Chain or valves?
 

Hi, I have a 1991 500SL with about 116K km's on it. When the engine is warm i hear rattling, sounds like a marble rattling in a tin can. The engine is very quiet so this noise really stands out. Everybody points it out to me. The noise comes when the engine is warm and at every stop light or stop sign or idling in traffic it is constantly making this rattling sound. However the noise goes away once the rpms increase. if i put the car in neutral at a light and rev the engine a little there will be no sound. I usually do this to avoid the embarassing noise. I feel that this noise has come after switching to 15W50 oil from 5W40. Could this be the reason? with 116K i dont think it could be the chain? I know the previous owner once went 30K with no oil change and another 20K with no oil change before selling the car. So maybe it is sticking valves? but i thought valves would make more noise when cold, not warm?

I forgot to mention....., I switched to synthetic oil after buying the car, to hopefully clean out the sludge that must have built up in there. I have done 3 oil changes since I bought it 8K km's ago.

Sid, it sounds like the timing chain tensioner needs to be replaced.

I was thinking about that too. is that a hard job. if i don't do it are the risks high of the chain breaking, becuase I really dont want to open up the engine since it only has 116K on it and has never been opened before. The engine never seems to be the same once it is opened.

Maybe but the cam oiler tubes are a better shot, does it sound a bit like light lifter noise?


Joe

it does sound like lifter noises. however only when warm? the oil pressure seems to be normal. this only started happening after i switched to 15W50. I am planning on switching back, what do you guys think?

30,000k without an oil change? Yikes!

Check the chain tensioner -- pull the right valve cover gasket and see if you can push the curved rail back towards the fender easily. If so, get a new tensioner pronto, as a slapping chain will break the upper (plastic) chain guide, and that usually causes the chain to break.

Chances are that the lifters are shot from crap in the oil. Hard sludge builds up terribly in the lifter gallery on this engine if dino oil isn't changed often enough.

Full synthetic oil will usually remove the sludge and clear the lifters after a while, but if you change, change the oil filter at 1000 miles and 2000 miles with a top-up for the oil (no need to change the oil) to get the slops out of the engine. The filter will plug very quickly.

If the noise is definitely associated with the valves AND you can see oil running out of the oil tube onto the cam through the oil filler, synthetic will probably fix you all up.

Otherwise, you need to check the oil pressure and oil delivery at the cam -- if you have poor oil delivery, it's probably cam time, low oil pressure means change the filter, and if that doesn't help, you need to investiage the cause.

Peter

Thanks for your help. i really really don't want to open up the engine but now im scared the chain might break :(

East to check -- the chain will rattle at the very front on the engine, and bad tappets will be further back.

Get it checked out soon, a busted chain is $$$.

The good thing to know is that broken chains in a 560 are very uncommon.

What is you oil pressure at idle?

Peter

when the car is just started it idles just below 3, then once it is warmed up it idles between 1 and 2, closer to 2.
when the temperature is at hundered it idles at 1, when the temperature is at 90 it idles at 1.5 and when the temp is just above 80 it idles close to 2.
its a 1991 500SL.
it does sound like it is coming further back.....
why would valves be more noise when the engine is warm though? when the engine is cold and first started it is very quiet?/

what happens if you continue driving a car with bad tappets/valves?

Those things tend to pick up a bit of light tappet noise when ageing anyway. As a preventive I'd do a chain and upper rails with a new tensioner and replace the oiler tube plastic bits as well. These engines do tend to scuff cams and rockers when the tubes start to go south and leak.


Joe

does my oil pressure seem good though?
everymorning i have started taking the car out at 4 a.m and do about 160Km/h for about 5 mins....would this clean the valves or am i wasting my time?

Sid:

The hydraulic tappets fill with oil when there is no pressure on them so that the cam follower actually rides on the cam at light pressure. When the cam lobe starts pushing down on the follower to open the valve, the small valve in the lifter closes off the oil vent hole, and the lifter becomes "solid" and the valve is pushed open.

When they get old, they no longer fit together as tightly as the concentric bits wear (notably the valve) and with hot oil, will squash down as the cam goes round. If the dont' pump back up by the time the cam comes round again, it will slap on the follower making the click you hear.

SEveral cures -- replace them (expensive), use synthetic oil in the hopes it will give you slightly higher oil pressure hot and dissolve some of the sludge preventing the lifters from filling, and (cheapest) check to see if there are some 0-rings on the center shaft of the oil filter cap (if you have one -- not familar with that engine). If there are two o-rings on there, no one ever replaces them, and when the get old and hard, the oi leaks out of the lifter gallery on some engines. New o-rings will go a long way towards fixing the problem.

Peter

Thank you Peter.....now that I read your post it makes very good sense it is the valves and not the chain. Like you said when the oil gets hot it doesnt hold enough pressure and I get that sound. The sound comes when I get to about 100 degrees and the oil pressure is at about 0.5 I hear that slapping sound. If the temperature doesnt get to near 100 degrees everything sounds fine.
Everyone I talk to says its normal for the temperature to reach 100 at idle and up hills. On straight roads with no traffic the temperature will stay at around 82 degrees and the noise will not be there.
When the noise does come it is pretty loud, you can hear it from quite aways.
when my tempeartre reaches 100 it will go down again to 90 once i start driving and if i drive long enough it will drop to 82.
i am using mobil 1 15W50 right now and when i wa susing 5W40 it wasnt making that sound. do you think my old oil was holding better pressure at high temps that is why i wasnt getting the sound?
so if it only happen at 100 degrees do i still have to worry about it or can i live with it??
thanx :)