Here is the technical service bulletin for timing chain stretch:
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Engine - Noise/Runs Rough/Hard Start/No Power

REF. NO. 05/93

TO: ALL MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: November 1995

(supersedes S.I. 05/91, December 1994)

Revision: Engine 606 included.

SUBJECT:
ENGINES 602, 603 AND 606
ENGINE RELATED COMPLAINTS DUE TO STRETCHED TIMING CHAIN

In model 124 equipped with engines 602 and 606; and model 140 equipped with engine 603 built between July 1992 and April 1994, the following complaints may be the result of a stretched timing chain:

Unusual noise from timing chain area

Rough running engine

Hard start

Loss of power

Increase in oil consumption

In order to check basic engine timing, turn the engine slowly (in normal rotation) using the crankshaft pulley bolt until the mark on camshaft sprocket aligns with the mark on the camshaft bearing cap (arrows, Figure 1). The position of the crankshaft will tell if the chain is stretched, i.e. is still within specifications (Figure 2). For engine 606, refer to SMS Job No. AR 05.20-6010 HA.

1. If the timing mark on the crankshaft pulley is off by 3 °- 10 °:

The timing chain is stretched and should be replaced (Engine 602/603 SMS, Job No. 05.10-320; Engine 606 SMS, Job No. AR05.10-7601 HA).
Visually inspect timing chain sprocket for wear or damage:
Turn the engine 2 complete revolutions (in normal rotation) using the crankshaft pulley bolt and inspect the camshaft sprocket (B, Figure 3 [undamaged tooth]). If the teeth are worn (A) or broken (C) the camshaft sprocket and injection pump timing sprocket must be replaced (Engine 602/603 SMS, Job No. 07.1-240) or (Engine 606 SMS, Job 07.1-8014) along with the timing chain.

2. If the timing mark on the crankshaft pulley is off by greater than 10 degrees:
Inspect the top of the pistons with a borescope to determine if any of the pistons have come in contact with the valves.

If there was any valve to piston contact, the engine must be repaired accordingly.

If the tops of the pistons do not show any visible damage caused by valve contact proceed with step 1 above.


Note: Timing chain guide wear such as grooves or track marks do not justify the exchange of the chain or the rail.
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Hope this helps. I use 15W-50 Mobil 1 in my "Black Pearl" and think it is a superior lubricant for a superior automobile!

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