M104 Cold start Knock/Tick
 

Hey All,
91' R129 (300SL-24) w/ M104.981, 99K miles.
About a month ago I changed my oil from a "cheap" non brand full synthetic 5W-30 to MB 229.5 5W-40 full syn oil along with an MB original filter. At the first cold start after the oil change, I noticed a Knock that will disappear after 3-5 seconds and is not present after. (as oil pressure builds up). I then changed my oil, this time using the Chevron-Delo 400 15w-40 (along with an MB original filter). The knock is still present.
Oil pressure readings:
Cold idle - "3"
Warm idle - "2"
Light acceleration - a tick below "3"
Harder acceleration - "3"
No other drivability issues whatsoever.
My driving style is the complete opposite from the italian tune up - which I was told to try..
I'm desperate to get rid of that knock which simply - was never there before!

some videos..
The cold start noise

idling

Thanks

As always it is difficult to tell from a video; but, the noise might be a timing chain tensioner. Suggest not continuing to drive it and taking it to an experienced Benz tech/shop for diagnosis. The tensioner is not a big job but is important to change if that is the problem. If it is diagnosed as a valve lifter instead, then it is a lot less urgent to repair.

Good news is that it doesn't sound like a bottom end/bearing noise.

Good luck and please complete the post.

I had the same problem,and discovered aluminum flakes in the filter.I have read that some engines,and v8s had bad oil pump sprockets,causing chain to wear into cover.
I di not fool around thou and put a low mileage motor in my car rather than rebuild.

Sounds to me like it's a noisy lifter/tappet/lash-adjuster. Does the M104 have hydraulic lifters/lash-adjusters? The tap, while annoying, isn't going to hurt anything since it goes away quickly when the engine is started.

You can try some Mobil-1 full synthetic for a couple thousand miles and see if it helps (Italian Tuneup does help, one of the absolute worst things you can do for a car is drive it like "Grandpa"). Some people have had success using synthetic oil to get the lifters to stop tapping, though it didn't work for me. I replaced the set in my SDL. The SL still taps when started from cold after sitting for more than 3 days. I'm not losing sleep. The SDL tapped all the time, cold or hot. That's when you know it's time for replacement.

I don't have access to the vids / audio.

Hammering on an engine will do _nothing_ to solve a mechanical problem and could make it worse. The "run it hard" is from the days of leaky / rich running carburetors.

Drive the car normally, turn it off , let it cool, pull the spark plugs. If they are white / tan, you are driving just fine.

Does this car get many short run / drive cycles? These engines tend not to like many start the motor, run a minute, shut off. My 97 C280 165 K miles ( pretty much the same engine as yours ) has a light intermittent lifter tap that I'm leaving go.

Changing oil type isn't going to help as you have tried thin / thick. There is a check valve in the lifter, when this fails to fully seal the lifter will bleed down causing too much lash. General valve train wear contributes to noise as well. Drive the car as you have been. Also, what climate are you in? 15 - 40 is kind of thick for cold climates.

couple of motors on ebay.

I appreciate all of your inputs, really.
The m104 does have hydraulic lifters. which makes me think that one lifter is bleeding overnight and will tap until pressure will build up. from my understanding, a timing tensioner knock will be noticeable at all time, unlike the lifter knock.
I try to drive it at least once a week, in reality, with snow and salt all over here in jersey , it can take two weeks between drives..
using a long screwdriver against the top of the motor, no noises/taps at idle.
Oil is and was always clean with no shavings.
I’ve read some other posts of others saying the tap disappeared after changing to the delo 400 and driving for a while.
I was able to find a post regarding the timing tensioner which was due for a replacement on an M104 after 200k miles..

Listening and re-listening to the video clips you posted, it sure sounds like lifter tick to me. Since it goes away after 3-4 operations of that valve, it isn't anything serious. When it starts taking several operations of the valve, or taking several seconds to go away, plan a replacement party. Simply changing to a higher detergent oil can sometimes help if the hydraulic element is clogged with sludge or varnish. Don't expect miracles, but some folks have had luck with it, though it takes about 1000 miles and some highway time to work its way through.

Tensioner problems would be causing chain slap, which is a different noise than what you have. I am curious about the whining noise and difficult start in the audio-only clip though...

Difficult to start (after 10 days sitting) was cured by replacing the fuel filter the next day. the whining is a fight for another day, I guess.
I will drive it some more with real acceleration and will report back regardless of the result. just pray with me for some nicer weather here at south jersey!

BTW
happy holidays to all.

I live in the country,so spilled oil no problem.I always clean my oil pan,I drain car's oil into.To look for moisture,flakes of metal.Also if present,examine filter good.

ytech15, some of the noise on cold start is the air pump. The engine sounds "normal" most of the time, but the loud bursts sound threatening. With a bad timing chain tensioner, likely the result of a broken internal spring that fails to keep the timing chain tight at start-up, you will hear the timing chain slap until oil pressure builds up inside the tensioner. Best to have a MB-trained tech familiar with that vintage engine diagnose the problem before your engine suffers potentially serious damage. I had the timing chain tensioner replaced in the M104 engine in our 1992 300CE around 100,000 miles. I always run Mobil 1 15W50 in our vehicles with that vintage engine (1995 and earlier).

Thanks for your input.
I'm planning to replace the drive belt tensioner, shock and adjustment road soon, It does not seem too hard to replace the timing chain tensioner while doing this job BUT I'm afraid that the chain will jump a link with no tension (while the tensioner is out, 99K Miles. didn't take the valve cover off so condition of chain is unknown.. ) .. what were the symptoms that made you replace your tensioner?
also, are there any kind of oil additives that can actually help revive the lifters?

ytech15, the 104 engine in our 1992 300CE had a disconcerting, abnormal noise at idle. A local indie told me not to worry about the noise; however, an experienced tech at our local MB dealer diagnosed the problem as a failing timing chain tensioner. A new timing chain tensioner (installed at the dealership) resolved the problem. As far replacing the tensioner yourself, it's critical to maintain the timing marks with the camshaft. If you decide on DIY, be sure to have detailed MB instructions that you follow exactly. Otherwise you could end up destroying the engine. I doubt that your timing chain would need replacement, but you should check for any stretch. Typically the timing chain guides need replacement on older, high mileage engines.

Mobil 1, as well as other high quality, oil has additives that keep the engine clean. As you probably realize, hydraulic lifters rely on oil pressure to keep them tight against the camshaft so they are quiet. Routine oil and filter changes with a high quality oil will extend engine life. If your engine has been neglected, it's possible you need to replace the hydraulic lifters. I have put 200,000 miles on a 104 engine without the need for any major engine work.

Finding dealer techs that actually have any knowledge regarding pre OBD II cars is an impossible mission, at least at the dealer by me (south jersey philadelphia area, that’s enough to figure out which dealership I’m talking about). I do have the detailed instructions regarding the tensioner replacement (which have no mention of the cam marks) and the tensioner is pretty inexpensive, which makes the replacement easy BUT the more research I do indicates that failure of timing tensioner will lead to constant rattle especially when hot.
The fact that an oil change has started this issue is driving me crazy.
I’m seeking for some more advice and options here.
Attached are some TSBs that I found.
Please continue to help me :) !

ytech15, call Mike Strickland (Service Director at MB of West Chester) at 484-313-1111 and ask if there are any techs still working there that are intimately familiar with the M104 engines. My timing chain tensioner diagnosis was at least 12 years ago so those skilled techs may be retired now.

Our M104 engine had a "slapping sound" with a slight RPM increase above idle. The more I think about it, due to the timing chain tensioner not building up enough oil pressure to keep the timing chain taut.