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X-Source: The Hotrod Mailing list
Date: Jun 1993
Subject: RE: Pistons
X-Sequence: 5626

>Now there is alot of hype about the hyperuetectic (sp?) or high silcon steel
>pistons.  What's the deal here?  Are these a "Good Thing" or a "Bad Thing"?
>Failing that generalization ... are they good for some applications and bad for

Most pistons are aluminum even the hyperuetectic (sp?).  Cast pistons
have their place but if your going to spend $3000 on a rebuild spend the
extra $200 and get forged.  Tight machining and longer connecting rods
(small Chevy) will limit the rock at TDC.

[Depending on the application, I'd conditionally argue otherwise.  While
they've improved them quite a bit, forged pistons still need lots of
clearance which means cold and maybe hot noise, extra oil consumption and
relatively short ring life.  Hypereutetic pistons are almost as strong
as forged but retain the low expansion coefficient of cast.  Unless
the machine is destined for high RPM use or can suffer severe detonation,
I'd not fool with forged.  Extra oil consumption is of particular concern
because oil in the combustion chamber lowers the octane of the mix
and leads to detonation.  Oh, lest I forget.  There seems to be two camps
at diametrical extremes regarding hypereutetic pistons.  One
camp says they're junk.  The other agrees with me.  Several engine
builders I respect as well as the performance branches of many OEMs
recommend hypereutetic.  JGD]

>A friend of mine put them in his Buick GS Stage I motor last year and
>they werebasically destroyed by the end of the summer.  He took it to the
>track only 3
>times that summer.  His 455 is relatively mild with 10.5:1 compression, MSD
>ignition, Mickey Thompson headers, KB107 cam, and B4B intake.  It has run
>13.0s on street tires at 105 mph through the mufflers.

>Anywa, I saw some of the pistons ... one was actually missing pieces of the
>outer edge and the others all showed some degree of cracking or breakage.  The

Could be pinging especially with 10.5:1.....

>spec sheet wasn't included with the pistons from the distributor and the
>machine shop set them up to"normal" clearances, somewhere around 0.020".   (In

Is that normal for _CAST_ pistons?

>fact, NO literature of any kind was in any of the boxes the pistons came in)
>After my friend wrote a letter complaining about the pistons, Federal Mogul,
>who turns out to be the manufacturer, responded that they should have been set
>up at 0.010" (tight!) ... and that they had no control over the aftermarket

That sounds about right for cast.

>distributors, blah, blah, blah.  Basically, a "not our fault" thing.  Kind of
>disappointing that the tone of the letter was so condescending, instead of
>constructive and helpful, since alot of the information concerning set up was
>quite good.

[While the damage he describes sounds like detonation damage, 0.020 clearance
is terribly loose and could lead to skirt cracking or even ring land
breakage as the piston cocks.  My rule for cast piston clearance is
0.001 + (0.001 * diameter_in_inches) for engines I build for others.
This assumes a GOOD hone is used such as the Sunnen SK50 and that a
deck plate is used during the boring and honing operation.  I set my
own engines up tighter because I break the pistons and rings in by
motoring the engine with an electric motor before final assembly and can
catch any tight spots before damage is done.  I get a lot of argument
from some quarters regarding my clearancing practices but experience
has shown my engines last a LONG time when built this way and properly
broken in. JGD]

>My question is ... any opinions on hyperuetectic pistons?  What is their
>advantage over traditional alternatives?  I freely admit that misapplication of
>a product can cause bad results, but then I don't think my friend really knew
>exactly WHY the pistons were supposedly the hot setup for his motor.

Good pistons for Street/strip with out NOx.  But those buicks put out
500 ft-lbs or torque...  maybe he was just pushing it.  Its still a cast
piston.  Try the Keith Black Silvo-lites - also cast but 20% stronger
than normal.  Then go with forged.


From: emory!!rlr (Powdered Toast Man)
X-Source: The Hotrod Mailing list
Date: Jun 1993
Subject: RE: Pistons
X-Sequence: 5629

John "Any Day Now, Trust Me" deArmond sez:

> I set my
>own engines up tighter because I break the pistons and rings in by
>motoring the engine with an electric motor before final assembly and can
>catch any tight spots before damage is done.

  An excellent idea, one I'd like to know a little more about.  Do you
use cutting oil or lapping compound or motor oil on the bores during this
pre-break in?  Or just spin the engine dry?  I've only had experience
rebuilding street engines and know the typical shadetree practice of
honing and assembly.

[I have an old 1/2 hp gearmotor I bought surplus a long time ago.  I think
the output shaft turns 200 rpm or something like that.  It has about a
2" pulley.  I just set the new short block on a stand, install the crank
pulley and vee belt 'em together.  I use moly disulphide powder in STP
for the bottom end assembly lube which stays in place forever until real
oil hits it.  Cylinder lube is just plain old motor oil.  I've tried
several fancy ways of applying oil to the cylinders including making a
manifold that would drip onto each cylinder but the KISS principle works
best.  A couple of shots from an oil can to each cylinder every couple
of hours works fine.  I'll run it for a couple of hours initially or
until the sound changes (the scraping of rings against brand new
hone marks goes away), then remove the pistons and look at them.  Any
tight spots on either the rings or the pistons will have started making
shiny spots on the piston or ring and usually on the cylinder too.
A little sandpaper can smooth a high spot.  after cleaning and reassembly,
I'll run the thing as long as I have the patience for, usually a day.

  Ron "Don't Chuck That Washer Motor, Honey" Rader

From: emory!!behanna (Chris BeHanna)
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: Re: Holed Piston
X-Sequence: 6306

In article <> emory!!ericm (Eric
Murray) writes:

>Chris BeHanna writes:
>>	Question #3:  Does TRW have pistons for motorcycles?  This piece is
>>cast aluminum, about 66mm in diameter.  One side shows severe galling, so I
>>will definitely have to go oversize to do a cleanup bore on the cylinder (so
>>I have to do the same with the other to have a matched set).
>Measure (or have your machinist do it) the inside of the cylinders
>for roundness, taper, and wear.   Measure the pistons also, and
>replace if they're too badly scored or the piston-cylinder clearance is
>out of spec, then replace or rebore and replace.

	As I said, the #1 piston shows severe galling, and I imagine that it
made matching marks on the sleeve (I haven't looked at it since I pulled it
apart the other night).  #1 piston is now a donut with a hole in the crown, so
replacement of the pistons is absolutely required.

[Old improvised tuner's trick:  When a piston seizes like that, most of
the marks on the cylinder walls are actually deposited aluminum and not
scratches.  It can be easily removed.  Simply degrease the cylinder,
position it to where a gall mark is down, facing up, and apply a bit
of common hydrochloric acid (as used to etch bricks).  The HCl consumes
the aluminum much faster than the iron.  The aluminum bits will be gone
in a few seconds while the iron sleeve will be barely discolored.
When the bubbling stops, wash, oil and inspect.  Likely the cylinder will
be in good shape.

Another tip, if you have to have the cylinder bored.  Take it to a shop
that has a Sunnen rod boring machine and have the cylinder finished on that.
The machine is capable of holding the tolerance vastly better than any
small boring setup I've ever seen.  JGD]

From: emory!!dave.williams (Dave Williams)
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: crazy idea: huge 2-stroke engine
X-Sequence: 6313

-> Now what WOULD be wonderful would be an oh, 350 cu inch 12 cylinder 2
-> stroke, perferably an opposed (a la volkswagen) design with a
-> scavenging supercharger instead of crankcase pumping.  Can you just
-> imagine the sound of 12 open expansion chambers at full chat?  Gives
-> me quivers just thinking about it.  JGD]

 <grin>  I think most people must think that one up once they start
getting seriously into engines.  I came up with it, my buddy Jay is
still in love with it, and a couple of other people have mentioned it.

 Of course, the 12 is in perfect primary and secondary balance, while a
flat-six would have the usual corkscrew couples unless you went to a
Lanchester layout, which'd screw your crankcase volume all to hell.

 Now that multipart ceramic/aluminum pistons are no big deal (Isuzu
Diesels have been using them for years) and coatings have improved to
where they usually stay in place, a big two stroke might be practical

 I've also wondered if cast iron pistons might make a comeback.  Modern
nodular-style irons are stronger than aluminum to start with and lose
practically no strength at temperatures that would let you pour an
aluminum piston out of your shoe.  With die casting instead of sand
casting, you could probably come up with a nodular piston weighing
little if any more than aluminum, more thermally stable, and able to
laugh at lean mixtures and detonation.  Even if you couldn't equalize
the weight, it'd be worth losing 1000 RPM or so if you could REALLY
screw up the boost.

[Even better would be a forged piston made from one of the exotic alloys.
Way back in the early 70s one of my cousins was a big wheel metallurgist
manager in the Army Missile Command at Redstone.  He made me a couple of
experimental pistons, one out of titanium and the other out of some
exotic stuff called Maraging 300.  This stuff hardens up to C60 rockwell
and yet stays very ductile and has a yield strength of 300,000 psi.

Anyway, the titanium piston worked but had problems of crown erosion.
I suspect a ceramic coating would solve that problem.  The maraging
piston was Wonderful!  Very thin-walled and lighter than the cast
piston it replaced, it laughed at detonation and leanness.  Even when
the engine was run lean enough to cause it to stick, the stick was
temporary and any damage was to the cylinder wall.  He never did tell
me how he made the piston, though he did say it was the same process
used to make the combustion chamber in the Sidewinder missile.  It
looked forged.  Hehehe, and you thought $600 toilet seats were bad :-)

From: Dave Baker
Subject: Re: what are hypereutectic pistons?
Date: 23 Jul 1999 03:20:14 GMT

>Subject: Re: what are hypereutectic pistons?
>From: Jeb (Jeb)
>They are round, and that's all you need to know.

Actually pistons are not round - they have a significant ovality which varies
over the length of the skirt and is critical to their proper function. It's
only an ovality of about 20 thou but if it wasn't there the piston would seize
in the bore almost immediately. Only the land area which contains the rings is

That's the trouble with trying to be witty - sometimes it just reveals that
even the basic things you assumed you knew turn out to be wrong.

Dave Baker at Puma Race Engines (London - England)  - specialist cylinder head
work, flow development and engine blueprinting. Web page at

From: John De Armond
Subject: Re: Reboring EU2000i was: bypassing low oil warning EU2000i
Date: Fri, 28 Mar 2008 16:25:07 -0400
Message-ID: <>

On Fri, 28 Mar 2008 07:25:01 -0800, "Ulysses" <> wrote:

>Aha!  A motorcycle shop!  Why didn't I thinkof that?
>Yea, I need somone with enough experience to "find" the right size piston.
>I may not cannibalize eu2000 #2 after all.

I think that a bike shop will be a waste of time.  Piston design is too complicated
to have very much chance of finding one off the shelf that will work satisfactorily.

I echo the advice to consult Wiesco.  They specialize in custom motorcycle and other
small engine pistons.  The cost will be a bit more (or maybe not) but you'll get
exactly what you need.

The factors involved in specifying a piston, among others.

Pin height (distance between crown and pin centerline)
Pin diameter
Ring height
Ring width (both parameters very important to prevent ring flutter/breakage at the
desired operating speed)
Ring type
Nominal diameter
Taper (a piston tapers from top to bottom
Barrelness (a piston is barrel-shaped, narrower over the pins than at the skirts.
Alloy - expansion rate
Crown shape (can majorly affect economy)

Taper and barrel are dependent on operating temperature, piston alloy, cast-in
expansion bands or not and velocity, among other things.  The desired end result is a
cylinder of proper clearance at operating temperature.  The parameters are different
for otherwise identical engines.  Watercooled vs air cooled or fan cooled vs free air
cooled, as examples.  These parameters are also dependent on whether the cylinder is
sleeved or chrome on aluminum or some other construct.

Wiesco has decades of experience in making pistons  AND they have a huge database of
engines.  They'll be able to nail what you need dead-on.  They may ask you to ship
them your old piston to take measurements from.

The biggest problem I'm anticipating is finding someone who can bore the cylinder to
the required precision.  The problem is the integral cylinder head.  Precision boring
machines are designed to bore cylinders and not cups.  They need clearance at the far
end for the mandrel to clear.  As does the hone necessary to put the proper finish on
the cylinder for proper ring seating.

I suggest that you first try to find someone who can bore the cylinder before
spending time and effort on locating a piston.  A machine shop with a very high
quality CNC lathe can probably do the basic boring but the surface finish is a
separate task.


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