Exhaust Leak

[Bruce Fenstermacher]

If we could go back to the exhaust leak for a minute, Looking at you pictures, I would advise you get that system properly repaired or replaced. I would not use NAPA tape on an aircraft exhaust system. ....

Looking at a picture of an exhaust system does not substitute for a close personal inspection. But from what I can see of the system Mike showed, there are no repairs to make. It looks to be in fine condition. Actually it looks to be in great condition. The system is made up of pipes that are slipped into a can. They are held in the can by rivets. The slip joints are not tightly sealed. They never were.

The suggestion that muffler repair tape be used to repair a cracked or broken exhaust is not mine nor has it been the recommendation of anyone here ever that I'm aware. However we recognize that these exhaust systems of either make, leak. And they leak when new. The leaks are at the joints. Some systems leak worse than others. Sometimes there may be better ways to address bad leaks. A different clamp style for example on the Hanlon Wilson system sometimes offers improvement. And some people have been able to improve the seal at joints, at least for some period of time, with the muffler tape.

I understand that we are not the originators of the idea of using muffler tape at the joints. I believe that suggestion came from a very well respected engine overhaul facility.

Let me also add that welding the joints closed is not the answer. I have a pancake muffler system that a professional exhaust "aero fabricator" welded the slip joint. It probably worked well right up until the gapping 2" rip in the can was formed. Shame because other than the rip the system looks like new.

[lowNslow]

Bruce, your exhaust system may be a fine example of a pancake system but you have to wonder why the went to Hanlon Wilson system. While it is not perfect either, its much better then the old pancake system. I would rather keep my exhaust leaks to a minimum.

[voorheesh]

I agree that you cannot make a determination from a picture but that exhaust system looks pretty well worn out to me. Looking at those rivet holes makes you wonder if there is enough strength left in that tube for another go around. My view on exhaust systems is based on what you can't see. Exhaust systems contain a fire, they are subject to quick changes in temperature, they don't last forever. I still recommend taking it to a qualified source who can advise if it is repairable. (I did not mean to suggest welding a slip joint). Kinsley welding is a well known repair station that inspects, repairs, sells aviation exhaust systems. They have the expertise to determine if this system can be properly repaired and made airworthy.

I used to investigate aviation accidents and will never forget a Tripacer that caught fire in flight and nearly resulted in the death of pilot and passenger. Why? Defective exhaust system and a pilot who ignored the obvious symptoms (smell, scat tube blew off). He flew anyway. Sorry to lecture but those pictures rang a bell for me and I thought I should say something.

[Bruce Fenstermacher]

Bruce, your exhaust system may be a fine example of a pancake system but you have to wonder why the went to Hanlon Wilson system. While it is not perfect either, its much better then the old pancake system. I would rather keep my exhaust leaks to a minimum.

Karl, probably more times than we care to think about decisions to change design or manufacture/vendor are more to do with economic pressure than the new part being better. I think the huge press and dies required to make the pancakes halves and the heat shields did it in. I think the advantage of the Hanlon Wilson system besides manufacturing is it is more modular. If you need to replace an exhaust riser, it is a bolt on with of course the associated leaks at the joint.

The pancakes are actually pretty tuff and thick. While I have no data to support this I'll bet the failures were mainly in two areas. The bell/flange area and the weld at the y of the middle and rear pipe. The later probably failed because the slip joint in the middle pipe froze.

The pancake system has not been available for some time. I wouldn't be surprise to find Aero Fabricators (Wag Aero) was the last to make them. Considering the market, they only fit half of the 170s made and there is an alternative they would rather sell in the Hanlon Wilson style, I'm not surprised. I've also heard few will repair the pancakes. Not because they can not be repaired but because it is not something they are use to doing, and maybe they'd rather sell you a whole new system. Wag just started advertising they will repair pancakes but apparently they might not. I haven't seen the mufflers in question but a local member just had his rejected there. They were sent in for cracks at the bell in the flange, a fairly common repair it seems on other systems.

AWI's current price for a replacement "overhauled" Hanlon Wilson system is $2400. Why would they repair a pancake for any reason.

I like Kinsely. They were very imaginative with the repair of one of my J-3 exhaust headers. If anyone might repair a pancake if needed, they might.

I'm also sensitive to exhaust issues. One of my closer flying buddies and his wife had an inflight fire in his airplane because of a defective exhaust. They barely escaped. This is a plane I flew in about every other week. It could have been me in it. I'd also like to see no leaks in any aircraft system but yet some leaking seems to be acceptable in design. Just look in the cowl of any SR-22 on the ramp and count the brown exhaust leaks at the slip joints.

Pancakes are ugly, they look bad I admit. And many of the aging systems are on their last legs. But ugly doesn't make them unairworthy so don't judge them by the first impressions. I'm not out to save pancake mufflers either. Like many parts they need to be inspected and evaluated closely.

[C170U2]

Thanks for all the replies. My IA assures me that my exhaust is just fine and in perfectly safe. Not the prettiest, but whatever.

I hopefully will start on the pushrods this weekend. After reading all the doom and gloom about shelling out my engine, I was reassured by my friends at the airport that it really isn't that big a deal. Reading through the instructions, it looks like I will be taking off the lifter bodies so it should be pretty obvious that everything is seated ok.....we'll see how it goes and I will report back.

Arash - the gasket you pointed out is actually included in the kit. After seeing your post I ordered 6 from spruce this morning before I got the kit in the mail. That being said, if anyone needs those gaskets let me know. I got 6 extras.

I'll post some pictures when I get through with it.

Mike

[C170U2]

No worries at all. At this point it is just kind of par for the course for me to buy wrong/extra hardware.

Hopefully you get your real plane running soon....and the mini one!

[Bruce Fenstermacher]

Mike, the job is not that big of a deal. And it is easy to screw up big in a flash with the hydraulic cup before you even see the cup. It is also easy to make sure you don't screw it up. But you would have had to know about and how to avoid the problem. You have now been sufficiently briefed. You have fun.

[C170U2]

Thanks Bruce, I do appreciate the heads up!

[C170U2]

One side is pretty much done...after much swearing and sweating. They do in fact have the C clips mentioned above.

The only issue I ran into was getting the rocker arms back in. My IA showed me how to do it on one cylinder but when left on my own, I couldn't get the 4 and 6 cylinder rod to push back through. Any tips? I was shown that I needed to rock the prop to find where the rocker arm was in its lowest position...but I wasn't having any luck. I was hot and getting frustrated so I left before I did something stupid.

[johneeb]

................... so I left before I did something stupid.

Mike some of the best decisions I have made have been by taking your exact tact. The result will come to you, just keep looking.

[Bruce Fenstermacher]

I don't think there is any trick to it. There might be a tricky tool that makes it easier though.

First if you followed the install instructions and removed and clean the hydraulic units, they are flat. In other words there should be no oil in then. They should compress rather easy. With both the crank set so that both valves should be closed, you should be able to push the rocker pin in while wiggling the rocker, pushing in against the hydraulic unit. After you get the first then wiggle the second rocker. You probably need to put the #4 in first because being in the center you will need to slip the rocker shaft for #4 just a bit into #6 or maybe all the way through #6 and into the #4 cylinder. You don't need to slide it through the #6 rockers when your passing the shaft through.

With the home made tool pictured you can compress the valve springs enough to wiggle the rocker arms to line up the rocker shaft without pushing in on the push rod. It is a simple metal bar about 1/8" thick with cut outs to clear the valve keepers and rocker arm tips. The AN-3 bolts screw into the valve cover screw holes and is what does the compressing.

Spring compressor tool %231.JPG

[C170U2]

That looks like exactly what I need. I was lacking a second set of hands when I was trying to finish up 4 and 6. That tool would solve that problem....or I just do it early in the morning when my friends haven't abandoned the airport due to the heat(98 degree day today). Thanks for the "tip"!

[GAHorn]

I have a home-made tool almost identical to the one Bruce shows which works just fine (and cheap.)

BTW... when we all share our techniques and ideas... Please, everyone... Keep in mind that unless you are a certificated aircraft repairman.... all maintenance other than preventive maintenance MUST be properly/directly under the supervision of a qualified A&P.

Exhaust leaks can be more insidiously-dangerous than one might think and unlike automobiles one cannot simply pull over.