Date: Sat, 15 Feb 2003 22:50:58 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: Gap of Sparks
Content-Type: text/plain; charset=us-ascii
I've been laying out of this because you guys have got the ignition
system pretty well down pat.
I've had some good and bad experiences with VW distributors, mostly 009
and the 205 that is on air cooled vanagons.
Good tight distributors with good cams are important to achieve full
power from an engine with a point set ignition.
Vertical shaft movement can cause point dwell to change because the cams
are traveling both in rotation and a vertical jump at various times of
acceleration or just idling.
Testing the cam is easy enough just by rotating the cam to each high cam
position and measuring the point opening with feeler gauges. You can also
use a dial gauge if you can get it rigged properly (not easy).
One revolution isn't enough testing, it needs to be tested for three or
more revolutions to verify properly.
I've found cam shafts with strange wear patterns that are .002 out from
one cam high to the other cam high positions. This in effect changes
dwell and will cause premature or late plug firing. The condition can be
caused by slightly bent distributor drives or on drives that have had
pitting due to rust. Running the shaft dry can cause excessive wear down
of a single cam lobe while the others appear correct.
The spring under the Vanagon and most VW distributor drives is supposed
to stop vertical bounce caused by the gear bouncing on the lower crank
contact gear. However under hard deceleration the drive will draw down on
the spring, this doesn't cause any problems but as the drive travels
upward it gives the distributor a little advance of 1+ degrees and can
cause an occasional backfire.
Vertical bounce happens under deceleration and acceleration of the engine
at high RPMs.
If the brass drive gear on the crankshaft is worn unevenly or is just a
sloppy fit it can cause advance / retard changes that you cam measure by
accelerating the engine several times and noting the variances.
I've proven to myself that good distributors are a necessity for proper
delivery of spark to the plugs.
Having a box of about ten distributors in various condition has given me
the tools to experiment and disparity can be detected even with simple
tach, dwell meters of good quality.
Carefully accelerating the engine while watching the advance on the
timing arc and multiple cycles at various RPMs can detect distributor
advance slowdown or vacillation.
One war story I might relate here is that I've found long screws holding
point sets down, they lock out the advance if they are longer than 3/8"
long.
If you've had a distributor showing rust, pitting or other signs of
moisture exposure that is abnormal you can find weak counterweight
springs that will cause too fast advance.
Someone just mentioned that the point set and electronic ignition coils
are the same ........... I doubt this.
My air cooled will not even start with the electronic ignition
distributor. I've been told that the electronic distributor produces more
current / spark.
It has been suggested that Air Cooled vanagons could run hotter plugs
without damage if you want to peruse it.
Hotter plugs can cause detonation in some operating environments so take
caution on going too hot.
Stan Wilder
83 Air Cooled Westfalia
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