Barry Hart
New member
We don't sub anything out to this chap - whoever told you this is talking absolute nonsense. Where did you get this mis-information from ?
Scored cylinders bores
- Thread starter Alexw
- Start date
We don't sub anything out to this chap - whoever told you this is talking absolute nonsense. Where did you get this mis-information from ?
Copperman05
New member
Æ’ound this http://en.wikipedia.org/wiki/Nikasil
and this http://en.wikipedia.org/wiki/Alusil
Looks like it was Alusil that was used in these engines as pointed out by Paul, apparently nikasil had issues with corrosion from sulfur in petrol.
Edd
and this http://en.wikipedia.org/wiki/Alusil
Looks like it was Alusil that was used in these engines as pointed out by Paul, apparently nikasil had issues with corrosion from sulfur in petrol.
Edd
422hp944
New member
Yes...Paul quite rightly pointed out our blocks are made from Alusil...not Nikasil as most on here seem to think. The Alusil blocks can be bored out and then a process of ' Lapping ' the bores on a Sunnen machine with a special paste to leave a high Silicon surface on the bores as per original state. You will then need to source oversize pistons depending on how much material is bored oversize, they MUST be Alusil compatible to have any kind of longevity. SERDI engineering in the UK do great work on this blocks....I would contact them.
Barry Hart
New member
As far as I am aware - the 944/968 blocks were cast in an aluminium that contained silicon particles. This has resulted in very strong cases and when they are bored out the surface is a mixture of aluminium alloy and silicon. The etching of the bores then errodes the alluminium alloy leaving a minute surface of hard silicon with small pockets to retain oil.
Nicasil is an elctroless plating proces on to other materials. The variation in plating tolerances and thickness is in proportion to the thickness plated so if a thin plating is used the surface is relatively even and diamond honing can correct any minor errors and result in a hard wear resistant surface but it is neccessary to hone a cross hatch to retain the oil film.
Nicasil can be plated on to steel or aluminium alloy. We use aluminium because it has the right expansion properties we want and transfers heat better than steel and is just as strong. When we were considering how to manufacture our liners, we contacted the manufacturers of alusil castings to obtain liners and it was possible but our experience of Nicasil was that it is just as good for long life (perhaps better but more expensive), good at resisting seizures and better in one way - that being harder a mild seizure only needs re-honing to remove slight distortion whereas with Alusil it usually results in a deep score and reboring and then the problem of oversized pistons comes into the equation, which are not yet available for Boxsters and 996's.
Furthermore after years of wear the surface of an Alusil bore can wear away to expose too much alloy and reduce the oil retaining properties and become a problem whereas Nicasil never seems to change. Finally - when retro-fitting liners the can be some mild distorion to the roundness and parallelism of the bores and it is easy to run a diamond hone (which we have) down such a bore and correct any minute iregularities.
Steel plated liners are good but you need more cold piston clearance to allow for the lower expansion rates and with short pistons this can result in cold piston slap.
The proof is that all three work very well - so there is no particular recommendation I can make. For us it is quicker to obtain ready finished Nicasil liners and fit them in house than to go the Alusil route.
Finally can I reafirm that we have our own machine shop and actually fit liners and rebuild engines for many of the independent specialists. We also supply a huge range of remanufactured suspension parts to the trade and private individuals. We do not use any other Porsche specialist for anything!
Baz
Nicasil is an elctroless plating proces on to other materials. The variation in plating tolerances and thickness is in proportion to the thickness plated so if a thin plating is used the surface is relatively even and diamond honing can correct any minor errors and result in a hard wear resistant surface but it is neccessary to hone a cross hatch to retain the oil film.
Nicasil can be plated on to steel or aluminium alloy. We use aluminium because it has the right expansion properties we want and transfers heat better than steel and is just as strong. When we were considering how to manufacture our liners, we contacted the manufacturers of alusil castings to obtain liners and it was possible but our experience of Nicasil was that it is just as good for long life (perhaps better but more expensive), good at resisting seizures and better in one way - that being harder a mild seizure only needs re-honing to remove slight distortion whereas with Alusil it usually results in a deep score and reboring and then the problem of oversized pistons comes into the equation, which are not yet available for Boxsters and 996's.
Furthermore after years of wear the surface of an Alusil bore can wear away to expose too much alloy and reduce the oil retaining properties and become a problem whereas Nicasil never seems to change. Finally - when retro-fitting liners the can be some mild distorion to the roundness and parallelism of the bores and it is easy to run a diamond hone (which we have) down such a bore and correct any minute iregularities.
Steel plated liners are good but you need more cold piston clearance to allow for the lower expansion rates and with short pistons this can result in cold piston slap.
The proof is that all three work very well - so there is no particular recommendation I can make. For us it is quicker to obtain ready finished Nicasil liners and fit them in house than to go the Alusil route.
Finally can I reafirm that we have our own machine shop and actually fit liners and rebuild engines for many of the independent specialists. We also supply a huge range of remanufactured suspension parts to the trade and private individuals. We do not use any other Porsche specialist for anything!
Baz
Also the honing of Alusil has to be done in a different and correct manner, with the correct tools. If you can feel the scratch with your thumbnail then it is unlikely to come out with a hone. It's amazing just how small a scratch can have an effect. If you have a catch can you'll notice it fill up more rapidly.
You can sleeve the block but only get this done by people that have had success. Also make sure of the sleeve and pistons compatibility. Friction and differing expansion rates being the things to avoid.
You can sleeve the block but only get this done by people that have had success. Also make sure of the sleeve and pistons compatibility. Friction and differing expansion rates being the things to avoid.
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