Matt H

Duke - such a thing exists for the Mazda Rotary and sells for 45 dollars. It was created out of a list much like this! A step by step would be a great tool and a pleasure to have around. Though I know how to do it you can count my 45 bucks first!
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Tom M'Guinn

I know that is the official position, but have you tried it? I asked the question because at least one guy at a well-reputed machine shop told me has done it many times without problems.

NZ951

Which shop?

Chris Prack

Well?

Tom M'Guinn

Ellsworth Brothers in Mt. View, California.

Danno

How about a coating on the piston. There's tonnes of places that can Nikasil coat a piston. Would be much more durable than the dry-slide Teflon stuff... So we need:

- donor engine
- JE pistons
- a location for a weekend or two
- documentary team to video and write transcript
- a date
- tools

Tom M'Guinn

If we wanted to get creative, we could do it with the motor in a car. Pull the oil pan and the head and swap pistons. Should be able to do that over the memorial day weekend, no?

Chris Prack

That makes the most sense of anything I have heard in a while. Why not Nikasil the JE piston's? For that matter why not Nikasil two of the piston's and not do the other two and compare any failure or wear between the two sets?

Tom M'Guinn

Are the factory pistons nikasil? I thought they were "iron" coated -- is that the same thing? If we could get the weights even, running different pistons would be an interesting science experiment. Who has a garage for this?

Mike S

I'm confused. So its the pistons themselves that are supposedly expanding too rapidly and contacting the piston walls? Or is it the piston rings that are being forced to expand and causing a seized piston/galling?

Chris Prack

IIRC do to the close piston to cyl. wall clearance the piston skirts don't mix with the Alusil cylinder wall.

FWIW I have the garage for this as I run/wrench at an independant Porsche shop. I just don't have any time in the near future.

Danno

"So its the pistons themselves that are supposedly expanding too rapidly and contacting the piston walls? Or is it the piston rings that are being forced to expand and causing a seized piston/galling?"

Well, it's more of the AR-average roughness of the surfaces that's rubbing. The Alusil cylinders are fairly rough due to the removal of aluminium from between the silicon crystals. Then an alloy piston in those bores would be pretty rough too, especially with a wave-grind to hold some oil. So the stock pistons are iron-coated, to be very smooth and very tough and durable to live up to scuffing against the Alusil bores.

The other factor is one of piston-clearance. The stock pistons are also a hypereutectic alloy that expands about the same rate as the block. Thus tight clearances are possible in the stock configuration. Using JE, or any aftermarket hypoeutectic forged piston in our engines would require much larger clearances due to the higher-expansion rate of those pistons.

No, you don't need to have so much clearance that they clatters when cold. Those engines were built by a lazy shop who bored out ALL of the cylinders to some ridiculously large clearance number so they could just stuff any piston they wanted in there. With proper adherance to correct clearances for the JE pistons, you won't get any clatter even with larger gaps than stock.

The only other thing that concerns me is that forged hypoeutectic pistons might be really strong at room-temperature, but once elevated to 350-400 degrees-F, they lose that extra strength much, much faster than cast pistons...

Jim @ EuroWerks

I would deffinitely be interested in contributing. Measuring, assembly and so on. I would be afraid of nikasil however thats really close to crome. I would much rather get one of the coating guys in on this and see what they thought. The 911TT uses what they call grafal on the skirt. If We need to head this up, let me know.

Geo

Neither. Aluminum rubbing aluminum causes instant galling. Aluminum against iron or steel is not going to gall. It might do other things with more than momentary contact, but aluminum will gall almost instantly.

Geo

I talked with Dan Swain at Swain Technology about this last year. They PC9 and PolyMoly coatings on piston skirts for the MB and BMW folks. He thought it would work for the 944 as well. You might want to call him.

Sadly, I cannot use any pistons but factory or identical to factory.