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Opinion on SB M20-282A


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Yesterday I had Lasar overhaul my landing gear mechanism per the SB (Lasar's new ownership seems to be on the path to improvement and expansion, by the way) and want to reinforce what one of the posters said on a long ago thread on the subject.  

His view, distilled, was that  a steel spring properly engineered and manufactured should last forever.  Replacing at 1,000 hours was silly given good engineering/manufacturing.

Well, based on a single datapoint I wholeheartedly agree.  The attached spring just got removed after 3,700 hours of operation.  Looks good, both to the naked eye and under 10X power.  

What do you think?

 

image.jpeg

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After 1100 hours, I could see microscopic damage around the bend of one side under a 100x microscope.  Was it about to fail? I don't think so but I did it and will be happy to replace it again after 1000 hours because not all the springs are made the same.

In addition, the brass clutch was badly damaged and I am not sure how much longer it would have worked if there was an emergency.

Just my few cents on this.  

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My M20J has about 4550 hours. Looking back, the first and only time the spring was changed in my plane was at about 2500 hours and I don't know the circumstances surrounding that change (were the gears chattering? etc.). So at ~2050 hours, I was due. There are so many hard feelings on each side of this SB (to change or not). Ultimately, after as much reading as I could find, I decided to go ahead and change the spring at my first annual this year while at a MSC. I figured going 2x the recommendation was good enough and now I'll hopefully never have to change it again. The plane was already at a MSC and I'd rather have them doing that work (who knows if I'll be able to bring it by there every year). I also got a thorough inspection of the gear and piece of mind at the same time. Now, if I go to resell, and the prospective buyer insists on this SB (and does a little more research than I), its already done. 

I couldn't help but wonder what an insurance company would do if, on some rare occurrence, that spring failed and they saw you had gone significantly beyond "recommendation" on the SB. I know "recommendations" are just that, and they'd probably pay up. But what about continued insurance after the fact? Nice rate hike?  Not to mention the lost value and hassle of fixing the plane.

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On 6/7/2017 at 0:18 AM, RobertE said:

 

His view, distilled, was that  a steel spring properly engineered and manufactured should last forever.

 

Did the new one meet this criteria, or not?

Because many did not meet this criteria, as evidenced by the increased surface cracks visually observed over time.

The part of the spring that is affected seems to be the area that gets the heat treatment for bending the loop/bend at the end... expect this particular stretched surface to show the detail...

The follow-up question... how does one know they got a good spring without taking it apart? Is There even an answer to this?

Did you put the good old one back in service?

Best regards,

-a-

Edited by carusoam
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8 hours ago, carusoam said:

Did the new one meet this criteria, or not?

Because many did not meet this criteria, as evidenced by the increased surface cracks visually observed over time.

The part of the spring that is affected seems to be the area that gets the heat treatment for bending the loop/bend at the end... expect this particular stretched surface to show the detail...

The follow-up question... how does one know they got a good spring without taking it apart? Is There even an answer to this?

Did you put the good old one back in service?

Best regards,

-a-

You know, this is a much debated topic that I probably shouldn't have refreshed with my comments.  In any event, I put in the new part and kept the old.  I can see no difference between the two, however, including under magnification.  I complied with the SB not because of my concern about the spring but, rather, because I feared that at some point the motor would burn out (one poster had his die after about 3,500 hours and I've got 3700 on mine).  Unfortunately, the motor got sent back to the overhaul shop so I don't know it's condition.

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