OM603: Freak failure of timing cover. 1987 300D

[gsxr]

Hi all,

While starting my 87 300D this afternoon after it had been sitting outside for a couple hours, it made an awful noise right at startup, which went away after about 2 seconds. Hmmm, strange, but everything seemed kosher after that so I ignored it. 20 minutes and 25 miles down the road, my oil level idiot light came on. Also odd - I just changed the oil 2kmi ago, the light shouldn't give me hassles until 8kmi, but I had done a bunch of 0-90mph tests recently (baseline stuff, pre-intercooler project) and thought perhaps oil consumption went up due to all the WOT runs. Funny thing was, the oil light usually goes on briefly at first & then off, staying on longer each time as weeks (and hundreds of miles) go by. This time, it stayed on steady from the first. Hmmm. Oil pressure is fine, no other idiot lights, so I drove on to the gas station (been on reserve for a while) and then home (another 10-15 miles total). I popped the hood before going inside to change, intending to check the oil level later, thinking perhaps the level sender was acting up - no WAY it should be low on oil already.

So I come out a half-hour later, peek under the hood, and notice oil ALL OVER the place. Oh, great, now what? A quick glance pointed out that it had to be something big - the alternator and whole front of the engine was soaked with black ooze. I checked underneath and found a foot-diameter black puddle. This was NOT looking promising. Then I saw the source: The serpentine belt tensioner lever arm, where it screws into the timing case cover, had ripped out! The tensioner was fine, the aluminum cover failed! The belt was chewed up and oil soaked and the tensioner idler pulley was rubbing against the water pump pulley. I could see the timing chain and 'banana' guide through the hole. My assumption is that it broke when I heard that nasty noise. (I should have popped the hood and looked, huh - wooops.) What blows me away is that I was able to drive another 40 miles with it in that condition! From what I saw, the belt should have failed almost immediately, which would have been obvious due to the alternator lights and no power steering. I don't know how it lasted that long. I must have been smiled upon from above in the face of adversity or something. (?)

The really scary part? Had the oil level light not come on unexpectedly, I probably never would have checked anything. I was going to run errands with the car after I got home and had I not popped the hood to check the oil, who knows what might have happened. For those who advocate disabling the oil level light as a nuisance when it doesn't work right, well, I'm glad I have it thank you very much.

Soooo.... Quick prognosis shows a new timing cover and serpentine belt at a minimum. Believe it or not, the lever arm bearing seems FINE - spins smoothly. I have NO IDEA what could have caused this. Marshall, is there a known weakness on the old case covers? My engine is number 000377, very very early in 603 production. Since I needed to change the oil pan gasket anyway, and this looks like a nasty job 'in car', I may pull the engine & tranny out and fix it on an engine stand. (*cringe*) Might as well put in new chain rails and everything else while I'm at it. New tensioner parts too, keep the old stuff for spares I guess.

Why yes, of course I took photos, you shouldn't have doubted that:

http://www.w124performance.com/images/OM603_timing_cover/
Updated URL

[duxthe1]

WOW! That is an unusual failure. You are gonna want to pull the engine out to fix that. I've got a 603 on the engine stand at work that got a new timing cover put on after a chain failure. Replacing the chain, chain tensioner, and all the associated rails is a good idea. While you're in there you should install the updated windage trays.

Wow Dave! Man, Do you think that there was some kind of "bind" on the tensioner to have made it break? Or some defect in the casing? When was the last time you changed the tensioner?

[Pete Burton]

Reminds me of what happened to me with my 617 about 2 weeks ago. My daughter noticed a trail of oil on the driveway which led (of course) to my SD. During my move last year, the last thing I did on the motor was reinstall the oil pump. Well, I guess I missed checking the bolt on the sprocket. Loosened up and backed out, punching a hole in the upper oil pan. I pulled the engine/tranny and repaired it, but I didn't need to put it on a stand (or I didn't because a friend is still borrowing it) Same nasty oil spray all over, but hey, think of all those rustproofed parts - just in time for winter!

[gsxr]

Updated windage trays? Tell me more! Might as well do all the updates I can when it's apart. The only windage tray I see in the EPC says it's not valid for my engine. Timing chain & upper rail are new, but I'll install a new lower (banana) rail while it's easy to access. Probably a new oil pump chain and rails as well.

Tensioner replaced 20-25kmi ago, and it still seems fine (despite being separated from the car at the moment). Smooth bearing, threads not loose, and it wasn't cocked at an angle either. No apparent binding.

The EPC shows the timing cover was updated twice (three part numbers total in the EPC), and mine must have the original. It will be interesting to see the casting differences when I get the new one in hand (current list price is $177).

Dave, Sorry this happened. Please continue the documentation of the repair, so all of us with the 603 engine can learn along with you.

[Habanero]

Oh no, not another 603ism. I guess I will start clearing space in my garage for the engine stand...

Seriously though, sorry for your problems but we all look forward to learning from your experience in this repair. Good luck.

[Hatterasguy]

Wow that sucks That is a weird problem I wonder what causes it? Maybe a bad casting?

[Pete Burton]

Whattya bet the new casting has wider ribs on the backside behind the idler mount?

[Ken300D]

You may have seen my thread on my similar events following tensioner replacement work.

I have almost the same breakage - will try to get a picture for your comparison. In my case it happened after about eight miles of driving on the test drive after repair. Before heading out I let the engine run for awhile watching it - smooth as could be, no bouncing on the belt. Repairs did include a new water pump because the old one felt a little rough in the bearing.

In my case it sounded like I had run over a rock, then some whap-ping around, then WORSE whap-whap-ping around and the alternator light came on. I hopped out and found the belt destroyed (just a ball of strands) the tensioner broken out, and the belt grabbed one of the transmission lines and ripped it apart. Jumped back in and got to a service station for a tow the remainder of the way home. Sure hope that 1/10th mile didn't crack the head - temp rose to abt 105 or so.

I'm at a loss to explain what happened. Never heard of it happening before, and figured I alone would have this kind of thing happen to me.

Here are my wild theories:

1) That new shock absorber seemed really really tight. Maybe too tight?
2) I used a thread sealant on the big tensioner lever mount bolt and applied the torque specified in the UK Haynes manual. Haven't checked it in the MB CDROM manual, but there are such things as misprints and mistakes on torque values. And I wonder if the sealant altered the desired torque - meaning I wonder if I over-torqued this and cracked the cover.
3) Some kind of bearing defect in the new tensioner lever.

I moved the mounted tensioner lever around and it seemed fine - no binding.

Just don't know what happened, and afraid it will immediately happen upon the repair with new cover.

Ken300D

[gsxr]

Ken - ouch, sorry to hear it happened to you too. (OTOH, yaaay, I have company!) I missed the other thread, please post a link here if you have it. Have you attempted repair yet? I can't even START on a repair for at least 2 weeks, I'm waiting on parts (ordered this morning) to put my E500 back together so I can free up the bay in the shop to move the dead diesel into. Then, I get to decide if I pull the engine or not - I want to, but I'm concerned that I may need to discaharge the AC and I really REALLY don't wanna do that (it's R-12 and COLD and I want it to stay that way, afraid I'd muck something up... d'oh.)

BTW - I need to check the casting number on my timing cover, but there were two revisions (3 part numbers) and I believe ours will be the first/original. I bet, as Pete said, the new part is beefed up. I'm not worried about it happening with the new cover, I figure if the old flawed design lasted 18 years and 250kmi, the new stronger one should last at least as long! The belt shock is VERY stiff, that's normal. Torque spec is quite high on the tensioner lever, I forget exactly, something like 70-80 lb-ft?

Weird stuff, that's for sure...

[kmaysob]

[QUOTE=gsxr] Then, I get to decide if I pull the engine or not - I want to, but I'm concerned that I may need to discaharge the AC and I really REALLY don't wanna do that (it's R-12 and COLD and I want it to stay that way, afraid I'd muck something up... d'oh.)


why not just disconnect the compressor from the engine and hang it to the side. i dont know what kind of clearance is on the 603 but if you can, just hang it to the side. thats what im gonna do when i remove mine. but mines the 617. hope this helps

Originally Posted by gsxr

pull the engine or not - I want to, but I'm concerned that I may need to discaharge the AC and I really REALLY don't wanna do that (it's R-12 and COLD and I want it to stay that way, afraid I'd muck something up... d'oh.

You should not need to discharge the A/C system in order to remove the engine.

Unbolt the A/C compressor mounting bracket mounted to the engine, with all hoses attatched, carefully pull the unit outward to the side, and lash it down with whatever works for you. Bunji cords work too!

You will be able to slip the engine up and out without discharging your A/C system...... BB

[toknow]

Hi,
gsxr, is the noise you heard seems like something squeeling, i.e. some component driven by the belt (Alt., water pump, p.s., or AC comp)? I think any failing one can put a huge load on the belt system. In many cases, the tensiner pully fails gradually to a tilted position, and this can place side forces on the bolt holding the tensiner (I think your car tensioner alignment was Ok before that!). The other thing is in the factory CD, they perform a test for the Klima to check if it actaully disengages the AC clutch if it is locking for few seconds. If the Klima does not do the job, or delay, this could add more forces on the bolt system, which suppose to be protected by the Klima. Also, advances in belt construction could have prevented the belt from failing earlier before the Bolt. May be it was tested 17 years ago with lower technology belts.
I think you are lucky that you have the radiator, fan, clutch etc. not being damaged by flying parts.

toknow

[Carrameow]

GSXR, I cracked my timing cover- put a 3/4" inch long crack in itwhen I took it off to redo the crankshaft seal and the oil pump chain guide. There was a bolt hidden under some grease and I pried on it, and put a 3/4" inch long crack on it. I bought a new one from Froghunter, but in the meantime I knew a guy, a real welding whiz who worked for ths skunk works around here ( dont want to get him in trouble), he has welded on all kinds of exotic metals on aircraft and missiles and he welded mine to perfection. I have it, I am only offering to you gratis. I test fitted it to my 87 but I figured I would use the new one from Froghunter out of superstition. You would only have to pay the postage ($86.00) haha just kidding , I will pay that too..