Date:         Tue, 16 Jan 2001 10:57:14 EST
Reply-To:     Wolfvan88@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Robert Lilley <Wolfvan88@AOL.COM>
Subject:      Re: BOSTON BOBS OIL PRESSURE THOUGHTS---STROKE CHANGE-CW crank
              NEEDED
Content-Type: multipart/alternative;

While the bolts may be different, one important factor that is often over
looked is:

What effect does the INCREASED stroke of the 2.1L have on the bearings and
engine life Vs the 1.9L?

(The bolts might not the real problem but only the symptoms)

The stroke increase of 7 mm, on the stock shaft causes increased stress on
the center main bearing along with increased stress on the rod bearings.  The
crank, being un-counter-balanced and having TWO heavy rod journals on one
side, causes the crank to increase the crank whipping (center of crank
flexes) on the center main bearing.  The crank has a heavy pulley and a heavy
flywheel to help to dampen the forces but not eliminate them.

In a T1 engine case (the WBX is a T1 engine but with an aluminum case) the
soft magnesium aluminum alloy mix case actually pounds the center bearing
saddle oval along with the rest of the bearing saddles out of round.  This
causes the engine to HAVE LOW idle oil pressure and a loss of oil pressure at
higher rpms and engine failure.  The T1 cases are almost always line bored to
restore the main bearing saddles to round.  Then over sized main bearing are
used.

In the WBX, the case is aluminum alloy without the softer metal.  The bearing
saddles do not pound out BUT THE BEARINGS DO.  The bearings wear out after
xxx miles.  The crank, as the center bearing wears out, starts to run oval
around the center line.  In the 2.1L with the increased stroke, the force is
greater than the 1.9L.

As the center bearing wear out, the crank is able to increase the flexing
(faster acceleration, higher revving increase the crank whipping) the rods
journals no longer run perpendicular to the centerline, but start to run at
an angle to the centerline. This puts uneven stress on the of the bearing
face and wears it out at an angle. Over time the bearing clearance increases
and when it reaches a point, it no longer can provide adequate oil pressure
to cool the bearing and the rod fails.

When you look at WHERE the most stress on the rod happen happens: On the
power stroke of the engine when the rod is being forced down.  IF the rod is
NOT ABSOLUTELY perpendicular to the force then one SIDE of the bearing gets
more force than the other side. Over time that side will wear out faster than
the other side. The clearance increases and the rod cannot maintain adequate
oil pressure and the bearing fails then the rod...Remember the clearance ARE
SMALLER than a piece of paper SO ANY INCREASE can have disastrous effects...

The only force that the bolts see is when the piston is being forced up on
the exhaust stroke and the piston wants to go through the cylinder head.  The
bolts are the only thing that stops this.

 Now I will not rule out the possibility of the bolts being A problem, I
think that it is more the lack of counter balancing ALONG WITH THE INCREASED
STROKE is the main problem and over time simply wears out the bearings to the
point of failure.


On a 1.9 L the same forces are present and BUT are magnified by the increased
stroke on the 2.1L.

Bigger strokes are available, why did VW stick with the 76 mm stroke rather
than the 78.4 mm stroke or bigger?

They did not want to add counter weights, because it has been proven that the
addition of the counterweights doubled the bearing life (or more) (Gene Berg
Enterprises proved this did this...) So, I think that VW ran into this
problem of failed engines, with bigger strokes, at lower mileage's with the
WBX engine with an uncounter-balanced crank.  The 76 mm stroke was the
probably best stroke to make the engines last past the 100,000 mark WITHOUT
adding the counterweights to the crank.  VW built the engine fail after a
certain point, because after, they do not want the engine to last forever.
VW did not want to buy new forging dies to make bigger stroked cranks or to
add counterweights to the crank.


We can start the TO or NOT TO counterweighting posting war over BUT look at
ANY performance crank for the T1 engine and SEE counterweights added.



THAT is WHY with the 2.1L the counterweighting of the crank is more important
When adding more power and when you do counterweight the crank, you get more
power...

Robert

[text/html]