can I get some pics of the engine with the top cowl off?

[rbridges]

I have a C model with the 201 cowl.  It had stress cracks in the top cowl that I lived with until last year.  I had the cowl repainted, and the areas with the stress cracks were reinforced.  I noticed today that very small cracks are forming again.  I think I need my IA to lower the insertion point of the front baffles slightly so that we can reduce the sheet metal "box" around the top.  It seems to be hitting the cowl harder in certain areas where the new cracks are beginning.  I'd like to see some others for comparison.

My cracks are reforming where the yellow circles are:  pilot side rear and passenger side front.  

[carusoam]

Andy,

See if you can find the photos from Byron.  He had done some work on his 201 cowl because of something that sounds similar to what you are experiencing.

You will be able to see what and where he used some materials to add some strength.

Best regards,

-a-

Edited February 5, 2017 by carusoam

[Guest]

It's interesting that your cylinder head baffles are quite wide and not secured directly to the heads. 

Clarence

[rbridges]

I figured mine may be different. 

[thinwing]

4 hours ago, M20Doc said:

It's interesting that your cylinder head baffles are quite wide and not secured directly to the heads. 

Clarence

I have never seen baffling done quite that way in any of the 20 or so continental/ lycoming installs I have own or flown.Not even in the experimental....who did the last install on that engine...is that the way they got a 201 cowl to retrofit on a c model?

[Guest]

6 hours ago, thinwing said:

I have never seen baffling done quite that way in any of the 20 or so continental/ lycoming installs I have own or flown.Not even in the experimental....who did the last install on that engine...is that the way they got a 201 cowl to retrofit on a c model?

It would be interesting to see what the STC instructions say about the installation.  At very least the corner of the #4 baffle needs some trimming to clear the cowl.

Clarence

[rbridges]

I read the STC in the past; I was trying to get some information for Sabremech was in the early phases of his cowl project.  It's not very detailed about some things.  It appears to reference other documents.  IMO the baffling works well.  My CHTs and EGTs run very low.  IIRC, the overhaul was done at zephyr hills.  Mooney mart did the 201 conversions in '98.

[jetdriven]

The top cowl cracks near the spinner hump because the cowl inflates in flight and flexes quite a bit there. The only way to stop that is to make it very strong and stiff in that area. Boat resin and fiberglass cloth only adds weight. Nothing froma hardware store should be used.  You need structural aircraft epoxy and either S-glass or carbon fiber. 

[rbridges]

11 minutes ago, jetdriven said:

The top cowl cracks near the spinner hump because the cowl inflates in flight and flexes quite a bit there. The only way to stop that is to make it very strong and stiff in that area. Boat resin and fiberglass cloth only adds weight. Nothing froma hardware store should be used.  You need structural aircraft epoxy and either S-glass or carbon fiber. 

thanks Byron.  I actually read through your thread about reinforcing the middle hump.  I had a body shop repair it for me.  I'll ask about carbon fiber.  

I actually used metal tape to secure strips of baffle material to act as a cushion on the underside of the cowl.  The silicone is still intact, but spider webbing is occuring on the top side in the areas I mentioned.  I guess the vibration and/or rattling is still too much.  I hope I can find a "permanent" solution.  

[jetdriven]

3 hours ago, rbridges said:

thanks Byron.  I actually read through your thread about reinforcing the middle hump.  I had a body shop repair it for me.  I'll ask about carbon fiber.  

 

Body shops usually use chipped strand mat or boat fiberglass and polyester resin. None of that really fixes the flexing. When you get RJ cowl back, install it. Then push down in the center of the top cowl with 50-80lbs of force. Look at the reflection in the paint. If it moves, it's not stiff enough. 

[rbridges]

12 minutes ago, jetdriven said:

Body shops usually use chipped strand mat or boat fiberglass and polyester resin. None of that really fixes the flexing. When you get RJ cowl back, install it. Then push down in the center of the top cowl with 50-80lbs of force. Look at the reflection in the paint. If it moves, it's not stiff enough. 

the underside of my cowl is fine (I think).  they created some kind of bridge in the past, and it's pretty stiff.  this picture is rotated 90 degrees, but you can see where the metal frame rests right against the underside of the cowl.  This is the pilot side rear; I took it through the door above the battery box.  I tried using aluminum tape over silicone chafe tape, but it obviously didn't add enough shock absorption.  I sent and email to Joey Cole to see if my metal walls could be trimmed shorter and the baffling reinstalled.  In my first pictures, you can see the wear marks on my baffle extend all the way to the metal attachment point.

[triple8s]

1965 M20C with Modsquad OEM 201 Cowl 

[rbridges]

30 minutes ago, triple8s said:

1965 M20C with Modsquad OEM 201 Cowl 

It looks like your baffling almost runs horizontal off the top of the metal walls. Did you have issues with spider webbing and cracks in the cowl over the side walls running front to back?  

[Guest]

Your picture from the inside shows the baffle metal very close, if not touching the cowl.  The picture by triple8 looked to be trimmed in the same location.

Clarence

[rbridges]

21 hours ago, jetdriven said:

Body shops usually use chipped strand mat or boat fiberglass and polyester resin. None of that really fixes the flexing. When you get RJ cowl back, install it. Then push down in the center of the top cowl with 50-80lbs of force. Look at the reflection in the paint. If it moves, it's not stiff enough. 

here's a pic of the underside of the top cowl.  IMO it doesn't have a lot of flex in the center.  

[triple8s]

I didn't have any trouble with cracks, I did have heating problems and replaced the baffle seal and the heating issues went away. 

[rbridges]

10 hours ago, triple8s said:

I didn't have any trouble with cracks, I did have heating problems and replaced the baffle seal and the heating issues went away. 

that's odd.  maybe your walls were a little shorter, but they look very similar in the pics.

[rbridges]

I spoke with Joey Cole.  We decided to remove the baffling, trim the box lower and reinstall new baffling so the cowl doesn't get so much impact.

[rbridges]

 

We took a dremel and removed ~3-4mm of left and right wall height.  I can't go any lower until the baffling is removed.  I figured this would keep it from banging the top cowl so hard until joey gets a chance to reduce it further.  I started thinking about the whole situation.  I shimmed the motor mounts a few years ago.  I bet this actually made the top cowling issue worse; the shims raised my prop about 1/8-1/4".

[ArtVandelay]

On 2/7/2017 at 9:35 AM, rbridges said:

here's a pic of the underside of the top cowl.  IMO it doesn't have a lot of flex in the center.  

Looks to me it has a couple of metal supports glassed in already to prevent flexing.

[rbridges]

Good eye. I never really looked at that area very close before. 

[rbridges]

Well, I ended up going to Cole Aviation.  They reduced the metal walls and reattached new baffle material.  He said you could fit your finger between the cowl and the metal wall, so I'm hopeful that I shouldn't get any more damage to the fiberglass.  Hopefully the small amount of spiderwebbing won't worsen, but I'll watch it closely.