Pros and cons of Nikasil?

[blue72s]

Greetings all,

I'm thinking of buying a set of new 2.2S pistons + cylinders for my 2.4 but first I need to know what are the advantages and disadvantages of Nikasil cylinders as opposed to Biral.

thanks

[1fastredsc]

All advantages, no disadvantages.
EDIT: Besides cost that is.

[Scott Clarke]

Nikasil cylinders need to be used with cases that have piston squirters, but your 2.4 should have those.
-Scott

[blue72s]

A specialist has just told me the following:

The difference between Biral and Nikasil barrels is that Biral barrels are an aluminium outer casing, with an iron liner, whereas the Nikasil barrels are aluminium with an electroplated lining.
Apart from certain factory competition cars, Nikasil barrels were first used on the Carrera RS 2.7, in 1973.
The main reason for the use of electroplated barrels in this instance was because the then current magnesium alloy crankcase, which had originally been designed for a capacity of two litres, with no intention of enlargement, had already been stretched to 2.2, then 2.4 litres. There was no cost effective way of increasing the stroke further, so the only way to achieve 2.7 litres was to enlarge the bore. The 'holes' in the case could not be enlarged without major redesign, to take larger barrels, so the only option was to increase the bore of the barrels, whilst keeping the external dimensions the same.This was achieved by doing away with the iron liner, which had a wall thickness of about 3mm., and electroplating instead.
The Nikasil lining was extremely hard wearing; far more so than cast iron, BUT.- Because the barrel was now virtually
100percent aluminium, it no longer had the dimensional stability of the old Biral barrels.
In effect, the biral barrels expanded at very much the same rate as the steel head/barrel studs; thus no significant stresses were set up. The nikasil barrels, having no cast liner to regulate their rate of expansion, naturally expanded lengthwise far faster than the steel studs. This almost inevitably resulted in the studs pulling out of the crankcase, stripping the threads in the process. Thus the 2.7 engines gained their deserved reputation for unreliability.
This problem was very soon remedied by Porsche, by the use of head studs made from a material called Dilavar, a steel alloy with very similar expansion characteristics to aluminium. Thus, everything was in harmony again, and the stud pulling problem was eliminated.
From your point of view, the use of Nikasil barrels on your magnesium crankcase would have to involve the replacement of your existing standard steel studs with Dilavar studs. It would also be very advisable to have the crankcase threads fitted with steel inserts, as the magnesium itself becomes weakened with the constant heating/cooling cycle over the years.
I can assure you that there is nothing worse than carefully reassembling an engine, only to have a head stud pull out as you torque down the cylinder heads. It means total re- strip down to repair the threads.
Unfortunately, these dilavar studs are about £30 each from a Porsche dealer. (there are 24 of them!)
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Comments?

[Scott Clarke]

Many, many folks in the know now strongly recommend against the use of Dilavar head studs. They tend to break. If you have case savers instaled (which you should do regardless of all else), you can safely use steel head studs. If you are really concerned, you can use raceware head studs. These are also steel, and have the reputation of being bulletproof.

Also, the spigots in 2.7 cases were, in fact, larger than those of the 2.2/2.4s. It is possible, however, to obtain a larger bore for a given outside dimension with Nikasil cylinders. This factor led to the development of Nikasil cylinders for the larger versions of the 917 motors.
-Scott