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Old 07-16-2015, 03:02 AM
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Join Date: Aug 2010
Location: Sacramento, CA
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OM617.952 Oil Pump Chain Tensioner Easy Replacement

My 1984 300D engine. When changing the oil pan gasket, I found the two pieces in the bottom - broken plastic and a bolt. I suspected the upper timing chain guide, but turned out the plastic was part of the oil pump tensioner and the bolt an oil pump mount. The rest of the tensioner was jammed against the chain and doing a good job keeping it tight, though probably wouldn't have lasted forever cocked like that. Several others reported seeing a crack in the plastic at the pivot.

Everything I read (incl. Haynes manual) said you must remove the upper oil pan, meaning engine out of car. But, you can do it fairly easy w/ engine in car. Note, that later 6 cyl diesels have a removable front cover so that gives full access.

On our engines, everything bolts to the front bearing cap as shown. You leave the chain in the engine. Trickiest is removing the gear from pump. The Haynes manual shows a 2 screwdriver pry (pump on the bench). The pickle fork shown easily separated them. Wedge it against the 2 bosses on the pump. I practiced first on a spare oil pump.

Not enough room to pull out the gear bolt, so just slide the pump back as you unscrew it. Of course, first unbolt the pump from the bearing cap (3 bolts) and outlet tube (2 small bolts).

Next, unbolt the bearing cap. Don't miss the small 3rd bolt (use a light). Tap slightly to drop it. Then you can easily replace the tensioner on the bench, and don't lose that special circlip. Also, inspect your main bearing. Mine looked fine (no particle tracks or copper base showing).

Re-install the bearing cap and torque to spec (very important), and of course first lube the bearing surface slightly. Then, bolt the outlet to pump and bolt pump to cap, not worrying about the gear yet. That aligns the outlet in the block. Of course, install a new O-ring first. I wanted to use Viton, but none were thick enough so used Buna-N (Nitrile). Then, unbolt pump from outlet and cap.

Now, the tricky part is getting the bolt started into the pump shaft. Playing with an open-ended wrench a few minutes got it going, then all gravy. If the pump needs a certain clocking for balance, I screwed that up. The manual was silent.

Note that the rubber pickup sits tight against the oil pan (leaves a mark), so can't fall off, but if the top gets too loose it could suck air, at least if the level gets too low. Mine looked serviceable, but I hope we can buy that rubber piece in the future. BTW, this is the most elegant oil pump I have seen on any car. Both it and our Sperry-Vickers power steering pump would look at home on an aircraft. I can't imagine that double-roller chain would ever wear out. In my old Chryslers, the oil pump is driven off a camshaft gear and those gears sometimes get chewed up. Earlier non-turbo M-B diesels drove the oil pump off the IP shaft, but the turbos need more oil flow to spray under the pistons for cooling so the designers went whole hog. Guys repurposing these diesel engines for off-road vehicles are often bothered by the lower oil pan. It seems it is only there to enclose the turbo's oil pump.

Don't continue spreading the falsehood that you must remove the engine to fix this little problem. You guys were scaring the bejeezus out of me with such mis-information.

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OM617.952 Oil Pump Chain Tensioner Easy Replacement-sam_0985.jpg   OM617.952 Oil Pump Chain Tensioner Easy Replacement-sam_0986.jpg  
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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Last edited by BillGrissom; 07-16-2015 at 03:09 PM.
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Old 07-16-2015, 09:33 AM
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Join Date: Sep 2012
Location: Wilmington, NC by the Atlantic ocean
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Good job, Bill! There's almost always a way to do these things if you're clever.

Dan

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