jhormaechea wrote:

> To all sharketeers, I have just picked up the August issue of the
> mentioned magazine and it brings a special on the 928. It really does
> not say anything we do not know about already but it is worth taking a
> look and maybe keeping the issue. One thing it says: When dealing with
> the engine reliability it says that being the engine bores coated with
> Nikasil (and no liners) any bore wear may require a new block since the
> silicon coating cannot be replaced. However, having read the relevant
> pages in the factory repair manual, the block can be re-bored (with a
> special process to bring the silicon crystals out again, since they form
> part of the upper block alloy) and even to a point in which you can fit
> 968 pistons (which gives a total capacity of approx 5.9 liters). Am I
> wrong on this or is it the mag editors who are wrong?
>
> Juan
>
> 928 GTS 5spd
>



From: Gary Casey [glcasey@gte.net]
Sent: Saturday, August 26, 2000 5:55 AM
To: 928
Subject: [928] Re: 911&Porsche World mag

I am sure there are better experts than I, but I am the one with insomnia right now....
I don't think any Porsche (maybe race air cooled engines?) had Nickasil bores.  That is a
process that puts basically a ceramic coating on the bores.  All the Porsche 944 and 928
engines have "etched" 390 aluminum bores.  The block is made from die-cast Reynolds 390
aluminum, a high-silicon alloy developed for the Vega (how's that for geneology).  After the
block is bored and the bores ground to a very smooth surface the bores are etched - I think I
remember at GM using drain cleaner, but I can't remember which brand.  This etching takes away
the aluminum from the surface and leaves the silicon, which is very hard and wear resistant.
In order to keep the pistons from galling on the surface they are iron-plated.  This plating
is a highly developed process and I would be very reluctant to use any pistons except
Porsche.  The early Vegas had poor plating on the pistons and they wore quickly - the very
latest ones were practically bullet-proof.  You can definitley bore the cylinders and it
doesn't take any incredible technology as long as they are ground to the appropriate surface
finish - but you have to do it exactly right, especially the etching process..
Incidentally, going to the 104 mm bore (anyone want to give me a free set of 968 pistons?)
will change the 5.0 liter engine to a 5.4 and a 5.4 to a 5.9.




From: Gary Casey [glcasey@gte.net]
Sent: Saturday, August 26, 2000 10:08 AM
To: 928
Subject: [928] Re: Vegas (a little off topic and too long)



Phil Tong wrote:

> not know about the other stuff but wasn't original aluminum block
> development for the Indy Cosworth engines?  The vega just came later as a GM
> byproduct.
>
> Phil

Might be, the aluminum block idea was under development for a number of years by
Reynolds and GM Research.  Just to drag this on, the Vega engine was actually an
accidental outgrowth of a project at GM called, I think, the "886" which was
going on while I was there - an idea of Ed Cole, the originator of the small
block V-8, the very last good idea that he had.  He liked rear-engined cars so
we built this rear-engined 4-cylinder thing with an Opel body.  It had a solid
rear drive axle with a transmission rigidly bolted behind that and the engine
rigidly bolted behind that.  Yup, the whole drive train was unsprung.  There was
a pivot back at the engine that the whole thing bounced up and down on.  Lots
and lots of rear overhang.  Evil handling thing that was just impossible, but we
tried for years to get the thing to work.  Anyway, to make the thing even close
to reasonable we had this aluminum block engine made as short as possible with
siamezed bores and very small bore and long stroke (something like 3.4 bore and
4inch stroke using chevy 5.7 inch rods).  It had to rotate "backwards" because
the rear axle faced backwards and we didn't make a new ring-and-pinion.  All of
a sudden we needed an engine for the Vega so we took the 886 engine and reversed
the rotation.  Die cast molds are really expensive so the block stayed the same
with the oil drain-back holes from the heads on the wrong side -  the oil from
the crank was slung up INTO the heads.  RPM was limited to about 5,000 because
of that.  The block was so weak that the head was made very tall out of iron to
give bending stiffness.  The head weighed more than the block!  As I recall, it
was heavier than the contemporary Opel 1.9 iron cam-in-head engine that was
really a fine, fine piece.  The Vega engine was total junk way before the Vega
was even thought of and stayed that way from then on.  The de-stroked 2-liter
version with the Cosworth 4-valve head, though was pretty good.  (we put one of
the short-stroke cranks in a standard engine and it was much quieter and had
more power than the 2.4)  A friend of mine still has an original Cosworth Vega
that has been up on blocks for more than 20 years.
Just to drag this out even further I looked up SAE paper #S397, from 1964.  It
describes the Ford cosworth V-8 as having an aluminum block with
centrifugally-cast iron liners.  Race engine didn't usually use aluminum bores
because to get the required grain structure it was necessary to die-cast the
block at high pressure, too expensive for a race engine.
sorry about long post - thought I had forced all that out of my memory banks.