<HTML><head><meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"><meta http-equiv="Content-Type" content="text/html; "><meta name="Generator" content="Microsoft Word 10 (filtered)"></head><body bgcolor="#ffffff" text="#000000"><span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial; FONT-WEIGHT:Normal;">Ran into the same issue with a 120 my Dad has. New piston and ring solved the surging and power issue, then we found that the needle valve body was so worn, we couldn't get it set lean enough. Also found that the rod was cracked. That engine was tired but ran great after we repaired it.<br><br>Jon Lowe</span><br><br><hr><span style="font-size:10pt;font-family:Tahoma; font-weight:bold">From: </span><span style="font-size:10pt;font-family:Tahoma; font-weight:normal;">Stuart Chale <schale@optonline.net></span><br><span style="font-size:10pt;font-family:Tahoma; font-weight:bold">Sent: </span><span style="font-size:10pt;font-family:Tahoma; font-weight:normal;">Tuesday, July 15, 2008 7:02 AM</span><br><span style="font-size:10pt;font-family:Tahoma; font-weight:bold">To: </span><span style="font-size:10pt;font-family:Tahoma; font-weight:normal;">General pattern discussion <nsrca-discussion@lists.nsrca.org></span><br><span style="font-size:10pt;font-family:Tahoma; font-weight:bold">Subject: </span><span style="font-size:10pt;font-family:Tahoma; font-weight:normal;">Re: [NSRCA-discussion] 120 AC issues UPDATE</span><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 cite="mid:014f01c8e629$c4ffdf90$b360f404@skunkputer" type="cite"><style>
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</style><div class="Section1"><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; color: blue;'>Mike</span></font><font color="blue" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; color: blue;'> </span></font></p><p class="MsoNormal" style=""><font color="blue" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; color: blue;'>>>>></span></font><font color="black" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; 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; font-family: "Comic Sans MS"; color: windowtext;'> </span></font></p><p class="MsoNormal" style=""><font color="black" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; color: windowtext;'>Mike</span></font><font color="black" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; color: windowtext;'> McCormick<<<<<</span></font></p><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; color: blue;'> </span></font></p><p class="MsoNormal"><font color="blue" face="Comic Sans MS" size="2"><span style='font-size: 10pt; font-family: "Comic Sans MS"; 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:16px"><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 class="moz-txt-link-abbreviated" href="mailto:nsrca-discussion-bounces@lists.nsrca.org">nsrca-discussion-bounces@lists.nsrca.org</a> [<a class="moz-txt-link-freetext" 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 class="moz-txt-link-abbreviated" 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:16px"><font color="black" face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p><p class="MsoNormal" style="margin-left:16px"><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 wrap=""><hr size="4" width="90%">
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