Cylinder Lining

[chriscoates81]

Hi guys, I was talking to one of my work collegues today and he said there was a piece on the 996 on pistonheads and the number 1 problem is the cylinder linings, i didn't think that they had any linings at all. Anybody that can clear this up would be welcomed.

Cheers

Chris

 

[Dodgy Geezer]

Hello Chris,
I have been looking through my book and it says that the cylinders are lined with LOKASIL, this is similar to NIKASIL which you may have heard of, which is a volatile chemical process laying a thin coating on the aluminium bores, if it's applied correctlly there will never be a problem, if the bores get scratched the thin film will start flaking.
I have personally not heard of any problems of this type, as with most things Porsche, if the quality is right it will last a liftime.
This coating applies to the 3.4L & 3.6L engines.

Regards
Ian

 

[thirteeneast]

It does happen, I dont know the stats, But the IMS is more of an issue.


Read "D Chunk"

D Chunk

But then not sleeping because of thinking your Engines gunna blow is also big Money for bussiness

 

[bazhart]

Lokasil is only similar to Nikasil in as much as they both use silicon particles (which are very hard) in the product.

Nikasil is plated on as described above, Lokasil is a metal matrix composite moulded in a tube (rather like a cast iron liner) and cast in situ in the main aluminium cylinder block.

It is then bored, honed and exposed.

The surface finish of the chrystals of silicon have to be exactly of the right machined surface finish, the right distribution, and then the matrix has to be exposed exactly the right amount while the sharp edges of the chrystals have to be rounded off. If this is not done correctly there will be premature wear or high oil consumption.

early engines had the core tube cast right to the top but the Lokasil deteriorated at the join so later engines left the tube a little lower in the block to offer a thin top of aluminium to the block just above the liner.

Composites like this have a relatively new but well known problem called "creep". Basically, because the small particles are bonded together in small local patches (microscopically) - continuous heat and strain cycles can very slightly move the contact patch of each particle resulting in gradual creep in size and shape.

Because the Lokasil liner occupies about half the wall thickness of the cylinder - the remaining aluminium is not thick enough to hold back the creep in the direction of the thrust from the piston - gradually leading to ovailty and "D" chunk.

The actual Lokasil material is a very good cylinder bore surface (if correctly honed and exposed) and hardly seems to wear but it will probably not be such a good material for heat transfer and may degrade over time if the temperatures are too high.

Lokasil is not now used in the latest Porsche engines that have returned to the other alternative they used in the 944 and 968 range - of Alusil bores in which the silicon is cast in with the whole aluminium block material and bored, honed and exposed afterwards.


Baz