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FCP Euro Service Kits

FCP Euro Kits

The Pump In QuestionMy wife called me on the telephone earlier this week to notify me that, without warning, our W124 Mercedes sedan began making an awful noise at a red light. She pulled over and turned it off immediately to avoid further damage, and reported that the coolant temperature and oil pressure were perfectly in range when the issue presented itself (invaluable data, no doubt). When I got off work, I wasted no time getting down to the parking lot where my car was left to go inspect the damage. Under the hood, there were no obvious signs of a struggle. Everything was in place and looked correct. Not having heard this sound myself, I built up the courage to crank the engine- of course, I disconnected the coil wire so the engine wouldn’t start. Upon cranking, I was met with a noise most foul…

There was a small piece of metal caught between the block

A hard mechanical clunking noise instantly made me think “rod knock.” I sat back and pondered life for a moment, then I noticed that the pulley on my power steering pump had some very unusual marks on it. After looking around the engine for a good while and seeing nothing else unusual, I got underneath and inspected the area around the harmonic balancer. Interestingly, there was a small piece of metal caught between the block and the balancer. I removed the metal piece to find that it was indeed a bearing roller. The next afternoon, I delved deeper into the engine.

It didn't take long to find the culprit

Following the same procedure outlined in my previous article Mercedes 6-Cylinder M103/M104 Belt Tensioner Replacement, I removed the fan, fan shroud, fan clutch, and belt. The idea was to roll every pulley and see which one appeared to be missing a bearing. It didn’t take long to find the culprit.

The water pump had ejected it’s bearing, and in clear daylight the next day, pieces of plastic seal were evident all around the crime scene. Indeed, I could grab the pump pulley and tilt it about 10 degrees in each direction. This pump was most certainly done for. The impeller had been striking the inside of the pump housing causing the terrible noise from the night before- I must replace the entire pump.

Bearings don’t last forever - including maintenance free sealed bearings. The bearings in a water pump are no exception. Accessory drive bearings (alternator, water pump, compressor, etc.) have a hard life. They are not necessarily under a constant load, nor under constant speed or environmental conditions. We often don’t think about bearings until they begin to squeal. Even then, we may just spray some lubricant into the bearing and let it ride out for a few thousand miles more. In my case, there was no indication that this bearing would fail, and the failure was catastrophic. Fortunately, there are plenty of things that we can do to keep these types of catastrophic failures from happening.

Replacing accessory drive belts at their recommended intervals might be one of the most important things we can do to prolong the lives of our bearings. The replacement of a belt is the perfect time to check the condition of your bearings by listening for unusual noise that might indicate pitting, corrosion, or roller damage. Spin each pulley individually and listen carefully for signs of wear.

I was very lucky

Perhaps even more critical, though, is the importance of not over-tightening a belt. Over-tightening a belt can increase radial loads on the bearings to far beyond their factory specifications. This will ruin a bearing in short order, not to mention damaging the belt and any other items in the line of fire when the bearing disintegrates. Such a failure can easily destroy other accessories, or even your fans and radiator if pieces break loose. I was very lucky in my case that the flying rollers didn’t do any other damage.

I feel that I can attribute the bearing failure to the old age of the pump, and the very hard life that it has lived over the years. I only wish that I had caught this before it took my car out of commission, as I had other major work planned for the weekend. As always, I will be replacing my pump with a reputable replacement model, and using the factory specified coolant at the factory specified ratio.

 

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Dan BullmoreDan Bullmore is a physicist and engineer from Houston, TX. Preferring the old to the new, Dan has owned many examples of Mercedes and Volvo vehicles and has devoted much of his time to maintaining and understanding them.

 


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Written by :
Dan Bullmore

Dan Bullmore is a physicist and engineer from Houston, TX. Preferring the old to the new, Dan has owned many examples of Mercedes and Volvo vehicles and has devoted much of his time to maintaining and understanding them.


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