Marton,
Thanks for the picture. I did not include your failure as new because we do not know 100%.
It is included as a failed rebuild to be safe.
Please remind me - did the impeller move on the shaft or the seal cartridge move?
Thanks,
Roger

 

That's the same as my failure. I can see the cartridge is in place. Your shaft has moved through the bushing.

 

Agreed

Already answered

marton

 

In (Marton's pic), it looks like the other failure mode, where the pulley and impeller are canted at an angle, unlike Mike's, where the impeller went straight back. I can't think of how this is possible, although it happens.

This is a classic overtension failure, but what is moving to allow the angle change?

 

Correct, this time (1.5 years ago) I replaced the TB & WP myself & rebuilt the tensioner.

Marton

 

Laso have been very helpfull and proffesional which is more than can be said for GPM who will not even return phone calls from there offices here in the States and Germany.

The engineers at Laso are in agreement that the casting will only take one insertion of the seal cartridge.
The tolerance is such that any further use of the interferance fit will be suspect.
They also feel that the same applies to the fitting of the impeller and pulley.
Laso do not make rebuilt pumps and went to great lengths to point that out.
They also have specific dimensions for the fitting of the impeller onto the shaft to ensure the correct gap between the impeller and the block.

Based on what we are finding out with the failures and the report from Laso - rebuilding is where the issue is and not new pumps. We need to work with the rebuilders to design a fool proof method to hold the seal cartridge, pulley and impeller in place.

 

I have owned a number of failed water pumps. Failure modes I've seen and verified on my cars:

Impeller was not properly attached to shaft, shaft pulled out of impeller. Roller migrated outward or impeller migrated inward or both. If allowed to continue, block was ground and shaft showed axial play. Seal allowed coolant to exit at that point.

Impeller tilted while shaft remained apparently in-place. I believer this mode to be most common, and I believe that indeed the shaft showed axial play *from over-tensioning*.

Seal leaked, no other apparent malfunction.

Bearing ground, no other apparent (pump-related) malfunction, belt broken.

***I have seen failed US rebuilds from major suppliers. I've seen failures of brand new Laso's. I've NEVER seen a new Porsche pump fail. I've seen rebuilds from some of the good suppliers here, with tolerances machined down to nothing. Comparing pumps side by side, it is shocking to see the difference in tolerance (thickness of the pump body) ... I've seen rebuilds with castings so pitted inside the housing I wouldn't consider installing the pump.

I just had a rebuild pump from a major 928 supplier fail after 20k miles under perfect tension. It failed in a safe way, the seal gave out and coolant leaked. Upon inspection, it was discovered that cam timing was not set properly, and all timing gears needed to be replaced with just 20k miles on them. This was an eye-opener to me. I believe cam timing has much to do with belt system wear. However as stated, the single most prevalent cause IMHO, is overtensioning or undertensioning.

Louie and PorKen were both at some point talking about replacing the pump with an electrical or other mechanical unit. Dave Lomas talked about a beefier bearing. Thurston was going to replace his with electrical, as was Lizard931. I've never seen one in living colour though ...

The best pumps I have ever bought, have been Porsche rebuilds with plastic impellers. I WISH someone would supply plastic-impellered pumps.

Contrary to Mark's findings I have seen an exploded pump with bearings and needles/***** that had come out.

 

So, do all water pumps have ball or needle bearings? I thought they were all sleaved bearings.

I can understand a needle bearing, but ball bearings could be a problem unless they are designed for axial loading. I sure they are, but the failures might be due to weakness in that area.

mk

 

H,
I will add your reported failures to the list. That is the first new laso pump failure reported.
By far the most common failure so far is the seal cartridge moving in the casting which backs up what Laso engineers say.
As for the plastic impellers - Laso will not use them as they come of the shaft to easily.

I received Mikes pump and it was the seal cartridge that moved in the casting. The impeller was tight on the shaft as was the pulley.
The impeller had started to grind the block but was stopped by the pulley hitting the casting. The pulley was being forced into the casting - I guess by the belt - and had started to grind its way into the casting.

Talking with a rebuilder about ways around this.

I am leaning towards fresh new Laso pumps - based on track record and cost.
We will see.

 

I'm not sure how helpful Laso's comments are. Since they have no interest in rebuilts, it's easy for them to claim, as they appear to be doing, that the pumps are one-time use only. Since Porsche sells rebuilt pumps (or am I remembering incorrectly), either their pumps are designed differently to allow for rebuilding or they use some process that overcomes the single use limitation.

 

H,
Can you supply pictures of all/any the failures?
Any other info would be real useful as you have seen more failures than us all put together.
Was the Laso pump returned to laso?
Any info would be good.
Roger

 

Bill,
I disagree 8>) and I think there comments just back up what we are seeing.
The main failure is the seal cartridge moving in the casting.
The casting is soft so it is less likely to maintain a tight tolerance after the first interference fit.
A rebuilder reuses the castings a number of times. How many times before the seal cartridge is not held in place at all.
The steel shaft is better able to retain the tight fit (impeller & pulley) with reuse, but after a while surely it will become loose with repeated use.

 

Wow, long thread and great info.

I would agree with Bill that Laso my have a bias due to their position in the market. It's interesting however that GPM isn't helping, I wonder if they are trying to hide something.

In the grand scheme of things is the water pump really a problem, seems that there are only a handful of failures/year as compared to I'm sure many more which are running fine. Any of the big suppliers care to share how many replacement water pump failure percentages/year they have? Or maybe this was already covered somewhere?

 

I'm sure a steel sleeve could be pressed into the casting so that it can be reused multiple times.

Dan
'91 928GT S/C

 

Sorry, Rog, I just can't accept Laso's comments in a vacuum and apply it to all 928 water pumps. If Porsche sells rebuilt pumps as well as new, they either have a different opinion, different design or different process.