Block damage from Water Pump impellor
 

Just doing the TB & WP and I have some pitting to the block where the impeller sits and I have seen in previous posts this was a concern but not sure why? The WP I took off has a metal impeller but it has not dislodged from the WP so the damage possibly occurred before this pump was done. Also the markings don't look like gouges from an impeller rather they look like pitting from wear.
I will post a photo tomorrow. Car has done 250k km or 160k miles. The pump was replaced 6 years ago after water leaking from pump, probably 6 months after I bought it. The mechanic didn't tell me there was a problem.

There is a tool and a repair kit floating around. Someone here will soon post up the details of the water pump housing repair kit. It possible some of the damage was done by the impeller striking the inner housing. The repair tool is quite elegant.

Dwayne has a write up on using it.
However, are you sure you have block damage?
Pitting can be from old coolant and/or infrequent coolant changes. The block comes with a circular type finish from the factory.
If the pricing was from a previous incident and you did not have any cooling problems, then I would just install a new pump and button her up.
Photos would help in ascertaining if you have a problem.

I think the OP's question is more about whether or not the damage needs to be fixed rather than how to. I don't think that the fact that there is some damage to the block surface means that it should be repaired. The question I think is just how much damage can you get by with before the pump impeller becomes too ineffective. I suspect that may take quite a bit of damage. I wonder if there is actually any data to help determine how bad it has to be to be repaired.

Like Bilal said.

If you don't have cooling problems, no need to do nothing.

You'll get diminished pump efficiency when the clearance between the front of the open faced impeller on the 928 pump, and the block suction recess face, is increased beyond its design minimum. Clearance on open faced impeller pumps is set at the bare minimum, considering debris likely to be encountered during normal operation, so that scoring and jamming is unlikely. As the clearance between the pump vanes and the suction recess face increases (from wear), you get greater and greater mixing between the high pressure and suction zones, to the point where pump output drops way below optimum output ... and the motor overheats. In reality, what usually happens with open faced impeller pumps, bearings get worn, impellers come loose, bearing packs migrate, etc, and allow the impeller to be drawn by suction into grinding into the suction recess. Then, when you then put a new pump in you're left with a ground away increased clearance .. and a drop in performance.

If you have only minor scoring or pitting, and you can still see a proportion of original factory machined face, the output won't be significantly affected. If you have deep scoring over the whole area, it's likely to be a different story, as clearance will be increased.

It would be worth posting a pic.

Edit: Increased clearance, with the resultant drop in performance, will be most noticeable at low revs/idling ... like in bumper to bumper traffic on a hot day.

https://cimg9.ibsrv.net/gimg/rennlis...65c90caf76.jpg


Damage to block under water pump



Posting a photo which shows the damage. It may have suffered from irregular changes of coolant as the passages show signs of rust or dirt.
Can I clean up the pitting a bit with fine wet & dry fine sandpaper or just leave it and put the new pump on?
Thanks for all your help.

I replaced my TB/WP ~60K miles ago when I bought my 86.5, and discovered some block scoring from the WP impeller, maybe not quite as bad as yours but close (trying to equivocate scoring with pitting so it's just approximate). I put in a new Laso and have never had any cooling problems since.

This block suffered from corrosion due to infrequent coolant changes. Pump failure and scratches in the block after the impeller made contact look differently.
Good news: you should be just fine with a new LASO pump. Just make sure that the contact surfaces of the gasket area are nice and clean, that´s it.

Hopefully a better picture of the damage and the impellor which looks like it sat in salt water for the 6 years. It also isn't the only problem so I am glad I bought the new harness.
By the time I have finished every cog and seal will be replaced. Took me 4 hours to get the old dirt and oil cleaned up. Tensioner fell apart in my hands before it got to the bench.
Thanks for the help guys it makes it much easier to own these cars. Really enjoy the challenge of keeping it on the road.

Infrequent coolant changes before you owned the car or no coolant (just water) before. Here is my GTS after 20 years and about 120 k miles.... :)

Make sure you change the seal behind the thermostat, where your blue rag is in the picture.

OMG! ... that harness is not pretty. Certainly a good thing that you got that sorted.

It seems like your block has been more affected by corrosion than milling by the impeller, and probably looks worse in your photo than it actually looks and feels to you. If you can't feel a lip at the outer edge then it is probably only corrosion ... but that's a bit hard to judge without actually feeling it.

My gut feeling from the pics is that you probably haven't got an overall clearance increase from milling by the impeller, but just irregularity of the surface, which shouldn't give much decrease in performance.

I've seen much worse in higher pressure pumps, with less tolerance for damage, without there being any measurable decrease in performance.

http://static.ibsrv.net/autocomm/Con...ber%202011.pdf

https://rennlist.com/forums/928-foru...ml#post6849829

http://jenniskens.livedsl.nl/Technic...6/MyTip684.htm

Åke

I made a tool that cuts this area, when damaged. Steve Hattori made inserts and tooling to take up the dimension removed from my cutting tool. The entire repair can be done in the vehicle. Really a great repair, for damaged blocks!

Your damage is minimal and certainly not worth the effort to cut and fit an insert. Install a new water pump and forget about it.

I think the really scary thing is what the rest of the water system looks like. Your heads and head gaskets should be really interesting.....