Bent push rod, a birds nest and now missing fuel

[Skip Miller]

No.

Those tubes contain a pushrod. If the valve sticks, the force of the tappet will push and bend the rod, which in turn bends the tube.

THIS!

Skip

 

[Bell206]

Undoubtedly, the reason a tube bends is because of excess heat.

Not quite. Perhaps a picture might explain a little as it appears you have limited experience with aircraft engines. As mentioned above, the tube bends due to mechanical force when the camshaft lobe (bumps on big lateral shaft) push on the tappet (flat disc touching cam lobe) which applies mechanic force to the pushrod. If the valve is stuck push rod bends then tube. No chance for heat to build up. Link to full motion below.

 

[MajorTurbulence]

Uh.....excuse me, but WTH?



No.

Those tubes contain a pushrod. If the valve sticks, the force of the tappet will push and bend the rod, which in turn bends the tube.

Thanks for correcting the underlying premise.​

 

[FastEddieB]

Reposting this...

The valve (I think it’s usually the exhaust valve) seizes in its guide. The cam lobe tries to open it on the exhaust stroke, but can’t so the pushrod bends. In my case, the pushrod tube hammered back and forth, damaging the ends and leading to some oil loss - when I first deplaned and saw oil all over the nosewheel fairing, my first fear was that I had left the oil cap off. But opening the cowl, the problem was immediately obvious.

 

[Salty]

Well, technically, the tube bent, because the rod bent, because the valve stuck, because of excess heat. So technically he's right, but not for the reason he thought.

 

[Dan Thomas]

One other thought about inspection of the valve tubes. Undoubtedly, the reason a tube bends is because of excess heat. Unfortunately in the OP’s photo, the condition of the other visible valve tube shows flaking paint, similar to that on the bent tube. If your airplane engine has a nice uniform paint job, can flaking or discoloration of paint on the tube be a telltale of increased frictional force or slop with a resultant heat buildup on that tube giving an early indication of a problem with that valve before bending and failure?

The pushrod never touches the tube until it bends. There's plenty of clearance in there. The rod is supported entirely by its ends at the lifter and rocker.

 

[nrpetersen]

Technically the pushrod (and its housing) buckles, not bends.

 

[Capt. Geoffrey Thorpe]

I can't find the STC for this mod...