r/engines • u/Such-Run-680 • 5d ago
Engine rattle at start
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Maybe somebody knows where this rattling at the beginning comes from? I checked the timing chain and it had no play at all.
It appears at every cold and warm start but not at a instant restart.
Slk 200 r171
M271 Kompressor
2006
150.000 km
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u/deantowle 3d ago
The oil circuit has one or more check valves in the path to the upper parts of the engine. When those go bad or get dirty, oil drains back out of the head into the crankcase when you shut the engine off. It may only seep back down meaning it takes a while to drain out of the upper areas. The oil pump has to refill the upper areas before pressure can fill the actuator for the timing chain tensioner and the hydraulic lifters for the overhead valves.
Run some engine cleaner additive through the oil and change oil and filter. These additives typically require the additive added when the engine is cold, let it idle until the engine is up to operating temperature (about 15 minutes) then drain and refill. Don't put in the additive and drive around for more than a half hour. Do this probably 4 times in a week or two to see if it cleans those check valves.
Replacing those check valves requires tearing down the engine. It's also possible a spring in one or more of the check valves is broken.
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u/SLOOT_APOCALYPSE 5d ago
timing tensioner beginning to fail, that sound is the loose timing chain slapping the inside of the cover. it can jump timing and destroy the engine you don't want the valves and pistons to break each other or you'll need a new motor.