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Old 07-10-2001, 02:59 AM
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Join Date: Jul 2001
Location: Las Vegas
Posts: 44
I just purchased an 1985 300CD which has suffered from a lack of TLC. I am trying to bring the car back to proper condition. I was experiencing much lower fuel milage than this car should normally have even after I had the dealer adjust the valves and do a "bunch" of other maintenance.

The lead mechanic at the Mbz dealer suggested that I take the CD to a local shop J+S Diesel to have the injection timing checked (he said that was where they sent all of their problems with diesels). This shop normally only works on big diesel trucks, but as they are the local Bosch dealer they are obligated to work on Mercedes also. (the dealer is kind of an "old grouch" even though he is youger than I am he think mbz people expect him to drop everything and kow tow to them and their schedules)

Anyway they removed and flow checked my injectors... all came out in great shape, checked compression... all cylinders were excellent, and then set the injection pump timing... here was the problem! The injection pump timing was off 6 degrees.

1-Is there anything other than stretching of the timing chain that could account for that much difference?

2-If I assume that the timing chain has stretched enough to cause a 6 degree change, how much of a problem is that? I know that it is a major disaster to have the chain break, so I have no wish of risking that. Is a 6 degree stretch an indication of imminent problem? At what amount is replacement of the timing chain called for? I have read posts of folks that have operated on the original timing chain for 300,000 miles, but I have no desire as I said to court disaster.

The dealer cannot get the car in for service for a week, so I am wondering if I should even be driving it around town. I am very new at these cars and 6 degree's sounds like a lot to me, but I would like to hear from you guys that actually know what the limits are! I think MBZ recommends replacement at 100k. This car's odometer says 153k, but I have no records as to whether this chain was replaced previously or not. The owner was apparently was having some independent shops work on the car, so they could have replaced the chain and just never bothered (or had the equipment to) reset the timing on the injector pump.

I do know that after J+S reset the timing the car drives like a different vehicle. It is now much more enjoyable to drive. I think they also tweaked the aneroid adjustment. Either one or a combination of what they did has greatly increased the bottom end and made the car much smoother.


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Old 07-10-2001, 07:10 AM
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The injection timing error does not necessarily indicate timing chain stretch. Unless you have full and complete records for this car, you don't know if the pump has ever been serviced or adjusted before.

The ONLY way you will know for sure about your timing chain stretch is to measure it. To do this problem, you need the exact MB procedure and a dial indicator. You can't really know for sure by merely lining up the marks.

If the engine has had religiously frequent and thorough oil changes, there should be no stretch. This is not a timing belt on a Honda, it's a steel chain. The original one in my 240D (same chain as a 300D) went 380,000 miles and was in good shape when I replaced it at the 380,000 mile overhaul.

Good luck,

PS Don't perpetuate the diesel shop's customer discourtesy by continuing to do business with them. You are a paying customer and should not have to put up with such discourtesy. LB
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Old 07-10-2001, 10:54 AM
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Join Date: Jul 2001
Location: Las Vegas
Posts: 44
Larry thanks for the response.

Your comment about religious oil changes and proper maintenance is exactly my area of concern. The previous owner (who was the original) apparently was having the car serviced at a local tire store instead of the dealer. I am sure this tire store did not have the capacity or tools to adjust pump timing or measure timing chain stretch. From the condition of the rest of the car, I presume that the care did NOT have frequent and proper maintenance, which coupled with the 6 degree error in the pump timing has me concerned for the status of the chain.

That is why I was wondering if there was any other explanation for the timing being off 6 degrees other than chain stretch. The only way to bring peace to my mind is to have the dealer check the chain and the stretch, but he cannot get the car in for another week....


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