<DIV>Stu,</DIV> <DIV> You have to measure the piston with an inside micrometer and the sleeve with a bore gauge. Ideally the sleeve should be installed in the case and if you're really anal, something called a "torque plate" should be bolted to the deck. The torque plate is nothing more than a thick piece of aluminum or cast iron with a hole slightly larger than the bore and a thickness sufficient to handle the head bolt torque. It simulates the head being installed. This is important. The cylinder will change shape as the head bolts are tightened. You must measure the cylinder / sleeve at several points: top, middle and bottom. At each point you should measure both ways: in line with the thrust and in line with the crank axis. The piston should be measured at it's widest point. This is usually close to the bottom (skirt area) in the the thrust axis. I'm pretty sure YS pistons aren't cam ground but measure it in a few places just to make sure it's not horribly
distorted.</DIV> <DIV> </DIV> <DIV>Take everything to a good machine shop - they'll have the tools to do this. This stuff is small so an automotive machine shop probably won't have a bore gauge small enough to measure the sleeve. You might get lucky though. A motorcycle shop might be a better choice.</DIV> <DIV> </DIV> <DIV>You can't stop now - we all want to know what's going on! :)</DIV> <DIV> </DIV> <DIV>BTW - If you really want to stop fiddling with this stuff, you could buy your son a nice, new OS 120Ax. <LOL> </DIV> <DIV> </DIV> <DIV>John Pavlick<BR><BR><B><I>Stuart Chale <schale@optonline.net></I></B> wrote:</DIV> <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid">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"> <META content="Microsoft Word 10 (filtered)" name=Generator> <STYLE> <!-- /* Font Definitions */ @font-face {font-family:Tahoma; panose-1:2 11 6 4 3 5 4 4 2 4;} @font-face {font-family:"Comic Sans MS"; panose-1:3 15 7 2 3 3 2 2 2 4;} /* Style Definitions */ 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;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in;} div.Section1 {page:Section1;} --> </STYLE> <DIV class=Section1> <DIV class=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></DIV> <DIV class=MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt;
COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"></SPAN></FONT> </DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV
class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV>
<DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=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></DIV> <DIV class=MsoNormal><FONT face="Comic Sans MS" color=black size=2><SPAN style="FONT-SIZE: 10pt; COLOR: windowtext; FONT-FAMILY: 'Comic Sans MS'"></SPAN></FONT> </DIV> <DIV class=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></DIV> <DIV class=MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"></SPAN></FONT> </DIV> <DIV class=MsoNormal><FONT face="Comic Sans MS" color=blue size=2><SPAN style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: 'Comic Sans MS'"></SPAN></FONT> </DIV> <DIV> <DIV><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></DIV></DIV> <DIV class=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> <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 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> <A class=moz-txt-link-abbreviated href="mailto:adriancwong@earthlink.net">adriancwong@earthlink.net</A>; </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></DIV> <DIV class=MsoNormal style="MARGIN-LEFT: 0.5in"><FONT face="Times New Roman" color=black size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </DIV> <DIV class=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></DIV></DIV><PRE wrap=""><HR width="90%" SIZE=4> _______________________________________________ NSRCA-discussion mailing list
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