Thorp Air Command - T18.net

I need to remove my exhaust during the upcoming annual as recommended by the manuf. to "exercise" and re-lube the cross over slip joint . While I have it off is there an advantage to changing out the "standard" steel studs with SS studs ? Or should I follow the policy of " If it ain't broke don't fix it ? " Ba BOOM !

RB

Rich;
I'm nobody when it comes to Lycoming, but I do know a thing or 2 about stainless steel.
Stainless steel nuts will gaul on stainless steel studs. I have much better luck with stainless steel nuts on carbon steel studs. I have had a lot better results getting them to come apart. My experience is in Marine Diesels, and some hydraulic hose fittings out in the salt water. JIC stainless fittings are hard, so they need lots of torque to seal. Then they fuse together and the threads stick. So we used plain steel hose ends on the stainless steel bulkhead fittings. Worked great for the 2 year life of the hoses (weathering in the salt water and sun).
I found Grade C Toplock nuts to be very effective at holding high vibration exhaust system flange bolts together, yet they still unthread, instead of rusting together. Use nickel antiseize too.
http://almabolt.com/pages/catalog/nuts/lock.htm This would be much cheaper than the silver plated stop nuts Continental specs for exhaust studs...
So my 2c would be to inspect the studs, and if they pass inspection, use antiseize with the Lycoming spec nut, or try the Toplocks if they are cheaper, and if you like the way they look/work.
They are punched around the top instead of cut and pressed like aviation high temp lock nuts, but they do the same thing.
Here is Fastenall's page:
http://www.fastenal.com

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

Thanks Scott : I guess my main concern is the nut/stud issue . How many of us have tried to remove an exhaust manifold off a car only to have one of the nuts break off at the stud ! OH MY !

RB

Rich,

Talk to your engine mfr. I my experience, stud removal and replacement is considered an emergency procedure. They are installed at the factory. You risk corrosion issues between the stud and the cyclinder, as well. I haven't found in over 2000 hrs of operation any need to remove and lube my slip joints. Your condition inspection of the exhaust should consentrate on looking for leaks, especially at the head. A leak here can lead to exhaust flange erosion. If you find that, then you will have the pleasure of removing the studs for resurfacing. The short answer -- leave them alone.

_________________
Bob Highley
N711SH
SN 835
KLAL

I read an article in some aviation magazine recently extolling the virtues of minimum maintenance and recommending avoidance of the "maximum" maintenance philosophy.
It was an interesting read, The moral of the story was, in essence, if it aint broke and won't hurt you if it fails then leave it be, wait and see. Sending time and money fixing stuff that isn't broken risks breaking something else that might cost you more.

Not sure if that applies to studs but buying nice new shiny stainless parts is always a bit tempting.

_________________
Stug

I'll stick to monitoring the exhaust . Thanks for the info. Bob .

RB

Guys,

I kind of like the approach Continental uses with their engines. The nuts are brass. I recently removed my exhaust for inspection and replaced the nuts with brass ones. It is simple to grind a notch with a dremel tool on the side of the nuts to release them from the stud
the next time.
I also found that the studs were rusted and the nuts did not want to easily spin on. I took a thread chasing die, ground it down in diameter and welded it to an old 9/16 socket. This made a simple tool for chasing the threads. Re-assembled using Permatex "weiner schlider" and hopefully the job next time will be easier.

Jim Mantyla

Gents: we are discussing 2 maintenance philosophies:
1. Fly to Failure and;
2. Preventative maintenance

Both maintenance approaches have their merrits.
Fly to fail may scare some; but if a visual inspection (like on a pre-flight) serviceability verified I see no issue with this maint approach.
With a Flt control bearing worn but within limits (it is prudent to me to replace on the annual inspection ~ preventative approach).
A combination of these 2 approaches should be part of your inspections.
Rich has identified a manufacture directed maintenance requirement to lube the slip joints.

Here is my 2 cents (appropreate as the CDN Government stopped making pennies yesterday).

On yearly annuals, the Bell Twin Huey, there was a requirement to dismantle the heater ~ resulting in virtually no heater issues.
When the Bell 412 entered into CDN military a maintenance decision to remove this heater inspection was made due to very low system failures. Since both helo's use identical heaters this rationalization seems valid, until the number of heater failures started occuring on the new helicopter. Draw your own conculusions,...

My suggestion before you disregard the manufacture inspection is:
1. Contact the manufacture ~ why do they call for the inspection, (is it due to a one time event, or poor installation,...)
2. What is the consequence of not performing the inspection, (warrenty issues, subsequent failure etc) and;
3. Do they have a alternate inspection method / periodicity (maybe they will approve every 2 years due to low flying rate etc. ?)

Usually there is some sound reasons for manufactures recommended maintenance requirements.
Points raised in this topic are all valid, we tend to over maintain, over inspect and do in some cases cause more expense WRT aircraft maintenance. Personnelly the only time I would be removing the exhaust system would be correct a visible exhaust leak, or to inspect the exhaust valve / seat condition with a bore scope via the exhaust port. I would deal with the nuts/ stud issues if they occure down the road.
Cheers.

_________________
Victor J Thompson
C-GIRQ
In memory of Dad

Jim: I guess that was my reasoning for swaping out the steel studs . Leaving on the steel nuts for an extended period of time causing them to rust to the steel stud and breaking off during removal , but after Bobs comments regarding the studs being factory installed , I'll back off on that one least I break one off trying to due "PM." I think I will go the brass but route and put on " a little dab will do ya" never seize .

Victor: I am a FIRM believer in PM and do not like the idea of fly to failure , especially in a single engine aircraft . The exhaust area gets a good looking over for signs of leaking !
RB

I agree with Scott... stainless on stainless equals great chance of galling. That is one of the reasons they plate high-end stainless steel aerospace nuts with silver - for lubrication. I would definitely leave the studs alone. I believe that they are a little special anyway, and you might have trouble getting the correct thing in S.S. Instead of a common size machine thread on the portion that screws into the head (like you would find on an automotive stud that you get at NAPA), that thread id slightly "off" on the Lycoming part, causing a tight interference fit for proper retention. A regular stud will work, but it's not correct. I do like to use S.S. nuts along with S.S. star washers. I also like the spiral-wound exhaust gaskets.

As far as exhaust system slip joints... here's my 2 cents worth - The joints are important, and should be serviced (and use the nickel stuff, like Scott said), but I don't think it's necessary every year by any means. I do mine about every 5 years. They do tend to seize with burned-out anti-seize, carbon, dirt, etc. They're there to minimize the stress on the system, especially at the flanges on the cylinders, when the pipes expand & contract. I'm talking about slip joints on a cross-over system especially. A little story- I had a friend who thought the slip joints were just to facilitate the initial fit & installation. He reasoned that they should be sealed, & he used high-temp silicone sealant. Of course the sealant burned & deteriorated, and the joints locked-up good. After about 100 hours he had cracks on 2 of the pipes at the bases of the flanges & exhaust was impinging on his cowl. It was a real trick to get those joints apart again. Definitely keep them lubed & cleaned periodically. I know there are guys who are going to say that they've never cleaned & re-lubed theirs and they don't have any cracks. All I can say is that the joints are probably still "slipping", but for how long? The nickel-based stuff has the highest temperature rating, & will reliably last the longest. Also, it's great with S.S. - try it, you'll like it.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

OK...while I was sittin on the can I was doing some technical reading in the Spruce catalog and came upon this about SS exhaust studs . "Produced from corrosion resistant 321 and are a direct replacement for the standard Lycoming studs . Stop stud corrosion and rust out problems , stop expensive cylinder repair caused by broken studs , allow easy removal of exhaust systems for gasket replacement/inspection ." I thought as long as I am going to remove the exhaust to "lube" the slip joint I might as well replace the studs . Replacing the studs is not going to happen now from info received , but I still plan to remove the exhaust and "lube" to cross over joints . I talked to the manufactuer of the exhaust , Custom Aircraft Products and they suggest/recommend removing the exhaust to reapply anti seize to the joints every other annual . This will be my second annual since the aircraft has flown and just to satisfy my retired brain I am going to pull it to see what it looks like . If it is not seized up , then I'll extend the interval to every 3 annuals . Got the "No Blo" gaskets off E-Bay for about $2.00 each so it's not a big expense to pull it , just labor .

RB

Let us know how many break off.......K-Boom K-Boom

I don't think Bill is talking about the exhaust. >:D

Blllllaaaaaaaaaaaaapppppppp.

I agree that there is no need to replace the studs. If the nut comes off every year you will not have problems with the stud. Over the years working on airplanes I have seen a few leaks where the exhaust flange meets the cylinder. On one of these it was directly related to frozen slip joints in the exhaust system. Without being able to slip when expanding under temp it puts stress in places where it shouldn't be causing problems.

Tom Baker KOLY Just an airplane guy living the dream.

One other quick thought, Rich... there is really no reason that the studs should get all rusted to the point that they are weakened. Mine still look great after about 28 years (22+ since first run). I know I live in a dry/no salty air environment, but I think that unless perhaps you have a seaplane, that area is DRY all the time. Just coat the threads, all the way up, with a thin film of that 2200 deg. nickel anti-seize. Then don't worry, be happy.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE