based on the condition of the HGs i would say they have been replaced and are not original gaskets
Make sure to do a valve job on the heads the carboned up valve may be leaking.
Test fit the new gaskets to make sure they are centered on the cylinders there should be 2 collars for each head to align the HGs, flycut the heads

 

Are the Piston Rings Toast?you have very clean Areas on the Outside of many pistons.not typical for a low Miles Engine without a broken Head gasket.

 

Forensic detective work. Great pics but this is very strange indeed.

 

It was running great, if maybe a bit down on power. Always started immediately, pulled smoothly and ran through the rev range without a stumble. Excellent oil pressure, normal water temps.

They do look too good to be original. However, during teardown, there was no evidence that anything had ever been apart, except for TB/WP. The lack of records for regular coolant changes had me expecting the worst, but all coolant passages look clean as a whistle, and no apparent corrosion on the mating surfaces (still need to clean and examine more closely).

 

I will add: Except for the ash-like deposits on #1 and #7 piston tops, these are the best heads I've seen the underside of (not that I have seen a boat load). There is no apparent pitting at all.

As for the 'clean' parts of the pistons tops: I note that, for the most part, the cleanest part of each piston is on the 'exhaust' side of the piston. This is also where the squish volume is the smallest (the 16v heads do not have a symmetric combustion volume like the 32v heads.)

 

That doesn't really make sense to me though. The hydrocarbon band is usually thickest at that narrow squish point of a wedge combustion chamber (which is what ours are, except asymmetrical in the 16V) is it not?

 

Why would the head gaskets be replaced on such a low-mileage, previously well running motor?

 

I agree. Mine fell apart in numerous pieces when I pulled the heads off my '78.

 

look at the surface of the head and block, if you see any small tiny tiny scratches it could mean that the head gasket was replaced before. Scratches are from cleaning process. How thick is the head gasket ? For S4 standard is 1.1 mm and 1.4 mm for thicker head gasket I believe.

 

Also, check the Studs. Do any of them look different than the others?

 

I really enjoy going to Dave C's garage for anything. Brian's car is really a time capsule, low miles and nice condition.

 

Because they were leaking,^^^^^

The new gaskets look to have had one not centered or it was a bad gasket the gaskets should trace around each cylinder perfectly. Pay attention to the direction indicators on the new gaskets there is a front and top indicator
IIRC the water passage holes get bigger to the rear of the engine.

 

Do headgaskets have a high failure rate on our cars?

 

No, not generally, as long as preventive maintenance was followed - in particular regular changing of coolant with appropriate coolant for our engines. I will say that I will only use G-05 coolant in my 928. There have been many threads about why, so I will not start another one.

The reason why some cars seem to have HG issues, is that on many of them the (wrong) coolant has been left in the car far too long and allowed to acrid. For some reason, the block doesn't seem to be as affected as the heads, but the aluminum in the heads begins to corrode and pit. This allows coolant to get past the fire-ring and enter the combustion chamber.

in my case, the head gasket was fine, it was the head that failed. In this thread, it appears the HG failed, which is fairly rare IMO. There are many 928's running significant horsepower (500+) with stock head gaskets and they seem to hold up just fine.

 

Erik B. gave me some Berrymans Chem Dip B-9 to clean the carbon off of my pistons and it did a pretty good job after soaking for 24 hrs. The carbon was pretty thick. Erik told me he picked it up in the US. Anybody aware of something like that available in the Great White North? I have tried different solvents and nothing seems to touch the carbon like the Berrymans.

Four pistons down, now to the right side heads and do the whole process again.

Is it best to change the rod bearings all at the same time or can i do i side at a time? I just dont want to mix up the different sides when putting it back together, even though I seperated everything.