engine mount surface rust

[andybean]

There is a small area of surface rust on what I know as the engine mount. (black tube coming from firewall). I'm thinking about cleaning it up and applying paint to the area. I'm told that this is pretty common on a turbo arrow. Also through limited research I learned that these engine mount tubes are very thin and you should never grind on them or even sand them down.
Any ideas are appreciated. My first inclination was to just sand it down and repaint it.

 

[N801BH]

There is a small area of surface rust on what I know as the engine mount. (black tube coming from firewall). I'm thinking about cleaning it up and applying paint to the area. I'm told that this is pretty common on a turbo arrow. Also through limited research I learned that these engine mount tubes are very thin and you should never grind on them or even sand them down.
Any ideas are appreciated. My first inclination was to just sand it down and repaint it.

220 sand paper and a light coat from a spray bomb would not hurt.... The real question is why did just that one section rust? Look close for heat and / or chafing damage.... And maybe a A&P to give it a quick glance would not hurt either.

 

[dell30rb]

I don't see why a light abrasive would hurt and hit it w some of the anti-rust spray paint. Maybe steel wool and some Wd-40 would take that rust off. Don't use power tools...

light surface rust should be no problem, maybe the paint just got chipped by a mechanic working on the airplane. If you are unsure if it is just light surface rust or something else its worth having a mechanic look at it for 2 seconds. Doubt they would charge you

 

[Tom-D]

DO NOT use abrasives on any structural tubing in aircraft.

For the most part the tubing is .035 wall, to clean it properly, remove it and have it cleaned by a soda blaster, and a patch placed over the bad spot.

the rust is caused by heat breaking down the protective coating, which allows the corrosion to take place.

 

[andybean]

What paint would you use once its cleaned up? My hunch is that it gets hot there. Probably from the turbo.

 

[N801BH]

What paint would you use once its cleaned up? My hunch is that it gets hot there. Probably from the turbo.

If it gets hot enough to burn the paint off the chromemoly tubing ,that area needs a heat shield for tubing protection... Your problem is since it is a certified plane, no matter how much sense it makes to correct a problem, you CANNOT alter the design...

I would suggest a high heat paint like what's used on exhaust headers or BBQ grills.

 

[CMTowner]

We used to send it out, get it media blasted, and then painted. We switched from black to white, at it makes it a lot easier to see cracks.

 

[denverpilot]

CPA points out in their tech sessions that heat shields on C182s save LOTS of money later on.

FAA has VERY tight limits on how deep that damage can be on the engine mount tubing since its structural and also hollow.

Better talk to your mechanic. If its corroded very much at all, you could be replacing that engine mount.

I'd say Tom may have BTDT seeing as he's replied with a possible repair. If its too deep, the repair won't be approved though.

Get it looked at and taken care of quick. It takes very little depth to completely trash an engine mount. And it's becoming more common on older airframes...

 

[Tom-D]

FAA has VERY tight limits on how deep that damage can be on the engine mount tubing since its structural and also hollow.

Better talk to your mechanic. If its corroded very much at all, you could be replacing that engine mount.

I'd say Tom may have BTDT seeing as he's replied with a possible repair. If its too deep, the repair won't be approved though.

Get it looked at and taken care of quick. It takes very little depth to completely trash an engine mount. And it's becoming more common on older airframes...

IF ..... it were my customers aircraft expecting my return to service, they would wash the area with detergent with a fine wire brush, to see how deep the pits are.

If the area is nothing more than surface etching, I'd repaint it with red zink oxide primer and painted with high heat paint.

If there are any pits that you can catch a finger nail on, it is coming off and going out to a CRS to have the tube replaced.

And yes you can weld a patch on a tube in the field and get it approved using the 43-13 as data for requesting approval. the FAA makes no difference between an engine mount and any other airframe structure. so, the repair procedures are the same. PROVIDING the airframe manufacturer has no other repair procedures that superseding the 43-13.

 

[denverpilot]

Good info Tom.

I bet by the time most folks notice it, "catch a fingernail" depth is already there. Not good.

I had a long chat with our mechanic about this after I went to class. We have some heat shields but not everywhere they might be prescribed.

He said we're "lucky" here due to our extremely low humidity and he rarely sees the problem.

He offered to fabricate shields if we were concerned about it -- and that they would be a lot cheaper even than the nice ones from a few different places, but that the critical areas where tubing and hot exhaust pipes cross closely are already adequately shielded on our airplane at the request of the former owner.

He does make them from time to time when he sees zero shielding in those close areas.

Another common mistake is letting the engine compartment get enough dirt/grit in it that it works it's way under clamps on the mounts and things and grinds away underneath them due to vibration. Spilling oil on things doesn't help this either, since that'll suck up dirt and carry it to crevices it shouldn't be in.

Plastic tie wraps are also often just devices to trap that dirt and then slide back and forth and grind away on the (very expensive) engine mounts.

Highly not recommended by CPA nor our mechanic. Use a proper clamp to hold wiring in place, etc.

Just sharing in hopes that folks take a look the next time their cowl is off. Corroded tubing can get spendy, real quick. $100 worth of prevention is well worth the money.

 

[andybean]

Here area a couple pictures. Strangely engough, this is the only spot where there is a problem. These shots were taken very close up so they may appear worse than they are.

 

[N801BH]

Here area a couple pictures. Strangely engough, this is the only spot where there is a problem. These shots were taken very close up so they may appear worse than they are.

Yup, radiant heat is cooking that area of the mount... Surface rust does not look too bad so do what Tom suggested..... Personally I would pass these pics on to someone like the FSDO and have your mechanic fill out something to help others address this problem.. If there was ever a place that needed a heat shield, that is the poster child..

 

[denverpilot]

That tie wrap is going to cut a hole in that SCAT tube too... eventually.

Ditto on Ben's comment. Poster child. Get 'er fixed and share photos with all your Turbo Arrow buddies and your bill... and tell 'em to go get some heat shields put on theirs.

 

[Clark1961]

I'll just pass on my experience with a CRS. They replace any tube that "might" have a problem. It's not for me to say anything 'bout yours but if there is the slightest surface mark, the tube comes out at the CRS.

 

[Tom-D]

I'll just pass on my experience with a CRS. They replace any tube that "might" have a problem. It's not for me to say anything 'bout yours but if there is the slightest surface mark, the tube comes out at the CRS.

Remember that a CRS have different rules for return to service than anyone in the field.

From what I see in the photos given, I'd clean with a non abrasive method, and protect.

I'd not paint it. I would use a good marine corrosion protection, applied and checked at each oil change.

At the next engine removal I'd have the whole thing stripped, repaired as required and then powder coated.

 

[N801BH]

No Heat shields Tom .

 

[Tom-D]

No Heat shields Tom .

That is an area that gets hot by the compartment heat. It isn't being blown on by any pipe or near proximity of a hot pipe.

To me, it looks like the area wasn't prepared correctly before painting

 

[Dan Thomas]

Plastic tie wraps are also often just devices to trap that dirt and then slide back and forth and grind away on the (very expensive) engine mounts.

Highly not recommended by CPA nor our mechanic. Use a proper clamp to hold wiring in place, etc.

I have seen that. Mount tubing with the serration pattern from beneath the nylon tie wrap, ground right into the tubing. Adel clamps that are snug so they can't move won't damage the tubing.

I was a truck partsman in the 1970s. When nylon air brake tubing came out it became very popular and quickly replaced the copper tube that was commonly used up until then. Copper was prone to work-hardening and cracking, and flying stones would dent and puncture it. Nylon was tougher and far easier to work with.

But one day a trucker came in and asked me to come see the frame of his truck. The half-inch nylon tube had been rubbing against the edge of the C-section frame rail and had cut more than a quarter-inch into it. This section was at least a quarter-inch thick steel and was heat-treated. The nylon had become embedded with sand and acted like a file as it vibrated against the steel.


That engine mount tubing will have a wall thickness or around .035", or the thickness of ten sheets of copy paper. IIRC, the allowable surface damage is 10% of that thickness, or the thickness of a single sheet of paper. Very, very little. Aggressive sanding can go that far real quick, especially on a surface that's already roughed by corrosion. I wouldn't use anything more than fine Scotchbrite on it.

Dan

 

[Tom-D]

. I wouldn't use anything more than fine Scotchbrite on it.

Dan

NO, NO, NO,

Scotchbrite is 180 grit..

to clean it I'd get a bottle of naval jell for steel. and a stainless steel platers brush, apply the jelly, allow to set 30 minutes brush it and wash off the jelly etch. dry and apply a good marine corrosion protection.

The heat will simply harden the corrosion protection and the tube will be protected and you can watch the tube for corrosion, and repeat as required.

 

[N801BH]

I have seen that. Mount tubing with the serration pattern from beneath the nylon tie wrap, ground right into the tubing. Adel clamps that are snug so they can't move won't damage the tubing.

I was a truck partsman in the 1970s. When nylon air brake tubing came out it became very popular and quickly replaced the copper tube that was commonly used up until then. Copper was prone to work-hardening and cracking, and flying stones would dent and puncture it. Nylon was tougher and far easier to work with.

But one day a trucker came in and asked me to come see the frame of his truck. The half-inch nylon tube had been rubbing against the edge of the C-section frame rail and had cut more than a quarter-inch into it. This section was at least a quarter-inch thick steel and was heat-treated. The nylon had become embedded with sand and acted like a file as it vibrated against the steel.


That engine mount tubing will have a wall thickness or around .035", or the thickness of ten sheets of copy paper. IIRC, the allowable surface damage is 10% of that thickness, or the thickness of a single sheet of paper. Very, very little. Aggressive sanding can go that far real quick, especially on a surface that's already roughed by corrosion. I wouldn't use anything more than fine Scotchbrite on it.

Dan

I agree with the scotchbrite idea.... Tom... you do know there are 11 different grits of scotchbrite, that vary from 280 grit, which is maroon in color to the light gray which is 1500 grit...

And just to make a point I will post the pic I have of a motor running on a dyno... The four head pipes are glowing red/white hot... The inner two pipes are running 1440f, the front one is 1480f and the rear one is 1510f..

Look how far back on the exhaust system the heat is so great the steel is glowing. Maybe 6-7 feet away from the exhaust ports. The exhaust pipe in your pic is at best 2 feet from the port and I bet your EGT's show 1400f+.. I can assure you that cross member on your mount is less then 1/2" from your exhaust pipe.... Radiant heat is not something to play with, just go to any electric range, turn the top element on high, let it get red hot and then move your hand over it.. So how long you can keep it there and how close you can actually get to it... Now, picture a steel pipe 1/2" away for hours at a time........ If it were my plane it would have heat shields protecting that mount tube... Just my .02 cents worth...

Ben

 

[Clark1961]

1640 is max turbo temp on the TSIO-360-FB in that aircraft. In flight it'll run at 1550 or above when leaned.

In other words, yup, the pipe will be glowing...

 

[Tom-D]

1640 is max turbo temp on the TSIO-360-FB in that aircraft. In flight it'll run at 1550 or above when leaned.

In other words, yup, the pipe will be glowing...

When the pipe is that hot and that close the heat shield isn't going to do much good.

Wrapping the pipe might help.

 

[Clark1961]

When the pipe is that hot and that close the heat shield isn't going to do much good.

Wrapping the pipe might help.

The CRS I used suggested aluminum tape anywhere the heat shield seemed to be lacking. So far the heat shields have proven to be adequate since none of the powder coat shows deterioration or discoloration.

The shop did suggest renewing the tape at each annual so any defects could be detected.

 

[denverpilot]

We have some tape in a couple of places. Our mechanic says he keeps an eye on it for signs that it's been compromised, and would replace it if it were after inspecting under it.

 

[andybean]

Not painting it makes the job much easier.

Here is the plan: Naval Jelly http://www.acehardware.com/product/index.jsp?productId=1876643

Then lightly sand or use Steel Platers Brush (if I can find one)

Then follow with Corrosion X (which I have also and works great)

On completion of this process, why would I not use the Chromate aviation primer that I have, then follow with some high temp paint. Would there be harm in this? Oviously this would be done before the application of the Corrosion X.

I really appreciate the help here.

Andy

 

[Skylane81E]

Tempo makes a nice aircraft engine paint, I've used it on mounts before and it holds up well.