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Date: Mon, 28 Feb 2011 13:47:28 -0500
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Steve Boese TDC Finder
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Al Gietzen wrote:
>>  Al
> 
>>
> 
>  
> 
> Let me offer this idea. If you know where the tip seals are, then you
> 
> can derive TDC. Level the base of the engine, and the tip seals should
> 
> line up verically. Pull the trailing plug, rotate the shaft until the
> 
> tip seal shows up in the first chamber, then make a mark on the starter
> 
> ring gear. Rotate the engine until the next seal shows up, and make
> 
> another mark. Count teeth to get the center one, or make the two marked
> 
> teeth line up vertically. This would eliminate the importance of the
> 
> spark plug hole location.
> 
>  
> 
> I'm not sure I understand this; but it suggests the assumption that the
> 
> TDC position is at the trailing plug hole. - which I don't think is correct.
> 
>  
> 
> Al
> 
>  
> 

I'm suggesting that TDC will find the opposing tip seals lined up vertically.  The first step is to mark the location of 
the seals on an externally accessible surface (the starter ring gear being acceptable), and then use those marks to set 
the vertical alignment.