Casting errors in the heads

[nob721]

Gents,

Just a quick question. I noticed a few casting errors in the spark plug cavity of cylinder 1, 4, 5 and 8. I have tried to take pictures - but unfortunately a borescope is not standard inventory in my workshop.

The interesting thing is, that I have found the casting errors in both heads,, and on both engines - a 28/13 and 28/09 engine. Identical errors, which in my book tells me its a production glitch more than anything else. The holes do not enter the water jacket, so structurally we should be good to go.

Anybody else identify the same issue?






Have a great Sunday

K.c.

[Opelotus]

Come to think of it, I believe my heads have a similar imperfection. I will check again.

[tmpusfugit]

I don't believe those are casting flaws, but rather the end of the drilled passages for the bolts that hold on the water bridge in the front and have closed off covers in the rear...

[lizard928s]

Last poster got it right.

It is just the end of the drilled hole for the bolts which hold the water bridge.

[bwmac]

The German engineers do everything for a reason.
If I was to random a guess it would be that the bolt heats up faster and since there is not enough space (at the end of the length of bolt required for air compression), if they didn't allow an escape hole, it could cause a crack

[Normy]

Susan Kirby, who worked at Devek, a few years ago told me some interesting things about the M28 engine.

Apparently, prior to 1987, the foundary that Porsche contracted with to produce the engine blocks did a poor job of arranging the sand castings that eventually defined the water jackets. It is common to find a pre-'87 block with cast cylinder barrels that are slightly off-kilter. What this means is that THESE blocks CANNOT be bored beyond 100 mm. Since the barrels are not straight in the block, if you bore them out beyond 100 mm, you wind up with too little metal on one side, and if this engine is used, the heat cycling will eventually cause a cylinder wall to crack.

She went on to tell me that if you want to build a 6.4 liter stroker motor, then you need to start with an '87 and later block, because your chances of success were FAR greater. She really emphasized to me that the early blocks were utterly "hit or miss". Porsche went on a rampage with the foundary over quality, since I suspect that they were planning their own 6.0 liter version [the GTS-R] with 450+ hp, but that car never went beyond the prototype stage since the 928 wasn't selling any more.

I suspect that this same foundary in Germany probably did the same with the heads. I highly doubt that this imprecision is uncommon in the automobile industry; the Toyota fiasco of the past 10 months or so kind of proves that quality really doesn't exist any more.

N!

[Danglerb]

I understand the people at Devek were very nice and well liked by many, but I would verify anything of importance from other sources. I haven't seen any core drift in any of the half dozen early motors I have taken apart.

[Normy]

Originally Posted by Danglerb

I understand the people at Devek were very nice and well liked by many, but I would verify anything of importance from other sources. I haven't seen any core drift in any of the half dozen early motors I have taken apart.

Mark Thomas's white car with a Devek 6.4 liter engine is famous for towing a small trailer from San Fran to Nevada with race tires. After the trailer was removed and tires swapped, at one point during the race his car was clocked at 211 mph.

N!

[porken]

Tangent: ever wondered what the square holes in the heads of the 4.5L engines was for?

They are vestigal castings for an old fashioned exhaust crossover for a carbed manifold, seen here in Project 928.

[nob721]

When I get the heads cleaned, I will see if I cant get some better pics. Until then - as always, great input guys.

K.c.