which
damn few VW owners ever do.

But there you are, wanting to over-bore the spigot-holes for a new set
of jugs. First thing you want to do is to be sure the fellow doing
the machining takes the trouble to measure YOUR set of jugs, rather
than the last set that came through the shop. Or the set that came
through two months ago. Or whatever. Because those over-size jugs
are generally a piece-rate product, imported from a country where the
size of a machinist's pay-check is determined by how many sets of
barrels he was able to crank out this week. Now, checking on the
machinist in this way is a bit of a trick because you should have
already blueprinted your new set of jugs. What you want is a hole
that's 0.005" over. No more and no less. At least, not for 92mm
Kolbenschmidt barrels. Why? Well, in the first case... getting the
spigot bores too big means your 'shuffle-rate' is going to go right
through the roof: Your jugs are going to be doing the fandango when
what you want them to do is a slow waltz. In fact, about the only
thing worse that a spigot-bore that's too LARGE is one that is too
small, because that one is going to start grabbing at your piston in a
process called 'scuffing.' That is, the aluminum PISTON inside of
your cast-iron BARREL is going to expand faster than the barrel... we
already know that because of the difference in their coefficient of
expansion. But when remember the spigot bore is going to be expanding
ALSO. And if you didn't provide enough allowance, it's going to limit
the barrel's 'growth' relative to the piston inside of it and that's
going to cause the piston to rub against the wall of the cylinder.
And you don't want that to happen.

So what if you've got something OTHER than Kolbenschmidt jugs? Well,
you gotta find out their recommended spigot bore allowance and use
that, since they know their product best; they know the spec for
THEIR cast-iron But since there's only about nine different makers of
after-market VW jugs -- and the odds are you'll only run into two or
three of them, you should able to work it out. That means, pulling
'Machinery's Handbook' off the shelf and looking up the RANGE of
thermal coefficients for finned, CAST IRON and coming up with a
figure. Typically it will tell you use so many thousandths of an
inch per inch of bore. So you run the numbers, round it up, do a few
tests and there you are. For that particular jug. (In fact, your
MACHINIST should be the one doing all this. And if he knows his
onions he'll already have the right figures for whatever brand of jugs
you have. The thing you really want to watch for is the fellow who
thinks One Size Fits All. Because it don't. Except for dune-
buggies :-)

So there you are, all set to cut your new spigot bores. And while one
half of the crankcase will lay flush to the table of the milling
machine, the other case-half is home to a number of studs and will NOT
lay flat. So the machinist will have made up an Accessory Table to
hold that side of the crankcase the required distance above the real
table of the milling machine. The accessory table will of course be
true to the milling machine, meaning it will be true to the crankcase,
which means the holes will at least be perpendicular to the deck of
the crankcase. As for bore diameter, we've already addressed that.

Now comes an interesting test of competence. After cutting you four
new holes for your four new barrels the machinist will pull all or
some of the plugs sealing the oil galleries in the crankcase. This is
because some of those galleries have dead-ends or 90 degree 'corners'
that become swarf-traps. If you don't get ALL of the swarf out of the
castings, they'll end up in your bearings and cost you an engine. Or
your life. So part of the expense is pulling those plugs so YOU can
get in there with your bore-brushes and what-not and CLEAN the
crankcase. The machinist's work is limited to pulling the plugs,
threading the holes to accept socket-head pipe plugs, and providing
you with a suitable set of plugs to match the holes. The cleaning is
left up to the Customer. And if any of this comes as a surprise, you
need to look at some other engines, such as those from Continental.
Or General Motors. Look for the pipe plugs. Because they are a
standard feature on a properly built engine.

If your machinist is experienced with FLYING Volkswagen he (or she)
will have drilled and threaded a couple of other holes in your
crankcase. Some are to be used to lock certain components in
position, others are used to improve the lubrication system and so
on. Every machinist varies a bit in this regard; you'll have to work
out which holes and plugs you expect to be done and those which you do
not.

Now, having read the above, you've got to ask yourself exactly WHERE
you planned to realize any savings by starting with a USED crankcase?

-R.S.Hoover