blown 87

As a person that had that happen, I would have to say, no, nobody ever did try to find out how much it would take to make the impeller move.

We have a few folks working on a fix, Roger is working on a deal with Lasso for a new pump with a plastic impeller, I think that is going to be a very good choice for many people.

Putting a new factory water pump that is 25% of the value of a car just does not makes $$ sense.

But on the other hand, many of us would pay good money for a pump that would not throw the belt or get into the block with out warning.

worf928

Without going through records to count'em I'd say 20-ish (at least) cars since I saw the first one in late 2005. That car had had a rebuilt pump installed around 2001. But, don't do your calculation just yet...

Around half of those 20-ish cars had a plastic impeller pump that I pulled. So, figure 4 out of around 10-12 928s that had metal impeller pumps that I pulled had block damage. Each of the three latest block-damaged 928s had metal impeller pumps installed no earlier than 2005. One in 2005. One in 2006. One in 2008. The "Strong Suspect" included in the numbers was the 2005 install by a dealer. I haven't confirmed this one for the four total, but I'm sure enough that I told the owner I'd do the labor for free if the impeller wasn't migrating.

Now do the math. It sucks.

ZEUS+

What actually causes the impeller to migrate off the shaft is rpm(speed), temperature and pressure. The impeller expands due to heat and the coolant adds resistance(pressure). This slows down the impeller causing migration. Have seen many over the years but the 928 suffers the most. I read an article about impellar migration a long time ago.

H2

Does anyone have a pic of a NORMAL block with no WP damage? You guys got me worried now. I'm going to pull mine just to look. Can't remember if my impeller is plastic or metal. It's a Porsche rebuild that was done in Germany.

H2

blown 87

That or a **** poor fit.

ZEUS+

Those factors play a greater role with a poor fit.

blown 87

Some fail, some dont, all have temp and other variations, the reason lasso redid the pumps was because of a poor interference fit.

The 928 has a poor design for a water pump, but when it comes to impellers there is not a lot of difference in it and a water pump off of many other cars, nor is the load or the temps different.

I have never seen or heard of this on a Chevy or a ford, but have only seen a metal impeller migrate on a shaft on a Lasso, and the problem with the lasso is not limited to Porsche, seen it on VW's also.

How about you, have you ever seen a metal impeller move on a shaft that was not on a Lasso?

ZEUS+

Just rebuilds, plenty of VW's and one oddball 3.8 taurus. The article I read was to find the cause of migration.

OBehave

After taking apart over a dozen of these pumps and comparing to new,rebuilt,Laso etc. the poor quality of the materials and press fit dimensions is the reason for all the migratory issues.The differences between the metals being used for the shaft and impellers and needing to understand the rate of expansion and contraction given the environment that they are subjected to combined with proper manufacturing techniques is all that is needed to solve the problem.Aluminum,steel plastic and bronze/brass all move at different times,temperature and pressures.Knowing that and knowing how to assemble them correctly with the correct tolerances,will ensure trouble free operation.
Ed

worf928

Here ya go. The brown-ish ring is very common.

jpitman2

Any idea how much more resistance to migration needs to be added? eg, a 1/8" roll pin staked in at both ends? What grade of drill would be needed to make the hole?
jp 83 Euro S AT 52k

blown 87

The problem of the impeller moving on the shaft seems to be a lot less than the cartridge moving in the housing, so that is not going to help much for most.

I personally will not put another metal impeller impeller pump in a 928 unless some one comes out with a better pump.

Roger and Lasso are coming out with a plastic impeller pump and I have heard talk that a few others are working on new designs.

jpitman2

So you also drill the housing until you mark the bearing body, and run a lock bolt into it, as well as pin the impeller....Once the methodology is developed, it should be a piece of cake. An option for ROger to offer?

jp 83 Euro S AT 52k

blown 87

Smarter folks than me have looked at this, seems to be a much bigger problem than it looks.

I have only been here a few years, do a search, you will see what has been done and tried.

jpitman2

Anybody know the drive ratio of the pump ? ie at 1000 crank rpm,whats the pump doing ? My mind tells me its less than crank, but by how much?
jp 83 S