Exhaust hitting cowl

[Paul Eastham]

Hi guys,

Is there some obvious trick I'm missing to getting the exhaust pipes to clear the cowl at the exit? Vetterman no-muffler pipes on a 9A.

On the right side, I have about a half-inch clearance at both the cowl and engine mount, which is what Bingelis' book says you need. Yet it is clearly hitting both the cowl and engine mount (based on rub marks), probably at startup.

The problem is that increasing clearance at the cowl means decreasing it at the engine mount. I have already trimmed cowl away forward of the hinge line. I have also tried rotating the pipes a litte, but need to experiment with this some more.

The only other clue I have is that a neighbor (asked to watch for oil leaks at first engine start) noticed that exhaust pipe was vibrating more than the other. How much he didn't say.

Any advice? Any chance I don't need more clearance, but more rigidity in the hangers? They are installed per Vetterman's plans.

Thanks - Paul

[kevinh]

Originally Posted by Paul Eastham

Hi guys,

The problem is that increasing clearance at the cowl means decreasing it at the engine mount. I have already trimmed cowl away forward of the hinge line. I have also tried rotating the pipes a litte, but need to experiment with this some more.

Hi Paul,

I think your answer might lie in the 'rotating the pipes dance'. I needed to tweak those a bit to get enough clearance from the -A engine mount.

It is also possible that the fellow watching saw more vibration from one exhaust because that was the one that was whacking on the cowl ;-).

Also check that the right muffler isn't rubbing up inside the cowl, that needed a bit of fine tuning for me as well.

[Paul Eastham]

I've got my pipes turned straight down now, and I improved the horizontal pipe-to-pipe brace with some stiffer hose. But it's still hitting! Seems like it's happening at startup (accompanied by a bang)

What kind of clearance are you guys running? I think I've got a solid half inch or more everywhere, yet I am still seeing evidence of contact at both the cowl outlet and engine mount. The photo shows where I am seeing the rub marks:



Possible problem: As you can see the center brace is a bit u-shaped to clear the gear leg mount. This is accomplished by re-aiming the steel hangers aft. It is not contacting the mount, at least not while in the hangar.

There is about 1/8" of play on the pipes if you try to wiggle them.

[Vern]

Put some split rubber heater hose (from any auto parts store) and hose clamps on that closest member of the engine mount because if the exhaust pipe clatters against the engine mount, it will rub a hole in the mount. I've seen it happen before and it doesn't take long! Move the exhaust tubes as far out board as you can.

[kevinh]

Paul,

I notice from your picture that your rubber cross brace is angled down to clear the nose gear weldament. This is different from how I did it. For my install (sorry - no picts I can find), I used slightly longer bolts on the exhaust brackets so I could have a 1/4" ish steel spacer to hold off the cross pieces horizontal.

My gap between the two vetterman cross piece tubes is only about 1/4" from tube to tube (under the rubber hose).

Not sure if it is important, but thought I'd mention it.