Exhaust Mount PIREP

jsharkey · #1 10-10-2010, 04:20 PM

During my last pre-flight walk around I noticed some missing rivet heads on the inboard end of one of the lower cowl hinges. Knowing that this is a weak area I removed the lower cowl with the intention of replacing the rivets and making some kind of a link that more effectively secures the exhaust outlet area of the cowl to the fire wall or engine frame.

Further investigation uncovered broken hinge loops on the other side of the aircraft, but sound rivets, and some local scorching of the inner surface of the cowl under the exhaust on the LHS where it passes close to the corner between the main cowl and the carb scoop.

I sanded off the scorched material and reinforced the area with a wet layup of glass fiber and epoxy resin before covering it with aluminum foil tape in the hope of adding some heat resistance. When I did a trial fit of the cowl I noticed that the tail pipes seemed very flexible and realized that the screws that join tail pipe supports to the engine sump were missing on both sides allowing the exhaust to drop slightly. I had initially assumed that this was due to overall engine drop as the AV mounts bedded in. Never assume.

Anyone else experienced this? And how did you better secure the supports to the sump? Wired drilled head bolts?

Also any ideas for better securing the lower cowl? I am thinking about fitting Adel clamps around the lower transverse engine mount tube (will they fit?) and then using these to connect to angle stock links that screw to the vertical cheek of the exhaust outlet of the cowl.

PS - Interesting how one fault discovered on a walk around lead to finding more which goes to show that you shouldn't ignore anything.

Jim Sharkey
RV-6 TT60hr

L.Adamson · #2 10-10-2010, 04:31 PM

My 6A's lower cowl is held with #8 screws & nutplates. I had heard that this was kind of a weak spot for hinges. Except for screws behind the prop, everything else is hinges.

L.Adamson --- RV6A

Ironflight · #3 10-10-2010, 05:56 PM

Lots of airplanes use the screws and nutplates like Larry mentioned - our RV-6 has them. I still have hinges and loops on the Valkyrie - replaced them a couple of months ago due to pulled-through rivets at about 1150 hours. I figure if they last that long again, I can replace them again at overhaul....

Paul

Walt · #4 10-10-2010, 06:41 PM

Quote:

Originally Posted by jsharkey

PS - Interesting how one fault discovered on a walk around lead to finding more which goes to show that you shouldn't ignore the small things!

Jim Sharkey
RV-6 TT60hr

Pratically all maintenance issues appear as "Minor" anomolies at first, if left unattended (or ignored), they will "Always" turn into bigger problems, so don't discount anything unusual, investigate and fix it now. Good job Jim!

Snowflake · #5 10-11-2010, 11:54 AM

I just replaced the inner 6" or so of my lower cowl hinges with a nut plate setup too. I dremel'd off four loops on each side, and used the existing rivet holes (after removing said rivets) to screw a backing plate to the lower firewall flange. Nutplates in the backing plate, and #8 screws into the nut plates through the cowl. Problem solved.

I did retain the hinges for the other half of the join... I think a more permanent solution is to go remove the entire hinge and replace it all with either nutplates or southco fasteners, but wanted a faster fix so I wouldn't miss as much flying time. Of course, now that it's fixed it'll stay this way until something else fails...

Flying Scotsman · #6 10-11-2010, 11:53 PM

All the responses so far have addressed the cowling attachment, but I'm *much* more interested in this:

Quote:

Originally Posted by jsharkey

When I did a trial fit of the cowl I noticed that the tail pipes seemed very flexible and realized that the screws that join tail pipe supports to the engine sump were missing on both sides allowing the exhaust to drop slightly. I had initially assumed that this was due to overall engine drop as the AV mounts bedded in. Never assume.

Anyone else experienced this? And how did you better secure the supports to the sump? Wired drilled head bolts?

Having just recently installed my exhaust, and torqued those bolts to the Lycoming spec...is there something else that needs to be done here?

Used new lock washers, etc...

JonJay · #7 10-12-2010, 09:27 AM

Quote:

Originally Posted by Flying Scotsman

All the responses so far have addressed the cowling attachment, but I'm *much* more interested in this:

Having just recently installed my exhaust, and torqued those bolts to the Lycoming spec...is there something else that needs to be done here?

Used new lock washers, etc...

Not sure what else you would do. No problems 330 hours on mine.

trib · #8 10-14-2010, 09:44 AM

No problem with mine, but only 80 hrs so far. Maybe some blue locktite would be a benefit also.

Mike S · #9 10-14-2010, 10:02 AM

Vibration issue, maybe.

Have you had the prop balanced??

jsharkey · #10 11-13-2010, 06:43 AM

Something else that I have noticed -

The tail pipes can move slightly left and right as a pair on the Vetterman mount with only the friction of the spherical joints to stop them.

When I center them in the outlet of the cowl they have a tendency to drift to the left again during flight.

Has anyone else noticed this? Do I need to tighten the spherical joints? Mind you that is controlled by the compression springs.

Jim Sharkey
RV-6 YO360-A1A Sensenich 72/85 FP Vetterman Cross Over