GregBBRD

Not worried about the softness. More concerned about the expansion rate.

Aluminum retaining a steel bearing is a poor practice, no matter how it is done. However, the reduced weight of the aluminum forces companies (Porsche) to do strange things....mount bearings in aluminum.

Having been around the "Porsche world" many years, I've got to see many results of this practice. Perhaps the single most obvious example of this problem can be found in the GT-3 race cars. The front wheel bearings are always "loose" in the aluminum housings, when the uprights are hot...this can de detected by simply grabbing the top and the bottom of the front wheels and shaking back and forth....there is always way much more play when hot. We have had to "play" around with the "kickback" springs in the Brembo calipers to compensate for this problem. If this is not done, the pistons in the calipers get "pounded" back too far and the "first" stab at the brake pedal can be very scary.

Certainly, the front upright, being so close to a huge heat source (the brakes) makes this an extreme example of this problem, however Porsche has had problems with other areas where a bearing is "pressed" into aluminum that gets hot when used.

This is certainly one of the "issues" that is going to be a problem, if someone makes a "billet" water pump. The expansion rate of billet aluminum is generally much greater than that of pressure cast aluminum...which is why the uprights in the GT-3 cars are cast and not billet.

A pressure casting generally has a pretty low rate of expansion. Sand castings usually expand at a greater rate...simply due to the increased porosity of the aluminum.

Since "my failure" seems to be related to heat soaking...I'm certainly thinking about this issue.

blown 87

How big a deal would it be to machine a housing our of steel?
Then just have the housing rebuilt.

Not sure if that is going to be cost effective, but there is nothing cost effective about broken timing belts.

GregBBRD

I would think that you could machine it out of unobtainium or noweightium and still have a pump cheaper than the factory pump. Kind of mystery how they can think that a water pump is worth 1K....unless they know what is "out there".

IcemanG17

good point

SharkSkin

For $1,000 or less you could probably build a pump with a re-purposed magnetic drive(no seal) from an industrial pump designed for corrosives and put a much larger bearing on the snout.

GregBBRD

Reading this thread back, it seems that people are overly concerned about the size of the bearing. I don't think the bearing needs to be addressed. I've seen a grand total of zero bearing failures, unless the seal had been leaking like a fountain for quite some time. Idiots that ignore the puddle of water under their car for months on end are going to have bearing problems...no matter how "big" the bearing is.

heinrich

THis post makes no sense at all. What do you think is failing then? I have had 5 bearing failures and not one where the impeller moved or came off. All of them were a bearing failure which allowed axial play on the shaft/axle and caused the impeller to grind into the pump body ,and then in one case into the engine block after destruction of the bearing. It was clear from the damage and bearing needles/pieces falling out, plus rust and damage to the pump body.

WHat is it you're thinking is failing? THere can be only those two failures ... bearing or impeller migration.

GregBBRD

I'm just saying that, for me, I've seen no actual bearing failures (where the actual ***** or rollers disintegrate), that were not caused by water getting into the bearing....for long periods of time. I've seen the bearing migrate in the housing. I've seen both the impellers and pulleys migrate off the shaft of the bearing. I've seen the plastic impellers spin on their cast-in bushing. Pure bearing disintegration from load...never.

SharkSkin

I agree that the bearing itself seems to be adequate(until it is flooded with coolant). If you read my comment about a larger bearing in the context of the rest of my post and the info I've added below hopefully it will make more sense.

The existing bearing has some beefy roller bearings on a stout shaft handling radial loads. It also contains a ball bearing to handle axial loads. BUT, if that space is taken up by a mag coupler as I suggested, a different bearing will have to be specced that can handle the axial and radial loads in a smaller package(measured front-to-back) which will likely end up being a larger diameter.

86'928S MeteorGrey

Greg,

Can you identify one of the Chinese knock off pumps visually?

EDIT- meaning, are there any tell tale signs or marks? Or did they do such a fantastic copy job that they can't be identified?

heinrich

Understood. Thanks for your reply. However, by definition, a bearing cannot get water in it until it has failed ... And there are no stresses on the bearing over and above normal stresses that all bearings take ... except for axial. And that is substantial. Because the leverage on the shaft is substantial.

worf928

So the bearing shields fail. But, how is going bigger in size going to cure that failure mode? And doesn't that failure mode require that the pump be leaking?

heinrich

I have never seen one leak (significantly) though I know they sometimes do. In fact, I've watched running pumps that are axially compromised spin on the engine, running, with no leakage at all. The shield will not fail absent some external unexpected strain, which I contend is axial play. The question in my mind is this:

Why does the bearing on the 928 water pump fail, when bearings on other water pumps seldom fail, or fail with far less frequency?

Our cars run no hotter, they run coolant, they have stresses on them just like other pumps from other vehicles ... nothing different. The only thing I can see, is that the pump housing, and therefore the bearing, are significantly thinner than those of other pumps. And in my mind, this clearly points to an inability to hold the shaft axially in-place. Certainly Greg's failure described here, has nothing to do with a migrating or loose impeller. Even if the impeller falls off completely or disintegrates .. how would this cause harm to the nbearing? Yet in most cases, the bearing is damaged.

GregBBRD

Yes, "chicken or the egg" thing. I've assumed that pumps without bearing noise that are just leaking...sometimes this goes on for quite some time....just have a seal issue. Seems like there is always a small amount of coolant on every pump, right around the "fluid relief" hole.

BTW...I have a Laso pump, here, that has no "fluid relief" hole...not sure why.

SharkSkin

Heinrich, it sounds like you are confusing axial and radial.

FWIW my failed WP had no detectable play whatsoever but was dripping coolant from the weep hole. If I ignored it long enough I am 100% sure it would have taken out the bearing.