<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt">I am following this discussion with interest. I have similar issues with a 140DZ. Runs great on the bench, but quits about 50% of the time after the final spin in Masters. It acts like you turned it off with a switch, will not respond to throttle and just kind of spins down. The motor was used but ran well for the previous owner and was freshly factory rebuilt.<br><br>I tried new plugs, a header tank, finally a new fuel pump. Nothing worked. In the end I replaced it with a 160, which has run like a clock in the same airframe. I removed the header tank, it was not needed. <br><br>I too suffered through the dreaded piston rock problem. That was "cured" in the 140's by either replacing the piston with a DZ piston or drilling 5 or so small gas ports from the
top of the piston to the backside of the ring grove. It is not hard, a drill press will do. I don't remember the exact drill size ( around a number 77 or so) but it is not all that critical. <br><br>I am going to get back to that 140DZ after the NATS, it is a shame for such a beast to languish in a box.<br>If I come up with anything I'll report it here.<br><br><div> </div>Bob Kane<br>getterflash@yahoo.com<div><br></div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">----- Original Message ----<br>From: Stuart Chale <schale@optonline.net><br>To: General pattern discussion <nsrca-discussion@lists.nsrca.org><br>Sent: Tuesday, July 15, 2008 8:02:46 AM<br>Subject: Re: [NSRCA-discussion] 120 AC issues UPDATE<br><br>
Interesting email.<br>
I guess in the betterment of science I should do one more test with a
different piston/ring in the offending engine before swapping it out
totally for another motor.<br>
I am getting tired of pulling apart motors though.<br>
What I really want to know is how to measure those gaps :)<br>
I tried but the best I good get was somewhere between 0 and 1 mm with
my rulers :)<br><br>
Stuart<br><br>
Dave Harmon wrote:
<blockquote type="cite"><style>
<!--
_filtered {font-family:Tahoma;panose-1:2 11 6 4 3 5 4 4 2 4;}
_filtered {font-family:"Comic Sans MS";panose-1:3 15 7 2 3 3 2 2 2 4;}
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;margin-bottom:.0001pt;font-size:12.0pt;font-family:"Times New Roman";color:black;}
a:link, span.MsoHyperlink
{color:blue;text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{color:blue;text-decoration:underline;}
p
{margin-right:0in;margin-left:0in;font-size:12.0pt;font-family:"Times New Roman";}
pre
{margin:0in;margin-bottom:.0001pt;font-size:10.0pt;font-family:"Courier New";color:black;}
span.EmailStyle18
{font-family:"Comic Sans MS";color:blue;font-weight:normal;font-style:normal;text-decoration:none none;}
_filtered {margin:1.0in 1.25in 1.0in 1.25in;}
div.Section1
{}
-->
</style> <div class="Section1"><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;">Stuart…..here
is an old email from </span></font><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;">Mike</span></font><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;">
McCormick that is interesting.</span></font></p><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;"> </span></font></p><p class="MsoNormal" style=""><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;">>>>></span></font><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">Because
the YS piston compresses in both the up and down
stroke, the ring is </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">serving
double duty. It must not only seal the mixture being
compressed, but </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">it
must also separate the two compressed mixtures. Once the
piston begins to </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">rock
and the ring loses its seal, then surge begins. If you
think about it, </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">the
YS engines with the highest compression are the most
problematic (SC and </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">the
L; the L is really just an SC version of the FZ). Why do
the pistons </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">rock?
No side wall. Plus (as Dick stated) the pistons are
made of soft 2017 </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">aluminum
and will wear quickly (especially if the engine is
run lean or fuel </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">with
low oil content is used). This piston design has been
in use since the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">AC
and always been a pain. But in the 1.2's we could alway <b><span style="font-weight: bold;">install an FS </span></b></span></font></p><p class="MsoNormal" style=""><b><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext; font-weight: bold;">Piston
and cure the ill's.</span></font></b><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">
FYI, I once did a test on an AC
just to see how </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">much
more boost the AC piston created vs the FS piston; it
was less than 1/4 </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">psi!
I also noticed that any engine in which I installed a
FS piston ran </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">better
than it did with the compound type piston. I figured
this occured </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">because
the FS piston ran "truer" in the bore; it
created less drag because </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">it
was less prone to rock or cock in the bore (more side
wall). But along </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">comes
the 1.4 and we no longer have the FS piston to fall
back on, Plus the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">1.4
piston was shorter and bigger in diameter,i.e, more
rocking force </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">(around)
the wrist pin is created and there is less length to
stabilize the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">force.
Things didn't get too bad until YS increased the
compression of the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">engine
(L version) and then the piston really started to get
beat up. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">Because
of the higher compression, the ring seal is even more
important and </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">the
piston/ring fit has to be right for the engine to perform
optimally. And </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">the
optimal fit is within a narrow range. I set the
piston/sleeve clearance </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">at
.003 to .0035". Max clearance is .005"
.0035" is tight, and engines I </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">set
up must be run rich for a long time to properly break
in. I also set the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">ring
end gap as tight as I can get it, usually at
.0055", though I like it </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">best
if I can get it at .003". But when set up at these
clearances and run </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">rich,
they will last 500 plus flights.</span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">So
what is boils down to is the old piston is soft and has
very little side </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">wall.
The forces on the piston are high and attack it from
both ends. This </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">creates
high side forces on the piston. The minimum side
wall works hard to </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">keep
the piston straight, but even in the best of conditions
(running the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">engine
rich and using lots of oil) it is a losing proposition
for the piston. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;"> The
new piston has 4 times as much side wall area under the
ring groove </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">(where
the old style piston experienced the greatest forces
and therefore the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">most
wear). It runs very smoothly and I believe this is
because it too tends </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">to
run very true in the bore. I am sure it will last longer
because of the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">increased
side wall area. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">Sorry
for the length of this reply, and I hope it answers
your question. But </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">heck
while I am at it I might quickly address one other issue
I see a lot of </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">problems
with. Many flyers tend to set the mixtures too lean
on 1.4's. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">Because
of the different plumbing in these engines, the
regulators do not </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">respond
as quickly as did those on 1.2's. To set these, you
must do it </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">slowly
and wait a few seconds for the regulator to equalize
with the change. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">If
you move the needle quickly, and not wait it is very
possible to get a </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">false
reading on the mixture and usually it ends up too
lean. Kills the </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">engine
quickly. </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;"> </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">Mike</span></font><font color="black" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: windowtext;">
McCormick<<<<<</span></font></p><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;"> </span></font></p><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style="font-size: 10pt; color: blue;"> </span></font></p><div><p><font color="blue" face="Times New Roman" size="2"><span style="font-size: 10pt; color: blue;">Regards<br><br>
Dave Harmon<br>
NSRCA 586<br>
K6XYZ[at]sbcglobal[dot]net<br>
Sperry, Ok.</span></font><font color="blue"><span style="color: blue;"></span></font></p></div><p class="MsoNormal" style="margin-left: 0.5in;"><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;">-----Original
Message-----<br><b><span style="font-weight: bold;">From:</span></b> <a rel="nofollow" class="moz-txt-link-abbreviated" ymailto="mailto:nsrca-discussion-bounces@lists.nsrca.org" target="_blank" href="mailto:nsrca-discussion-bounces@lists.nsrca.org">nsrca-discussion-bounces@lists.nsrca.org</a>
[<a rel="nofollow" class="moz-txt-link-freetext" ymailto="mailto:nsrca-discussion-bounces@lists.nsrca.org" target="_blank" href="mailto:nsrca-discussion-bounces@lists.nsrca.org">mailto:nsrca-discussion-bounces@lists.nsrca.org</a>] <b><span style="font-weight: bold;">On Behalf Of </span></b>Stuart Chale<br><b><span style="font-weight: bold;">Sent:</span></b> </span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;">Monday,
July 14, 2008</span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;"></span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;">10:07
PM</span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;"><br><b><span style="font-weight: bold;">To:</span></b> <a rel="nofollow" class="moz-txt-link-abbreviated" ymailto="mailto:adriancwong@earthlink.net" target="_blank" href="mailto:adriancwong@earthlink.net">adriancwong@earthlink.net</a>; </span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;">General
pattern discussion</span></font><font color="black" face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; color: windowtext;"><br><b><span style="font-weight: bold;">Subject:</span></b> Re:
[NSRCA-discussion]
120 AC issues UPDATE</span></font></p><p class="MsoNormal" style="margin-left: 0.5in;"><font color="black" face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p><p class="MsoNormal" style="margin-left: 0.5in;"><font color="black" face="Times New Roman" size="3"><span style="font-size: 12pt;">I have
been mostly using
Cool Power 15%, but tried 30% heli today with the same results. No
special YS blends available locally.<br>
This plane is for my son to fly. Sure makes my electric Beryll seem
real
easy :)<br>
Stuart<br><br>
</span></font></p></div><pre><hr size="4" width="90%"><br>_______________________________________________<br>NSRCA-discussion mailing list<br><a rel="nofollow" class="moz-txt-link-abbreviated" ymailto="mailto:NSRCA-discussion@lists.nsrca.org" target="_blank" href="mailto:NSRCA-discussion@lists.nsrca.org">NSRCA-discussion@lists.nsrca.org</a><br><a rel="nofollow" class="moz-txt-link-freetext" target="_blank" href="http://lists.nsrca.org/mailman/listinfo/nsrca-discussion">http://lists.nsrca.org/mailman/listinfo/nsrca-discussion</a><br></pre></blockquote></div></div></div><br>
</body></html>