The engine in my dad's 300D has a good amount of stretch (can't remember how much ATM but I think it was 6 or more degrees). I know Mercedes recommends using a woodruff key to correct the stretch, but what exactly does that do? Would I still need to time the injection pump if I just put in an offset key?

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

The woodruff key offsets the cam gear to bring it back in time with the rest of the engine.

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2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

Shouldn't have to reset the pump timing unless it was adjusted to account for the stretch at some point...even then it would probably be close enough. My advice would be to replace the chain and time the pump if you know how. Otherwise just replace the chain and tensioner, I've seen a few 240D chains break and it is not good.

The chain is relatively easy to replace by (this is over simplifying but...) cutting the old chain, attaching the new chain to the old one, turning the engine by hand until the new chain is in place, separate the old chain and crimp the new one together.

Good luck!!!

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

Only consider the woodruff key if you used the 2mm method to check the stretch. That allows you to pick the proper sized Key.

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84 300D, 82 Volvo 244Gl Diesel

+1, dial indicator method is best. Ive never really understood using the keys though... By the time you cut open the chain to insert, youre 50+% of the way there, and could have a known good and new chain... A critical part!

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Chain doesn't need to be broken to insert the key.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

On the 617.952 you wire or otherwise tie the timing chain to the camshaft gear so it does not jump teeth (look for more complete instructions on this job). Then you remove the end cap on the timing chain tensioner, remove the spring and check it for worn coils, remove the timing chain tensioner and housing with the piston/plunger still in it.

After you do that you have enough play in the chain to pull the crankshaft gear forward enough to get at the Key. You need to be carful.

When you go to put the timing chain tesioner back on you need to pull out the piston in the direction it would move when it applies tension. Install the timing chain tensioner housing. Then re-insert the piston/plunger (don't shove it in hard let the spring do the pushing) followed by the spring and the end cap with crush washer.

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84 300D, 82 Volvo 244Gl Diesel