Exhaust Leak

[C170U2]

I pulled the cowl today for the first oil change since I got my plane back airworthy after 20 some years.

I found that both of my pancake mufflers were leaking exhaust from where the pipe exits the bottom of the muffler. Those pipes were held to the inner shroud by about 6 pop rivets. The fit seemed tight enough but obviously it wasn't based on the visible soot in the surrounding area. Is this a known problem with this muffler system? Has anyone tried using some sort of muffler sealer (commonly found at napa) to help seal these pipes? What are other options to make this a nice tight fit? I don't really want to upgrade to a more modern system if I don't have to.

I will post some pictures tomorrow.

[C170U2]

Here are some pictures. Are the pipes supposed to be riveted?

[Bruce Fenstermacher]

Yes the pipes are suppose to be riveted and they look about normal. Or at least they look about like mine. You could try some NAPA tape if you wish. Exhaust leaking in that area into the cowl isn't a problem in my mind any more than the exhaust that exits the end of the pipe.

[Bruce Fenstermacher]

BTW if you think the newer style Hanlon Wilson system might be a tighter exhaust, you would be wrong. They can be real leakers as well.

[KG]

BTW if you think the newer style Hanlon Wilson system might be a tighter exhaust, you would be wrong. They can be real leakers as well.

This is true.....

PB140054.JPG

[C170U2]

Thanks for the replies. I went to Napa and got some muffler sealer and will see how it works. It has to be better than nothing.

I also bit the bullet and ordered the real gasket pushrod tubes. I figured with the exhaust being off it was a good time to do it. Mine are leaking really bad so I figured it was time. Only bad part is that all of this ruined all my memorial day weekend plans because I doubt I will get them installed in time. Oh well...

[C170U2]

Thanks Arash, but one of my friends has the tool and let me borrow it.

I never realized these exhaust leaks were that common. Good to know, but I still am glad that I am sealing it up. I just wish I had pulled the cowl after this upcoming weekend.

[170C]

If you have the opportunity some photos of the vrs stages of removing things to get at the old push rod tubes, their removal and replacing them with the new ones would be nice. Do these new, spring loaded tubes fit all O-300 cylinders regardless of mfg? Someone commented some time back that it looked like there might have to be a small mod to the cylinder head where the new tubes fit. Did any of you experience this?

[Bruce Fenstermacher]

Mike, be careful when removing the push rod from the tube in order to replace it.

There are two types of hydraulic units. One has a c clip that holds the cup in place the other doesn't. No telling what you have in your engine. If you don't have the c clips when you remove the push rod the cup tends to stick to it and get pulled out because of surface tension from the oil. If this happens your not like to know it and rotating the engine will crush the cup into the lifter and you will end up splitting the case of your engine (in other words an overhaul) to replace the unit.

So what you do to remove the push rod is to take some compressed air and blow a quick blast of air through the push rod to blow it off the cup.

Also don't change positions of the push rods. They may not be all the same length.

[C170U2]

Thanks for the advice. I was unaware about the issue pulling the pushrod tubes out. My friend who did the same mod (on a C-85) didn't mention needing to blow air into the tube....my IA didn't mention it either. I'm sure the paperwork included will speak to it. I should get the parts on Friday. I will post some pictures when I get done. With a little luck I might get this done this weekend.

[Bruce Fenstermacher]

Thanks for the advice. I was unaware about the issue pulling the pushrod tubes out. My friend who did the same mod (on a C-85) didn't mention needing to blow air into the tube....my IA didn't mention it either. I'm sure the paperwork included will speak to it. I should get the parts on Friday. I will post some pictures when I get done. With a little luck I might get this done this weekend.

No I doubt the paper work will speak to it which is why I mentioned it. Either of the hydraulic body styles can be used and you will often find them mixed. My first engine had half without the c clip.

See this thread which tells of 3 members who broke hydraulic bodies by removing push rods and pulling the cup out of place. http://www.cessna170.org/forums/viewtop ... ken+lifter

[Bruce Fenstermacher]

Follow this sequence in your mind.

• You can not remove the tube or the hydraulic unit cover without removing the push rod. To remove the push rod you remove a valve cover rotate the engine so this cylinder is on TDC so you can slide the rocker shaft out and remove the rockers. Without thinking you pull the push rods and one of them pulls a cup out and cocks it in the hydraulic body. The proverbial gun is now loaded and cocked.
  
  You have decided since you are doing all the cylinders you remove the next cylinder valve cover and discover a valve is open and you must reposition the crank so that cylinder is on TDC in order to remove the rocker shaft. You move the prop and bang you've pulled the trigger as you hear the cup crack the hydraulic body in the first cylinder you do. Your engine is now dead.

or

• You decide you will do one complete cylinder. You do everything in in the first paragraph above and the gun is once again loaded and cocked.
  
  In order to remove those push rod tube you decide to remove the clamps and grab a vise grip and clamp it on the tube crushing it so you can twist it out. It is tougher than you think and that dam prop is in the way and without thinking you reach out and reposition it. Bang you've pulled the trigger and the cup has split the hydraulic body. Your engine is dead.

There is plenty of opportunity to brake a cam follower body before you can check the cup. Just think about what your doing before you do it. Use a blast of air to blow the push rod off the cup.

Other note: It is important to reassemble the push rods and the rockers in the same place they cam from. Some push rods can be over sized and are matched to the rocker and the rest of the valve train at that position. Early intakes rockers did not have the oil hole at the top of the foot like the exhaust. Make sure the exhaust rocker have the hole.

[Bruce Fenstermacher]

Off the cuff I would say yes the smaller Continentals can have cam follower bodies that do not incorporate the c clip. I should know as I own and have overhauled both but to be honest I don't remember. I just treat all of them like there is no c clip just like a gun is always loaded.

The newest intake rockers now have an oil hole. In fact besides the different part number I don't know there is any difference between the newer exhaust and intake rockers.

Valve lash is set to within a tolerance with longer push rods. Things that effect the lash are wear and correction/line boring the case halves, cam follower wear and reconditioning, rocker arms condition, valve and valve seat set and condition.

[voorheesh]

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. Even though it is not associated with a cabin heater, exhaust leaks can be very serious and it does not take much to migrate into the cabin which raises the potential of carbon monoxide. If you carry your family in this airplane, you would not want to take that chance. These old exhaust systems are primitive but they can be repaired or better yet replaced. AC 43.13 has guidance on repairs but I would recommend finding a reliable repair station such as Knisley Welding which is right down the street from you in Loomis. I think you may find that replacing this old system with a Hanlon Wilson exhaust is the best way to go. Thereafter, it still needs to be thoroughly inspected at each annual and exhaust leaks should not be accepted or taken lightly. Please don't take this advice the wrong way, just my opinion in the interest of safety.

[Joe Moilanen]

Nice job thinking through the whole thing Bruce. I was tinkering with your W&B spreadsheet last night and I think you have a gift for being able to visualize the abstract!

Does this apply to the older A-65/75 engines too? Meaning do some of those engines have lifter cups not retained by circlips too?

Other note: It is important to reassemble the push rods and the rockers in the same place they cam from. Some push rods can be over sized and are matched to the rocker and the rest of the valve train at that position. Early intakes rockers did not have the oil hole at the top of the foot like the exhaust. Make sure the exhaust rocker have the hole.

I instinctively do this anyways, but now know why it's so important. All of my rockers have oil holes, but I didn't know they made some that did not.

Yes they do, I helped a friend of mine split the case on his 65 (Airknocker) after he busted one......