Timing chain lifespan with good oil changes ?
 

Just wondering how many miles most can go with normal oil changes 300, 400,000 mi ? I know they are strong but what is the average they really need to be replaced , checked ? Is it the guides and chain that wear together or a combo of one before the other . How many of folks out there have gone this many miles without replacing the chain or guides ? This seems to be relatively one of the very few parts that amazes me about these engines. Thanks.

This is brought up at a good time.

I just sold my 190D to a close family friend. It has 105k mile on it, with original chain. Now I've had a chain break on me before and I don't want one to break on him either. I don't want to keep looking at stretch either, so what is a good safe number of miles to give for chain replacement?

Just my own personal opinion, but I wouldn't really want to exceed much over 250,000 miles on a chain. You can have a car throw a chain even earlier than that though. You should check the timing chain stretch when you adjust your valves, assuming you have a model that requires manual adjustments. That will give you a good idea of the amount of stretch/wear. That still doesn't rule out the possibility of catastrophic failure of the chain due to guide/tensioner failure, etc. It's probably not a good idea to push the life on chains. I would consider it a very important routine maintenance item. At most you shouldn't have to replace it but a few times over the life of the car so the $/mile cost of a chain replacement really isn't that bad. The potential cost of putting it off, however, can be very substantial indeed.

I had mine changed at 150k just to be safe. I felt it was better to spend my money being sure about it than to wish I had later and have a bigger bill (not that it cost too much $$ anyway).

The life of a timing chain is variable. Some OM60x engines exhibit considerably less than 1 degree of wear every 100kmi, while I've seen OM61x/621 engines that showed several degrees of wear after only 100kmi.

Wear is mostly a matter of how often the oil is changed - the more often you change the oil, the slower the chain will wear. The makeup of the oil can have an effect too. Timing chain wear rates in my cars have been lowered to less than 50% of what they were before, following changing from conventional oil to Mobil/Delvac 1 oils. Other synthetics MAY afford similar wear reductions.

Fortunately it's VERY easy to measure chain stretch (and that corresponds with chain wear). The measurement adds only about one minute to adjusting valves on engines (OM61x and older) that require 15kmi periodic adjustment (it's a LITTLE more of a pain to do on OM60x engines and may take 15 minutes to a half hour).

When chain stretch exceeds 4 degrees on an OM60x engine, the chain should be changed. I have used 5-6 degrees of stretch as the criteria for older diesel engines (OM621/61x engines) although they can probably tolerate 50% MORE stretch without increasing the chance of breakage very much (but performance WILL be detectably degraded).

Marshall

power & performance?
 

What is the most obvious sign of chain stretch/wear? Power/performance?

Hi to all.

I just bought my '83 300TDT
and I have no idea when it was done last
so I'm changing it anyway,engine has 368K on it.

I'm planning on changing the chain every 120K-150K
just as regular maintenance and run protection.

I'd rather pay $134 for a chain,chain tensioner and
tensioner guide rail than paying a few thousents for
rebuilding the engine or a rebuilt.

This way you do the chain every 9-10 years orso
and you're more or less safe,if you do your oil changes
on time.

Just my 0.25

Louis

Marshall,

I didnt realize that you are now a member here on our fine forum. Glad to have you here and posting, the wealth of information that you have is amazing.

A belated Welcome!

JMH

(who pokes around various forums very inquisitively, trying to learn as much as possible)

Well, some of us don't take that long to rack up the mileage. 92,000 on my 99 MB, and 80,000 on my 2000 VW. And there are quite a few members here who drive more than me! :D

OM61x engines require valve adjustement EVERY 15 kmi. Measuring the chain stretch adds ONE MINUTE to the job. On OM60x engine you can get the job down to 15-20 minutes (well - I did). When stretch gets up to 6+ degrees, smoke will increase. Until stretch reches 4-5 degrees there is no easily detectable loss of performance.

MEASURE chain stretch!

Marshall

Come on guys, these cars aren't M116 or M117 V8 gassers, that's just TOO soon.

My father had an '84 300D turbo that he retired with 463K miles on the clock. Original transmission, and my father never replaced the chain. He drove it since 176K miles or so, so I guess the minumum on the chain was 287K miles.

I am assuming good oil changes and overall maint, will keep the timing chain good for quite a long time . Now there must be more more accounts of high milage 240 and 300 d cars out there . How many motors I wonder have self destructed defenitly due to timing chain failure guides etc ? Oil pump failure is another cause of major engine damage. There sure are others but We here a lot about checking chain stretch so that makes me wonder when you see motors going for many miles without a new chain on these simple strong motors.

Mercedes diesel timing chains are VERY robust, but they DO fail. Just NOT very often if the chains are checked every 30-60kmi and changed when total chain stretch results in injection pump timing that is retarded by 2-3 degrees (about half the amount of chain stretch so that's more than 4 degrees of chain stretch on an OM60x engine and 6 degrees of stretch on an OM61x or older engine). Chain wear is seldom more than a degree every 50-100kmi, so 200-300kmi would ordinarily be safe if you're using proper oil and changing it at recommended intervals. When chain stretch exceeds about 6 degrees, the engine will smoke at idle. It's rare that a chain will fail before the stretch reaches 8-10 degrees (that's considered the outside limit of safe operation on an OM61x engine according to the microfiche I'm told).

The chains on all of my engines (all OM60x) with an average of 200kmi on each, have less than 2 degrees stretch. If wear continues at the same rate (the rate of chain wear on ALL of these engines dropped by more than half when each was switched to Mobil 1 so wear will be LESS then previously) these chains will require replacement at between 400-600 kmi (based on a limit of 4 degrees of strecth as shown in the OM60x engine manuals).

The chains on these 4, 5 & 6 cylinder diesels just don't break if you keep track of the wear (MEASURE IT) and change the chain when the chain IS worn. Most failures occur because NOBODY CHECKED TO SEE IF IT WAS WORN! Since it's so easy to do on the OM61x and older engines - that seem inexcusable to me!

Every mechanic that EVER does a valve adjustment on an OM61x or older engine (they ARE required every 15kmi or so) should measure stretch and write the number on the ticket! It only takes ONE additional minute to do it and I expect most owners would even pay an extra $5-$10 to have a record of it being done! It is VERY rare that a chain not worn to 8-10 degrees of stretch will break - unless then chain is defective.

MB installed chains in the early '90s that wore VERY fast (4-10 degrees in less than 100kmi) but these were measured during a recall and replaced - very few of the bad chains actually broke - many, many more were caught and replaced before they broke.

As to oil pump failure - it is also VERY rare on MB engines (gas AND diesel). It does happen, but usually ONLY when the pump ingests something that shouldn't be in the oil that circumvent the oil pump pickup screen - like parts from a broken vacuum pump, Woodruff keys or springs that have fallen into the sump. Oil pump failure is almost always the result of some other problem that was NOT properly addressed during routine service. Every once in a while a pressure relief valve may fail open (but MOST of these result from engine abuse or poor or extended storage) and oil pressure may not be maintained. But that really rare.

Marshall

I have over one million miles on 5 of these with an average of about 220k per car. I have assumed (right or wrong) that performance will fade considerably if I have significant stretch because it will affect timing. Is that a fair assumption? Right now, all of mine are running better than when I got them due to periodic value adjustments and general upgraded maintainence.

However, measuring stretch is something I need to learn how to do.

Don

DslBnz,

The reason I did change the chain at 150k is because it had almost 4 degrees of stretch already. I attribute this to the fact that it had been "dealer serviced" every 3-5k miles and the oil was changed with a non-diesel rated oil every time, this was before I got it. Talk about oil leaks when I switched to Delo, the good news is that oil usage is usually less than a quart every 3k now (even with a small leak)... it was a lot more when I first got it. I don't plan on changing the chain before the car hits 400k now unless it is really stretched.