Engine Mount Paint/Heat Question

[Garrett Gee]

This one has had me up all night (evidence is posting this at almost 3am). In going through the inspection with a local mechanic, he pointed out an area on the engine mount that has an area where the paint looks like it has “bubbled”. He is thinking possible heat damage to the mount. I don’t have a picture currently (a massive rain storm from hurricane Laura cut us short today), but has anyone experienced “paint bubble” on the engine frame/mounts? I will try to get some pictures if the weather cooperates. Has had me up all night thinking the worst. I can’t really find any guidance in Rotax or CT maint manuals.

Thanks in advance for any thoughts.

[GrassStripFlyBoy]

The mounts are heat treated, so the "possible damage" would then become is an area annealed / lower harness which would run the risk of dimensional distortion over time.  A softer region of steel would not pose a risk such as cracking, the question is does the softer section loose some of the strength.  To anneal low carbon steel the temp needs to be in the 500F to 1400F ranges, I'd think if the mount became 500F + there would be other signs of that much heat effecting things besides the mount.   This could be confirmed by taking some hardness checks at the area in question, and comparing to other areas of the mount.  There is a drop ball steel harness tester that is non-marking, but would need to remove the paint to test on the raw surface.  I've seen skilled machinists take a file to a piece of steel, and with one wipe across the sample are able to get darn close to hardness value by feel and sound of the file.  If you can't measure any distortion to the mount, and the only evidence is the paint, I'd not be too concerned here.

[Tom Baker]

In all of the CT's I've worked on I have never seen a mount have any heat damage. I have seen paint damage in the form of staining. This is normally from fuel, and I have also seen it from contact with rubber. Unless you have had a broken exhaust that was blowing hot exhaust on the mount I wouldn't be too concerned. I don't think the heat required to bubble the paint would be significant enough to do damage to the mount itself. For that to happen the paint would be completely burnt away.

Darrell, I too had always thought the mounts were heat treated, but there was some discussion about this in the engine removal thread, and some thought it was not.

[Roger Lee]

Seriously doubt it's heat damage. Seeing paint bubbles, cracking, chipping and flaking has been normal for many years.

Now you can go take a nap.  

 

[Garrett Gee]

2 hours ago, Roger Lee said:

Seriously doubt it's heat damage. Seeing paint bubbles, cracking, chipping and flaking has been normal for many years.

Now you can go take a nap.  

 

That is kind of what I figured, but I am far from an expert.  He voiced concerns, which is what led to my worry.  Lots of coffee consumed today.  Thanks!

[sandpiper]

At the very least I would try to protect the mount with some fire sleeve. And, if something has moved making the heat source closer to the mount than it was, I would try to move it back to original position.

You didn't say what the heat source is. Looking forward to your pictures.

I know about that kind of worry. Many years after college graduation I used to wake up in the middle of the night in a cold sweat. The dream (nightmare) was that a final exam was the next day and I had been skipping class and had not studied. 

Did you come through Laura OK?

[Garrett Gee]

3 hours ago, sandpiper said:

At the very least I would try to protect the mount with some fire sleeve. And, if something has moved making the heat source closer to the mount than it was, I would try to move it back to original position.

You didn't say what the heat source is. Looking forward to your pictures.

I know about that kind of worry. Many years after college graduation I used to wake up in the middle of the night in a cold sweat. The dream (nightmare) was that a final exam was the next day and I had been skipping class and had not studied. 

Did you come through Laura OK?

 

I appreciate the concern.  We came out fine, but I am a couple hundred miles inland and not on a direct path.  We are getting some of the outer rain bands though.  We got a pretty crazy wind/rain storm yesterday, and its been gusting 50+ mph all day today, but no damage thus far.

I talked about fire sleeve with my mechanic yesterday, and he agreed that it would be a good idea, as long as there was no damage obviously.  I was able to get some pictures today.  Some of the discoloration is just grime that needs to be cleaned up.  Any thoughts are appreciated.  As far as we can tell, there isn't any sagging or deformation, but since we had to cut it short the other day, we haven't been able to get back and really look closely at it.

For perspective, these are taken from the left side of the aircraft, looking aft.  The last one is the rear of the mount bar.  As for the heat source, we can't really figure it out.  Everything looks normal in the since of space and clearance.  But again, I am far from an expert in these matters.

[Roger Lee]

Now that I have seen pictures that is heat blistered damage to the paint. The pictures tell the story. I've not seen an FDCT do that before. The pipe is usually far enough away. You ought to see if the exhaust can be moved some over to the side a little more to put a bigger air gap in there. I would recommend that you wrap those exhaust pipes. The wrap Mfg states up to a 70% reduction in heat and I don't always believe some Mfg's claims, but even a 50% reduction is big.

[Garrett Gee]

3 minutes ago, Roger Lee said:

Now that I have seen pictures that is heat blistered damage to the paint. The pictures tell the story. I've not seen an FDCT do that before. The pipe is usually far enough away. You ought to see if the exhaust can be moved some over to the side a little more to put a bigger air gap in there. I would recommend that you wrap those exhaust pipes. The wrap Mfg states up to a 70% reduction in heat and I don't always believe some Mfg's claims, but even a 50% reduction is big.

Thanks Roger.  I hadn't thought about the header wrap, but I remember seeing the LOA for it.  I'll go look that up now and get it on order along with some fire sleeve.

[Roger Lee]

The size fire sleeve you can use is #16. Slit it length wise and since it is so close to the heat use safety wire to secure it vs the usual plastic wire ties. If you wrap the exhaust then you could get away with the wire ties.

[sandpiper]

Who has been doing the condition inspections on your plane? It's hard to believe all of this happened since the last inspection. Or since the last oil change.

[GlennM]

I don't think that is heat damage.  Why would the dark streaks "run", like below the rubber mount and side of the tubing?   I believe I see the red nylock (anti-rotation feature) of the nut on the end of the engine mount bolt. If it were heat damage, I would expect the nylock to be melted. It does not appear to be. 

 I would guess auto fuel over time from the carbs.  The bubbles are probably spallation of the powder coat.  I had to get mine powder coated again due to spallation and subsequent rusting.

[Roger Lee]

I didn't think it was heat in the first post until I saw the pictures and it looks like cooked paint.

 

[Garrett Gee]

3 hours ago, sandpiper said:

Who has been doing the condition inspections on your plane? It's hard to believe all of this happened since the last inspection. Or since the last oil change.

Rex Johnson did the last condition inspection a year ago and didn’t mention it. We did an oil change back in April,  I really didn’t give the mounts much of a look over. I pulled the drain plug, emptied the oil, and my mechanic put it back in and safety wires it, and filled it back up. Right after purchase 2 years ago, I noticed what looked like a paint run or overspray on the mount through the oil access door, but didn’t think much of it. Last April was the first time I personally pulled the cowling, and I didn’t notice anything, but again, I wasn’t really looking either. Note to future self though. I will be pulling the cowling more often after this.

We are going to take a wire brush to the paint and look for any corrosion. If there isn’t any, we are going to paint, header wrap, and fire sleeve the mount, and probably check it again after a few flights. Also going to very meticulously look for any fuel, coolant, oil, etc leaks. I haven’t noticed any fluid in the ground in the hangar though, so I don’t know. If it is deemed good, going to very closely watch it though.

If there is corrosion, I don’t know what I am going to do. No other option than to replace I guess. Anyone know the lead time on engine mount?

[GrassStripFlyBoy]

On 8/27/2020 at 9:12 AM, Tom Baker said:

Darrell, I too had always thought the mounts were heat treated, but there was some discussion about this in the engine removal thread, and some thought it was not.

I was repeating the tribal knowledge I've read here as well, and can't speak to what the design is.  I would think, and only assuming so big qualifier here, that the material used to fabricate the mount is similar to 4130 and in a normalized heat treated condition.  It's not likely the whole fabricated mount is heat treated after being welded up, but more likely the stock used to create it has something to it.

[GlennM]

I still think it is the breakdown of the powdercoating and corrosion, so you will have to get it re-powder coated.   They will blast off the old powder coat and the rust and in my experience, it will be good as new.  The hard part is pulling it and sending it off. 

Check the nylock nuts, if they are intact and not melted, it is not overheating and you won't need firesleeve or a wrap.

[MEH]

In my opinion, the blistered paint is likely due to osmotic blistering.  That occurs when salts and moisture are present on the paint.  Are you near the ocean?  Does the bird get rained on from time to time.  Was the engine compartment cleaned with aggressive alkaline degreasers? The corroded bottom of the mount and the staining of the paint coming down from below the rubber mount tells me that the corrosion products are flowing down past that point.  Not a heat problem but a corrosion problem.

[Garrett Gee]

42 minutes ago, MEH said:

In my opinion, the blistered paint is likely due to osmotic blistering.  That occurs when salts and moisture are present on the paint.  Are you near the ocean?  Does the bird get rained on from time to time.  Was the engine compartment cleaned with aggressive alkaline degreasers? The corroded bottom of the mount and the staining of the paint coming down from below the rubber mount tells me that the corrosion products are flowing down past that point.  Not a heat problem but a corrosion problem.

I have only owned it 2 years.  To my knowledge, it has never been routinely left in the rain.  It has been in the rain a time or two, since I had it, but not left out for days at a time or anything.  Has pretty much always been hangared while I have owned it, and I am pretty certain both previous owners as well.  As for degreasers, I have not used anything other than the composiclean products, but I can't speak to before I owned it.  I am about 250 miles north of the Gulf of Mexico, so I can't imagine that would be an issue.  And the previous two owners, from what I know were also a good distance away from the ocean.  About the only real "soaking" the bird has been in is a good spray down with a water hose, but even then, it isn't drenched in water, but sprayed and then dried (the airplane, not the engine!).  Your theory makes sense though, because it does look like some type of liquid "ran" down the mount.  The more I look at suggestions here, the more I am tending to agree that it may not be exclusively heat damage, but possibly a combination of heat and something else, just not sure what that something else is.

We have checked for leaks inside the cowling, and can't find anything, so it has to be something external, right?

[MEH]

Since there are no active exhaust leaks, I would do my best to mitigate the corrosion that is visible and just monitor.

The trick is stopping the current corrosion problem.  Since there is some sagging of your engine mount that is in the picture, it may be time to swing out the engine, address the corrosion, and replace the rubber mounts.

[CT_MATT]

This is right below the carb drip trays.  Is it possible there was a leak that spilled over, burned off (causing the paint to blister), then all looks fine again?

[Roger Lee]

Hi Garrett,

Wrap the exhaust pipes in header wrap and you won't have this radiated and convected heat issue. The wrap Mfg says 70% drop in the excess heat. I don't always believe Mfg's, but even a 50% reduction is really good. Think about all your wires and hoses with all that heat under there. I just wrapped another CTLS pipes yesterday. He had a ton of blow-by. I adjusted the muffler to align the knuckles on top of the muffler and wrapped the exhaust pipes. Night and day heat difference.

[Garrett Gee]

1 hour ago, Roger Lee said:

Hi Garrett,

Wrap the exhaust pipes in header wrap and you won't have this radiated and convected heat issue. The wrap Mfg says 70% drop in the excess heat. I don't always believe Mfg's, but even a 50% reduction is really good. Think about all your wires and hoses with all that heat under there. I just wrapped another CTLS pipes yesterday. He had a ton of blow-by. I adjusted the muffler to align the knuckles on top of the muffler and wrapped the exhaust pipes. Night and day heat difference.

That’s the plan. Header wrap and fire sleeve the mount after we clean it up, check for damage/corrosion and paint it. Thanks for the help.

[Roger Lee]

You won't need the fire sleeve if you wrap the pipes.