Mrmerlin

near as i can tell the coating was good just the lands were filled with carbon as were the rods and the undersides of the pistons apparently the hot tank dissolved the tin iron coating in spots

GregBBRD

No.

The last Porsche part I had put in a hot tank was a 356 crankcase, in 1970.

I got back the studs.....and got to buy my buddy a new crankcase, out of my own pocket.

Since then, I've used elbow grease.

85euro928

From my limited personal experience that coating is pretty tough. That's why I asked what they used in the hot tank.

Mrmerlin

well not that makes much of a difference ,
but the owner of the shop where i am working has been trying to hurry this rebuild along,
and I swear every time I try to go beyond my normal stay focused and do it right to hurry up lets get this party started ,
the whole thing grinds to a halt and then takes lots more time to restore.

this happened once I figured out I needed new pistons,
and then once it was determined that the block had to be decked,

taking the carboned pistons to be cleaned seemed like a good way to speed things up , in retrospect I will never do this again.

Like Master Greg said to me once,
every day I learn something new about these cars,

Guess what?
I am still learning , damn its tough.....

danglerb

Are you thinking about trying some coating added to the pistons?

FBIII

Maybe expand the search to include the slightly lower compression 80 - 83 Euro S pistons. They might be easier to find.

GregBBRD

With the need to skim .020" off the block, the compression ratio will be higher, regardless of which piston he uses.

The pistons are going to be anywhere from .015" to .025" out of the holes...far from ideal and probably requiring that the pistons get "cut".

Stan:

I'm off, next week.

If you still are stuck when I get back, I'll pull apart an engine and see of I can find you a decent short block to start with.

Or buy that engine you found and I'll buy the top end pieces from it.....

You are trying to repair scrap metal and the "mechanic gods" are sending you a message.

Jerry Feather

Why not, Stan? What do you think would be the issues with this process?

James Bailey

Experimenting on a customers car is often not a good thing.....unless THEY are calling the shots and footing the risks even then it may not end well. Watching a 911 engine with aftermarket pistons grind to a halt and seize during the initial start up makes me really question how simple it is

Mrmerlin

Well I spent a few days making calls and I talked to many people about this piston coating and at this point ,
I found a few others that have used this coating process from a company called Calico Coatings in Denver NC.
they are going to coat the pistons with a spray and baked coating called CE-3.

I was explaining to the guy that was working with me how special this mating must be and he offered that he has a Porsche engine builder that brings in pistons by the hundreds to be coated and some are used in Alusil engines.

I am really just bummed that I did something this stupid to ruin a perfectly good set of pistons.

But there are other issues that have to be dealt with like getting the block decked since it appears that it was overheated enough to move some of the cylinders out of position and require a .020 in. cut to restore the level.

And I think Greg is right the 928 engine gods may be letting me know that this engine is well past its useful service life due to the inferior treatment it has received in its past.
At this point I am close to making the engine run. and I dont want to throw in the towel yet,
though a good short block would be an ideal replacement

So I will use thicker head gaskets and put it together and see how it runs,
if no good then it will be time for plan B

mark kibort

after all we have talked about here on rebuilds and pistons, you send them out to be hot tanked.
really sorry too see. I dont know if we have a good coating sourse, but you might be better off just boring the block and using 5 liter pistons.

dont force the issue. that block can be bored for under $750 and im sure you can find 8 x 5 liter pistons. this might be a good thing for you. no experimenting or "seeing what happens " with experimental coatings. save yourself the aggravation and do what will almost be guaranteed to work.
you dont need anything but 8 pistons and a bore job. then you will have a NEW more powerful engine!

FBIII

Mark, if a 4.7 block can safely handle the enlarged bore, that is a great idea.

Cosmo Kramer

The cylinders would have to be bored out 3 mm to accommodate. How about the valve clearance with a piston designed for 4 valves instead of 2?

James Bailey

you machine in new "eyebrows".....makes an ugly looking piston But works does make it an interference valve bender however.

mark kibort

nothing changes as far as "valve bender". the valve reliefs become the same as they are on the 85 euro pistons, they are the same depth... .175 "