Join Date: Mar 2018
Location: Charlotte, NC
Vehicle: 1999 slk 230
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It's not the chain tensioner or the timing chain at all. Unless you have over 250k on odometer or have not changed the oil every 5,000-7,000 miles, the noise you hear is from the VVT valve timing system and is easily remedied. All VVT engines will make a noise after sitting for more than 3 days. However, some do not make the noise by which we can hear them. The noise is indicative of a lack of full oil pressure at the lifter sprockets on the cam and VVT mechanisms.
There is nothing wrong with the engine. It probably has been making this noise since day one. If your windows are shut when you start the car after sitting for a few days, or even overnight in temps below 70 (f), you will hear that noise after a second past ignition and it will last for 1-2 seconds and stop.
To fix the problem, simply press the brake pedal firmly, not by smashing it, but by pressing it as if you were traveling at 40mph and had to slow down a bit. Press the pedal 2 times, and before starting, press the brake pedal firmly and start the car while pressing that brake pedal. The result will be to create a "vacuum pull" in the valve train and intake manifold, simulating the sane vacuum force created within the engine when it's running. The R170 and R171 do not require that the brake pedal be depressed during starting like all late model push-button started cars. Hence, none of us bother to press the brake pedal before starting.
Simply press firmly on the brake pedal twice, then prior to turning the key, simply press the pedal firmly a third time, but hold it, start the car, and release the pedal. No more noise; guaranteed.
I learned this when I had the same cold start noise on a 2002 Lexus GS 300 as well as a 2007 Lexus GS350. Both had VVT valve systems. You see, all VVT engines use vacuum as well as hydraulic and electric/mechanical aspects to the variable valve timing.
It's not really a design flaw in any of these engines, at least not the SLK or any other car I've owned. Usually, a TSB will be issued if customers complain enough about the fears that their engines are grinding. Most TSB's for valve clatter on cold start involve changing the vacuum orifices in either the power brake systems or at the camshafts. It's so much easier just to create a simulated vacuum pull by pressing firmly on the brake pedal a few times then holding the pedal firmly when cold starting. Once the engines fires, let go of the brake pedal and you will not hear a rattle, clank, etc.
I've found this out by studying engine schematics on Mercedes, BMW, Audi, Chevy, Ford, Toyota and even Chrysler products. Each time a friend would complain about cold start clanking/clatter, I would advise them to try my method and they all reported that the noise was gone.
Why don't the dealers or other mechanics tell you this procedure? I have no idea, but it works.
Try leaving your car for as long as it takes to simulate that clatter. (for my R170) it was always 5+ days. If it is only 24 hours, overnight, or three weeks, just try my method and you'll see your noise is gone. My friends R171 has 272k on the odometer, and he replaced his timing chain tensioner three times and it did nothing to stop the clatter. Once he started the car using my 2 second fix, his noise went away.
Now, if you allowed OCI's of 10k miles and used a less than wonderful oil blend, you could have a partially clogged timing chain tensioner. However, the difference between cold start valve clutter and timing chain clanking is night v. day.
Please let me know how this starting procedure works. Oh, no need to ever bother with a warm engine. Vacuum remains in all engines for up to 12 hours.