So I know this topic has come up, and I found a few threads about it but having trouble finding good information. I took my 1984 300td wagon into the shop, and the mechanic has diagnosed that the problem is at the very least coming from the bottom of the engine. I know once he has to go that deep into it can easily top $1,000, so I'm starting to look into the possibility of rebuilding the engine. I don't mind putting the car out of commission for a few months, and I don't mind getting my hands dirty. Have done the normal maintenance like valve adjustments and vacuum system troubleshooting, is it a terrible idea for me to take on the rebuild myself? Aside from the expense and difficulty of having a machine shop rebore piston sleeves, with the right manuals and guidance is it something I could pull off? Are there any the websites, books, or videos that provide some guidance?

Daniel - I would suggest that you take time to describe the problem first, instead of starting with the foregone conclusion. Just a suggestion.

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

x2, what’s wrong with it?

I consider the cost of a proper rebuild prohibitive. Whatever Metric Motors (mercedesengines.net) wants for a short block, long block or complete engine is a reasonable price vs doing it yourself, but I can buy a couple of three good runners for the cost of a fresh short block. I’d look for a good running engine.

Sixto
98 E320s sedan and wagon

X3. Try to get a specific diagnosis before diving into rebuild. A rebuild may not be needed.

Is the mechanic that diagnosed the problem an experienced Benz tech? This matters.

What is the symptom? How many miles? How long have you driven it? Use oil?
Do it yourself??? It can be done if you have time, patience, $ and people to ask questions of.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Unless it was run low on oil, doubt it need a a bottom end.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Ive seen inexperienced techs claim a nailing injector was a bad rod. I would start with oil pressure then crack each injector while its running and see if the noise stops.


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The injectors were recently replaced and the valves adjusted to the proper specs. I took it to an experienced Tech who came with some good recommendations, he took off the cover and looking at the valves and injectors to make sure, and said it would cost more money to dig in deeper to diagnose. I hate the idea of putting hundreds of more dollars in it just to get a diagnosis. At this point, if I'm going to put money into it I'd rather be spending it on permanent instead of temporary solutions.

Symptom is a rattling that is coming from the bottom end of the engine. Odometer has stopped but the car has about 300,000 miles.

A timed rattle or a worn chain rumbling? I know it sounds like armchair guessing but.....


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Timed rattle, doesn't sound like a warm chain, and one of the two mechanics of I've spoken to I'm sure would have been able to spot that. I'll take armchair guessing over no help at all, appreciate it.

Dubyagee mention starting with oil pressure. What would you recommend I do to diagnose oil pressure issues?

If you think you have an oil pressure issue, you would likely notice something going on with the gauge at the cluster. Does your oil pressure fluctuate or ride at a low level when you're driving and or idling? It's normal to idle at 1.5 bar but if not pegged at 2k rpm full bar to have an issue.

If that gauge doesn't work, hook up a mechanical oil pressure gauge.

A rattle could be a worn guide or timing chain. At 300k, your due for guides and a chain. Before throwing away this motor, pull the valve cover and check the chain stretch. If it's over 4 degrees, time for a new chain and guides. You don't mention running it low on oil, so I highly doubt your bottom end is having any issues. The mechanics theory or diagnosis is absurd to me. I daily drive a half million mile turbo diesel on the original motor. A lot of mechanics are idiots when it comes to these cars. They think it's just some normal throwaway civic that blows up at 150k.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Check the pulley bolts 6? at the crankshaft and the large bolt in the center 27mm? for tightness.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Oil pressure is normal as well. The mechanic hasn't diagnosed anything, all he told me was that it definitely wasn't coming from the top and that he'd have to dig deeper into the engine. The only reason I'm entertaining the idea of a rebuild is that for the expense of getting into the bottom end and diagnosing, not to mention repairing, I'd rather just put that money towards fixing everything and start with a like new engine. I've taken it to two very reputable Mercedes mechanics who have both told me that it's not something that they can tell simply by looking at it. I do appreciate everyone's help trying to diagnose, and I'll probably end up going that route, but for now I'd just like to know how realistic it is to do a diy rebuild if I'm patient and am willing to put the car out of commission for a few months. If it is realistic, I'd love some resources that would help guide me through it.

Before considering a rebuild, measure compression pressure in each cylinder. If >350 psig, don't rebuild. Even if low, it could be due to valves (cheaper head job), and a leak-down test determines that. Once you tear it open, you can't test.

Main and rod bearings can be changed with the head on. In most old U.S. cars, you can do in the car, but the OM617 must be removed to take off the upper oil pan. That is the main thing that restores oil pressure. But, the low-end rarely wears and bad main bearings would give a low clunky sound.

Your symptoms sound like the oil pump chain tensioner failed, which would cause a loose chain and slapping sound. It did on my 1984 300D. I changed it thru the lower oil pan (engine in car). The part is <$10 here at P-P. Read my post w/ photos since tricky to remove the sprocket bolt but can be done. Others claim you must remove the upper oil pan (big job, engine out). You must remove the oil pump, so replace the O-rings on the outlet tube (Viton is best, and no you don't need a dealer for O-rings). You also must remove the #1 bearing cap, which lets you inspect bearing wear. Might combine w/ a front seal change if needed. I don't recall that I did, but might help (get more fingers in there).

When you do actually need a rebuilt, search for my post. I took my 1985 block to the "new sleeves" level, but haven't taken it to a shop to deck and hone to the pistons. Another guy posted many photos. People thought he was crazy, but he showed photos where he has a full machine shop in some remote ranch, and decked the block etc. I noticed that rebuilt OM617.952 engines appear to have dropped from $8500 to $6500 (ebay), but still out of my reach. There is also a set of new turbo pistons on ebay for ~$1200, which seems a deal since 1 new piston was $550 and you can't even find them. Someday, a custom piston maker like Egge might find the market, or someone here might front the NRE cost to get some made and hope they can resell them. Even cylinder sleeves are getting expensive and rare.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans