Cylinder lining question

[chrisg]

All Just to check my understanding - 944 turbo has an aluminium block with the liners alusil coated. If this is the case, how thick is the alusil ? If you need to/have to rebore the liners, even a light hone, do you then have to have the bores recoated ? If so, where do you take the block who can do this ? Yours C

 

[bert gear]

The block is aluminium which is impregnated with silicone, if you bore the block it has to be worked on to bring the silicone to the surface, I would recommend Country Engineering 01454 419866

 

[sawood12]

As Bert has said, the alloy the block is made from has a very high Silicon content and Silicon is very very hard, almost as hard as Diamond which is just about as hard as it gets. The name Alusil is in reference to the Aluminium Silicon alloy used. The Silicon exists in the metal as minute beads close together with aluminium binding the beads together - a bit like aggregate in concrete. Once the cylinders are bored out an acid etch is used that dissolves the aluminium from between the Silicon particulates hence exposing them leaving an extremely hard wearing surface behind. It is only microns thick if that but it doesn't matter because it is so hard it wont wear.

This process was revolutionary because up until this process was developed engines with aluminum alloy blocks had liners which bring a whole host of complications. They are fine for one off engines where an expert engine builder can lavish time and attention on one engine, but not fine for a production line where you want semi skilled workers to simply bolt these things together. I'm not sure if Porsche deveolped it, I know Mercedes and BMW used similar processes if not the same.

The only downside to it is its robustness and resistance to debris. Because the hardened surface is just microns thick if debris gets it scores the cylinder wall creating a weakness.

So the engines don't have linings. They are a one piece block which has the advantage of simplicity of manufacture and lightness. Contrary to what we might think the 944 engine was very light for its day.

 

[chrisg]

Scott a fantastic in-depth description - thanks for taking the time to put this in words....

This has really helped and once I get the block out and stripped down I can get the block bored and retreated - will approach the company Bert suggested.

 

[sawood12]

I know that Helen Goff's S2 had an engine rebuild at Zentrum in Nottingham and her cylinders needed a very light skim bore. Mike at Zentrum scoured the country to find someone who could carry out this etching process. Not sure if it was the same outfit that Bert has suggested but at least you have a potential second contact. It might be worth you contacting Helen to get more details of what she had done.