Date: Tue, 16 Apr 1996 09:41:00 -0700 (PDT)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: "Maher, Steve (SD-MS)" <SMAHER@gi.com>
Subject: V6anagon un-V6'ed (continued) - LONG (sorry, Gerry)
With the engine and trans apart, the remains of the clutch look remarkably
like the piece the PO had showed me when I first bought the V6anagon from
him, after he installed the new clutch I sent him.
Several possible causes as I see it:
1.) Defective clutch from the factory? Very unlikely, since these are
original German clutch parts (Sachs), and there seem to have been two
very similar failures in a row.
Only spring-center clutches are available thru normal channels for the
'80 Vanagon's stock 228-mm clutch and flywheel. Kennedy makes some
solid-center clutch discs for racing use, but they're REAL solid-- don't
even have the thin leaf springs between the linings of the disc, as all
normal bug and bus clutches do, solid and spring center alike. Kennedy
recommends against using them for street, which is all I use the V6anagon
for. When you let the clutch pedal out, the clutch suddenly engages all
the way, within only about 1/8" of pedal travel.
He did suggest one possible source for custom-made aftermarket
solid-center clutches, which I may check out. But depending on other
circumstances that may have led to this failure, I may be better off
with a spring-center clutch disc. Read on:
2.) Engine-transmission misalignment? Possible. This would be an adapter
problem if true. Ideally, the centerline of the crankshaft should exactly
match the centerline of the trans input shaft. Actually, the trans is
built with a slight wobble to its input shaft, so you can be a *little*
off and still make it work.
But if you are too far off, then you'll get a slight angle between the
input shaft and the flywheel, instead of the perfect right angle they
should be to each other. This would make the clutch disc sit not quite
flat on the flywheel; and when you let out the clutch pedal, the clutch
will force the disc to sit flat on the flywheel, slightly flexing the
center of the disc on the input shaft. Then when the engine and input
turn together, the clutch center will flex once with every engine
revolution. Can you say "metal fatigue"? I think this would toast a
solid-center clutch even faster than it did these two spring-center
clutches so far.
There are ways to measure for this, I think. Now that the flywheel is
removed, I'll cut a stick to the exact distance from the surface of the
crank, to the ridge machined in the adapter that seats the adapter into
the (round) tranny opening. If this distance doesn't match for all 360
degrees around the crank, then BZZZZT...
3.) Dynamic imbalance of the flywheel? This one's a little more esoteric,
though with this particular engine it may be possible. Most engines require
a balanced flywheel, for obvious reasons. If the engine's balanced and the
flywheel isn't, it'll shake the car apart... sort of as the V6anagon's
been doing since I've had it. The PO even commented on this droning
vibration
before I bought it from him.
BUT... a very few engines are deliberately built unbalanced, and require
a flywheel that's unbalanced in the opposite direction, to compensate.
Yup, the Chevy 2.8L V6 is one of those few (the 4-cyl engine that also
came in the citation isn't, by odd contrast).
When I removed the flywheel, which was made from a Vanagon flywheel, I
was astonished to find fourteen drill holes evenly spaced along one side
of the rim. Looked like some casting shop had done a REALLY bad job when
they originally made it, and a lot of machining was required to balance it.
But I stuck it on a dowel rod, and the undrilled side flopped right down
to the bottom, time and again.
Called Kennedy, sure I had found the problem, and he told me about Chevy
V6 balancing oddities. This extra drilling to deliberately "unbalance" a
flywheel by a certain amount, is called match-balancing. I learn something
new every day... usually right after my car breaks down.
But now I wonder... the VW flywheel is heavily dished, like a frisbee with
a real thick rim. I wonder if the original Chevy flywheel for this engine,
was this deeply dished. If not, then the metal that was removed on one side
to properly match this VW flywheel to the (unbalanced) Chevy V6 engine,
may have been removed from an area that was farther from the flat bolting
surface of the crankshaft, than the Chevy flywheel would have been.
Now that you are all throughly confused, imagine a wheel on your car,
perfectly balanced. Now put a 10-pound weight on the top of the rim, on
the outside where everyone can see it. Then duck under the car and put an
identical 10-pound weight on the bottom of the rim, on the inside where
only your engine can see it.
If you jack up the wheel and set it to any rotational position, it will
stay there, because it's still perfectly balanced. This is "static
balancing". Rotationally, the two extra weights cancel each other out,
even though the top one is 36" from the car's centerline and the bottom
one is only 30" from the car's centerline.
But if you start spinning the wheel, it's a whole different story. In
short, when the wheel spins fast, both those weights will try to go as
far from the axle as they can. But a line drawn from one weight to the
other, will NOT be at right angles to the axle, since one weight is on
the outside of the wheel and the other is on the inside. The two weights
will try to rock the wheel enough to make the line a right angle with the
axle. Instant wheel shimmy!
This is why, when you have your tires balanced at Goodyear or wherever,
they put the tire/wheel on a machine that spins them, before the mechanic
puts on the little weights. He's looking for this kind o "dynamic
imbalance", which he wouldn't see if he simply hung the wheel on a
stationary balance point.
Well, coming back to the vibrating V6anagon...
The flywheel for the Chevy 2.8L V6, is required to be heavier on one side
than the other ("statically unbalanced"), to make up for an opposite
imbalance built into the engine. If the flywheel is perfectly flat, that's
fine (I wonder if the original Chevy flywheel was flat?)
But if you set the VW flywheel on a table, with the center that bolts to
the crankshaft resting on the table, then look where metal was removed to
deliberately unbalance the flywheel. That part, is half an inch above the
table. Seems a small difference, but at 4,000 rpm it can start to matter
a lot. On the opposite rim, the heavier part of the flywheel, is also
half an inch above the table.
This is a lot like taking ONE of those ten-pound weights, off your wheel.
The other ten-pound weight, will still try to rock the wheel the same
amount it was before. And I suspect that the heavy edge of the flywheel,
is trying to rock the flywheel in the same way.
Since the Chevy 2.8L V6 engine requires an unbalanced flywheel, and the VW
requires a dished flywheel, the two may never get along-- the vibration
may be incurable.
Well, I'm going to see if the engine is properly centered on the adapter
first-- at least that is curable, if it is. Then I'll ask Kennedy for a
list of their customers who have put this particular engine into their
Vanagons. Hope there's more than one name on the list! If I (or the PO)
is the only one, then I'll ask for customers with other match-balanced
engines and flywheels.
I may not get to do much more analysis on this beast-- the apartment
security guards have been asking me what kind of tune-up requires the
engine to be resting on the ground in the apt. parking lot as it is now.
They're my buddies, so they're cutting me some slack, but I don't want to
put them in too bad a position. But I must get the V6anagon back together
by the end of the coming weekend. Maybe just have to rename it Shaky Jake?
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Steve Maher smaher@gi.com '80 V6anagon w/Chevy 2800
'66 Mustang Coupevertible, for sale
Check out the cars at http://www.lookup.com/homepages/76242/home.html
*** It takes all kinds to make this world.
That's why we aren't all Irish. ***
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