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<body class='hmmessage'>Sounds like what I was attempting to describe, but Mike McCormick's write up is better......<BR>
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Mike Cohen<BR><BR><BR><BR><BR>
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From: k6xyz@sbcglobal.net<BR>To: nsrca-discussion@lists.nsrca.org<BR>Date: Mon, 14 Jul 2008 22:20:42 -0500<BR>Subject: Re: [NSRCA-discussion] 120 AC issues UPDATE<BR><BR><BR>
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<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'">Stuart…..here is an old email from </SPAN></FONT><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'">Mike</SPAN></FONT><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"> McCormick that is interesting.</SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"> </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'">>>>></SPAN></FONT><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Because the YS piston compresses in both the up and down stroke, the ring is </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">serving double duty. It must not only seal the mixture being compressed, but </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">it must also separate the two compressed mixtures. Once the piston begins to </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">rock and the ring loses its seal, then surge begins. If you think about it, </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">the YS engines with the highest compression are the most problematic (SC and </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">the L; the L is really just an SC version of the FZ). Why do the pistons </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">rock? No side wall. Plus (as Dick stated) the pistons are made of soft 2017 </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">aluminum and will wear quickly (especially if the engine is run lean or fuel </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">with low oil content is used). This piston design has been in use since the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">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=EC_MsoNormal><B><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Piston and cure the ill's.</SPAN></FONT></B><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'"> FYI, I once did a test on an AC just to see how </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">much more boost the AC piston created vs the FS piston; it was less than 1/4 </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">psi! I also noticed that any engine in which I installed a FS piston ran </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">better than it did with the compound type piston. I figured this occured </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">because the FS piston ran "truer" in the bore; it created less drag because </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">it was less prone to rock or cock in the bore (more side wall). But along </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">comes the 1.4 and we no longer have the FS piston to fall back on, Plus the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">1.4 piston was shorter and bigger in diameter,i.e, more rocking force </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">(around) the wrist pin is created and there is less length to stabilize the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">force. Things didn't get too bad until YS increased the compression of the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">engine (L version) and then the piston really started to get beat up. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Because of the higher compression, the ring seal is even more important and </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">the piston/ring fit has to be right for the engine to perform optimally. And </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">the optimal fit is within a narrow range. I set the piston/sleeve clearance </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">at .003 to .0035". Max clearance is .005" .0035" is tight, and engines I </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">set up must be run rich for a long time to properly break in. I also set the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">ring end gap as tight as I can get it, usually at .0055", though I like it </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">best if I can get it at .003". But when set up at these clearances and run </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">rich, they will last 500 plus flights.</SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">So what is boils down to is the old piston is soft and has very little side </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">wall. The forces on the piston are high and attack it from both ends. This </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">creates high side forces on the piston. The minimum side wall works hard to </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">keep the piston straight, but even in the best of conditions (running the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">engine rich and using lots of oil) it is a losing proposition for the piston. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'"> The new piston has 4 times as much side wall area under the ring groove </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">(where the old style piston experienced the greatest forces and therefore the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">most wear). It runs very smoothly and I believe this is because it too tends </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">to run very true in the bore. I am sure it will last longer because of the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">increased side wall area. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Sorry for the length of this reply, and I hope it answers your question. But </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">heck while I am at it I might quickly address one other issue I see a lot of </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">problems with. Many flyers tend to set the mixtures too lean on 1.4's. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Because of the different plumbing in these engines, the regulators do not </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">respond as quickly as did those on 1.2's. To set these, you must do it </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">slowly and wait a few seconds for the regulator to equalize with the change. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">If you move the needle quickly, and not wait it is very possible to get a </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">false reading on the mixture and usually it ends up too lean. Kills the </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">engine quickly. </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'"> </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'">Mike</SPAN></FONT><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'"> McCormick<<<<<</SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"> </SPAN></FONT></P>
<P class=EC_MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"> </SPAN></FONT></P>
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<FONT face="Times New Roman" color=blue 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><BR></DIV>
<P class=EC_MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma">-----Original Message-----<BR><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> nsrca-discussion-bounces@lists.nsrca.org [mailto:nsrca-discussion-bounces@lists.nsrca.org] <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 face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma">Monday, July 14, 2008</SPAN></FONT><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma"> </SPAN></FONT><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma">10:07 PM</SPAN></FONT><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma"><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> adriancwong@earthlink.net; </SPAN></FONT><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma">General pattern discussion</SPAN></FONT><FONT face=Tahoma color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: Tahoma"><BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [NSRCA-discussion] 120 AC issues UPDATE</SPAN></FONT></P>
<P class=EC_MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" color=black size=3><SPAN style="FONT-SIZE: 12pt"> </SPAN></FONT></P>
<P class=EC_MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" color=black 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><br /><hr />It’s a talkathon – but it’s not just talk. <a href='http://www.imtalkathon.com/?source=EML_WLH_Talkathon_JustTalk' target='_new'>Check out the i’m Talkathon.</a></body>
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