There has been a lot of talk lately about chain rail guides breaking.
The guides do not break by themselves because they get old and brittle.
The reason the left head inner rail breaks is that the chain is so loose
it is slapping the guide. When the over-abused guide finally breaks off
it falls between the chain and the sprocket raising the chain off the
sprocket with two rather disasterous effects.
1. The left cam looses timing and pistons and valves hit.
2. The chain has very little running clearance between the sprocket and the valve cover and usually when the guide rail places itself between the sprocket and the chain it punches through the valve cover (really great sound effects).
Please realise that long before this happens the chain has been making
all sorts of slapping sounds at startup and the driver has not bothered
to have this noise diagnossed. If you telephone almost any Benz mechanic
and tell him there is a slapping noise at start up, he will probably
tell you to not risk driving the car over and have it towed in. The
slapping noise is the chain flailing away in the timing chest hitting
everything it is not supposed to hit.
Rules on chain replacement for V-8 motors.
1. 350's and 450's from 71-80...check the chain every 30,ooo miles.
2. 380's from 81-83..IMMEDIATELY replace the single row chain with a double and follow the 450 maintenance interval.
3. 380's and 500's and 560's from 84-91..same as 450
4. Newer V-8's..sorry folks, not enough service history to report in yet. Maybe in a few years.
4 and 5 and 6 cylinder motors. Take the valve cover off and check the
chain condition. The chain run is so short on the inline motors that the
chains go a long way, anywhere between 100-200,000 miles and beyond
depending upon oil change frequency. But, they should be checked every
once in a while. With the shorter chain runs, if you ever hear the chain
slap or make any noise, immediately stop the motor and tow it to the
nearest repair facility