My cars are babies. The blue 300D has 170k currently. My 300SD has about 280k. Both bearing replacements were done during the pandemic. I had pulled my pumps earlier to change gaskets and I left them alone after finding minimal play. But during the pandemic boredom I swapped bearings.

I later dug the old bearings out of my junk box and played around with them. They were worn but still ok. They had play like an ABEC 1 though I bet they were originally 3. Yet nowhere near falling apart. The quality of the original bearing is superb. They easily had another 100k in them. It was clear they wouldn’t last forever but at the same time there was no emergency.

My kid has recently taken ownership of the blue 300d. I really wanted to take care of things like the pump bearings before handing the car over to him.

The OE bearings aren’t going to last forever. I decided to risk changing mine out for new ones. There is some degree of risk because I don’t know if the ones I used (8 ball SKF) actually met spec because I don’t know much about all the different variants of annular bearings. So there is some risk in messing with the existing setup.

That being said the bearings wear. And failure is damning.

I’m sorry it’s not definitive. Decide what you want to do. I decided to swap mine out. I got tired of worrying about it.

I swapped my entire pump out with a less worn out one from a junkyard motor, I'm now thinking of rebuilding the old one and trading it back after seeing horrors of them failing.

I'd certainly want to use a quality bearing, Is any reasonably top tier brand good, or would SKF be the only one? I feel like timken and some others are similarly held in high regard and may be easier to source locally?

I've got no issues ordering some SKF bearings, just curious on the consensus of quality vs ease of acquiring.

Update & Vacuum Pump Bearings
 

No ;

I have not heard from my Mechanic, I hope to go by today and give him a nudge, maybe I'll ask if he wants me to take it elsewhere, I'm sure Rich will do a bang up job if I top it up to his place .

The bearings, you local bearing house will be able to look at them and tell you if more balls bearings are available, I have done this with various non Mercedes rear wheel bearings and always got better results than stock as O.E.M. (apart from Mercedes) tend to be specced to a price not the best possible .

C., I'm curious ~ did your original bearings have play or any noise when you spun them ? .

-IF- it turns out to be the vacuum pump's bearings that failed let this be a warning to you ~ I'd heard of many who's pumps failed after 250,000 mile so I knew I was risking disaster .

I'm religious about 3,000 mile HOT oil and filter changes so if it failed, my fault 1,000 % .

I miss having a bearing house nearby. There has been a lot of consolidation in that industry. It’s like the number of machine tool and welding suppliers has shrunk at the same time.

Yes they had a bit of end play. I had to take them out of the pump to feel it. In the pump they felt good but when I got them out in my fingers the inner race would have a little wobble it from wear. You know how on a really good annular you can hold the inner race in your finger tips and the only degree of freedom the outer race has is rolling rotation. Something like an ABEC 5 or CN 3 just doesn’t have any side to side rattle. My worn OEM bearings had a little side to side wobble in them. Kind of like if you wiggle a wheel with the car jacked up and you get some side to side play. Basically they were worn or they shipped with loose tolerances.

Not sure what you mean by “nice”. I’d say the old ones were good to continue using but they definitely had seen some wear and tear. My cars had lower miles than yours. By 400k I’d say yes, pull them out and inspect them.

I’m sure it has a lot to do with how the car was maintained. My cars were abused by the multiple POs.

As for brands, I chose SKF because that’s what was in there as OEM. There are other good brands like Timken, NSK, NMB or GMB and others. Just don’t get cheapie no name ones from India or China that are made for toys. I got a really good deal on some Italian made SKF that came in a four pack. It was perfect because I have two cars.

I’m still not sure I got it all right as far as the bearing specs go. My bearings are good quality but they aren’t the same as the SKF OEM I pulled out. Will I regret changing them out? I don’t know. I hope not.

Bringing the originals into a bearing house sounds like a smart way to go. They may be able to make sense of the specs on the original part.

Oops ~
 

I really do try to proof read before I click "post" ~ I meant NOISE as bearing tend to make slight noise as they get loose .

I was thinking about this today and I remembered thinking the alternator bearings were making noise last October ~ we'll see if that was what I heard .

I too miss bearing houses, do you remember "House Of Brushes" ? I do .

Anyways, we live in So. Cal. so there are still bearing houses although I din't know if any "King Bearing" shops remain .

Last time I needed some Viton oil seals I went to Applied Technologies in No. Ho. that name is flat stupid as they used to be called "Kind Bearing" and had much more foot traffic than after .

Anyways, you know what you need and the internet is your friend here .

Be aware : Timken no longer guarantees only Timken bearing in the box ~ they might be any other brand so BEWARE .

Oh yeah, no noise. No grinding. Just a little loose.

Update
 

I went by the shop today and the owner said he'd begun to look at it but was (of course) interrupted .

He says he'll have a situation report by early next week .

I asked him if he wanted me to take it elsewhere, he said no so we'll see .

Update
 

My guy called today and says a connecting rod let go and broke the cylinder block .

Now I have to see what's what with the engine Rich offered .

Stand by .

Oof.

RIP.

Good luck Nate.

I'll need it .

IMO this battered old relic is well deserving of the $ to fix it .

Arrrgh...sorry Nate. Any chance of using a 300 engine or do you want to stay 4cyl?

Good luck!!!

So, what’s the typical root cause of this? A bad bearing that then beats the rod mounting points into oblivion until it breaks? I can’t imagine it broke the rod.

These engines are so robust, that they usually give you early warning of impending doom. A rod knock almost always is the first indication of a problem. If an oil cooler hose fails, all the oil will get pumped out in short order, but even then, an engine can be repaired if shut down soon enough. A rod through the block is very rare with one of these engines.

Connecting Rod Failure
 

That's a very good question ~ I've had some older European engines that were *so* close inside the block that a loose rod would hit the case and break hole(s) in it .

I find it hard to believe Mercedes would allow such design .

Once I get the engine out and apart I'll know what's what .

Occasionally after many years a connecting rod bolt will come loose, back out and drop, then it's just a matter of the perfect storm of load & RPM's before the other bolt lets go or gets lose and allows the rod's big end to come off the crank where it's often knocked aside and through the block's wall .

I don't have any interest in making this into a 5 cylinder car .

Indeed 40,000 miles is a very short length of engine life .

It didn;t smoke nor drip and always started in less than one revolution .

Sigh .

:eek: Sorry to hear the bad news. Wow. Your car ran really well. I’m stunned the rod let go like that.