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Old 05-21-2018, 10:29 AM
ChuckC ChuckC is offline
Join Date: Apr 2011
Location: Meridian, ID
Posts: 82
Default Exhaust Spring Rubbing On Cowling Air Duct

The spring on the left front of the exhaust (just below the #2 cylinder) has been rubbing the cowling air duct. The rubbing has gone through the heat shield and is now working on the fiberglass. The air duct is dimpled to make room for the spring; but, in my case, it looks like it could use another 1/8? to 3/16? of space to keep the spring and air duct from rubbing together. This is the original exhaust system on the 912ULS. This condition was found during the 200 hour engine maintenance (replace spark plugs, etc.).

I am thinking of cutting an oblong hole around the spring?s mark on the air duct and fiber glassing in a bubble to make more room for the spring.

Any suggestions?
Chuck Carlson
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Old 05-21-2018, 10:41 AM
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,683
Default At a quick glance - -

Looks like you could bend the spring connection loop closer to the exhaust and gain some clearance.
John Bender
Flying RV-12 - Serial #120036
Paid in May ( 5-2021 )
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Old 05-21-2018, 10:50 AM
alexe alexe is offline
Join Date: May 2013
Location: Temecula, CA
Posts: 304

Most of the builders I know of had to cut out and re-fiberglass the area in question. If I recall correctly, there were also clearance issues between the cowl and the valve cover of cylinder #2. Same solution there.
Alex Erdelyi
RV-9A Purchased
RV-12 Built and Sold
Paid through December, 2022
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Old 05-21-2018, 11:28 AM
DHeal DHeal is offline
Join Date: Sep 2006
Location: Windsor, California
Posts: 1,012

Yup, like Alex said.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 1,170+ hours (as of May 2022)!
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Old 05-21-2018, 01:02 PM
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f1rocket f1rocket is offline
Join Date: Jan 2005
Location: Martinsville, IN
Posts: 2,345

I just seating the spring in some RTV on the cowl and monitored it. It never got worse in three years.
Randy Pflanzer
Greenwood, IN
Paid through 2043!
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Old 05-25-2018, 04:45 AM
BigJohn BigJohn is offline
Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,588

No pictures showing up. Go with the fiberglass bubble and never worry about it again.
John Peck, CFII, A&P, EAA Tech Counselor, Flight Advisor.
Master Pilot Award, UFO Member.
RV-12 N37JP 120176, built 2011, sold 2020.
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Old 05-28-2018, 09:51 PM
DaveWelch DaveWelch is offline
Join Date: Mar 2005
Location: Huntsville, AL
Posts: 478

Originally Posted by DaveWelch View Post
Ya know, that?s not a bad idea. Assuming Chuck is happy with his oil cooler to muffler clearance, temps are OK, and nothing else is clattering against the cowling...just patch over the area with a piece of new foil, add some high-temp RTV and fly on. No messing around with more fiberglass if you don?t have to.
On second thought, I'd recommend cutting it out and glassing in an area that gives you some clearance as you first mentioned and others have recommended also. That's what I did during the original build. Not that much trouble and gives you much piece of mind.
RV12 N951DZ
First Flight 9/23/16!
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Old 05-29-2018, 04:16 PM
ChuckC ChuckC is offline
Join Date: Apr 2011
Location: Meridian, ID
Posts: 82

Thank you all for your responses. Took the majority's vote and installed a bubble in the air duct. Now have a good 1/8" clearance all around the spring.

Chuck Carlson
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Old 05-29-2018, 04:20 PM
ChuckC ChuckC is offline
Join Date: Apr 2011
Location: Meridian, ID
Posts: 82

Alex, I also checked my cowling valve clearance on #2 and #4. #2 has at least 1/8" clearance; but, #4 is a little closer - but, still, not touching or rubbing on the cowling or coolant radiator.

Appreciate the help! Thanks!
Chuck Carlson
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