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M20J Corrosion red flags


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Hi guys, I've been doing extensive searches to find a good clean J to purchase. It seems like every time I find a decent one with all avionic updates etc I'm seeing what appears to be corrosion on the yoke rod, mixture rod, or door stop bar. Would this be a sign of bigger corrosion issues or is this just normal?

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My 231 had a quite some surface corrosion on the yoke rods. With a bit of work, this was polished to a "like new" mirror-like sheen. I would expect that high gloss steel surfaces deteriorate, particularly in moist climatic conditions. (Corrosion on structural aluminum components is a different story.) I wonder if there is a good way to protect the rods going forward.

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Really no way to tell without pulling some interior panels and/or some inspection plates in the wings. But many of us who are a bit OCD (or CDO, if written properly) about our planes would probably have cleaned up those spots before we put it on the market. A logbook entry stating SB 208B was completed with no problems by a reputable shop would go some ways towards making me feel better about any potential corrosion in the cage area, but I would still have someone examine the spar in the places more likely to show corrosion.

But there is no such thing as a guaranteed corrosion-free plane as many here would agree. Flying and owning a plane are sometimes more about risk mitigation than anything else.

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19 minutes ago, tomatl said:

My 231 had a quite some surface corrosion on the yoke rods. With a bit of work, this was polished to a "like new" mirror-like sheen. I would expect that high gloss steel surfaces deteriorate, particularly in moist climatic conditions. (Corrosion on structural aluminum components is a different story.) I wonder if there is a good way to protect the rods going forward.

Regular application of Tri-Flo?  I started doing that recently, and was a bit shocked at how much smoother the yokes moved as well :) 

The corrosion you need to worry about is the stuff that's hard to visually monitor over time.  I looked at a J that turned out to have corrosion on some of the steel cabin tubing, on the ailerons under the paint, as well as corrosion on the control push rods in the empennage.  That's when the guy doing the pre-buy told me "I know I'm not supposed to say this, but this isn't your plane."

 

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4 minutes ago, jaylw314 said:

Regular application of Tri-Flo?  I started doing that recently, and was a bit shocked at how much smoother the yokes moved as well :) 

The corrosion you need to worry about is the stuff that's hard to visually monitor over time.  I looked at a J that turned out to have corrosion on some of the steel cabin tubing, on the ailerons under the paint, as well as corrosion on the control push rods in the empennage.  That's when the guy doing the pre-buy told me "I know I'm not supposed to say this, but this isn't your plane."

 

Sounds like you found yourself a good honest pre-buy guy who probably saved you a lot of money. 

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1 hour ago, jaylw314 said:

Regular application of Tri-Flo?  I started doing that recently, and was a bit shocked at how much smoother the yokes moved as well :) 

The corrosion you need to worry about is the stuff that's hard to visually monitor over time.  I looked at a J that turned out to have corrosion on some of the steel cabin tubing, on the ailerons under the paint, as well as corrosion on the control push rods in the empennage.  That's when the guy doing the pre-buy told me "I know I'm not supposed to say this, but this isn't your plane."

 

I know what it feels like to work with a mechanic that good during a pre-buy.  Mine saved me $17,000 in repairs - and you already know who he is.

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1 hour ago, Fred₂O said:

I have a logbook entry saying that the 208B inspection was completed by a reputable shop about 13 years ago.   Sadly, it needs doing again, and that is in the queue for the next major expense.

I just pulled up the SB from the Mooney site, and it appears to indicate it needs to be done at every annual. Am I reading that correctly? Seems a bit onerous, but looking at the 100 Hour-Annual inspection checklist, it appears to be #2 under the airframe section. 

Is this really getting done at every annual for everyone?

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3 minutes ago, Oldguy said:

I just pulled up the SB from the Mooney site, and it appears to indicate it needs to be done at every annual. Am I reading that correctly? Seems a bit onerous, but looking at the 100 Hour-Annual inspection checklist, it appears to be #2 under the airframe section. 

Is this really getting done at every annual for everyone?

I haven't seen it notated in any of the resent logs I've reviewed. 

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Chriman,

it helps to be a materials engineer for some things...

We have so many different materials in so many different applications...

Two basic types of corrosion... surface and inter-granular...

and a few key places to not have corrosion...

If it is surface corrosion that is easy to see... that helps.

If it is sheet metal... that is often common...

If it is steel landing gear... a nice clean and paint answer....

If it is deep into a flaking thick piece... that is probably bad...

This is why the PPI is a popular tool to protect your wallet...

Not everyone is a materials engineer.

Not every mechanic knows the expensive parts to look for the worst corrosion.

Then there are the un-see-able cam issues...

Go PPI...

PP thoughts only, not a materials engineer or mechanic...

Best regards,

-a-

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3 minutes ago, carusoam said:

Chriman,

it helps to be a materials engineer for some things...

We have so many different materials in so many different applications...

Two basic types of corrosion... surface and inter-granular...

and a few key places to not have corrosion...

If it is surface corrosion that is easy to see... that helps.

If it is sheet metal... that is often common...

If it is steel landing gear... a nice clean and paint answer....

If it is deep into a flaking thick piece... that is probably bad...

This is why the PPI is a popular tool to protect your wallet...

Not everyone is a materials engineer.

Not every mechanic knows the expensive parts to look for the worst corrosion.

Then there are the un-see-able cam issues...

Go PPI...

PP thoughts only, not a materials engineer or mechanic...

Best regards,

-a-

Yes I will, but I'd like to try and do a little homework up front so I'm not having multiple PPIs done on multiple planes. When I see a lot of surface rust on visible components, it leads me to believe it has been exposed to some sort of moisture and without knowing you can only assume there's hidden more critical areas in a similar condition. 

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Oops, I didn’t mean to deter you from doing the home work first...

Many planes don’t get past the logs, pics and first visits... before getting to the PPI.

Not that many planes fail... they just don’t meet the expectation of the owner at this point.

There is just so many things that will show corrosion that aren’t very expensive...

And some things that are expensive for one individual vs. the next...

corrosion free everywhere externally doesn’t tell much about tube steel or spars...

Same with surface corrosion everywhere doesn’t tell much about the spars...

It helps to get familiar, that’s what you are doing here...:)

Anything that can be easily unbolted and replaced isn’t much of a problem...

Take some pics and post for the questions you have...

Best regards,

-a-

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5 hours ago, chriman17 said:

So basically the surface corrosion may be meaning less, what really matters is the SB 208B inspection of the Spars and Cage if I'm understanding you guys correctly.

Mine had SB compliance documented by a reputable shop, didn't mean squat.  At one of my subsequent annuals we removed the side panels and found surface corrosion on the cage under the pilot side window.  Had to be done again but it was only surface corrosion and not pitted.  The previous repair looked like Krylon or something like that but after preparation we put the Zinc back on.  Last year I found some very light surface corrosion on the center beam by the roof vent control and took care of that quickly too.  Only way to really know is to look at the airplane, not the log book.

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Discussed this with Don Maxwell at MooneyMAX. When the pilot storm window leaks, the water collects in a sheet metal channel beneath the window that is attached to a structural tube with PK screws. Eventually, the screws rust out and water enters the inside of the tubes through the holes. Once inside, gravity carries the water to the bottom tube where it sits and rusts the tube from the inside. 

After completing 208, you should keep the storm window seal in good shape and maybe pull the interior panel beneath it every few years to make sure water isn’t getting in. 

Skip

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Plane cover will only help somewhat.  Water can still run in. 

Window seals are critically important. 40+ year old sealant can be cracked and embrittled.  

Probably hangaring, lack of fiberglass style insulation and ensuring no little rodents have taken up residence are the best insurance policies.  

If you really want to see if you have a leak, pull the interior panels and run a garden hose.   

When I purchased my plane, Top Gun ran a magnet along the lower longitudinal tubes (I think that’s part of the SB) to look for corrosion. 

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SB208b only refers to the tubular structure.  It says nothing about corrosion elsewhere.  I passed on a J due to airworthiness level spar corrosion.  SB208b was recently signed off.  There’s no substitute for inspection panel removal followed by a thorough inspection using an inspection mirror by a knowledgeable Mooney expert.  

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  • 2 weeks later...

From the factory our planes came with open faced fiberglass batt insulation.  When the window next to the pilots seat leaked the insulation absorbed the moisture and held it in contact with the steel tubing which resulted in it rusting.  SB 208 called for replacing the insulation  with foil enclosed insulation so it wouldn't absorb moisture.  SB 208 calls for removing one of the bolts that attaches the wing to the fuselage tubing and running a magnet inside the tube several feet forward.  The magnet is withdrawn and checked to see if there rust flakes.  This is a PITA. Notwithstanding the factory checklist I don't think there is any good Mooney shop that recommends or requires doing this every year.  

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