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The engine won't stop - now what?

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The engine won't stop - now what?

Old 17th Oct 2020, 23:00
  #21 (permalink)  
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papa_sierra,

Definitely a fatigue failure due to, what is in my opinion, poor design. Here's a picture of the mixture cable in the ICO position:




The mixture control wire goes through a hole in the vertical pin which passes through the aluminum washer and then through the gold coloured mixture arm. The castellated nut at the bottom pulls the pin and therefore the wire down onto the washer. In order to fix the wire without clamping the assembly to the mixture arm, the washer has a concave top, so that the wire is bent as it passes over the edge of the washer and then bent again as it goes through the hole in the pin. Significant potential for fatigue failure at the contact points.
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Old 18th Oct 2020, 09:54
  #22 (permalink)  

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The clamp for the outer cable seems to be fixed very close to the end. Because the arm swings through an arc each time it operates, a side load is applied to the inner cable. If the clamp were fixed further away, it would allow a small amount of flex, reducing the side load on the inner.
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Old 18th Oct 2020, 13:40
  #23 (permalink)  
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In I42's photo, the sheath of the cable appears clamped too closely to the end. Unusually they're clamped 4" - 6" back or so, so the sheath can flex. And that whole crimping washer assembly must pivot freely in the bronze arm when it's done up and cotter pinned.
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Old 18th Oct 2020, 14:28
  #24 (permalink)  
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Well spotted you two. I forgot to mention that what you are seeing is a temporary fix, using the old, broken cable. Pawnee mixture cables, being about 10’ long, are not a local “off the shelf” item.

We will replace it during the winter, along with the throttle cable, for good measure.
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