Rough engine and low EGT on #2 just after t/o. Any ideas?

[Doug]

Originally Posted by Clint B

... hose clamp over the female portion of a slip joint.

Clint,
I thought the hose clamp was for the EGT probe and we all have those. Isn't the slip joint further down the pipe?

I like the idea of anti-seize on the ball joints. Good idea?

[Captain Avgas]

Originally Posted by Sid Lambert

I am also a believer in Moose Milk now. That is the only stuff that keeps the joints free.

Now you tell me I've got to go and milk a moose and all these years I've been milking a mouse.

[BillL]

Originally Posted by Mark Albery

I think the LCF is from motor movement rather than exhaust pressure. The biggest deflections are on starting so it was more likely in the hundreds of cycles. I do mouse-milk all the joints every time the cowls are off, but it still gets stiff. The anti-seize on the joints is a good idea if it keeps them free.

p.s My RV-8 has about 600 hours and is not for sale.

Good thought, and good humor. When researching my AWI 4-into-1 exhaust it was recommended to use some high temperature nickel based anti seize for the ball joints 3-4"from the head, or they would bind, stick and break a pipe. One commented then that the mouse milk was not sufficient for that purpose. I don't remember who. I bought the AWI, and the recommended anti seize.

I was not thinking about pressure in the pipe, it was the head wagging about with firing pressure and piston side loads. Isn't that why the baffles break between the heads? I have heard of slow motion videos that show the jugs bouncing around like a . . ahhh . . . . well . . . jogging jugs. Quantifiably, either I suppose.

[az_gila]

Originally Posted by Doug

Clint,
I thought the hose clamp was for the EGT probe and we all have those. Isn't the slip joint further down the pipe?

I like the idea of anti-seize on the ball joints. Good idea?

PowerFlow recommends anti-seize on all of their exhaust slip joints every annual.

Use the really high temp (2400F) nickel stuff though -

http://www.permatex.com/products-2/p...bricant-detail

[Noah]

I have used Mouse Milk on my exhaust joints every time I open the cowl. Last week, I had to disassemble the exhaust for the first time in 3 yrs/385 hrs. The joints took a lot of force to break free, so I questioned whether the mouse milk did anything at all. However, it is easy to apply since it is a thin liquid solvent. I would think that the nickel-based anti-seize requires exhaust system disassembly to properly apply it? Can the spherical exhaust joints even be disassembled? This would be a pain, but would provide an opportunity for a good inspection.

[ao.frog]

Hi gang.

Yesterday, I think I found out why the exhaust tube failed:

I was in the hangar, taking another close look at the exhaust-system. After a while I discovered that the left angle (LV-706 tab) holding the left exhaust-hanger to the engine was broken in two.

That means that the left part of the system had lost most of it's support. Therefore, I guess the added loads and vibrations caused the tube from cyl 2 to fail.



The tab had broken by the outer circle of the bolt-hole. That's where the material where at minimum.
I found signs of slight rubbing on the engine case by the broken tab. Therefore the tab must have broken at least a few hours ago. Then a crack must have developed in the #2 exhaust tube, resulting in an exhaust leak. Then, after a few hours, the tube failed.

I don't know why the 706 failed, but the tab looked very small and fragile to me. The little material around the pre-drilled hole looked fragile too.

In addition, there's a possiblity that we installed the exhaust hangers in such a way that the hangers produced a small upward or downward pull on the 706 angle.
Those forces can have been enough to make the angle break.
I guess I'll never know that for sure.

I've now made a simliar angle, but it's made of aircraft grade stainless steel. It looks and feels much sturdier than the orginal angle.

I'll also make up another angle, replacing the one on the right side.


So now I know why the exhaust tube failed: lack of support.
What remains, is to find out why the angle failed. Until further, I'll assume that we installed it incorrectly or that the angle where alittle weak for it's mission.

At least., it's good to know that the exhaust tubes themselves didn't fail without a good reason.

PS: I hope I can hijack this tread back on it's track: why cyl 2 had low EGT and why there where vibrations...

[Bill Dicus]

Bill - What was the anti-seize? Do you have a source? Thanks in advance...

[BillL]

Originally Posted by Bill Dicus

Bill - What was the anti-seize? Do you have a source? Thanks in advance...

I got the same stuff referenced by Gil in post #34 above. I ordered from o'Reillys locally.

Back on track - -
Why LOW EGT? - when the exhaust valve opens there is 50 psi or so pressure in the cylinder, that blows a high velocity pulse in the exhaust pipe. That pulse "inertia" then creates a low pressure area, and the valve overlap sucks in some cool air. From above posts, that would seem to be the reason for fouling the plug. I am still not sure that I exactly understand the mechanism, but the fact that experts agree it does the plug does foul, then the fouled plug and resulting misfire is largely the cause of the instantly low EGT. I would have though that as soon as the pipe separated that the EGT would have dropped some, then with the misfire, much more. No data, but logic would say that plug would not foul that fast after the pipe separation. If so, it is a good safety mechanism.

I have run a lot of engines without the exhaust pipes and with leaded gas without this happening, but that doesn't mean it isn't true. That's partly why my hearing is bad

[skylor]

Originally Posted by William

Is it then a big NO NO to trouble shoot the engine on the ground without the exhaust mounted?

Bill

Bad idea. I've heard it said (though it could be an old wives tale) that running an engine without the exhaust system can be potentially harmful to exhaust valves because the open ports leave the valves too exposed to ambient air upon shut down thus causing rapid cooling and possible warpage.

Skylor

[Bill Dicus]

Thanks Gil.