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I have the rattle on start-up after 3 or more days standing.* Not long after a major service, I had this loud rattling on start-up, after standing for 3 or more days - it begins immediately on turning the key and only lasts for a second then goes quiet. Sounds like it could be the timing chain tensioner has failed but I have been doing some research and it may not be that?

The problem appears to be that the oil drains out of the chain tensioner so it has to wait for pressure to build up*to push it back onto the chain. This suggests that the tensioner may be OK and the problem is the failure of one of the two oil relief valves that stop oil draining back into the sump when the engine is not running. There is one behind the pulley housing that is the most likely culprit and worth changing as a matter of course while repairing your supercharger. There is another valve in the oil filter.

I also noticed that there appear to be two types of chain tensioner: one has a ratchet in it and the other does not and relies on oil pressure, although the plunger will only travel towards the chain and not back so it has some sort of non-return clip. I have watched youtube videos on both types that show how to "repair" them. I doubt they wear out (opinion) and might only need cleaning if there is a blocked oil way?

I also found a reference to the hydraulic tappets and that they also need oil pressure to be maintained but I am convinced it is the timing chain tensioner.

I have attached some pictures of the valves and the tensioner. These videos are not all for the SLK but are worth watching:

That is all I know so far so, Roger and out
 

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If the tensioner is failing, it will make noise ALL the time.
That was my thought as well. Mine make a fair amount of noise on cold start and it seemed to be the secondary air pump. I think that's fairly common on Kompressors. Have you tried a stethescope to locate the noise?
 

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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.
 

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That is a terrific response, thank you. I will leave my car for at least 3 days and try this technique to see if works for me... I will report back!

I had a 1999 SLK 230K for 6 years and it never did this (40K miles) - due to illness, the car was left for weeks such that the battery went flat (that's when I bought an AccuMate) and it did not rattle on start-up. I then had a 2007 SLK 200 (40K miles) and that did not rattle. Now I have a 2001 SLK 230K and it did not rattle (43K miles) until June 2019. However, my current SLK has a very slightly spongy brake pedal compared to my previous 2 cars... I had it checked by the garage and they said it perfectly OK.

Could there be an explanation for the variable symptoms?
 

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I have the rattle on start-up after 3 or more days standing.* Not long after a major service, I had this loud rattling on start-up, after standing for 3 or more days - it begins immediately on turning the key and only lasts for a second then goes quiet. Sounds like it could be the timing chain tensioner has failed but I have been doing some research and it may not be that?
The problem appears to be that the oil drains out of the chain tensionerThere is another valve in the oil filter.
Hi,

Sorry not had much time recently, manic busy last week ;)

I think it may well be you have answered your own question here !!

First thing I would do is change the Oil again being certain to use correctly specced Oil and a genuine MB Filter , it is highly likely especially if this service was done at a "local garage" type business that cheap and perhaps wrongly specced Oil and / or Filter have been used.

If that turns out to be the case I would avoid using that garage again !!

Edit, re that garage, just saw your post 6, re spongy brakes, they definitely sound like one of the "Can't be bothered" Garages I have much experience of up here in the NW Highlands :wink:

HTH, Cheers Dave
 

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Mitch, I have been experimenting with your idea and it works. In my case, the rattle appears after 3 days standing (mid-summer). I press the brake pedal 3 times, holding the third depression, then start the engine and NO RATTLE! I have done this several times, now, and it works every time. It will be interesting to see if anything changes in the winter as my rattle did not appear until the start of the summer.

I tried depressing the pedal only once but the rattle appeared shortly after starting (it normally starts with the engine) but was shorter in duration. According to your diagnosis, this may be because 1 depression of the pedal is not enough to raise the vacuum sufficiently?

I did not have this rattle on my first SLK R170 that I had between 1999 and 2005 (42k) and I did not have it on my current SLK R170 (2001, 43k) until recently, 6 weeks after a full service/oil change. I have had a 2007 SLK and two C-Classes and they did not do this, either. I want to know if there is a component or a condition within the braking system that causes this? So, the case is not closed but at least I have a "work-around"! Could it be that the vacuum is held much longer on cars in perfect health - maybe there is a leak in the vacuum system?
 

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Hi @jacksonsinliss ,

I do not understand what you are saying / getting at above .........................

By pressing the Brake repeatedly you are exhausting the vacuum in the Servo, not increasing it, so what you are effectively doing is admitting more air to the Engine upon start as it is drawing that Air in the servo into the Engine to create the Vacuum :confused:

What may be happening here, (just a guess), is that the extra Air causes the Engine to run at faster Idle speed as it fires up, and thus the Oil Pressure builds up very much quicker eliminating the rattle ??????

Try comparing your RPM as soon as she fires by doing the pedal pressing, and next time without it :wink:

HTH, Cheers Dave
 

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Discussion Starter #11
Dave2302,

I agree with you that I expected that depressing the brake pedal would pressurise the system but I am only following Mitch's findings and it works.

The problem I have is why does pressing the brake 3 times work and can it be "fixed" so that a single depression of the brake pedal is sufficient to avoid the rattle? I will try your suggestion of comparing the revs and see what happens!

Roger
 

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Hi Roger,

No .............. I don't think Pressurising the Brake Fluid Circuit has anything to do with it.

What is happening is as you repeatedly press the pedal you exhaust the Vacuum retained in the servo, when you then start the Engine, there is then a sudden rush of extra un metered Air into the Inlet manifold until the Vacuum has built up again ....................

That extra Air will likely have an effect on the speed the Engine runs at, for about 3 - 4 seconds, which, if there is a noticeable increase in revs, it would circulate the Oil quicker thus building Oil Pressure quicker, hence tensioning the Chain almost instantly.

If you see a difference in those Revs, then this is likely an Oil Pressure issue, and not wishing to repeat myself, but it started after an Oil and Filter change :wink:

HTH, Cheers Dave
 

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Registered 1999 slk 230
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Hi Dave,
The servo air on virtually all Mercedes models from 1981-today will deplete within 10 hours or less. By depressing the brake pedal a few times when the engine is cold (not started for 10+ hours) simply pushes non-bound servo air back into the VVT cam lifters. I tested the RPM using a database in my scan tool plugged into the OBDII port. No difference, whatsoever. On my R170, the engine RPM always moves up to 975 when cold. After the cold start using the brake pedal pressing, the RPM was 972-981. No difference.
I did try starting cold after it sat for 5 days, by pressing firmly on the brake pedal without pumping, and the rattle noise did not fully appear. I did hear a slight variation. I waited a few days, Started it cold after pressing two pumps on pedal and holding firmly on pedal during starter engagement and zero noise and no RPM bounce.

I have tried this with my 2017 QX50 which tends to have a slight rattle after sitting for a day or so. Same fix. I'm convinced the all VVT engines will make a harmless, but annoying cold start rattle after sitting for a day or a week. I do not think oil pressure itself, not oil filter properties affect this issue.

I used to store the R170 for an entire winter when I lived in the far North. After 6 months of sitting, the rattle on initial start was amazing. It could wake the dead. Lasted for 2-4 seconds. The engine now has 29,000 miles, 99% highway driving. What originally made me research the engine mechanical schematics was the fact the another car I own, a 2015 GS 350 with a Toyota 3.5L never makes a sound. I carefully looked and found a small 12 volt air pump connected to the brake booster line. Sure enough, on a cold start, the valve opens and the small electric motor pumps air into the VVT air ports. Never a rattle.

On the R170, I use the factory labeled oil filter. It's a Mann filter, but the specs are quite different from the OEM off the shelf Mann branded filter. The top end fits snugly onto the oil filter cap. The only way to ever install these filters is to snap the top of filter into the bottom of the cap. Then, slide the assembly over the inner tubes and to tighten to 25nm. For whatever reason, the Mann aftermarket filter never fits snugly onto the canister top. I use Amsoil Euro 5w-40. Been running it for 25,000 miles. I happen to love Amsoil, but there are a number of great 229.50 approved oils out there. Amsoil Euro Classic is 229.50 approved; not simply recommended.

Good luck to all about the cold start noise. Just gently pump the brake pedal a few times, press and firmly hold the brake pedal, the start the engine. No more noise. By the way and as mentioned, no need to jam the pedal or press with more than 15-20 pounds of force. It will push enough air into the cam lifters to allow instant oil pressure.

Cheers.
 

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Discussion Starter #14
Mitch,
That is a comprehensive and convincing response, thank you.
It sounds like the problem is that the vacuum gradually leaks away over time and that interval varies between vehicles? I read somewhere that diesel engines do not generate enough vacuum and have a pump to assist them.

I noticed there is a vacuum pump on the system and on my 2001 SLK R170 there is a pump at the front of the engine bay, on the right viewed from the front - I think the part number may be A0004351301, location C098A5. As this problem has only affected one car (current SLK) out of all the Merc's I have owned since 1999, I have to ask if there could be a leak or failure of the pump that is the cause?

Your observation on the aftermarket oil filter not fitting snugly also suggests there could be a loss of oil pressure over time, which may be a contributory issue?

Roger and out
 

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Discussion Starter #15
Mitch, a question on the oil filter, if you have one handy, what are the dimensions of the OEM Mann filter, vs the aftermarket one?

The only filter I found on Amazon that has dimensions is the Oil filter Evotop replacement MANN 65002848: outer diameter: 62 mm. Inner Diameter: 23 mm. Height: 159 mm.

Roger and out
 

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Hi @Mitch Kranes ,

I have owned and worked professionally for over 40 years on an abundance of Mercedes Vehicles from 1981 to 2017 model years and never once had one that rattles on start up.

I have also never found anything to suggest air pressure / vacuum is connected to lifters.

I do not have very much experience with 4 Cylinder SLK Petrol Engines, because they are not common in my locale.

I have however been intimate with MB older single OHC Petrols, N/A older Diesels, various CDI's, V6, V8 and V12 Motors, so on that basis I cannot offer anything further that might be useful :wink:

Very "Confused . com"

Cheers Dave
 

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Discussion Starter #17
The mystery continues?

I have been having a good look around my engine bay and I cannot see any connection of the vacuum hoses to the cylinder head other than the one from the inlet manifold - of course, there could be a channel internal to the cylinder head that feeds the tappets? It is a fact that depressing the brake pedal 2 or 3 times before starting the engine will avoid the rattle so, Mitch may have a good point and Dave may still be confused, as am I. As I said before, I have had many MB cars since 1999 and this is the first to have this problem (and only since May) so my guess is that it is a "fault" on some engines as opposed to a "feature" of vehicles having hydraulic tappets.

Loss of oil pressure sounds plausible, hence I am keen to investigate the after-market oil filter query I raised with Mitch. If the new oil filter is slightly smaller than the OEM one then would that be guilty of causing the problem? Changing my oil filter (without draining the oil - that is crystal clear) could be worth a try? Can someone tell me where the oil filter is located and if this idea is a good one?

Roger and out
 

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I'm just wondering if the service guys put 0W/30 in after it having had a lifetime of 5W/40 ... sometimes they just don't like it, gaskets can leak, seals can unseal, chains can rattle and tappets can tap as a result. Could this be the case here?
 

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In regards to the rattle on start, I've always had a bad rattle for 2-4 seconds on start, whether she's sat for 2 days or 2 hours.

I had nothing to lose so tried the brake pump as suggested. It may be my imagination but on a 2 day wait, it seemed to almost eliminate the rattle (did this with the doors open so I could hear better).

On a 1 hour wait, not so much. It seemed less than normal on a one hour wait but .....

I can't say definitively that pumping the brake before a start helped but my experience told me that there does seem to be some sort of connection here.
 
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