Doghouse Gap Seal Material

[Skates97]

I was doing an oil change and rotating/cleaning plugs when I noticed something. I had a work light sitting behind he doghouse and when looking inside on the left side I noticed light shining through. I "thought" that it was sealed up pretty tight, but apparently it isn't. More investigating showed that there is about a 1/2" gap (I should have taken pictures) between the back wall of the doghouse and the top piece. This is filled in with some kind of a rubber material that has degraded over time and has resulted in the gaps I see. I want to replace the old piece back there with some new material.

My CHT's haven't been as bad as some I have read about. On a hot day like last week leaving Delta UT with DA over 8,000 and temp 34 degrees it sat right at 400 degrees initially and then I got it down to 380-390 for the rest of the climb. However recently I am seeing 370-380 in cruise which I didn't see. I think it is because that baffling must be slipping out of place more.

I'm trying to figure out what kind of material to use back there to fill that gap. There's some different stuff at Aircraft Spruce but I think there has to be a better material than what is currently on there. I know some of you have done some work rebuilding doghouses @M20Doc @Andy95W @Sabremech and @Hank had extensive work done on his in recent annuals. What material is used to seal the big gaps in the doghouse? Around the starter/alternator it looks more like a felt like material.

[RLCarter]

The felt looking stuff is felt, the rubber stuff and the felt can be had at Aircraft Spruce

[Raptor05121]

I filled all the small holes with high-temp RTV silicone. Sadly the 600 degree+ stuff only comes in orange and is an eyesore, but it works.

[Guest]

There is no sealing material between the top cover and other pieces.  The 1/2" gap suggest the top is not installed correctly.  All of the parts are held together with #4 PK screws and # 4 Tinnerman nuts.  Felt is used to seal the generator opening, and rubber material seals the front of the baffles to the cowl and should be tucked into the groove in the cowl.  You can use silicone baffle tape for the front.  

Clarence

[Hank]

Richard, the overwhelming majority of my doghouse resurrection was sheetmetal work. Good luck with yours!

[Skates97]

1 hour ago, M20Doc said:

There is no sealing material between the top cover and other pieces.  The 1/2" gap suggest the top is not installed correctly.  All of the parts are held together with #4 PK screws and # 4 Tinnerman nuts.  Felt is used to seal the generator opening, and rubber material seals the front of the baffles to the cowl and should be tucked into the groove in the cowl.  You can use silicone baffle tape for the front.  

Clarence

Thanks, I will have to take the top off all the way off along the back edge and take a closer look. Everything else on the doghouse is tight and I wouldn't have even noticed this if I hadn't been working on it at night and had that work light sitting where it was. It just caught m eye when I was looking in and saw the light shining through. It wouldn't be the first thing that I found "not quite right" but everything so far has been a fairly easy remedy. 

[Ned Gravel]

This is what Clarence did to rebuild mine when the overhaul was done in 2009.  CHTs never go above 320 on climbout.

[Raptor05121]

That looks beautiful. Is that done by hand?

[HRM]

38 minutes ago, Ned Gravel said:

This is what Clarence did to rebuild mine...

Good grief, you could eat off of that. Beautiful for a 52 year old bird.

[Andy95W]

Richard- good luck, it just comes down to keeping at it until you've sealed as many gaps as possible as well as possible and then  being happy with the result.

That thick felt is good, but not easy to find or shape.  Below is another method using the 1/8" thick silicone material.  Specifically, look around my starter.  (And, as Clarence pointed out 2 years ago. The seal material at the lower edge is supposed to fit in the slot in the cowling.  I had loosened and pulled my lower cowl to do work.)

 

[Skates97]

On 7/22/2017 at 5:05 PM, M20Doc said:

There is no sealing material between the top cover and other pieces.  The 1/2" gap suggest the top is not installed correctly.  All of the parts are held together with #4 PK screws and # 4 Tinnerman nuts.  Felt is used to seal the generator opening, and rubber material seals the front of the baffles to the cowl and should be tucked into the groove in the cowl.  You can use silicone baffle tape for the front.  

Clarence

Are you sure they are #4? Aircraft Spruce doesn't have a listing for #4 that I can find. I have replaced a few of the screws and I thought they were #6 that I used, but it could be my memory off or me just using a bigger size because the speed nuts were stripped out a little.

I'm going to go out Tuesday evening and pull the top off the doghouse to get a better look at what is happening along that back piece where someone added the filler. I was going to take some extra speed nuts/screws to have on hand just in case and wanted to grab them ahead of time.

[carusoam]

The tinnermans are smaller than AS has in their system.  I had the same problem 15 years ago...

Since that time, I have learned to call AS directly and tell them, I know they exist.  AS is pretty good about taking on a challenge and trying to get them...

Best regards,

-a-

[RLCarter]

After many many years of being taken a part and put back together my doghouse had about every size screw and tinnerman available in it.....

[Skates97]

32 minutes ago, carusoam said:

The tinnermans are smaller than AS has in their system.  I had the same problem 15 years ago...

Since that time, I have learned to call AS directly and tell them, I know they exist.  AS is pretty good about taking on a challenge and trying to get them...

Best regards,

-a-

I may have to peruse the hardware drawers in my parts departments at our dealerships tomorrow... I know that we have some smaller stuff there. I'm fairly certain the plane won't know if it came from there or Spruce...

Thanks for all the info guys. I will have to post some pictures and results after I get into it.

[carusoam]

The small ones didn't have the spring clip style, back in the day...

See if you can get them in that style while you are at it...

Best regards,

-a-

[Skates97]

Took the top off. This is the material around the back. It is screwed and riveted into place, but falling apart and there are gaps. It looks like it's supposed to fill I the gap between the engine and the back panel of the doghouse as it goes all the way around. 

[Hank]

No, there's nothing like that in mine . . . This is the only photo I can find right now, from when I replaced the ignition harness, so it's not really a doghouse photo  (but it works).

[Andy95W]

Richard- I would buy about 5 feet of baffle seal material, with fiberglass mat, from Aircraft Spruce.  Then I'd remove all of that felt and cut and manipulate the new rubber so that it conforms to the curves at the back of the case.punch holes in it in the proper locations with a sharp leather hole punch, and reinstall with the same hardware.  Talk with your local maintainer before you commence the removal and work out a game plan for bending, cutting, and installation.

Then, while you're back there, look at your vernitherm mount location.  I'll bet you have a pretty substantial gap there, too.  That one will be more difficult to patch, but also very worthwhile.  

http://www.aircraftspruce.com/catalog/appages/siliconecowlseals5.php?clickkey=526923

[Hank]

Silly question, Richard:  why do you remove the entire top of the doghouse? As in my photos, I only remove the outer panel on each side, perfect for plug access. Surely your top isn't all one piece???

[RLCarter]

If you consider its age, it's in pretty good shape. If you go back with Felt, really sharp scissors work well for cutting it. 

[Skates97]

2 hours ago, Andy95W said:

Richard- I would buy about 5 feet of baffle seal material, with fiberglass mat, from Aircraft Spruce.  Then I'd remove all of that felt and cut and manipulate the new rubber so that it conforms to the curves at the back of the case.punch holes in it in the proper locations with a sharp leather hole punch, and reinstall with the same hardware.  Talk with your local maintainer before you commence the removal and work out a game plan for bending, cutting, and installation.

Then, while you're back there, look at your vernitherm mount location.  I'll bet you have a pretty substantial gap there, too.  That one will be more difficult to patch, but also very worthwhile.  

http://www.aircraftspruce.com/catalog/appages/siliconecowlseals5.php?clickkey=526923

There is a huge gap back at the base of the #3 cylinder where it looks like whoever put the baffling in just decided it was too much work to finish it off. It ranges from about 1/2" to 1". Shining a flashlight from outside the doghouse you can see it easily. That will be more difficult to get the material down in there but I'm sure will make a difference. Here you can see it with the light from behind.

1 hour ago, Hank said:

Silly question, Richard:  why do you remove the entire top of the doghouse? As in my photos, I only remove the outer panel on each side, perfect for plug access. Surely your top isn't all one piece???

I only remove the top/side panels to get to the plugs. Very simple and easy. However, when I did my oil change last time and was also rotating plugs I had left my work light sitting on top of the oil filter behind the doghouse. When I was doing the top plugs on #2/#4 I noticed light shining through a gap at the back of the doghouse and thought "that can't be right..." I tried looking at it closer but couldn't really tell what I was seeing. I had a trip to take, and my temps have been typically 380-390 in climb and 370-380 in cruise so I put everything back together with plans to dig in more after the trip. Tonight was my first chance to pull the top off and see what I was really dealing with. 

1 hour ago, RLCarter said:

If you consider its age, it's in pretty good shape. If you go back with Felt, really sharp scissors work well for cutting it. 

For a 50+ year old plane it really is in good shape. After seeing pictures of some other dilapidated doghouses I'm glad I have the one I do. I'll get the felt replaced and if it lasts another 50 years I guess my son can worry about replacing the next time.

[carusoam]

Silicone is the modern version of felt.

The felt had been in there for 50 years, but stopped working 40 years ago...

Go silicone, as discussed above...

Did you also review the front of the dog house where the starter and alternator had felt there once?

Check in with our silicone guy Guy G he can be pretty helpful... @???

Best regards,

-a-

[Skates97]

Going to go with the silicone that Andy linked above. Already have it set for will-call tomorrow at Aircraft Spruce. I'll have my wife run out and pick it up. (The blessings of having an awesome wife and AS about 10 miles away.)

[Andy95W]

On 7/25/2017 at 11:58 PM, Skates97 said:

There is a huge gap back at the base of the #3 cylinder where it looks like whoever put the baffling in just decided it was too much work to finish it off. It ranges from about 1/2" to 1". Shining a flashlight from outside the doghouse you can see it easily. That will be more difficult to get the material down in there but I'm sure will make a difference. Here you can see it with the light from behind.

 

That's the vernatherm I was talking about. You may have to use a combination of aluminum, pop rivets, and the silicon material- plus a good bit of imagination. 

I will also bet that most people who think they have a pretty tight doghouse have the same gap as yours.  Nobody seems to look down there, and when they do, it looks too hard to attempt.

EDIT- I wrote this after a long day of walking around Oshkosh and my brain was pretty tired.  This is the Oil Pressure Relief Valve to adjust oil pressure and is located above and aft of the #3 cylinder.  But I'll bet most people do have a pretty sizable gap in the baffling around and below it.