X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mx2.netapp.com ([216.240.18.37] verified) by logan.com (CommuniGate Pro SMTP 5.4c2o) with ESMTPS id 4885245 for flyrotary@lancaironline.net; Mon, 28 Feb 2011 12:18:17 -0500 Received-SPF: softfail receiver=logan.com; client-ip=216.240.18.37; envelope-from=echristley@nc.rr.com X-IronPort-AV: E=Sophos;i="4.62,240,1297065600"; d="scan'208";a="524215626" Received: from smtp1.corp.netapp.com ([10.57.156.124]) by mx2-out.netapp.com with ESMTP; 28 Feb 2011 09:17:26 -0800 Received: from [10.62.16.200] (ernestc-laptop.hq.netapp.com [10.62.16.200]) by smtp1.corp.netapp.com (8.13.1/8.13.1/NTAP-1.6) with ESMTP id p1SHHQoE015336 for ; Mon, 28 Feb 2011 09:17:26 -0800 (PST) Message-ID: <4D6BD8A1.8080904@nc.rr.com> Date: Mon, 28 Feb 2011 12:17:21 -0500 From: Ernest Christley Reply-To: echristley@nc.rr.com User-Agent: Thunderbird 2.0.0.24 (X11/20100623) MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Steve Boese TDC Finder References: In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: quoted-printable Al Gietzen wrote: > > When I got my 20B with a 12A front housing from Atkins, the=20 > relationship of the pointer to the marks on the pulley made no sense.=20 > I used my simple method to determine a TDC mark, and worked from=20 > there. On the dyno we put a pressure transducer into a trailing plug=20 > hole and adjusted timing a bit while operating (I don=92t recall=20 > conditions =96 I think 22=94 MAP) to get the pressure trace to look rig= ht.=20 > We chose a point 2 steps retarded on the EC2, - 3.75^o . > > Subsequently I did some variation at cruise conditions to see effect=20 > on performance, and again ended up at two steps of retarding, although = > I found performance change almost undetectable over a 3-4 step range=20 > (~7^o ) to either side. So that setting is pretty consistent with=20 > Lynn=92s data that the method leads to a TDC that was a bit BTDC; but i= s=20 > of no consequence. > > That=92s my story, and I=92 sticking to itJ. > > Al > Let me offer this idea. If you know where the tip seals are, then you=20 can derive TDC. Level the base of the engine, and the tip seals should=20 line up verically. Pull the trailing plug, rotate the shaft until the=20 tip seal shows up in the first chamber, then make a mark on the starter=20 ring gear. Rotate the engine until the next seal shows up, and make=20 another mark. Count teeth to get the center one, or make the two marked=20 teeth line up vertically. This would eliminate the importance of the=20 spark plug hole location.