Subject:
Altered Adjustment Procedure for Automatic Toothed Belt
Tension Roller.
Vehicles:
All vehicle types listed above as of MY '93 with the
following engines:
OHC petrol
engines: 16 LZ2, C 16 NZ2, 18 SV,
C 18 NZ, 20 NE, 20 NEJ, C 20 NE, 20 SE and
X 20 SE
DOHC
petrol engines: X 14 XE, C 16 XE,
X 16 XE, X 16 XEL, C 18 XE, C 18 XEL,
C 20 XE, C 20 LET, X 20 XEV and X 22 XE
OHC diesel
engines: 17 DR and X 17 DTL
Condition:
In individual cases in both production and in the field, the
toothed belt tension roller is incorrectly adjusted.
If the toothed belt is excessively pretensioned, the thermal
expansion of the engine in operation can lead to excessive tension, resulting
in breakage of the toothed belt tension roller's cast stop.
This can lead to engine damage.
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Cause:
In the first hours of operation, a new toothed belt is
subjected to so - called "settling behaviour" (running -
in procedure). After "settling", the toothed belt tension roller's
pointer (I), originally set to the centre of the notch, moves to approx.
4 mm / 0.16 in. to the left of the notch centre (II), i. e. to
about the left edge of the notch.
Thereafter, the pointer drifts slightly more to the left as
usage progresses.
Measure:
With immediate effect, a differentiation is made between
1. new toothed belts
and
2. run - in toothed belts
for adjustment of the toothed belt tension roller.
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Altered Adjustment Procedure:
1. New toothed belt
For new toothed belts, the toothed belt tension roller's
pointer is set exactly to the centre of the notch (I), as before.
2. Run - in toothed belt (all toothed belts
after running - in procedure)
When reinstalling run - in toothed belts, regardless
of the mileage covered, the pointer of the toothed belt tension roller must
always be set to the position approx. 4 mm / 0.16 in. to the
left of the centre of the notch (II), i. e. set to approximately the left
edge of the notch. The same applies for correction of incorrect adjustment.
Beforehand, always check whether reuse of the run - in toothed belt is
still economically viable (observe change interval). The replacement of the
toothed belt must be documented on a new toothed belt sticker.
Remark:
Oily toothed belts or toothed belt tension rollers must
always be replaced. Determine the source of the oil and eliminate.
This alteration will be included universally for all
specified vehicle types and engines in the relevant subsequent revisions of
the Service Instructions.
Time Allowance:
The time allowances remain unchanged.
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