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The theory of the design of the 928 belt path and tensioner is that a seized WP will not cause a catastrophic failure if the belt path is in nominal condition, and the driver stops when the belt tension light(where applicable) comes on.
In real life practice, on my 88 I changed my belt, left pulley, tensioner bearing, and refurbished the tension asm but did NOT change the WP, as it was functional, and I was askeered to put something else in. After ~1300 miles(tension checked @1000 mi as req), I suffered a seized WP with bearing failure and shaft canted up ~15deg, loss of tension light, and I stopped the car immediately without catastrophic engine damage.
This is one case, and the only conclusion I can draw is that it all worked as Porsche designed. YMMV.
The theory of the design of the 928 belt path and tensioner is that a seized WP will not cause a catastrophic failure if the belt path is in nominal condition, and the driver stops when the belt tension light(where applicable) comes on.
The problem occurs when the tow-truck driver arrives and says 'let's see if It'll fire up?!?' and promptly rips the belt that has melted to the seized WP pulley to shreds.
As for the rest, some folks on this forum (not naming names, don't even remember 'em) stand-by the notion that a 'used' water pump will always fail after you tighten up a new belt. I'm not sure I buy it. Not satisfied with explanations of the physics. Maybe if the 'old' belt was too loose all the time. But, if the 'old' belt was properly tensioned why would the same tension with a new belt put any different stress on the WP? Because it's new. Magic.
Or maybe if the WP was a zillion miles old. Then it was gonna bust anyway. New belt or old.
Here's an interesting one from an early 93 GTS with 47k on it. Owner had it changed not so long ago in 2013 and wanted to be able to tell any new buyer that it was done this year by me. The pump has an '86 stamping but I've not seen this impeller before. Anyone seen one like this before?
Is this an Autopac rebuild? The first pump replaced on my 928 had a pump with a metal impeller. It's look was very similar to this, but a receipt showed it to be an Autopac rebuild. I don't remember if there was an "R" on the casting after the 928 part number.
The step around the shaft is a new one on me. Never seen an impeller like that before. Not Lasa, Autopac or Porsche. No-name rebuild? What was the part price on the previous invoice?
The step around the shaft is a new one on me. Never seen an impeller like that before. Not Lasa, Autopac or Porsche. No-name rebuild? What was the part price on the previous invoice?
Trying to find that stuff out, customer is out of town starting today and won't be back until Friday.
The center bushing reminds me of what Laso did with their plastic impeller on the redesign. Perhaps this bushing even stopped the walking of a metal impeller as well?
Supposedly this is a Genuine Porsche water pump (rebuild???) from the dealer just down the road from me. Fairly inexpensive, and makes me believe it really is a rebuilt pump from Porsche.
02-22-2017, 10:36 PM
