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Not sure of the source - saw this on a BMW forum. Interesting info, though not specifically for Porsche - we seem to rehash this debate quite often... eh, Danno

[quote]BMW released the M60B30 and M60B40 V8's with the 93 model year 5,7 and 8 series. These engines ran until the 95 model year. From the 96 model year, they were

replaced by the M62B44. The 3.0L was dropped in the US, but the rest of the world got the M62B35, a 3.5 litre V8.

There are many rumours about the fate of the M60 engine, but only one is true. The engines have been known to suffer damage to the cylinder bores from the

excessive amounts of sulphur in the US fuels. The blocks are made of Nikasil, which is Aluminum impregnated with Nickel and Silicone. Apparently, sulphur

reacts adversely with the Nickel, causing very slight blemishes in the top few millimetres of the cylinder bore. The cylinder bores are crosshatched, which

is the name given to a pattern scratched into the surface of the cylinder wall. These scratches help seat and seal the piston rings, allowing good

compression.

When the cylinder walls become damaged, the piston rings can no longer seal properly. As a result, the engine suffers from leak down. This is the term given

for the amount of air that can escape past the piston as it attempts to compress the air into the combustion chamber. A near new engine , in good condition,

should have a leak down rating of approximately 5-8%. BMW's maximum allowable leak down, on any engine, is 15%. Anything beyond that requires repair to the

engine.

Leak down can also be caused by poorly seated valves.

The problem in the V8's manifests itself as an EXCESSIVELY rough idle. These engines, due to their performance oriented cam shafts, have a noticeable rock at

idle, this is completely normal. However, excessively rough idle will cause the entire car to shake, usually unevenly. The problem can also cause the engine

to lose so much compression that it will no longer start.

While BMW was investigating the cause of the problem, several different methods of repair were tried.

First, they decided to raise the operating temperature of the engine, in an attempt to get a better burn of the gas, and therefore lessen the damage. The
benefits of this campaign, which included replacement of the engine EPROM and thermostat, were negligible, if existent. However, they were making an attempt

to fix a problem that was not yet fully understood.

Once it was decided the engines needed to be opened and repairs made, the first try was installation of new pistons and rings, this was only tried on a few

engines and was immediately dismissed as not viable.

Next step was to replace the short block assembly. This is what is still being done now, however, until the problem was 100 percent diagnosed by BMW, the
replacement short blocks were of the same material as the original engines. This was not so much an oversight, but the only possible way of keeping cars on

the road until a permanent solution could be found.

As a measure of good faith, BMW initiated an engine warranty, covering all internally lubricated parts, which includes the short block, for 100,000 miles, or

6 years. Until this, the engines were only covered under the standard 4 year 50,000 mile warranty.

Now, as the short blocks were being replaced with the same exact part, future problems could be expected without a doubt. The result of this situation is

that some cars have had 2 and even 3 short block replacements.

As of early 1997, all replacement short blocks were of the new material, called Alusil. This material has been used in the V12 engines since their inception.

No reason was given for the change to Nikasil, but I'd like to bet that guy no longer has a job. Anyway, Alusil does not suffer the same problem as Nikasil

and if the Alusil short block has been installed, you no longer need to worry about the situation.<hr></blockquote>

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Jfrahm

As far as I know, Nikasil is a bore plating, not a block alloy as the above author implies, but that's neither here nor there.
I also don't know if our motors would suffer from this fuel-related problem but some people do say to stay away from Citgo gasoline as it is generally made from Venezuelian crude oil that is high in sulphur, which can make for a stinky exhaust and possibly other problems. Some blame Citgo for all sorts of ills, but I've never had a problem with it but have not run it in my Porsche.
Given this information, I will probably avoid high-sulphur gas if I can until I hear more.

-Joel.

TT

I researched this problem a couple of years ago when I was looking to buy a 740. BMW was using Nikasil for their motorcycles and decided to make the new V8 out of the material. Lower compression and use of lower octane gas than in the bike motors resulted in lower combustion temperatures which could not completely burn off the sulfur in the gas. The sulfur eats away the Nikasil resulting in the problems described. Some 740 owners with Nikasil blocks avoided the problem by burning higher octane gas and are still on the road today with no problems. BMW bikes still use Nikasil blocks.

Danno

Yah, I have some friends with the earlier 740 V8 engines. They went through two engine replacements under warrantee before BMW figured out the problem. The third and final replacement Alusil block seemed to have solve their problem. The similar V8s used in the 540i all appears to be the later Alusil models.

Which doesn't explain the 911s getting away with Nikasil-lined cylinders. I guess their higher-compression hotter air-cooled engines manages to burn away the sulfur that plagues the BMWs.

Good thing we have Alusil engines, eh? Interesting thing to note is that the solution limit for silicon in aluminum is 11%. Alusil is 30% so it is a hypereutectic alloy where the silicon percipitates out as crystals. So really, we have a metal-matrix composite block

Some further links of interest:

<a href="http://vista.pca.org/stl/928.htm" target="_blank">The Porsche 928</a>
<a href="http://www.koalamotorsport.com/tech/misc/v8shortblock.htm" target="_blank">BMW M60 V8 Engine - Nikasil versus Alusil</a>
<a href="http://www.mbmw.com/Problems%20with%20early%20production%20V8.html" target="_blank">Problems with early production V8's</a>
<a href="http://www.lestac.co.uk/bmw/nikasil.htm" target="_blank">The BMW Nikasil issue</a>
<a href="http://www.babcox.com/editorial/ar/ar90058.htm" target="_blank">Cylinder Bore Surface Finishes</a>
<a href="http://www.aircooledtechnology.com/thoughts/cylinders-selecting.html" target="_blank">Why is cylinder choice important?</a>
<a href="http://www.kolbenschmidt-pierburg.de/KSWebGate/KSPG_WG_51.nsf/vwFiles/lpdc_engine_blocks/$FILE/lpdc_engine_blocks.pdf" target="_blank">Audi/VW engines with Alusil</a>
<a href="http://www.ifinishing.com/3600-3799/3605.html" target="_blank">What is Alusil?</a>
<a href="http://srd.yahoo.com/goo/alusil/7/T=1023931094/F=6bb9fce4425e9e13d0fcdc88b3539bbf/*http://www.indiainfoline.com/sect/alum/ch04.html" target="_blank">Alusil production</a>

Note: the Boxster engine uses a lower silicon-content alloy called Lokasil...