87 300D Timing Chain/Vacum Pump
 

Had a conversation yesterday with an engine rebuilder that has done MB's forever. I told him about the new 87 300D and he said "put a timing chain in her" and suggested it would fail.

He said he is bidding on one this week with 193K where the vacum pump failed, timing chain went and the engine toasted

What says the group?

A failed (original) vac pump can take out the timing chain. So if you recently bought an 87 300D, you should replace the vac pump post-haste if it's not the new style. Look for four Torx screws on the front cover. If it has them, you're fine, it's the newer pump. If it doesn't have the screws, install a new pump ASAP.

The timing chain itself almost NEVER fails if the oil has been changed at a reasonable interval. You don't change it for fun, only if it's stretched more than 4 degrees, per the OM603 factory engine manual. It's not an easy or fun job - I've done it on my car, and posted the results here. Search the diesel forum if you want to read it... but don't lose sleep about a chain "failing". These aren't VW timing belts, for cryin' out loud! Who is this "pro" rebuilder anyway? :rolleyes:

Maybe he was thinking about the bad batch of chains in the 2.5's. :confused:

AH, that could be. Those who want to know more about the small number of defective 2.5 chains in the early 90's, read this short PDF file:

http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain_TSB.pdf

:)

Small number? I heard of more actual cases of 2.5s with snapped chains than actual cases of 3.5s with bent rods. I guess it's relatively small in both cases, but I'd take my chances on 3.5 rods if my life depended on it. How many posts about 3.5 rods are by folks who've never owned a 3.5 with bad rods?

[edit] Dave - I hope that didn't come across as condescending.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Now that's good information to have! I'd never heard of the problem appearing in 603s or 606s.

Heh-heh. Actually, I'd take the timing chain issue any day over the rods! It has to get REALLY bad before it causes problems, and I never heard of many actually breaking- just stretching and causing the symptoms mentioned. The 3.5L bent rods pretty muc ruined the short block before symptoms became obvious. The cost to repair each has about a 10x price difference, too....

:D :D

GSXR,

I checked my 300D and I have the old style vacuum pump. Is the replacement a fairly easy DIY? I have searched the archives but haven't found any good leads. I will order a new style pump ASAP. BTW, I'm just now at 175k.

Thanks. :)

Marcb,

I'd say it's a medium DIY job. It's not simple but nothing like pulling the head, for example. No special tools are required. Draining some coolant and pulling the upper radiator hose might make some extra room, ditto pulling the fan clutch & shroud (actually I think the fan MUST come out). I think the belt tensioner can stay in place. That reminds me, look at the tensioner pulleys... if they are not PERFECTLY parallel to the engine block, you need to replace that ASAP as well. this is another common failure. If the pulleys are "cocked", the bearing is shot, and if let go it can eventually tear up the timing case (very expensive, nasty job to fix.)

About the vac pump. If your engine number is something like 600 or below, you should remove the "basket" behind the pump (per the instructions) and use the "dam" gasket supplied with the pump. If you have engine 600 or higher (which is much more likely), ignore the instructions and leave the basket installed, and do NOT use the dam gasket. Use the "outline" gasket without the dam. If the new pump doesn't come with a "non-dam" gasket, order one from the dealer ($5-$10). The basket doesn't hurt anything and can prevent an exploded pump from taking out the timing chain (which we all hope never happens). And this way you can't lose it in your garage (if you pull the basket, keep it - it's needed if you ever R&R the injection pump). Oh yeah - don't put any sealer on the gaskets. They usually are a coated metal gasket. Just clean the surfaces VERY VERY well, and install it all dry. Don't overtighten the bolts either! :eek:

More details are in this PDF file (you'll need to scroll down to the vac pump section) :

http://www.meimann.com/docs/mercedes/OM603_modifications.pdf


Have fun! :) :)

Thanks so much for the information! I will have a good look this weekend after I get my PartsShop order! :) I will post any questions that arise during this "fun" project. ;)

Is there anything to inspect in the timing gear while the vacuum pump is off?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

You want to make sure the cam on the face of the timing device, that drives the vac pump roller, is not chewed up. If it is, you'll need a new timing device (which is expensive and hard to replace). That's rare unless the pump bearing failed, and the car was driven for a long time afterwards. Here's a photo of mine, which is NOT all that great, but not bad enough to warrant replacement:

http://www.meimann.com/images/merced...device_cam.jpg

After reading this thread and realizing I have the old-style vacuum pump I decided to start this operation. Right now I'm stuck on removing the fan shroud. I understand I have to remove the fan first and my repair manual lists special Mercedes tools to do this. Is there another way to do this without these tools? Please help.

Actually, you loosen the shroud first - unclip the two metal U-clips up top, and press it towards the engine. That gives you access to the front of the fan. This is where the stubby 8mm socket from MB helps a LOT. The alternative is to find someone with tiny hands to get an 8mm Allen wrench down there. Of course you'll have to try and hold the pulley in place while breaking the bolt free, which is a challenge in itself - the MB tool works wonders here but isn't cheap. Here's the skinny on the tools (none are *required*, but they reduce the removal time to about 3 minutes if you have them!)

http://www.meimann.com/images/merced...belt_tools.jpg

HTH,

Thanks gsxr. I was wondering what size that allen bolt was and now I know. I also realized that there are 4 10-mm bolts that apparently hold the fan in place. Today I bought a very short socket and tomorrow I'll see if I can remove the fan that way. I already tried with a slightly longer socket and I was almost able to do it. The nice thing about this is that you don't have to struggle to hold any pulley in place, instead you just hold the fan in place which is easy. BTW, I did have to remove the belt tensioner because I didn't see any other way to get to the bolts on the right side of the vacuum pump. I'll report on my progress...