Not wanting to be the next Cirrus Engine failure

bnt83 said:
Still waiting... :-D
Click to expand...


Whoops... Here are the photos.
Sorry, my thumb got in part of the second one.

Here is a photo of the complete assembly.
Try not to get too caught up on the photo quality. I have a really nice camera.
pinwsleeve.jpg
This one is with the sleeve removed. You can really see the fracture here.

pinwosleeve.jpg
 
I tried to have my engineering department autocad that for you but they just kept giggling.


Sent from my iPhone using Tapatalk
 
Sorry for the delay.
Here is the broken Pin.

Scary stuff...

wp1.jpg

wp2.jpg

wp3.jpg

wp4.jpg
 
Hard to tell from the picture, but the dark spots on the end of the break look like inclusions, or defects in the metal. They would act as stress concentrators where a crack would begin and get larger as it is hammered thousands of times per minute as the engine runs. Scary stuff, glad you found it before it all came apart.
 
Well, you can see how the fracture proceeded in stages over time which makes you think of a defect in the steel as a stress riser.
But far more interesting to me than the fracture are the wear marks on the surface of the pin. It looks like the pin possibly became tight inside of the piston on one end after a period of time and quit rotating (or rotated very slowly after that) From then on most of the rocking motion between the pin and the piston/rod occurred inside of the connecting rod leading to localized heating. This would result in a slight cocking of the piston in the bore and repetitive asymmetrical sideways rocking stress for the pin.
As opposed to symmetrical stress where the pin takes on a smooth bow shape under the thrust of the firing stroke - the outer ends of the pin are under compression downwards and the middle is under compression upwards from the connecting rod pushing back. The elastic bending then relaxes and the pin rotates slightly as the firing stroke ends, so that the bowing is distributed around and around over time.
 
I have never seen a wrist pin with an inner pin!
In this case the real wrist pin is intact, but that extra inner pin fractured and broke,
probably pushing out on the keeper buttons to cause cylinder wall problems... is that what i think is goin on?????
 
This engine was less than 12 years old and under the hourly TBO?
 
SixPapaCharlie said:
Whoops... Here are the photos.
Sorry, my thumb got in part of the second one.

Here is a photo of the complete assembly.
Try not to get too caught up on the photo quality. I have a really nice camera.
pinwsleeve-jpg.45292

This one is with the sleeve removed. You can really see the fracture here.

View attachment 45293
Click to expand...
pinwsleeve-jpg.45292

pinwosleeve-jpg.45293

honestly....those sketches don't do justice. :D
 
Dr. O said:
Well, you can see how the fracture proceeded in stages over time which makes you think of a defect in the steel as a stress riser.
But far more interesting to me than the fracture are the wear marks on the surface of the pin. It looks like the pin possibly became tight inside of the piston on one end after a period of time and quit rotating (or rotated very slowly after that) From then on most of the rocking motion between the pin and the piston/rod occurred inside of the connecting rod leading to localized heating. This would result in a slight cocking of the piston in the bore and repetitive asymmetrical sideways rocking stress for the pin.
As opposed to symmetrical stress where the pin takes on a smooth bow shape under the thrust of the firing stroke - the outer ends of the pin are under compression downwards and the middle is under compression upwards from the connecting rod pushing back. The elastic bending then relaxes and the pin rotates slightly as the firing stroke ends, so that the bowing is distributed around and around over time.
Click to expand...
Checkout_my_Six said:
pinwsleeve-jpg.45292

pinwosleeve-jpg.45293

honestly....those sketches don't do justice. :D
Click to expand...
Sixie, are you channelling that Bobbitt dude again?
 
I think those first "photos" are really good approximations, nice job. Even the thumb looks correct.
 
robert lomax said:
I have never seen a wrist pin with an inner pin!
In this case the real wrist pin is intact, but that extra inner pin fractured and broke,
probably pushing out on the keeper buttons to cause cylinder wall problems... is that what i think is goin on?????
Click to expand...

I wouldn't consider the inner part to be "extra" or that the "real" wrist pin is still intact. It looks to me like the inner part is a structural piece of the wrist pin to me, and that its lack of integrity possibly caused the remaining part of the pin to flex and caused the heating marks on it.
 
What was the finally outcome? Did you check the other 3 cylinders?
 
.....and was Savvy helpful?
 
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