Exhaust Gaskets

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

Post Reply
User avatar
darhymes
Posts: 78
Joined: Fri Jul 24, 2020 7:29 pm

Exhaust Gaskets

Post by darhymes »

I am in the middle of trying to get a few exhaust leaks repaired and have questions that I'm hoping some of you may be able to provide insight for me...

1. My AP has decided to go with the Blow-Proof (SS single piece) exhaust gaskets. I had requested the Spiral Wound (No-Blow) since that is what was installed before and it is all I can recall using on various other aircraft but he insists that the thin gaskets are good...I trust the guy-he knows a lot more about engines than I do. One side of the exhaust already has the gaskets and risers installed but not tightened. When I looked at the gaskets, I noticed there is only one gasket per cylinder. Most of what I have read regarding these gaskets is anecdotal but they appear to be installed with two per cylinder (one groove recessed into the other). The only solid document on this (that I have found) is a service letter from Lycoming that gives instructions on how to install the two gaskets. I haven't found anything pertaining to Continental or Rapco that mentions two gaskets for the O300. Do any of you have any solid info that describes using one or two of these gaskets per cylinder?

2. Since I am used to the Spiral Wound gaskets, that is what I am comfortable with. I welcome any advice on which gaskets you recommend and why...

3. The previous exhaust installation included a lot of RTV. I can't really see why as the flanges and ports all seem to be in good condition. Anyway, it is really nasty stuff to remove. I have been doing this part myself-very carefully with mineral spirits and a Q-Tip. It's taking forever. Does anyone have suggestions on how to remove this stuff? I am trying to avoid scraping with sharp/metal tools.

Sorry to be so EXHAUSTIVE with my questions but I'm getting kinda BURNED out... :lol:
Dustin Rhymes
'55 170B N4410B S/N 26754
'06 G550 “The Silver Bullet”
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Exhaust Gaskets

Post by GAHorn »

Without re-facing the cyl-ports and ex-risers…. a small wire-wheel on a drill motor might remove the RTV.

RTV is NOT a good sealant in this location despite some RTV “High Temp” claims. RTV does not have the capacity to hold pressure except on perfectly-fitted surfaces….and certainly not exhaust pressures at 1200+F temps.

The spiral-wound gaskets are the only ones I’ve ever had success with…. usually as replacements for the thin/doubled set you are describing.
I wonder…if the method chosen by your A&P doesn’t work….. will he do it all-over-again with spiral gaskets at his expense? :twisted:

Here is how Lycoming recommends the use of both types:
Exhaust Flange Gaskets.pdf
(109.35 KiB) Downloaded 371 times
Here is how Continental does it (notice that Pn630635 is a thin gasket and is slightly differently shaped than the Lyc part, but is assembled similarly):
22339237.pdf
(193.99 KiB) Downloaded 411 times
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
darhymes
Posts: 78
Joined: Fri Jul 24, 2020 7:29 pm

Re: Exhaust Gaskets

Post by darhymes »

Thanks for the info, George. Your recommendation of the wire wheel gave me an idea. I have a Dremel with a flexible extension and a small, nylon brush wheel. It should be gentle enough to avoid scratching yet aggressive enough to pick away at the RTV a little better. If it doesn’t work, then I’m back to the sloooow removal process. Don’t worry…I will never use RTV on an exhaust installation.

I may be reading the chart incorrectly but it appears the Continental SB only recommends doubling the thin gaskets on certain fuel-injected engines (but not the C145/O300). I like the Lycoming Service Letter since it describes the installation of either gasket in detail. It doesn’t help me with the C145, though. At this point, I feel more comfortable going with what I know and trust. I’ll make sure the spiral wound gaskets are installed instead.
Dustin Rhymes
'55 170B N4410B S/N 26754
'06 G550 “The Silver Bullet”
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: Exhaust Gaskets

Post by n2582d »

Dustin,
I haven't tried these sealant cutters but they may be an option. Anyone tried these, and if so, how well would they work in removing sealant around the exhaust port?
Gary
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Exhaust Gaskets

Post by Bruce Fenstermacher »

Dustin, the thin stainless gaskets are ALWAYS installed two per port.

I change a lot of exhaust gaskets at work. Not because either blow more than the other or blow at all but because we change a lot of cylinders. And our company does not reuse the no blow spiral wound which are reusable.

Personally, I'd use spiral wound. You or your mech will have to grind the steel frame of these to fit as the small Continental cylinder ports are so close together.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
mit
Posts: 1049
Joined: Wed May 01, 2002 1:54 am

Re: Exhaust Gaskets

Post by mit »

I have seen a lot of different ways to install ex gaskets..... Not according to the book. Some where leaking and some not. Having a true surface is important.
Tim
User avatar
darhymes
Posts: 78
Joined: Fri Jul 24, 2020 7:29 pm

Re: Exhaust Gaskets

Post by darhymes »

I tried the Dremel tool idea and was able to remove the RTV very effectively from the exhaust ports. It was more like dental work than exhaust maintenance. Much quicker and effective than using solvents. Had to wrap the Dremel chuck with tape to keep from scratching up pushrod tubes, etc.

Ordered some spiral wound gaskets also. Installing everything tomorrow.

Thanks again for all of your comments and suggestions.
Dustin Rhymes
'55 170B N4410B S/N 26754
'06 G550 “The Silver Bullet”
User avatar
darhymes
Posts: 78
Joined: Fri Jul 24, 2020 7:29 pm

Re: Exhaust Gaskets

Post by darhymes »

I meant to show pics (before and after) of how well the brush attachment on the Dremel worked, just in case anyone else runs into this problem. There is very little chance of damaging anything yet the brush cleaned the RTV off very effectively. I took extra care to make sure any residue was removed before installing the new gaskets.
Attachments
IMG_7116.jpeg
IMG_7117.jpeg
IMG_7118.jpeg
Dustin Rhymes
'55 170B N4410B S/N 26754
'06 G550 “The Silver Bullet”
User avatar
gfeher
Posts: 571
Joined: Fri Sep 26, 2014 9:19 pm

Re: Exhaust Gaskets

Post by gfeher »

Anyone have any experience with these exhaust gaskets supplied bt Fresno Airparts: https://www.fresnoairpartsco.com/produc ... t-exhaust/

They are not the usual spiral wound or paired stainless steel types. They are an asbestos layer sandwiched between two layers of copper sheet, and are a little flexible. Two of the flanges of the exhaust “inlet” tubes on my 170B are slightly warped and I don’t want to sand/grind them flat any more than I already have. If i use spiral wound gaskets on them I’m afraid they will leak. I’ve heard that the Fresno ones will seal flanges like mine, but I don’t have any experience with them. My tubes are otherwise in great shape.
Gene Feher
Argyle (1C3), NY
'52 170B N2315D s/n 20467 C-145-2
Experimental J3 Cub Copy N7GW O-200
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Exhaust Gaskets

Post by GAHorn »

It’s been my experience that if the surfaces aren’t “true”..(flat)… they cannot be sealed regardless of which gasket is used.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Exhaust Gaskets

Post by Bruce Fenstermacher »

I've been told they, the copper asbestos, tend to deteriorate quicker that the later replacements such as the stainless and no blow readily available today. Leroy loved them and would reuse them over and over til I replaced them with no blow type. Can't say I ever used one long enough to confirm the rumors. I just replaced one I found on my Vagabond and I can say that lasted at least 2 years and I only replaced it cause I removed the cylinder for other work.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: Exhaust Gaskets

Post by n2582d »

Gene,
What Avweb says matches what Bruce wrote about these copper/asbestos/copper sandwich gaskets:
The fiber/copper sandwich type is thicker, allowing the gasket to fill in where gaps would occur between cylinder flange and exhaust stack flange due to misalignment. The soft metal (copper or similar) also will fill in minor surface imperfections just as the plain copper style would.The problem with the copper/fiber and the plain copper type of gaskets is that they do eventually blow out, as they are soft material and do not seem to stand up to the continued heat and pressure.An additional “crutch” used by mechanics has been to use stove-pipe cement to help seal uneven sealing surfaces such as the cylinder surface, and even around exhaust clamps, typically used in Cessnas. While using the cement works to seal up leaks in many cases, you need to be honest with yourself and properly repair the parts if the leaking areas are in poor condition.
I was a bit disappointed that my rebuilt exhaust from AWI had 3/16" thick flanges rather than 1/4" ones. While I don't think it is worth the hassle of welding on new flanges to old risers, flanges are available for this purpose. Compare the cost of repairing your old risers to just getting new 321 stainless risers from Acorn/AWI/Knisley. OEM flanges are p/n 21492. Aircraft Spruce and Wicks sell 1/4" flanges in 1018 mild steel and 321 stainless.
Gary
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Exhaust Gaskets

Post by GAHorn »

The ONLY types I will use because they are the only ones with which I have had consistent, no-leak performance. The spiral portion is soft enough to conform to minor surface imperfections and do not “disappear” after many hours of use like copper ones do.

(This set of four is more economical …especially considering shipping cost….and often you’ll need more than one when you disassemble/reassemble your exhausts anyway…but singles are also available):

https://www.aircraftspruce.com/catalog/ ... ey=3010011
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
Post Reply