Weird main pulley failure. HELP....
 

1980 300D. No turbo. 280K+

I’m driving down the road today. All’s well. Then all of the sudden, I loose power steering. Then about a quarter of a mile down the road I notice the temp gauge screaming for the red-line, and the battery light comes on. Engine at idle, I coast into a parking lot and shut it down. Water boiling out of the overflow. Open the hood, thinking I’m going to see some missing belts, but no. All the belts are fine, but the main pulley is no longer connected to the crankshaft. The harmonic balancer is fine, and still attached to the crank but the main pulley assembly will slide right out the front of it. I can see the bolt holes in the back of the pulley assembly. They look fine. I can’t get the assembly out, do to the A/C hose in the way, and will have to tow the car home to pull the fan, etc to get it out through the top. I haven’t reached into the harmonic balancer to see if the (6 ??) bolts have sheared off, or just backed out.

Has anyone else experienced this? Is there a trick to pulling the balancer off if I need to? Special puller?
What are the odds of those (6 ??) bolts coming out? I’ve never touched them in 26 years. I don’t mind a failure with a 26 year old car now and then, but this one seems rather odd.

These crank pulleys sometimes want to take a walk for unknown reasons. From what I've read it because the pulley bolts shear. Kind of has me worried myself. Doesn't seem to be any way to prevent it. Hasn't happened to me yet, but it has to a lot of others. Fun part about it is getting the balancer/pulley assembly aligned properly when you put it back together. There are round metal dowels on either side of the crank, make sure you still have yours. They're easily damaged when the whole thing is reassembled. Hopefully the crank nose is not damaged.

Up-Date. And thanks.
 

Thanks for the reply.

Further investigation with a flash-light and a mirror, reveals 6 bolts sheared off in the harmonic balancer.
The balancer, the big bolt and the crank (which I’m assuming is covered/protected by the balancer and the bolt.) seem to be fine. If the pins you speak of are between the balancer and the crankshaft, they are probably still good for now.

So, I guess the balancer will need to be pulled. Any tricks to getting it off? What’s a good way to hold the crankshaft while I loosen that big bolt holding the balancer on?
I hate broken bolt extractions!! Especially when they’re recessed down inside something. Should I just replace the balancer at this point and age/mileage?

I put a socket and bar on the crank bolt and bump it over. It works every time and has done so for years. Just make sure the bar is solit against the frame or floor just a little bump of the starter should do it.

Go to the nearest machine shop
 

It is a difficult job to get those six broken studs out of there. But there are any number of small shops that can do it with the HB on the crank. I wouldn't take that off unless there is no other way. Getting it off is difficult, getting it back on right I understand is near impossible for a novice mechanic. So find a mechanic who will come out, or one that has a shop, pull the radiator and do it. From reading past threads, I think that over tightening of the belts can really do a number on those six small studs. Don't make those belts too tight!

The only trick to getting the balancer off is loosening the big bolt. The balancer should have a couple of cutouts. One option (per FSM) is to jam the balancer with a chisel or 1/2" extension bar through one of the cutouts. Use a wrench with a long handle, 24" at least. Once the bolt is out, just pull the balancer off with a generic balancer puller. Autozone will lend you one for free.

The trick is getting the balancer back on. Getting it lined up properly is just about impossible. So don't take it off if you don't have to. It's entirely possible that the bolt ends will come out easily since they are under no torque. If you do remove the balancer, match mark it to the crankshaft so you don't put it back on upside down.

WVOtoGO, did you experience any load vibrations/noise at a particular rpm band leading up to this? I ask because I'm having really annoying vibrations between 2800-3300 rpm and its a devil to track down. Thanks.

Let the fun begin !!
 

Thanks for the help guys.

I got the car home tonight, and will dig into it tomorrow or it will have to be next week.

I figured I’d better go with OEM bolts and not something out of the NAPA bins. I talked with the parts guy at the dealer. He did say they were hardened. Duh, Like I didn’t figure that much out already.:rolleyes: I have a guy that runs his own "MB Only" shop that I’ve dealt with for years. He’s got his OEM parts supplier delivering a set Tuesday. He’ll cut the dealers price in half for sure. $4.50 each is a bit much for that small of a bolt, regardless of its hardness.

So, I figure I’ll pull the fan out. Then the radiator out. Hopefully that will give me enough room to center punch and drill the studs. A soak of some penetrating oil, and if I’m lucky, they should unscrew with an easy-out. They are all broken off flush with the balancer, so no chance of grabbing them with small Vice-Grips.

If that doesn’t get it, I’ll look into pulling the balancer. I have a box full (tractor owner thing) of various size/length breaker bars to get after the bolt with. I have a few different pullers, but most would need to incorporate two of the bolt holes. (Unless there’s two other holes in it for pulling. Fat chance, huh?) So, I guess if I get one stud out, I’ll shoot for the one 180 out from it next. I’ll be sure to mark the alignment well before I pull.

Thanks again for all the help. Comforting for sure. Beats the heck out of diving in blind. I'll keep ya posted.

Funny you should ask...
 

Seth;
Funny you should ask.

Not really any odd/new vibrations, but a couple of days ago, I had it idling cold in the hangar. Man, was it making a weird knocking noise from the front of the motor! Too metallic to be a rod but seemed to be inside the front of the motor. One of those funky detonation dirty injector type of knocks. I had just (within 20 miles) run a can of Purge through the injectors, I figured maybe it was an injector thing. I took my stethoscope to it but couldn’t find it. Soon as I touched the throttle it stopped. After warming up it seemed to go away. Yesterday, it didn’t do it at all when cold. But had a weird knock after sitting at idle for 5 minutes or so. Stopped when I touched the throttle. This morning it did it, but not for long. Numerous stops and starts today before the failure. I’m actually hoping this was the cause of the knock.

If I were you, I’d get a mirror and a flash-light and crawl under. Count the small bolt heads. Grab the main pulley assembly and hope it doesn’t wiggle. If it does, you may have found your problem.

BTW - Do you sail (or is that a Navy thing)? Texoma? Always looking for a good tach/trap-tician for the Laser-II regattas !!

I just had my balancer off ('82 300D) for a front crankshaft seal replacement. The original bolts were grade 8.8. My local Ace hardware store has 12.9 grade for $1.00 each. Just make sure they are the correct length. If too long, they will damage the front seal.
And if you wind up having to pull the balancer, you might consider changing the front seal while the balancer is off.

Great thread.
So, it is recommended that we check our pulley bolts, yes? Also be sure the belts aren't too tight, and wiggle the pulley to check for play which would indicate one or more sheared bolts.
I must admit this is one failure that scares me, because it can damage the nose of the crankshaft.

It happened on my "79" 240D. The fan pulley on that car had 3 bolt holes and the bolts had sheered off. There were 6 bolt holes in the balancer so I just rotated the pulley to "new" holes using new OEM bolts and lok tite.

So far. So good. But not really into it yet.
 

Well it only took about 15-20 minutes to pull the fan, radiator and shroud out. No problems there. The main pulley assembly lifted right out the top, no problem. The crank and balancer look fine as well. But, the busted bolts don’t look like they’re going to be such a walk in the park to remove. Not quite as recessed as I had envisioned though. Just not a lot of room to work down there, even with the radiator out. I’m still set to go at it with the balancer installed. Think I might try to track down some reverse drill bits, too.

My chiropractor is going to love me for this one. :(

Here is something of importance that I’d like to pass on to those now worried about such a fate. When inspecting your pulley assembly for those 6 bolts (Allen head, by the way, not hex.), don’t be fooled by their presence alone. Just because you see the 6 heads doesn’t mean they aren’t broken. I pulled my pulley assembly out, and all 6 bolt heads are still stuck in the assembly looking like they are at proper torque and doing just fine. I think only one was backed out about a 16th of an inch, and that is seen only when looking at the correct angle. So, upon inspection, don’t just look. Get in there with a wrench and give them a check for “snugness“. (Neat new word there. You pros can stick with “Proper torque“.:) )

Well - it’s back to the back breaking trials of bolt removal for me. I’ll keep you posted on the job as things progress. Thanks again for the helpful tips.

It might be easier if you do it on your back, from underneath.

My theory is that the bolts shear pretty much simultaneously, probably after loosing torque and allowing the pulley and vibration damper to rotate relative to the balancer. I would think that the best preventive action action would be to loosen and retorque all six bolts using thread locker. (Replacing all six bolts with a higher strength bolt would be the next level of prevention.)

As far as the crankshaft being damaged, it is not likely with this failure mode. The crankshaft snout is completely "enclosed" by the balancer and the washers on the crank bolt.

Are you saying that new bolts with a higher hardness would be better? I thought the harder the brittler, and in this instance brittle I don't reckon is a good thing.
Perhaps I shall see how much some new OEM crank pulley bolts are, and look into replacing them one by one. TangoFox- What color threadlocker would be sufficient, what direction are the threads, and what torque spec for the bolts? Are they likely to be siezed inside their threaded holes, necessitating liberal application of penetrant, and what are the chances that trying to loosen them will cause the heads to break off? I'd be interested in nipping this one in the bud, but as far as I know ain't nothin broke yet. I currently have no vibration issues, nothing that would cause me to worry, but then again I haven't really checked things out. It is beyond measure how much I care about this car, and this particular failure is disconcerting.

Update on the repair
 

Well - It’s 1330 central time, and I’m into the beer!!

Things with the repair were going so good there for awhile but then…………Ooops. Ok - maybe two Ooopses.

I center punched the first stud just fine. Got the drill to it and it drilled just fine. #2 easy-out pulled the stud right out. I’m think’n this is going way too smooth. Second (adjacent) stud. Center punch. Drill. Looks like I may bust the easy-out, so I step up a size. Go to drill and the drill catches the stud and before I could get my finger off the trigger, I drive the stud into the front crank seal. Ooops. But after that the stud comes right back out. Go 180, thinking I’ll now be pulling the balancer off, and that one snaps my easy-out off in it. Ooops (again). But so far I’m not teaching the world any new dirty words. Go 180 out of the first stud, thinking this one has to come out or I’ll never get my puller attached to the balancer, take my time, all’s well. Out it comes. ½” breaker bar and a 24” pipe loosen the bolt, no problem. Attach the puller bolts, the puller, and the balancer pulls right off. Sure enough, I’ve pushed the seal back about 3/16” on one side. It’s been leaking (for years), so it needed attention anyway.
Why those two alignment pins on the balancer don’t go all the way down the shaft is beyond me. If so, it would be a snap to align and install. Oh well. That’s another day.
Crank is set to #1 TDC so getting the balancer on straight (not 180 out) shouldn’t be an issue. I’ll scribe the pins to help get them aligned before I start pushing/pulling it on with the bolt. May take a couple of shots to get it. Oh-well. Also thinking of milling the pin ends to help it align itself if I’m only off a smidge.
Good news is, the balancer is off the engine, so getting the other 3 studs out will be much easier on the drill press and the bench. I can even hit them from the smooth back side and not worry about hitting the center of the broken surface with the punch.

As for doing this from the bottom, I don’t think so. It’s blind drilling with your hand pushing the drill while also pushing against the A/C condenser as it is. With the A/C hose and the radiator lower frame mount piece running across there, I think this may be a “from the top” only job. For me it is anyway.

I wont have the new bolts and crank seal until Tuesday, and am heading out of town for the weekend. This job will have to wait until next week to finish. So far, I’d call it a bigger inconvenience than anything else.
It’s all just nuts and bolts. Righty-Tighty - Lefty-Loosey stuff. There are worse repairs that could be made to a 123 I‘m sure. I’m thankful that this one requires no special M/B tools. My HD steering wheel puller pulled the balancer, no problem. ½” drive breaker and a 24” pipe turned the bolt. I’ve been cussing the slight seal leak for years now, so that’s going to be addressed. Haven’t set out to mount that balancer yet, but so far - all is well.

I’ll keep you folks posted when I’m back into it.
Thanks again for the helpful replies. Have a safe Easter weekend.

d. delano,

The pulley bolts are right hand thread, M8 x 30mm on the 617.95 engine. The ones on my car were "ordinary" grade 8.8 socket head cap screws with a black oxide finish. When I removed them, they were only "finger tight" as soon a I broke them loose. But mine were completely rust free. I used Loctite Blue on the installation. The bolts showed no signs of thread locker originally, and the service manual does not call for it. The service manual lists 25Nm torque on one page and 35Nm on another page. (The page that shows 35Nm also lists the bolt length incorrectly as 65mm, so 25 Nm is probably the correct figure. That (25Nm) agrees with the typically listed maximum torque for a grade 8.8 M8 bolt.)

I think your concerns about brittleness are not necessary. A stronger bolt is a stronger bolt. As far as hardness goes, there is only a slight difference between grade 8.8, 9.8 and 10.9. In fact, in those grades, there is an overlap between the minimum and maximum allowable core hardness anyway. So an 8.8 at the upper limit could actually be harder than a 10.9 at the lower allowable limit. There is a significant jump in hardness at the 12.9 level, but the overall strength is about 50% greater than at 8.8.

But I don't think that bolt strength is the issue. I think it's torque. As long as torque is maintained, the pulley, damper and balancer are clamped tightly together so that there is little shear loading on the bolts. It's when torque is lost that the failures occur, I suspect.

I don't think there is much chance of breaking the heads off. Stripping the internal hex with a cheap allen tool is a more realistic concern.

If you replace the seal, I would highly recommend replacing the crankshaft spacer ring as well. Or at least removing the old one and turning it around to reposition the worn area. Put the new seal in first, then install the spacer from the front of the seal. The lip on the back of the seal does not like to slide over the spacer if it's already in place.
I got my old spacer ring out by prying simultaneously with two flat screwdrivers 180 degrees apart. One at a time did not work!!! A little penetrating oil can't hurt, either.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1PY1E2LZD1S20X5BUG&year=1980&make=MB&model=300-D-002&category=A&part=Crankshaft+Seal+Spacer

Roger that. I'm in this far - might as well tag all the bases.
Thanks.

Don't worry about putting on the balancer upside down. The two pins are not at 0° and 180° - they are more like 0° and 183° (give or take a degree or two). If you eyeball it really close, you will notice it.

Good luck!

-Larry

Thanks I'll do that. I got my sailing instruction on a 22' Dolphin on Lake Thunderbird(I guess you're from TX so you might know where that is, just east of OKC). I live right by there and my family and I are members of the sailing club. I've sailed a few sunfish and one laser. I've never sailed on Texoma but I've been camping/fishing down there more times then I can count. I'm joining the club at my school(University of Oklahoma) when enrollment comes around this summer and I'm going to rack up a lot of hours on Laser-type boats. I'm actually planning on buying one when I get back from my graduation-present-to-myself-vacation and see how much money I have left. I'm not sure how much help I'd be but I'd love to come out and learn.:D

For aligning the balancer on the way back in get a couple of longer same thread bolts as these little six and cut the heads off. Lube the new homemade studs a little and put them into two of the holes. Slide the balancer on over them, put in a couple of the retaining bolts, remove your guide studs, proceed. Makes lining things like harmonic balancers and fan pulleys SO much easier.

A little bit of work loose over the years will be enough to shear a small bolt like these. A good maintenance/preventative regimen would be to replace them before they break or at least be sure they're torqued now and then.

--------------------------------------

I know Lake Thunderbird at Norman. Big surprise to me from SF bay area to find a little hotbed of sailing activity out in the middle of Oklahoma! I spent a total of just under six months over ten years attending seminars at the University.Fished the lake a little bit but never got on the water for lob (lack of boat) :)

i would be concerned about the hb. if it were wobbling a little that would maybe shear the bolts.

so when it is all back together i would take a hard look at it to be sure it is not wobbling. also i would put new pins in.

and finally one more time... be so careful instlling the hb with its pins. it is extremely easy to damage the nose of the crank and then you need a new crank. one car i bought for parts had this. i was planning to rebuild it anyway but before that i had to find a new (used) crank because someone before had ruined the keyways and pins.

the hb wobbled a bit at idle.

tom w

Krs,
What do you screw those "homemade studs" in to?

I can’t see how a wobbling HB would require a puller to remove it. Seems to me that if it can wobble on the crankshaft, it would be able to slide off by hand. Mine was tight as a drum, and the puller had to work to get it off. Nothing “nasty tight“, but it was tight all the way to the end.
I guess the big bolt is what pulls it back on. That wanting to turn the HB on the crank is what makes it such a pain to reinstall. Maybe a dead-blow mallet might get it down to the pins, but that may be more blows to the crank/bearings/etc than I want to inflict. I’ll need a new way to hold the crank from turning, for sure.
Aligning the pulleys to the HB should be no problem. I’ll either do like KRS said or use my T-Handled allen drivers to hold the first bolt through the hub. Thread it a few turns and shoot the second bolt.

It’s pushing the HB onto the crank that seems to be the big issue.

the HB
 

The HB, I'd say. His idea would help align the pulley assy to it. I don't think my fingers want to reach in there to get them out though. They'd need a slot for a screwdriver in them.

A zillion spacer Qs
 

What’s the story on the front seal spacer? Should I replace it? I’m thinking “yes”, as I’ll be right there.
Does it get lubed up and pushed in after the new seal is in place? Or, does it go in first, and I take my chances with the seal not going around it? What does it space? Seems to me it controls the depth that the HB is inserted into the block/seal onto the crank. If so, it seems to me it would be back far enough to not contact the seal, as the HB goes all the way through the seal. What part of it actually wears? I’m thinking the ends might, but isn’t it rotating with the crank/HB? Sorry about the zillion Qs here, but I just want to make sure I’m not missing something important. This forum seems to be the ultimate place of information for us DIYers. My thanks to you all.

The lip of the crank seal actually rides on the spacer. So the spacer likely has a groove worn in it. Depending on the extent of the wear, you might be able to turn the spacer around so the seal lip has a "fresh" surface to ride on. (On mine, the groove was almost centered in the spacer (albeit offset slightly) so I did not feel that reversing the spacer was a wise move.)

But the spacer really needs to come out, regardless. The design of the rear seal lip is such that it will not easily slide over the spacer if the spacer is already in place. It is much better to install the seal first, then install the spacer from the front of the seal.

What does the spacer space? It fits between the chain sprocket and the balancer. The balancer will bottom out on the spacer, which bottoms on the chain sprocket. The balancer absolutely does not go all the way through the seal. The rear lip seals on the spacer, not the balancer.

As far as the balancer alignment goes, you can't really see how things are going until the balancer is on far enough for the pin holes to start matching up. I found that it was best to make adjustments by pulling the balancer most of the way off, but not all the way. Then I could tap the balancer to rotate it slightly in the appropriate direction, then draw it back down with the big bolt. Repeat as necessary. Don't pull the balancer completely off, as you will loose your "frame of reference" and be back at square one. I greased the large washers on the crank bolt and I had little trouble with the balancer rotating as it was drawn on. There is so little tolerance in the alignment pins that it only take a fraction of a degree error and they are not going in. Patience will be your greatest asset.

Thanks...
 

ThanksTF007 !!
That's what makes this board great.
All is pretty much as I say it to be, with the exception of the spacer and it's relations with the other parts. Thanks for making it all clear.

So - as I'm tightening up on the HB bolt - what do I do to hold the crank from turning? Jam the flywheel/TC with something?

If I don't reply back today, I've left for the ranch. I'll be back Sunday night to catch up.

Have a great and safe Easter Weekend to all. Thanks again.

yeah, if it was good and tight you are prob fine.

excellent post above.

that space thing might be better called a wear ring. leave it to those germans to give you a removable wear surface! excellent!

tom w

I was able to draw the balancer all the way on without the crankshaft turning. When it was time to apply the final torque of 270-330 Nm, I jammed the balancer by placing a 1/2" extension bar through one of the balancer slots and underneath the upper oil pan lip. This is exactly what is illustrated in the engine service manual for my year model ('82.) (Yes, the manual actually shows a picture of a 1/2" extension bar through the balancer.)

For earlier models with the 722.120 transmission, the service manual calls for the use of a tool which appears to lock the flywheel. Maybe those vehicles have a different balancer without the cutouts. My balancer had a rounded notch into which the extension bar fit nicely.

We're up and running again !! Thanks to all !!
 

Well - We’re up and running again. My thanks to the many of you who have helped along the way.

I must be the luckiest DIYer in town.
The old front crank seal popped right out with the removal tool. The spacer behind it slid smoothly off the crank. I cleaned all that up real good. Put the new seal in (quite slowly) with a soft mallet and a block of wood. I see what you mean by the spacer going on after the seal. It really didn’t look worn, but I flipped it over and put it back in through the seal. The HB took more time to clean then to install. I hit it dead on the first shot. I could push it on with my hands and then light tapping with a soft mallet about a third of the way. Looked like it was aligned, so I put the bolt in, and that pulled it right on. Pulled the bolt just to check everything was on and flush. Spent a fair bit of time cleaning the pulley assembly before installation. Enough dirt/grit/grease in there to throw everything off balance. Yuck. The face that mounts to the HB was a bit nicked up around the holes from the shear. So, I did a little draw filing across it turning 90 degrees every few draws, then 120. Didn’t really take anything off of it, just got it nice and flat/smooth and clean for mating. Getting the first bolt in was a chore but didn’t take more than about a minute. Thanks for the torque specs. I did go with a drop of Lock-Tite blue just for grins. Belts. Radiator. Trans lines. Fan. Coolant. Then, a nice smooth start up. Idled up to normal operating temp. Trans fluid check. Shut down. Checked belts. Checked coolant. No leaks. No worries.

Oh - I did go with 6ea MB OEM bolts. They were 2.00 each. (Ouch - for a bolt? Almost like aircraft parts!)
The new MB ones are T-45 head and not Allen head, for some reason. Oh-well - Was not a problem.

My thanks to all of you for the words of wisdom. This was my first venture into that area of the motor. I appreciate all your help.