[DeTomaso] [TPR] Piston Ring Rotation.

[Charles Engles]

Dear Asa,


            The first and second engines I built were done with the standard
ring positioning protocol.  I then learned the truth: the rings *move*
during engine operation.  They do not remain permanently in place.    The
first two engines were with Aussie heads and made 401 and 385 hp.

            The next two engines were built with 4v heads and absolute
carefree disregard for the prime ring directive.  Dyno testing showed 440
and 485 hp.

            I am about to begin the next engine and I will continue with my
laissez-faire piston ring assembly.  It doesn't seem to hurt engine
performance.....!


                  Scientifically yours,  Chuck Engles


Original Message-----
From: tpr-bounces at teampanteraracing.com
[mailto:tpr-bounces at teampanteraracing.com] On Behalf Of Asa Jay Laughton
Sent: Saturday, May 26, 2012 1:59 PM
To: detomaso at list.realbig.com; tpr at teampanteraracing.com
Subject: [TPR] Piston Ring Rotation.

Most of us are aware of the proper ring positioning when assembly an engine:
http://www.351c.info/gallery2/d/218-1/ringspacing.jpg
The two compression rings should be spaced about 30* (or about one inch)
from the front centerline of the piston, one on either side.  The oil ring
segments are the same on the opposite  side of the piston toward the rear.
The illustration above shows this quite well.

But do the rings rotate after assembly?

A few years ago at the POCA Fun Rally, Jack had an expert who was familiar
with pistons.  He said indeed the rings do rotate, so in the end it doesn't
really matter where you index them to start with... 
they're going to move.

Today I recorded the ring locations on my forensics engine.  I had been
careful not to turn the rings on the pistons when I removed the pistons/rods
from the engine previously.  Because I can't insure they didn't move at all,
the relationships below are rounded.  Here are the results.  My "timing" is
from the -front- of the engine, moving clockwise.  The piston position at 12
o'clock is the part facing front, the position at 6 o-clock is at the rear.

The first compression ring is at the top, the second on the bottom.

Piston    1st Comp    2nd Comp    Oil/Oil
#1        8 o-clock   4 o-clock     4/2
#2        10          11           12/3
#3        10          2            10/1  (probably the only one closest 
to installed)
#4        8           8             8/8  (All ring gaps were lined up)

#5        9           2             5/5
#6        12          9             5/5
#7        5           4             6/5
#8        9           3             3/7

As you can see, they are all over the place.  I'll work up a good
illustration and post it later.

Does this mean I won't index them the next time I assemble and engine?  
Actually, I'll most likely still index them when assembling, only because
I'm anal about those things and I do believe spacing them does assist with
initial break in.  If they are spaced the same, I look at that as an easy
path for compression gasses to get past.  In other words, gases might get
past the lower tension oil ring segments and past the gap in the bottom
compression ring but then they'll have to travel around the edge a while
before they meet up with the gap in the upper ring.  In the end, it may not
really matter.

Asa Jay
Pantera Research Institute, Pacific Northwest

--
Asa Jay Laughton, MSgt, USAFR, Retired
&  Shelley Marie
Spokane, WA
******************************
http://www.racingagainstautism.com
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