Chopperharris

Ouch. Yes - planning on those needing replacing too.

Cheers
Ben

GregBBRD

I'd love to have you explain how a broken valve spring can get into the combustion chamber (or into the piston rings) and cause damage.

Think about it....

gbgastowers

What do you think this is then? Is was stuck in the ring. I don’t know for sure what it is

gbgastowers

Maybe a piston pin clip?

Mrmerlin

that looks like a wrist pin retaining clip,
as to how it could have gotten stuck in the ring land,
I dont have a clue with a piston in the bore

GregBBRD

I agree that the tapered end makes that look like the tail of a valve spring.

Clearly there is no.possible path (unless there is a new force in the universe, like a Star Trek transporter room) for a valve spring to migrate into the rings.

I'd be inclined to believe that this had migrated down from the head into the oil pan and just happened to fall into that broken piston when you turned the engine over to remove the pan. When you removed the piston, it came out with that piston and fooled you.

The failed piston is a very typical broken ring land on a cast Porsche piston. The cylinder pressures get too high for the ring land to support the top ring and it fractures. SUPER common on supercharged or turbo charged engines that are not properly tuned. I rebuilt a 1980 928 engine in the early '80's that had the very first turbocharger installed (that I'm aware of). It broke several pistons, exactly like this.



This can also occur on a stock engine, if the ignition timing is set wrong.

One of the versions of the 911SC had a complicated method for setting the ignition timing, and "rookies" who would set the timing wrong would have this happen 100% of the time. This was super common. I probably fixed 50 of these engines, with broken ring lands.

gbgastowers

Do you see many broken valve springs? Is that usually due to over rev (too much heat)?

Chopperharris

I’ve been recommend a shop by a couple of knowledgeable guys on 928.org.uk that can do the correct honing/laping on Alusil blocks so I’ll be speaking to them tomorrow about the block, heads and pistons. Will update when I know more - in the meantime I’ll get on with the cleaning and valve removal.
Cheers

GregBBRD

Rare to see a broken factory Porsche valve spring, but all valve springs can fail....they are made from metal and anything metal can fail, at any time. One tiny flaw, a tiny pit from corrosion, sitting for long periods of time compressed (engine not turned over) are all very hard on valve springs.

Any engine that has a chronic tendency to have water vapor collecting on the oil fill cap (seeping head gasket leaking water up the head studs; engines that never get run long enough to get the oil hot) will have to have the valve springs replaced. This is common to see, on 16 valve engines.

Valve springs are asked to compress and expand millions and millions of times in 100,000 miles. Most of the 16 valve engines have passed this point....long ago.

I never would re-use an early 928 "single" valve spring with 100,000 miles on it. Too much risk of catastrophic damage from failure. The dual spring 16 valve engines are a bit less scary, but by 150,000 miles, they also have done their service and should be replaced. If there is any sign of corrosion on any valve spring, it should be replaced...regardless of mileage.

The 32 valve engine valve springs defy logic. I've yet to find a limit to their life. Super rare to even see a "weak" one, much less a broken one. Perhaps worth noting, these engines all "force" a large percentage of their crankcase vapors into the intake system, which "carries" with it most all of any water vapor.

Chopperharris

Hi

Does anyone have the valve springs pressures for installed and free heights on a 82' 4.5 Euro? Looked everywhere but can't find them. I have the early dual springs types - p/n 928 105 903 00. As well as testing mine i'd like to see if there are some alternatives, to new from Porsche, out there..... i'm doubtful there are but want to explore options.

Thanks
Ben

Chopperharris

Just to close he loop on this one. I've had to dump the engine as the bores were too out of spec (as was the crank, pistons etc). It would have been too expensive to repair so i've found a 4.7 Euro to go in its place. Hopefully the report back from the machine shop is more favourable on that one although i've got to strip it down and inspect it first.