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Failed Porsche pump of the 1990 S4 I am putting back together.
The bearing failed leaving the impeller cocked and jammed against the housing. I have to wonder if this could be caused by an over-tightened belt. Car had +100 miles on it when it failed.
The cam gears look like this:
Last edited by Kevin in Atlanta; 03-01-2016 at 04:37 PM.
Failed Porsche pump of the 1990 S4 I am putting back together.
The bearing failed leaving the impeller cocked and jammed against the housing. I have to wonder if this could be caused by an over-tightened belt. Car had +100 miles on it when it failed.
The cam gears look like this:
I do not use the word "failed" in place of old and worn out.
"Failed", to me, designates some sort of a defect.
I'm not. LOTS of scare tactics used around here. If you look at the bigger picture and do things right (important) catastrophic failure is not common.
I don't think they're necessarily scare tactics. When I purchased my car we could not tell if the timing belt had ever been replaced. So we replaced it. We also replaced the water pump at the same time. Not because I was scared what would happen if it went bad without any warning, but because getting to the water pump is so time consuming (and therefore expensive, whether in terms of $ or in terms of your own time), it made sense to replace the old pump while everything was apart.
Turns out it was a good call. The old pump's bearing was starting to go out. The shaft had no noticeable play while mounted on the car, but there was too much play once the pump was off. A little bit of hard water deposits seemed to be restricting the impeller's side to side movement when it was in the car. Once off, the play was noticeable. Do I count myself as extremely lucky to have swapped out pumps when we did? Not really. I'm pretty sure that the pump would have started leaking before it completely failed and cause any damage. I'm just glad I didn't have to replace the pump 6 months after having replaced the timing belt.
I pulled a Laso out of my car in 2013 that had been on the car since 2007. The timing belt was fine, but around the age it should be changed (but definitely under the mileage). The pump had zero play in it. I think if these cars have the belt tensioned correctly, premature wear will be minimized (maybe even on cam gears, who knows). Naturally, overtightening any timing belt will cause wear to multiple components in the timing system, and maybe even the oil seals.
Still kind of odd how the cam gears got wasted so bad.
My water pump and belt were original on my 84, so, 30 years old, 78,000 miles...and the cam gears looked great. The water pump wasn't leaking when I test drove the car...but leaked the next day. No biggy, I was planning on doing it anyway.
Anyhow, looks like someone got in there and over tighten the belt or something. Using my pump as a barometer...this pump may of actually...failed...since it may have been over tightened...and would possibly still be going if it weren't.
My gears on the S4 were trashed at 90k. Completely unuseable. They had never been changed, and just one tb done at 50k. I wish I would have checked the tension before doing the job. Tensioner was crispy and looked like it had been drained of oil for years. I chalked it up to a hack job.
Those gears were made of a very soft alloy with a poor spray on wear coating - wear like that is not a surprise at all. Now the new gears are made of a much harder alloy and hard anodized as well - should last for ever.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
As a general rule, it's much better to use a water pump with plastic impeller than a metal one. If the bearing wears on a metal impeller pump, it becomes a milling machine into the block.
That seems to be the general consensus - but let me play contrarian.
When my son's car (87S4) began overheating I put a pressure tester on it. The waterpump leaked. What I noticed after the antifreeze evaporated was a grey cast to my driveway. That was when I suspected the block had been 'milled'. I was proven right when we pulled the waterpump. Lucky for us the damage did not ruin the block.
That got me thinking about metal versus plastic and periodic maintenance intervals as specified by Porsche and that Porsche uses metal impellers.
When a plastic impeller waterpump's impeller migrates toward the block there are no outward signs that could be detected while inspecting the antifreeze. The car will lose cooling efficiency.
We all know folks on this web forum that send off their oil for analysis looking for possible thrust bearing failures and the like. Maybe we should add an annual antifreeze service that includes a similar visual analysis? Not sure if our aluminum radiators would generate false positives.
03-01-2016, 04:12 PM
Worn out Porsche waterpump
George Layton March 2014