reasons for bearing failure? - PeachParts Mercedes-Benz Forum

vegburner · #1 12-13-2007, 11:29 AM

Hello. I spun a rod bearing and am wondering the reason for this failure.

I understand that heat from lack of lubrication is the reason but am wondering specifically what might have caused this lack of lubrication. I had just run it up to 105 mph (curiosity got the better of me!) about 5 miles before I heard the tapping sound. The engine was still pulling strong and I wasn't over revving it.

I'm having to face either replacing the crank or replacing the engine. It has under 200k miles and was running real strong. I don't want to put the money into a reconditioned crank if there's a possibility of it happening again. The pistons and cylinder walls look fine. Any ideas from experience?

Thanks!

Randy

pawoSD · #2 12-13-2007, 11:35 AM

Did you have enough oil in the engine? I run mine to top speed all the time....I ran flat out yesterday for about 5-6 miles w/no prob. And I am at 266k....my dad does it too with his at 293k.....

vegburner · #3 12-13-2007, 11:40 AM

Yeah, the oil was good. When I got the car, maybe a month or two before, I noticed a slight noise. It's possible the cap may have already been loose.

JimmyL · #4 12-13-2007, 11:53 AM

Quote:

Originally Posted by vegburner

Hello. I spun a rod bearing and am wondering the reason for this failure.

I had just run it up to 105 mph (curiosity got the better of me!) about 5 miles before I heard the tapping sound.

Thanks!

Randy

Seems like you included your answer in the body of your question. You might want to reconsider your driving habits.

Curiosity seems to have done something detrimental to the cat also......

vegburner · #5 12-13-2007, 12:03 PM

No doubt the high speed run hastened the demise of the bearing, but I don't think that CAUSED the bearing to fail anymore than doing something once makes it a habit, IMHO. If indeed these engines cannot withstand a short run at 4000 rpm then they are indeed fragile engines (I would disagree with that viewpoint)!

r

JimmyL · #6 12-13-2007, 12:13 PM

Quote:

Originally Posted by vegburner

No doubt the high speed run hastened the demise of the bearing, but I don't think that CAUSED the bearing to fail ......
r

Agreed

Skid Row Joe · #7 12-13-2007, 12:19 PM

Start buying newer MBs, and reduce your breakdowns running flat-out. What's the reason for running flat-out all the time. anyway?

#8 12-13-2007, 12:27 PM

Quote:

Originally Posted by vegburner

If indeed these engines cannot withstand a short run at 4000 rpm then they are indeed fragile engines (I would disagree with that viewpoint)!

4000 rpm = 105 mph?

Kestas · #9 12-13-2007, 01:02 PM

Is there any sludge or coking inside the engine? This condition will choke off oil flow through the thin passages in the crank that feed oil to the rod bearings.

Chas H · #10 12-13-2007, 01:06 PM

That engine can run all day at 4000 rpm. The previous owner likely ran the engine low on oil and then sold it.
Be aware that swarf from the bearing can circulate throughout the engine, and cause problems if not cleaned out. This is particularly true of the oil cooler, which is almost impossible to clean.

winmutt · #11 12-13-2007, 01:38 PM

Quote:

Originally Posted by Craig

4000 rpm = 105 mph?

If that is true my speedo has a much greater margin of error than I thought.

#12 12-13-2007, 01:43 PM

Quote:

Originally Posted by winmutt

If that is true my speedo has a much greater margin of error than I thought.

Yup, 105 mph is closer to 4700 rpm.

pawoSD · #13 12-13-2007, 01:50 PM

My dad's SD has a working tach and we've had it at flat-out 5250rpm for a while according to the gauge. We were moving! His speedo is a little off but it said 121mph (its a 160mph speedo so its a little inaccurate)

Hatterasguy · #14 12-13-2007, 01:53 PM

Pushing old engines to their limits can cause things to fail. Old stuff doesn't like to be pushed, do it at your own risk.

However the bearing was probably already on its way out, for what reason who knows. Slight factory defect; no oil changes in the cars past. Maybe when it was newer it was ran without oil for a bit, who knows.

JimmyL · #15 12-13-2007, 01:54 PM

Quote:

Originally Posted by pawoSD

My dad's SD has a working tach and we've had it at flat-out 5250rpm for a while according to the gauge. We were moving! His speedo is a little off but it said 121mph (its a 160mph speedo so its a little inaccurate)

He is certainly a good influence on his son, based on this and your posting above.....

{unless of course yall live near the Autobahn}
I hope and pray my son doesn't do such stupid things!