Cabin Heat Muff Chaffing

[jmorrical]

Working the engine area to complete the first condition inspection. Noticed the #1 and #3 intake manifold (Induction tubes) has been chaffed by contact with the cabin heat muffs. While it's hard to get accurate measurement I would say the chaff is about .015 to .02 inches of the tube taken off in an area of less than 1/2 inch. Here this photo is with muffs removed.

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Should I replace the intake manifold (induction tubes)? Or be satisfied with some reshaping of the muffs to prevent future contact and putting it on the watch list.

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Sharpie mark showing edge of the area where either the induction tubes or the muffs need to be shaped to prevent chaffing.

[Andy]

"Should I replace the manifold? Or be satisfied with some reshaping of the muffs to prevent future contact and putting it on the watch list."

I think you would need the nominal wall thickness and a better estimate of the erosion to make an informed choice.

If the damaged area fails you will have one cylinder running very lean and the engine damage may cost far more than a new intake tube.

[aeroaddict]

Agree with Andy. Find out the wall thickness and make your risk tolerance decision.

In regards to the muffs, I recall that I had to shape a depression/concave area on 1 or 2 of the muffs to prevent contact.

Congrats on the first condition inspection and good eye!

[jmorrical]

My earlier wording that the induction tubes were 'very' thin walled might be somewhat overstated, but they are light weight. Only CubCrafters provides this part. They must be aluminum or some aluminum alloy.

I asked CubCrafters Kit Support about tube wall thickness. They said the induction tubes had a wall thickness of .035 inch, but that likely varies when bent. The CC340 Titan on CarbonCubs have oil sumps fabricated by forming aluminum sheet then welded. I understand this was a CubCrafters initiative and design to save weight. I don't know the wall thickness of the induction tube that are integral to the sump design but they seem to be similar.

Here is how the CC340 Engine Manual explains the sump options on the CC340.


The CC340 engine has two sumps available. One is cast aluminum and the optional .080” sheet metal sump saves approximately 11 lbs in weight. The cast sump has a maximum capacity of 8 quarts of oil, while the sheet metal sump is 6 quarts of oil. Both sumps are bottom inlet, hot induction sumps for the MA4SPA carburetor attachment. Both sumps incorporate a drain plug for changing oil.

[jmorrical]

A $700 lesson learned. I'm replacing the #1 and #3 induction tubes.

I just thought this fit was the way it was. Didn't expect movement between the muffs and tubes. My inexperience set me up.

Wish there had been a Note or Caution in the Firewall Forward Manual bringing attention to this potential problem and suggesting shaping the muffs somehow to avoid contact. Or better yet couldn't the muffs have been built to address or prevent this hot spot...this chaffing.

This photo and others in my EX(1) Fire Wall Forward Manual are not representative of my installation. They show good clearance between muffs and tubes. My muffs were right up hard against the induction tubes.

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[aeroaddict]

Ouch! Good news is you found that down here not up there. Or on short approach to your favorite "no go around" strip.

[guidoperez]

Better to catch it here than on a tricky approach.

[jmorrical]

An update. Waiting on parts.

When I took the induction tubes off I could see there is really very little chaffing. What I thought was chaffing was deformation of the softer aluminum tube just conforming to the contact with the stainless steal muffs. I could not have know that without seeing inside the tubes.

All in all I am glad to be replacing tubes so there is no question about them in the future.

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Here you can see the bump inside where the muff pressed on the tube. It's deformed just a bit. Actually I know now the exterior of the tube has very little chaffing.

[aeroaddict]

Agree. Thanks for the update. It's too hot to fly here anyways. Might as well do maintenance.

[jmorrical]

This is not too important, but it might help others with this experience. Had several ideas including asking a muffler shop for help. I just couldn't bend the stainless steal by hand. In the end here's how I shaped the muffs for clearance I needed from the induction tubes.

I was able to hammer shape them. Several four inch diameter circles were cut with a four inch hole saw I had in the tool box. Then I used a rasp to shape a depression in what I would call a wood buck. With the wood buck and a couple other wood circles inside the muff for extra support the hose clamps held it all together. This made the muff rigid enough for hammer shaping. It took a couple tries to get the shape I needed for clearance but it worked.

I'm ready for parts tomorrow to finish the Condition Inspection.

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