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-   -   cracking clear coat on Cowl (https://vansairforce.net/community/showthread.php?t=147948)

Mark C. 03-23-2017 03:28 PM

cracking clear coat on Cowl
 
I have just over 58 hours on my 9A and I now have spider cracks in my clear coat, its not down to the paint just in the clear. The location is a little forward of the oil door. My observation says it might be the top cowl expansion while in flight. The bottom cowl is open where the 2 exhausts come out plus I added while building on each side of the bottom cowl 4X12" louvers. My temps are good EGT's at 340 and CHT at 1260. What have other flying 9 builders done to get the forced air through the cowl. Pictures would be helpful.. Thanks, Mark C. 119RV

petehowell 03-24-2017 07:51 AM

Lycoming shake
 
Hi Mark,

It might be the back right corner of the baffles hitting the top cowl on shutdown shake. I have a similar spot on my cowl and determined that was the cause. Reach in and check the clearance there,

So glad you are up and flying - it was great to meet you and have your help on the PnP mission years ago!!

bhester 03-24-2017 08:29 AM

Me too
 
Mine did the exact same thing :-(

Mark C. 03-24-2017 09:20 AM

Pete, this is back to you... Amazing!! shut down shake.. My clearance on to that corner is 1/8th inch. That's has to be it. I'll file that corner down before the next flight.. Visit me at Schaumburg, I now have a hanger their.. Thank You!! Mark C.

lr172 03-29-2017 10:00 AM

Quote:

Originally Posted by Mark C. (Post 1160362)
Pete, this is back to you... Amazing!! shut down shake.. My clearance on to that corner is 1/8th inch. That's has to be it. I'll file that corner down before the next flight.. Visit me at Schaumburg, I now have a hanger their.. Thank You!! Mark C.

Make sure you get good clearance after filing. Clear is usually pretty flexible, so you must be getting a good amount of movement/pressure on that area. Does the center of the cracking coincide with the location of that baffle corner? If that is the issue, you should see a witness mark on the inside surface of the cowl where the contact is being made. Assuming that is the issue.

Good news is that that you can blend some clear into that area and wet sand / buff it if you chose to repair.

Glad to hear you finally got a hanger at Schaumburg. Look forward to seeing you around. We need more RV's here.

Larry

Mark C. 03-29-2017 10:28 PM

Thanks Larry, yes the fractures in the clear are just forward of the oil door. I filed down the baffle last week to provide at least 1/4" clearance and yes visible is a small impact from the corner hitting the inside top cowling. I am going to change my engine shut down technique by very slowly closing the mixture, that should help the engine torqueing when it stops.

Have a safe trip this weekend heading to NC.. Mark C.

lr172 04-03-2017 08:48 AM

Quote:

Originally Posted by Mark C. (Post 1161778)
Thanks Larry, yes the fractures in the clear are just forward of the oil door. I filed down the baffle last week to provide at least 1/4" clearance and yes visible is a small impact from the corner hitting the inside top cowling. I am going to change my engine shut down technique by very slowly closing the mixture, that should help the engine torqueing when it stops.

Have a safe trip this weekend heading to NC.. Mark C.

Mark, There was another post on baffle clearance in the General section. The poster indicated that the Van's spec was 3/8-1/2" of clearance. I vaguely remember using 3/8" minimum. You may want to consider filing it down to 3/8" to avoid continuing issues. Don't want more problems with that beautiful paint job :-)

Larry

Mark C. 04-04-2017 09:39 PM

thanks Larry, good catch on the 3/8th spec. I did file down the right baffle corner. When I pull the cowling again I'm also going to cut the baffle along the top it doesn't touch the top cowling, but just to be safe. I'm also going to replace the Vans sealing material I just don't like the way it sits and flexibility performance. AS appears to offer some good choices. Did you and your son make the trip to NC?? Mark C. 119RV

lr172 04-06-2017 08:52 AM

Quote:

Originally Posted by Mark C. (Post 1163375)
thanks Larry, good catch on the 3/8th spec. I did file down the right baffle corner. When I pull the cowling again I'm also going to cut the baffle along the top it doesn't touch the top cowling, but just to be safe. I'm also going to replace the Vans sealing material I just don't like the way it sits and flexibility performance. AS appears to offer some good choices. Did you and your son make the trip to NC?? Mark C. 119RV

We did. Friday night the Wx was bad with icing forecasts. Wound up leaving at 5:00 AM on Sat:mad: It was a great trip and we had a great time. It was almost 70* and we enjoyed being warm again. My other son liked the stories and pictures enough that he chose the same location for his trip. We plan to go next weekend.

Larry

Bavafa 04-06-2017 09:18 AM

Mine has done the same but I don't think it is due to the space between the cowl and baffles. I have a couple of layer of fiberglass added to this area which holds the push/pull cable to my oil door. Adding fiberglass does effect the cowl or wingtip as I believe it will shrink a bit and distort the material.

On mine this happened initially during the first 50 hours or so and has not changed since.


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