The International Cessna^® 170 Association

As a bit of a noob to airplane ownership, can someone point me in the right direction on exactly where I should be looking to see if my exhaust flanges are leaking near the pushrods? Photo or circled area on a diagram would be helpful.

Trying to determine if I have a problem before the summer rolls around. Since starting to fly my airplane, I have noticed that on warmer days (say high 70s to low 80's on the ground) I get fairly high oil temp when trying to climb above 5000'. (temp gets above the old 225 redline, but just about right at the new 240 redline with the SAE 50). Once I level off and reduce power, temp comes back down to a little below 225 on the original gauge within a few minutes.

So, I am trying to narrow down whether or not I have a problem before it starts getting warmer and I try making any trips to AZ. I will obviously check the gauge, but if the problem is the exhaust flanges, how big of a job is it to fix? I also may end up moving my plane from San Diego to Norfolk, VA in August, so best to address this now.

Thanks!

look for whitish or grey haze or film on areas surronding the exhaust where the flanges mate with the cylinders, and around the areas where the connector clamps attach the risers to the mufflers. if any leak is enough to be the sole cause of your high oil temps then you might be seeing black scorch marks on the pushrod tubes etc or a buildup of grey depsosits.

Andrew,

Exhaust leaks are most often detected by the presents of light brown exhaust deposit around the leak. There is no magic to the inspection. Using a light and mirror to look at the back, inspect around the exhaust flanges. No brown deposits then you aren't likely to have an exhaust leak. Another place your likel to see the brown deposit is at the exhaust pipe joints.

Once found, fixing the leak can take several steps. Assuming only the gasket is defective, replacement is in order. Many times the flanges on the exhaust header become warped and drawing them tight doesn't seal them against the gasket and the cylinder. In a few cases the header flange could be surface planed flat again but most likely replacement of the flange or the entire header is in order. Now in the worse case the jet of hot exhaust escaping has acted like a cutting torch and cut a grove in the cylinder exhaust mating surface.

If the grove is not to bad there are tools available that can be used to plane the surface flat. Some of these tools are designed to be used while the cylinder is installed. In the absolute worst case the cylinder is trash and needs to be replaced

The exhaust leaks I've witnessed in these areas have a chalky-appearance.
Look beneath the cylinder where the exhaust short-pipe (riser) bolts to the cylinder with only two studs/nuts. That is the flange area which can erode if left leaking unattended too long. The sheet-metal clamps beneath that, which attaches the riser to the muffler inlet-tubes are also leak-prone. There are various sealants and muffler tapes that can be used in that area (which is a poor design feature of this installation. I wish someone would create a C-206/210 type exhaust system for this airplane.)

On the C-170 stock engine exhaust system, there are two types of clamps used between the rizer pipes and the muffler. The most common clamps have four bolts, the others use only two bolts. I have had much better results with the two bolt clamps in both the eaze of installing them and in sealing for leakage.

The two-bolt clamps have a channel on one end...into-which the flat of the opposing clamp enters...and two bolts secure the opposite edge....and the bolts "clamp" the system together. I haven't seen any for many years.

That's about the only advantage in being almost ninety years old. I've seen all that old stuff.

Here is a picture of evidence of an exhaust leak....... and is this a two bolt clamp?

Aryana wrote:BL, I've been trying to find a picture to see an example of the 2 bolt clamp. Do you happen to know where to dig one up?

I have 6 of them on my engine. I might even have a few extra at the hangar. I'll look next time I'm at the airport and take a picture if I can find the extras.

I just received my new exhaust system from AWI and I have to say that it looks top notch. I ordered new riser clamps as well. The two bolt style shown on the above picture. I had the old four bolt style. The question I have is why is there a tang on one side that keeps the two halves from coming completely together? I'm guessing it has to do with heat expansion and contraction. The old style had no such tang. When we install the mufflers should there be some small movement of the muffler at the riser clamp or should it be solid with no movement? Any insight would be appreciated.
Thanks in advance

twlareau wrote:I.... The question I have is why is there a tang on one side that keeps the two halves from coming completely together? I'm guessing it has to do with heat expansion and contraction. The old style had no such tang. When we install the mufflers should there be some small movement of the muffler at the riser clamp or should it be solid with no movement? Any insight would be appreciated.
Thanks in advance

From a previous post in this thread:

gahorn wrote:The two-bolt clamps have a channel on one end...into-which the flat of the opposing clamp enters...and two bolts secure the opposite edge....and the bolts "clamp" the system together. I haven't seen any for many years.

These clamps may be better sealed by going down to your local hobby shop or ACE hardware and purchasing a sheet of stainless steel foil. It comes in 12" X 24" sheets and is heavy duty. Cut a strip about 2 inches wide and 8 inches long, wrap it one and 1/2 times around the joint, THEN place the clamp over it and secure the clamp.
NO leaks.

George,
I have tried various ways of using stainless steal foil to no avail. No matter how carful I am tightening the exhaust coupling bolts the foil always bunches up at the clamp flange and leaks. I have had much better luck using a very high temperature Hylomar product between the clamps and the stack joints. The Hylomar compound I am referring to can be viewed here http://www.valco-hylomarproducts.com/exh_sealant.htm

Arish,
I promise to look at the tube the next time I am at my hangar and report which one I used.

johneeb wrote:George,
I have tried various ways of using stainless steal foil to no avail. No matter how carful I am tightening the exhaust coupling bolts the foil always bunches up at the clamp flange and leaks. I have had much better luck using a very high temperature Hylomar product between the clamps and the stack joints. The Hylomar compound I am referring to can be viewed here http://www.valco-hylomarproducts.com/exh_sealant.htm

Yes, I guess my technique of wrapping must somehow differ because I can imagine such a problem...I've just not had it. I make certain the ends are overlapped not at that flange, but at the back-channel.

As for Hylomar, .....I agree they make fine products. I wrote about their exhaust paste here:
http://www.cessna170.org/forums/viewtop ... mar#p62318

Aryana wrote:I've talked with other folks who swear by the Hylomar paste too John. Did you use the assembly paste or the repair putty?

Arish I maybe slow but I am forgetful, here is the Hylomar product I use.