hacker-pschorr

The issue with rebuilds is quality control. Talk to mechanics who have been working on these cars for 20+ years and you'll hear stories about rebuilts were fine.....up to a certain point....then they started to fail at an alarming rate to the point they will never use one again.

I've done quite a bit of research on this and may have discovered what happened and I've explained this in detail in other WP threads.


What suggests the 928 is any worse?

Talking to my local Indy mechanic, he's very picky about what he will install on any car due to failure rates, especially those with plastic impellers. Some cars it's random what material impeller he will receive so he calls upon ordering to make sure a metal one is shipped.

I'm not aware if any of these will suffer block damage if the impeller comes off or the bearing fails and shifts, so that risk is not an issue.

With some cars it's gotten so frustrating he will only order from the dealer, at a significant cost to the customer. Even then, no guarantee it will last but it'st he best he can do.

This falls back on something Greg Nettles talked about a lot. There is factory installed, OEM, OE etc... all have the same part number, all are listed for that application, but quality is rarely the same and gets worse as time goes on.


Quick search found this:

http://www.audiworld.com/forums/a4-b...wsuit-2374335/

GregBBRD

If this was possible, all metal impellers and pulleys would be welded to the bearing cartridge, from the begining.

Welding heatt turns the shaft on the bearing cartridge into virtual glass.

soontobered84

Do we absolutely KNOW that Porsche even makes their own water pumps: casts the bodies, makes the bearings, turns the shafts?

At what plant location is that done?

Real world experience would tell me that Porsche designs the product and has a nameless subcontractor that actually produces this product on license from Porsche. If that is, in fact, the case, then Porsche is no different than any of us, except that they "control" the specifications. I would presume that they have some sort of quality controls in place to verify that the pumps being built are built to the contracted specifications.

polecat702

John, I just did a Google search, and it revealed that GEBA is the OEM source for Porsche water pumps that the factory uses when building the cars.

I guess, GEBA, is the way to go.

soontobered84

Joe,
I guess GEBA is the way to go if you want a metal impeller.

You and I both know what kind of pumps we put on our cars. I think that it's is the only pump that makes sense for an interference engine.

Jfrahm

That seems overstated, plus we are talking about a little booger weld that is not going to cause the shaft to shear off some distance away (where I expect the shaft temp did not rise above 100C). It's been done before many times and might even be a feature of some decent aftermarket water pumps for other makes. Common domestic V8 trick for high RPM operation too.

-Joel.

ROG100

GEBA is NOT the Porsche supplier for the 928 water pump - never has been. GEBA supply pumps to Porsche but not the 928 pump. The 928 pumps - both early and late - are made by a small German company called GPM.
I have talked to GEBA twice about supplying the water pumps with a plastic impeller exactly the same as the Porsche unit but they declined due to the "start up" cost of changing from metal to plastic.
The GEBA pump is aftermarket just like the Laso pump. Laso also supplies lots of different WP's to Porsche but not for the 928.
I have talked with GPM about supplying me with the 928 WP's, however their contract with Porsche forbids them from doing this and they are too small to argue the point.

GregBBRD

Let me reword this, now that I'm at a computer and not a telephone.

I played with this idea, quite a bit.....and tried every welding technique I had at my disposal (considerable). Nothing I tried would stick the shaft to the iron impeller. I was told by an materials engineer that the specific materials and heat treating of a bearing made it virtually impossible to weld to something made from iron....something about carbon migrating to the weld and making both the shaft and the weld extremely brittle.....which is what I experienced. Glass brittle pieces is what i ended up with.

I'm not an engineer or a materials expert. I'm just a dumb mechanic with a hammer and a chisel at my disposal.

If you have some specific knowledge on how to do this, I'd be thrilled to know how.

Cosmo Kramer

Greg, have you ever attempted to drill a metal impeller and pin it to the shaft?

ROG100

As far as my business is concerned water pump failures are now very rare. As long as you follow the guide I subscribe to. Only use a new water pump with a plastic impeller.
Fact - I have sold over 600 Laso water pumps in the last 18 months. I have had four failures. I have sold one Porsche pump.
All the Laso failures were leaking seals and shown by coolant leaking from the front weep hole as designed.

GregBBRD

The failure mode of the plastic impeller is to separate the knurled shaft (that the plastic is formed around) from the plastic. Logic tells me that quicker accelerating engines (which accelerate the water pump quicker, too) would have this problem more than pure stock engines.

Since one of my specialties is building higher horsepower, faster accelerating engines, this always concerned me.

I found that once Laso inserted the spacer that went between the bearing shaft and the impeller (version 3 of the Laso water pump?) that I had zero issues with the metal impeller migrating. I was very disappointed when they went to the plastic impeller, as I saw no need for this change.

Obviously, if GEBA has already taken care of the dimensional problem with the bearing to impeller issue and can control this dimension problem throughout their productions runs, this would be a very viable water pump.

I have not "disassembled" and inspected a GEBA pump to know this for a fact, nor do I know what they are using for a bearing cartridge.

ROG100

I agree with GB - we tried to have it done a couple of years back and it was not possible. IIRC dissimilar metals and too much heat - heat would damage the seals. This was a few years ago when all we could get (apart from Porsche) were WP's with metal impellers.

It may be possible to pin the metal impeller however (for my business) that is not needed as we can supply with a plastic impeller as Porsche defined.

GregBBRD

Yes. The shaft "laughs" at carbide.

polecat702

On my Guardian, the impeller is pined to the shaft with a roll pin. I don't know if Ed still does this though.

Hobibill

I "staked" my metal impeller by using a chisel to peen the shaft at the end. The impeller cannot slide off. Had to be really careful and ensure the other end of the shaft was well supported and taking the full force of the strike.