Do M104 motors have timing chains? If so... when should they be replaced?
What is a timing chain...? Or what is it's function?

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

An M104 definitely has a timing chain. Maybe two.

The timing chain keeps in synch the camshafts and the sprockets. Well, maybe not quite in synch. The camshafts make one rotation for every two crankshaft rotations. The timing chain along with the sprockets are the mechanical link between the crankshaft and the camshafts. A two-to-one ratio of camshaft sprocket teeth to crankshaft sprocket teeth ensures that the camshafts are in phase with engine cycles.

There isn't a factory recommendation on when the timing chain should be replaced. Anytime you do work on the head, is probably a safe bet. Some might say every 100-150K miles, but that's probably for engines older than the M104.

I say there might be two timing chains because some MB engines have a second timing chain off the crankshaft that turns the oil pump.

Hope that helps.

Regards,
Sixto

This engine has a ratcheting tensioner which serves to do away with many timing chain problems.

If the oil is religiously changed hot and often, you will probably NEVER experience a timing chain failure. If the oil is left in the engine very long, particulate matter is circulated which will wear the chain. If the oil and crankcase are kept squeeky clean, the wear problem virtually goes away.

Good luck,

The timing chain may not fail due to the ratchet system, however, one may experience an out of timing problem with much stretch. We aren't talking about a rebuild here, folks, the job is simple. Roll one in a forget about it for several thousand more miles.

My car has had religious oil changes most of it's life... even more so in the past 30k miles (90k miles total).

Well the reason I ask this is because when idling, the engine doesn't seem mellefluous. When revved, the engine just purrs, but when idling it sounds like... (hard to explain), kind of a slight rattling. So I bought a new radiator mount (one was missing) and a new fan cover bolt (one of the 2 was missing, just the plastic snap on kind). But it didn't help. I have heard about this timing chain rattle on start up with other models. The noise is slightly louder when the engine is cold, but everything in the engine seems louder when cold.

How costly is the replacement of a timing chain? What differences are noticed if it's done done?

Larry,
Are you saying that if you change the oil often enough, the timing chain could partially heal itself?

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Southern_Son,

The ratcheting mechanism does not cause timing chain problems, on the contrary, it prevents them. If the chain does stretch, the ratcheting tensioner takes up the slack and prevents it from "whipping". It would take enough stretch to warrant chain replacement before there would be a noticable power or economy degradation. If it's stretched that much, I agree, roll in a new one.

David,

Frequent oil changes prevents timing chain stretch, it cannot heal it.

Have a great day,

Larry,
Is it possible that a new chain tensioner is needed? Because of the "rattling?" It might not even be out of the ordinary, or even the timing chain... I'm just a *little* concerned. Thanks for your help.

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Not-specific-to-MB considerations would include lash adjusters (sometimes called lifters) that need cleaning (dirty lash adjusters can 'tick' when the engine's cold) an off brand oil filter (that doesn't allow full pressure to the chain quickly enough).

I haven't looked into an M104 or even my M103 to see how the hydraulic lash adjusters work on these cars. But anything that can trap oil can accumulate sludge over time.

Sixto
91 300SE

Checklist for rough idle:

Platinum plugs- get rid of them.
Air to fuel ration adjustment- take to shop and have adjusted (really easy and simple to play with)
frequency valve
bad plug wires, distributor and rotor

Larry, for a V8 I have read that 10 degree difference in the two cams at TDC is justification for chain replacement. Car will run and one may not realize the degradation in power and MPG. Of course, some chains jump without any prior warnings. It is best to know the history and keep up with intervals between changing of chains. No clean oil is going to make the difference of 50k vs. 200k, that is simply ludicrous and misleading. Most wear is dry start up and this occurs no matter what type or condition of oil is used.

David,
Your engine has a double row timing chain as opposed to the M103 which has a single row chain. The double row chain is extremely durable and can go much longer than the single row chain. If it makes you feel comfortable you can replace the chain at around 100k. This seems to be the popular concenus among MB owners though no specific recommendation is made by MB.
It is possible that you have a hydraulic element bleeding down after the engine has been shut off for awhile.

Larry,
Timing chains will eventually stretch no matter how often you change the oil. Its a law of pyhsics. Apply heat to metal, the metal expands. Timing chain rattle occurs for one of three reasons; a) A guide has broken allowing the chain to slap, b) The tensioner has failed and bleeds down when the engine is shut off, c) The chain has stretched beyond the limits that the tensioner has to keep proper tension on the chain.

__________________
Scott Diener
89 300E
93 300E
92 Volvo 740 Wagon aka "Mutt mover"

One more item for the checklist, bad gas.
My car recently suffered hard starting problems.
Fuel cleaner, and water remover did not help, new plugs didn't, cap, wires and rototr all ok.
refueld at one station and problem went away. refueld at another next time, problem happened again. Refueld the last 8 times at same station, problem has not happened since.
Low octane in the hi test pumps to make more profit is what I have experienced first hand at a few stations here. It will cause similar symptoms to what will cause rough idle and wierd probs.

As for chains, MB chains are known to be quite reliable. Most last 100k if not more.

What larry says is great advice. He has put hundreds of thousands of miles on his cars, before any major work was done. Changing the oil hot and often is preventative maintnance at its cheapest and easiest.

It costs me maybe $25 every 3000 miles for oil changes. The car will be better off as long as the oil is clean and the filter is new.

I agree that damage occurs on startup, thats a given, but mb engines were designed to pressurize in seconds to reduce the wear.

My brothers car has 160k on the odo. Its a 1985 380SL with the double row timing chain. Our mechanic recommended doing the chain as preventative maintenance sometime in the next 10k miles. We have no idea if it was ever done before, but the car still drives great. The mech would charge only $500 or so to do the chain, which I think is very cheap. I told my brother he might as well do it now, but he's the kind of person that likes to break cars and abuse them.. He's the only person I know, who has had to get rid of every car he had because of catastrophic failure.

All my cars were still running very nicely when I got rid of them.

Maintenance works, preventative maintenenace works. Find a good mechanic, or buy the manuals and cdroms and do it your self, either way you can't go wrong.

Every thing you do to be preventative helps.

Alon

__________________
'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon

David,

If you have noise, this is a different situation. You need to determine the noise source. It could be harmless, or it could indeed need some attention to the chain or related components. My comments regarding timing chain replacement relate to an engine that sounds good, runs good and is properly maintained. Whenever there is noise it should be investigated. You are doing the right thing seeking information. The best approach would probably be the helpful ear of someone experienced with these engines. We just can't diagnose noises over a discussion forum.

Southern_Son,

Chain wear resulting in 10 degrees of chain stretch is SIGNIFICANT. Typically, at least in the inline MB engines that I am familiar with, five degrees of "stretch" warrants chain replacement, but may not display noticeable performance or fuel mileage degradation. But, yes, ten degrees would probably result in noticable performance and fuel mileage changes in an engine. Ten degree "stretch" in any engine would warrant, or even DEMAND, chain replacement in my way of thinking.

Chowpit,

Yes indeed things expand with heat, but they also contract when cooled again. "Stretch" of a timing chain is due to one thing, wear of the pins and bushings. Infrequent oil changes allow build up of microscopic particulate matter that accelerate this wear. In the case of a drive chain, the term "stretch" is misleading. The chain "lengthens" due to the wear of the individual links.

Your list of items which would cause chain noise is good information, except the chain, at least in an MB, could probably not wear beyond a point where the tensioner can maintain tension. If the chain and components are this worn, the engine has probably never seen an oil change. This would probably be a completely worn out engine that is about to "let go" any minute.

Have a great day,