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Date: Fri, 13 May 2005 13:39:51 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: fuel injector size, O-rings
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kenpowell@comcast.net wrote:

> Engine side:                    Electric side:
> before oring-0.521         0.518
> with oring   -0.569          0.567
>  
> So it looks like both sides are the same since the oring  makes 
> measurement of  'thousands' irrelevant.
> The measurements originally quoted (0.55) was an old Ford injector and 
> the oring had been compressed for years while in the engine.
> Ken Powell
> Bryant, Arkansas
> 501-847-4721
>  


That's perfect. 

I've was looking at the SDS EFI website.  They have a page discussing 
how to build a fuel rail.  They say the "O-ring crush must be .020 to 
.035 for proper sealing".  For the injector bosses, we'd need an inside 
diameter of .535 to .545.  Unfortunately, I don't have a lathe.  I have 
access to one, but scheduling to get to it is sometimes a hassle.

So was in the workshop last night measuring a lot of different sizes of 
scrap tube.  5/8x.035 seemed like a good candidate.  Inside diameter is 
.550, is a little large.  Neither squeezing it between thumb and 
forefinger or the old Jedi mind trick seemed to work.  What to do?

There was an old blade from my tube cutter laying there on the bench.  
Those work great on 4130 when building a from plans tube airplane.  Cuts 
the tube nice and square, but the steel does tend to eat up the blades.  
Knocks little chips off of the sharp part of the cutter.  Should've 
thrown that one away a long time ago.  I used it on a thick piece of 
tube, and actually rounded off the blade edge.  Hmm?

Instead of throwing it away, I put a bolt through the center and chucked 
it in the drill press.  Used a file, then a stone to completely round 
off and smooth the sharp edge.  Swapped the blade into the tube cutter.  
Now it's a tube roller.  Dialed in a couple of turns of pressure, rolled 
it around the tube.  Not very easy.  Tube just wants to roll in my 
hand.  Grab my 'tube holder', one of those excercise straps made out of 
surgical rubber.  You see them in all the aerobics classes.  Hmm, 
haven't been to one of those in a while.  Wrap a few turns around the 
tube.  The rubber grabs the tube and increases the diameter to give the 
hand something to hold onto.  Now I can use the new roller with ease, 
dialing in the perfect diameter.  Just a couple passes and then move 
down the tube just slightly and make a couple more passes.  Now theres a 
little valley for the O-ring to fall into.  The injector sort of 'pops' 
into place.

That's perfect.

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