The International Cessna^® 170 Association

Got a new knisely exhaust and the tailpipes that exit the bottom of the cowling just miss the old holes.
I am pretty sure these are just plain stainless steel pipes and I could probably bend them at the local auto exhaust shop.

Anyone had these issues? I am trying to avoid cutting larger holes in the cowling. I am looking at only bending them about 10-20 degrees.

I'll call knisley when they open, but the auto shop is across the street from the hangar and knisely is across town. I figure this one might take a few fitting and bending iterations.

WArning: Your engine mounts may have sagged. Don't cut that cowl or bend any pipes until you determine the condition of your mounts.

I had a similar problem at my last annual. Replaced the heater side muffler and one of the risers. Reassembled, the stack didn't quite have the clearance from the cowling pass-through hole that I would have liked, in fact it was touching.

Solved it by rotating the index of the stack at the connection to the muffler, which bought a little extra room. I never considered that sagging engine mounts could have been the culprit, but since the stack exited the cowl with perfect alignment prior to switching out the muffler, I assumed all was well with the engine-cowl relationship and that the new muffler was just barely different enough to cause a problem.

George, you are talking about the engine-to-chassis mounts, right? Not the chassis-to-firewall mounts?

So how do I determine the condition of the mounts?

I am more suspicious of the exhaust than the mounts because the old one fit perfectly. The new one just seems to be a little different. All the parts are the exact same measurement but they just don't seem to fit as well.

Zane I think he is talking about the engine to chassis mounts. My mechanic was looking at it today and said that the rubber between the mount and the engine is in good shape. I think it is just at matter of different exhausts. Talked to knisley and they said a small bend won't hurt.

I will post and update next week as we are finishing up the rest of this annual. Overhauled bendix mags, new cylinder from gibson, exhaust from knisley, and seat rails.

All the rubber mounts should be inspected for condition. Also, be aware that the steel tube dynafocal mounts can also be bent/stressed and that the exhaust installed when YOU acquired your airplane may have already been altered to fit. Just because it seemed to fit doesn't mean it was jigged correctly when you bought the airplane.

It's a good idea to install an exhaust system LOOSELY and then, only after it's all adjusted to the configuration you like, THEN tighten it all up. Run the engine to temperature and then re-torque all the fittings.

Later airplanes (subsequent to SN 26996) have larger openings with adjustable plates that use tinnerman nuts and PK screws to accomodate minor tailpipe exit differences. It would not be disqualifying to adopt that system to an earlier lower cowl, and it' can easily be done. See page 83A of theB-model IPC.

buzzlatka wrote:Got a new knisely exhaust and the tailpipes that exit the bottom of the cowling just miss the old holes.
I am pretty sure these are just plain stainless steel pipes and I could probably bend them at the local auto exhaust shop.

Anyone had these issues? I am trying to avoid cutting larger holes in the cowling. I am looking at only bending them about 10-20 degrees.

I'll call knisley when they open, but the auto shop is across the street from the hangar and knisely is across town. I figure this one might take a few fitting and bending iterations.

I had this exact problem with my last Knisely muffler. The muffler outlet was pointed to far inboard and I confirmed this by comparing it to my last Knisley muffler. They must have changed there jig but they would not admit it was a problem. I got one from AWI that fit perfectly.

Well upon further review and lower cowling installation it looks like the fit is not that bad. The left tailpipe fits perfect. As it turns out our old exhaust tailpipes were pretty close to the edge of the holes. In the past someone shaved some cowling off the right side hole to make it oblong. That allowed it not to rub. The new tailpipe rubs on that hole. My options are to widen the hole or bend the tailpipe.

The other difference with the new knisley tailpipes is that they do not have the angled cuts on the end. The exit ends are cut at right angles not slanted.

Depending upon how you feel about that... I'd send them back, make them cut them properly, and while they're at it, make them correct the one that fits poorly. (Sounds like it wasn't jigged right or that it was welded to the flange without good temperature control. A weld at the flange on the long side will shrink it in the direction it needs to move.)

buzzlatka, I too had difficulty fitting my Knisely muffler. However I called Knisely and he was very accommodating. After discussing the miss-fit he said to return the muffler and he would fix and return it. I was finishing up the Annual with Dave Sos at Hrefi Aircraft in Orland CA (a great bunch to work with), UPS picked up the muffler at 2 PM and it was back at 2 PM the next day (on charges to me). The muffler fit perfect. So, give them a call their nice people.

The exhaust stacks were probably left long and square on the end so you can cut them to the exact profile for your airplane cowl. Some folks like them long and square and some like them short and angled parallel with the cowl. The old factory photos show the tips cut off angled and parallel to the cowl and sticking out about 1-1/2" to 2". It's your choice.

I had the shop cut mine off angled and parallel to the cowl like the factory did originally did but made them longer so they stick out of the cowl about 3". This helps keep soot off the cowl but still looks 'original'.

One thing you DO NOT want is to cut them off so short that the exhaust gasses can flow back into the cowl holes. This will soot up both the outside and inside of the cowl, lead to accelerated corrosion, and potentially create a situation where the hot gasses could overheat something inside the cowl like heater hoses, wiring, etc. I saw this on my plane. The stacks were cut too short on the previous muffler replacement before I bought my 170 in 2006 and the stains on the cowl are still there.

Dam Richard that is just a nice lookig Rat plane. Of course the wheel pants almost push it out of the category. BTW I took note in some other threads that it appears you will not be at Brandson to challenge my Rat plane in that category.

Bruce-
Thanks for the compliments! It looks worse in person. Although the wheel pants are original, they look bad too.

I was trying to keep it quiet about not going to Branson. You probably have an unfair advantage on the other guys. If I had gone, you would have had some serious competition.

I've had three transactions with Knisley, and two of them have been complete disasters. I'm NOT impressed with the quality of their work or service.

One of our good supporters is AWI (Aerospace Welding Inc, Eagan, MN) Tell 'em we sent you and talk to Charlie Felds. 1-800-597-4315

http://awi-ami.com/

Aerospace Welding Minneapolis, Inc.
1045 Gemini Road
Eagan, MN 55121
651-379-9888
Fax 651-379-9889