Hi all,
So far my research has yielded 2 methods of measuring timing chain stretch on a OM642. One method is to lock the camshafts at TDC #1, and then measure strech up to 11 degrees on the crank hub. Somewhat similar to OM60x engines. Given the amount of disassembly involved, MB also developed a tool that looks like a tensioner and is used in lieu of the tensioner to measure stretch much more quickly.

Unfortunately, I cant find any details on how this tool works? Is it just inserted, torqued and the measurement on the external plunger read? Do you have to manually turn the engine thru several cycles to get an accurate reading? Do you run the engine momentarily with the tool installed to get an accurate reading?

Has anyone done, or seen this done and can share some insight?

TIA

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

I have two of these cars and check the timing chain wear annually. Measure with the engine off. There is a screwed plug on the passenger side of the engine. Remove the plug and screw the tool into the hole. The stem of the tool contacts the chain. when it contacts the chain the stem quits moving while you continue screwing the tool into the hole until it stops turning. This will make the stem stick out of the tool farther and you can read a measurement on the stem. I do not recall the measurement value where the chain has to be replaced. It is in my notes with the tool.

My oldest car is a 2008 E320 with 278,000 miles. The measurement has not increased over the years. The tool is very simple and somewhat expensive. Maybe $350 if I remember right. However much cheaper than an engine teardown to measure the wear.

DDay
Thanks so much for the info, very helpful. A few questions if I may:
1. The hole that the tool is inserted to is the Timing chain tensioner location correct?
2. If you would be so kind as to post the limits of wear (your notes on the tool) would be great.

Using this tool is a far more convenient method than a multi hour tear down of the right upper side of the engine just to take this measurement.

Also good to know that you are not seeing much wear on your OM642 of the same vintage as mine. From what I understand the 2010 onwards engines used either a single row chain or a low friction chain that was prone to stretching, not as common in our earlier double row engines. For me, I need to establish a baseline.

Thanks again

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

To insert the special tool, first remove the air filter on the passenger side. It is roughly in line with the oil filler opening but down on the side of the block. The hex on the special tool is 22mm. The hex on the plug is probably the same size. At 221,000 miles my chain measured 73-74mm. At 262,000 miles 74-75mm. I have not found my notes on the max allowed, I have sent an email to get that number.

Many Thanks DDAY that's great info. Once I get it done, I'll update with my results in the event that it gives others some insight.

I believe the tool goes up to 90mm max? (dont have it in hand yet) and I also read (albeit in German and my German is marginal at best) that >80mm is indication to change, although that might be higher up to 90mm. Can't confirm this for sure though, but seems in line with your readings and your rate of stretch would indicate that these can indeed last a long time, or the life of the engine. Will be interesting to see where I'm at with 152k mi.

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

I was told that 82mm is the maximum allowed.

What is the part number for the tool?

Tool part number 642 589 03 63 00

Just searched it on the forum sponsor, it is $765!!

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

MSRP is $440, can be found for less than that at several of the different online dealer parts websites.

Thanks again, I'll update my notes with that upper limit.

The tool number has been posted, and yes it is available at numerous prices from $200-400 depending on the source mostly. Beyond that you are overpaying IMO.

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

i bought my tool from the dealer. It hoes not look like a high production unit. It is machined all over and the hex was probably a milling operation which is slow and expensive.

So my tool came in, and I was finally able to measure my OM642 timing chain stretch with 152K miles. Measurements came in at 67-68mm, not bad at all, I wish I knew what the starting point with a new chain is/was. If someone know, please post.

Tensioner was a factory original stamped OM642 05/14/07. The tensioner seemed to be in fine working shape, no collapsing, just some wear on the chain guide tip. I had a new IMA tensioner on hand so I swapped that in, the original goes into the spares box.

Some tips and observations for anyone else doing this.

1 The air filter assembly needs to be removed as suggested to give you some working room and access. The tensioner sits right above the alternator bracket on the right side of the engine.
2 The oil dip stick tube may be in the way depending on your packaging. In my Jeep it was just in the way enough to be a pain,. Removing the dip stick tube upper mounting bolt on the cam cover allows just enough wiggle room to overcome this obstacle.
3 When inserting the tool and or later the tensioner, you must overcome both the tension of the chain, plus the tension of the springs inside the tool and tensioners themselves. Trying to overcome this and get it to thread is very difficult. If you use a suitable long lever thru the oil filler hole, you can relieve the chain tension significantly enough to allow you to thread the tool or later the tensioner in all the way with just your fingers. This is a huge time and effort savings and is not mentioned in any repair manual. Make your life easier and use the leverage to your advantage.
4 Tighten the tensioner when done to 80Nm or 59ft/lbs

Overall job time is 1-2 hours for your first time and learning curve, doing it the next time should take less than an hour.

Hope this helps others, again, if someone knows what the baseline for a new chain is, please post. At this point, I will likely take measurements every 50k miles to assess wear.

Thanks to all especially DDay for your help

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)