(2003 CLK 500 with 156kms) I've noticed a slight valve sound on some cold startups recently which lasts only a few seconds. I did an oil change ~800km ago and am planning on doing spark plugs soon as well (with any spark plug recommendations welcome). I may look into the oil pump as well. In addition to this the engine seems to be idling very slightly rough and there is a ticking/clicking sound coming from underneath the car when things are quiet. There are no DTCs besides a P20DD which I've already purchased an accelerator pedal for (been lazy about putting it in).

I'm not really worried but I've been trying to keep on top of the preventative maintenance with this car. I know about the EGR tick and the valve train noise seems about what is normal although it does seem louder from cyl. #1 but that could be my imagination. I've also heard that the cats can cause this but unless its the primary ones that do this the secondary cats have already been deleted. I'll have to put it up on the lift and see. Other than that I'm not too sure. As for the idle vibration I can somewhat feel it when I put my hand on the engine but I wasn't really paying attention previously so I can't really compare. I've checked the mounts too and they aren't leaking but they could otw out.

I can take a video if any of you care but the startup noise is definitely intermittent (only somewhat noticeable in the open air but easily heard being started in the shop) and I only noticed the vibration + underneath tick/click today so it could be as well. If any of you have experienced any of these I'd really appreciate your input.

 

I have heard about ticking on startup, could be cam chain tensioner, due to chan stretch or the dreaded balance shaft, not sure if there is one on the 500 as it’s V8 and I think they balance themselves.

 

Forgot I posted this... must've been pretty sauced. Its still doing the thing, but it hasn't got any better/worse though. The m113s have a bushing in the crank shaft pulley that acts like a harmonic balancer but I'm unsure if they have a balance shaft. My bushing is worn (wobbling a bit) and I need to replace it but I've been a bit lazy. I don't think that's the cause of the issue. It could be chain slap but, to me at least, it sounds different. At this point I think I'll just ignore it until it gets worse or something happens. Worst comes to worst the clk gets a 5.4 in it or I end up buying a R129, W140, W124 like I plan to in a year or so anyway. Thanks for the input though, I wasn't thinking about the chain. I should take another listen.

 

Re: ticking. Sure it's not the charcoal canister purge valve solenoid? Circled red in the (not my car) pic below. Quite noticeable on a cold start and normal.

And re: changing plugs. Make sure you have these. It's a cow of a job. Changing 12 on mine was bad enough. 16 in a more crowded bay all by touch will be super fun!

For my M112 the genuine plugs were A 003 159 94 03 and were NGK PFR5R-11. Same for the M113?

 

Thanks for the info Rich! I'm pretty sure those are the same spark plugs the M113 uses, although I might end up grabbing NGKs iridium ones. I'm very certain that it's not the purge valve as the noise is a different tick and the valve is constant, not just on startup. That lil fker scared me when I first picked up the car though. I'll make sure to pick up one of those wrenches too (since I've been meaning to for work anyway). Is it recommended that I do coils and wires as well when swapping the plugs?

 

I just went to the dealer, asked for the correct plugs and they price matched what I'd seen online. Friendly dealer too because they lent me both those tools to do the job. Tbh I'd read loads online about changing plugs on these and so much focus was on having that 17mm tool to pop off the leads but once you realise what it's for then really there are probably 100 other suitable tools. The handiest thing was the multi angle socket. The whole job is done by touch. I've done V8s, straight 6s, 4s before but never needed anything like that.

Re: coils and leads. I didn't but I'm sure some would. Easy enough to change while you're in there but I suppose it depends how deep your pockets are.

 

The plugs (FR8DPP33+) themselves weren't too bad for me. The part I had trouble with was removing the leads. The special tool was useless for that as the previous owner installed wires with a rubber boot and not the metal boots like OEM.