From: Jim Bailey [jim@928intl.com]
Sent: Monday, March 26, 2001 7:55 PM
To: 928
Subject: [928] RE: timing belt warning light

The "timing belt tension" warning is considered by Porsche to be a class "B"
warning not on the level of oil pressure or brake failure but equal to brake
pad wear sensors , low fuel or stop light s being out , low coolant . That
said the system is very primitive , the contact strip on the tensioner arm
must always touch the pin in the end of the tensioner providing a ground .
As long as there is a ground the warning light does not come on . There is
no adjustment to the contact it either touches or it does not . As Wally
pointed out the tensioner is oil filled (if the last mechanic filled it) and
uses the oil to dampen the movement of the arm ( like a shock absorber)
during times when the belt maybe less tight ( cold engine) or prone to
flutter (high RPM ) , It is possible that it is low on oil . The tensioner
does not tension the whole timing belt but just picks up the slack on the
loose part of the belt . From the crankshaft to the passenger camshaft
sprocket as the balance of the belt is pulled around the engine by the
crankshaft gear .




From: Jay Kempf [mailto:jkempf@tds.net]
Sent: Monday, May 27, 2002 12:26 PM
To: 928
Subject: [928] RE: T-belt light


You are both correct. The oil does provide a dampening effect that helps to
keep the spring pack from creating belt slap at some rpms that would create
a constructive interference pattern. But it is the lubricating effect that
keeps the tensioner assembly reading properly. A dry tensioner will bind and
mess with tension. It is not true that there is any hydraulic effect other
than dampening. The spring packs provide ALL of the pressure that tensions
the belt. Mostly what the oil is does is provide a thermal transfer to the
springs. Air is an insulator. Secondary is lubrication. Third is dampening.

Just to review for any newbies the tensioner is not automatic it must be
manually set to the correct belt tension periodically. Especially after a
new belt is installed as the initial stretching/settling is somewhat
unpredictable.

Also, on early cars there is no way to refill the tensioner without removing
the belt and arm and actually pouring 90 weight in. Later cars have fill,
drain, bleed ports. I actually believe that grease would work just fine. It
would have a tendency to stay in with a ripped boot and would provide all
the thermal transfer, lubrication and dampening effect. But it could alter
the dampening characteristics and it would certainly start out hard as a
rock on cold days. But it would probably work fine. I haven't tried it, but
if I had thought of it I might have :) A tensioner boot is all that is
normally required for a rebuild an a few ounces of hypoid oil. don't let a
mechanic tell you that you need a whole new...multi hundred dollar tensioner
assembly. There is almost no way for it to actually wear out. It just needs
to be taken apart, cleaned and put back together normally.

Jay Kempf
79 US 5ish speed.




From: Jim Bailey [mailto:jim@928intl.com]
Sent: Thursday, August 22, 2002 9:31 PM
To: 928
Subject: [928] RE: Timing Belt Light


As Randy points out the timing belt tension warning system has a built in
time delay 3-5 minutes during which the central warning brain is not looking
for a ground . After the delay , the metal contact on the tensioner arm
which is insulated from the water pump by the plastic bushings on the
shoulder pivot bolt
must be touching the pin in the tensioner to be grounded . This way if the
tensioner pin is not touching the arm the belt must be loose and the warning
brain displays the dreaded belt tension light . But if the single wire which
passes through the plastic cam belt cover gets stretched and broken you now
have an open circuit (no ground) and you get the warning immediately after
the delay . Some mechanics have been know to just cut the wire and attach it
to any bolt on the engine this gives it the ground forever! You can test the
circuit by temporarily grounding that wire and running the engine until the
time delay is completed and see if you get the warning light if the light
does not come on the problem is not between the new ground and the brain but
between the new ground and the tensioner arm contact .
Jim Bailey
928 International
Jim@928intl.com
www.928intl.com
(714)632-9288