Timing Chain vs. Catalytic Converter?????

[greglittle]

This is my situation. I have a 1994 c220. I have a mechanic friend, who I trust, that runs a shop (but he is the only employee). He works on a number of different cars, but is not specifically a Mercedes mechanic. I know that he knows them, though, because he replaced my engine when I blew a rod last year (replaced with a used engine that had approx 80,000 miles). My car currently has about 170,000 miles on it (it's been about 7,000 since the engine swap). Okay, now the situation...

There is a rattling sound that the car is making that was very light (and only in second gear) before an accident a month ago. The rattling sounds like a chainy type of rattle. Since the accident, the rattling is much more prevalent. It rattles in sub-10 MPH, between 2500 & 3000 RPM, and between 4500 & 5500 RPM. My friend checked it out and after placing a stethescope to the right side of the engine, said that the timing chain probably needs to be replaced. Since I have an insurance claim pending, though, and need a loaner, I took it to the dealer to have it checked out.

The dealer here (I'm originally from California and very happy with my dealer) in Utah has not impressed me so far. (Wait of 15-30 minutes even with an appt to drop off, fix of my window motor was sub-par, no customer service.) Anyway, after dropping it off there, they called me and told me that the problem is that the catalytic converter is bad and needs to be replaced ($1000). They also told me at the same time that the computer is showing no engine codes. Okay, now my question....

Wouldn't the computer show a problem if the catalytic converter was having problems? According to my limited knowledge, the converter makes a low rumbling sound when going bad and it's usually accompanied by a smell. Is the dealership trying to rip me off (or the insurance company) by replacing this "old" part, and then when that doesn't fix the problem say that they also need a timing chain? Or, should I trust them over my friend with the guise that they are authorized Mercedes mechanics? Please help ASAP! Thanks!

 

[andy_k]

it's far more likely to be the belt tensioner than the chain - this is a little hydraulic damper on the front of the engine and would cause a rattling like you describe.

It could also (theoretically but unlikely) be the cam chain followers wearing out. They are a bit more awkward to change so I'd start by checking out the tensioner.

HTH

Andy

 

[greglittle]

Soo...

So, should I tell the dealer to check the tensioner? Since it's an insurance claim, I'd rather have someone else do it. Also, I'm sure they won't take too kindly to being told that they don't know what they are talking about.

 

[yvrbenz]

in my experience...

most "service advisors" and an alarmingly large number of "service technicians" do NOT know what they are talking about. but that isn't relevant to this thread.

Disclaimer: my experience is with the M102 engine found in 190E 2.3-16s, so the specifics may differ, but, in general, what follows should hold true for your engine as well.

The timing chain IS a possibility. This is easy enough to check: remove the valve cover and check the tension on the timing chain.

The timing chain tensioner could also be faulty, so after you've had the chain's tension checked, have the tensioner inspected as well just to cover your bases. I'm not sure where it would be on your engine but on the M102, it's located on the right side of the block and is covered by the alternator.

Since changing the chain can be a big (read: expensive job) you don't want to go there unless you have to. Check the slack in the chain after the tensioner is removed. If the chain does not need to be replaced, leave it. If you DO decide to replace the chain, have the plastic guide rails renewed as well. They can grow brittle with age, break, and pieces can go where they shouldn't (like in the oil pump relief valve) and cause major damage.

The 16v had timing chain issues and the recommended replacement interval is approx 90,000-100,000 miles. Some people got further than others on the original.

A rattle does not necessarily mean that the cat has gone bad. In some cases, the heat shield could have come loose resulting in a rattle.

Other things to check are how secure the exhaust pipes are. I had a rattle that turned out to be missing exhaust hardware which allowed the pipes to vibrate against the mounting brackets.

This is all i can think of at this point. It's tough to diagnose a sound without actually hearing it and having the car nearby to investigate, but hopefully this gives you a couple of directions to pursue.

That all having been said, it's pretty tough to mistake the source of a rattle when the possible sources are THAT far apart. I mean, if it's either the timing chain or the cat, it should be obvious which one is producing the noise.

As far as computers and engine codes go, well...they're only as helpful as the service tech's ability to actually diagnose a problem in ADDITION to what the codes say. Too many "factory trained" techs only know to read codes.

 

[Tony]

I've had two blown cats and the symptoms you describe do sound like the cat - a rattling sound at certain rpm caused by the broken bits moving in the pipe. On neither occasion did the engine throw a code, or the exhaust smell any different. The cats still function when they're breaking up and the MB cats are so over-specced that you can lose quite a lot of them and they still work. The problem is that it can get sucked into the engine so it's best not to leave it too long.

 

[rotaxman]

I had a ford mondeo,with a really loud noise at low revs,sounded like it was going to throw a conrod,,,turned out the cat had fell to pieces inside ,replaced and all was well,,give em a bang with your hand and you will hear them rattle

 

[big x]

Step 1 is to buy a Haynes manual.W202 really are simple cars to work on.
If you use your hand and lightly thump the cat you can hear if the honeycombe inside is breaking up.
To test the belt tensioner pry it forward with a screwdriver whilst the engine is running...often the rattling tone pitch will change and you've found the problem.This is a cheap thing to fix.
Re-timing chain these double row chains found in the C-class go on for ever.Ignore any posts about 190's they use a different engine design.

adam

 

[cossiedude]

RE the last thread ? the timing chain tensioner is mechanical and hydraulic I dont understand how you can pry it with a screwdriver ??

The tensioner is on a rachet with a weak spring behind it, the engine oil is then pumped into it to provide the stronger hydraulic pressure
It can be serviced and replaced, the centre part on the rachet needs to pushed through and back in again, if all is clean, unworn and there is oil present then everything should be ok.

The timing chains generally do go on forever.

The Cat is a fairly fragile item and can break up, it can be tested with the thumping method but not too hard!!!!
G.

 

[yvrbenz]

RE the last thread ? the timing chain tensioner is mechanical and hydraulic I dont understand how you can pry it with a screwdriver ??

The tensioner is on a rachet with a weak spring behind it, the engine oil is then pumped into it to provide the stronger hydraulic pressure
It can be serviced and replaced, the centre part on the rachet needs to pushed through and back in again, if all is clean, unworn and there is oil present then everything should be ok.

The timing chains generally do go on forever.

The Cat is a fairly fragile item and can break up, it can be tested with the thumping method but not too hard!!!!
G.

Big X was referring to the serpentinbe belt tensioner. Not the timing chain tensioner.