Recurring exhaust pipe cracks - advice wanted

[Kevin Horton]

I'm looking for advice on resolving a recurring problem with exhaust pipe cracks. I've got a Lycoming IO-360-A1B6 engine on an RV-8. The exhaust is by Vetterman, purchased in 2001. Originally it was mounted with the tail pipes supported from the engine mount, as recommended by Larry Vetterman at the time the exhaust was purchased. After the second time that an Adel clamp broke, I replaced the pipe and rubber pieces with springs, copying the idea from the way exhausts are supported on Mooneys.

The first major problem was in 2011, on the way home from Oshkosh, with 136 hours on the aircraft - the #3 exhaust pipe broke completely off at the flange at the top. Luckily we were right overhead CYYB airport, so we landed there without incident. We rented a car and drove four hours to get home. I sent the exhaust back to Vetterman for repair. Larry said that the IO-360-A series engines on the RV-8 had been his most problematic engine/aircraft combination, and that he had made many detail design changes since my exhaust was shipped, as exhausts returned for repair showed where the problem areas were. Larry and Clint replaced the top part of the #3 pipe with a thicker wall piece, and made a few other changes to put the system in a configuration that was close to the current shipping exhausts.

In July 2012, with 197 hours on the aircraft, I discovered that the exhaust was cracked in the Y that joins the pipes from #3 and #4 cylinders. It was sent back to Vetterman for repair. Note that I also discovered metal in the oil filter at that time, and the engine was found to have cam lobes that were wearing. It is possible that the cylinders were not all producing equal amounts of power, leading to more vibration than normal. When remounting the repaired exhaust, I changed the exhaust mounting to hang it off the back of the oil sump, as per current recommendations.

A week ago, with 241 hours on the aircraft, I discovered a significant crack at the weld at the flange on the #3 pipe. There wasn't time to ship it back to Vetterman Exhaust in SD, and get it back before Oshkosh, so I had it welded locally. I'll treat this as a temporary repair, and will either ship it back to Vetterman for a proper repair after returning from OSH, or replace the whole exhaust system with a new one.

Given that I have had three significant exhaust cracks in 240 hours of flying, something is clearly amiss. I see the following possibilities, in no particular order:

1. Excessive vibration - I don't perceive that the engine vibrates any more than other Lycomings, but maybe I'm wrong. I flew big radials for a few years early in my career (S-2 Trackers) so perhaps I am not as sensitive to vibration as some other people. I usually cruise LOP, and all four EGTs peak in a band of 0.1 to 0.2 GPH fuel flow, so I don't think vibration from lean running should be the issue. I'm not sure what the best way is to objectively determine whether my engine has excessive vibration though. Comments?
2. Poor maintenance - every time I check the exhaust system I find the ball joints seized up. Sometimes I manage to get them freed up by using Mouse Milk, but sometimes I have given up.
3. Previous damage - the aircraft had a significant engine overspeed during the early flight testing (almost 4000 rpm). Maybe that event somehow stressed the exhaust system, and later cracks are a delayed result.
4. Quality control issue with exhaust system - I know that most people have pretty good service history from Vetterman exhausts, but maybe I've got a bad one.

I really want a more reliable exhaust, so I can travel without worrying about it. After getting back from Oshkosh, I'll call Vetterman Exhaust to get their thoughts on why my aircraft is getting these frequent cracks, and how best to avoid them in the future.

I'm considering ordering a brand new exhaust system. That will avoid missing several weeks of summer flying while having Vetterman rebuild my orginal one, it'll give me a system in the latest configuration, and I'll have the original one as a spare system in case the new one ever cracks. I'll also make a point of pulling the cowling more often and won't put it back on until I've ensured the ball joints are moving freely. I'm not sure what inspection interval will be required so that the ball joints don't seize between inspections. I'll start with a fairly short inspection interval, and gradually increase it.

Questions:

1. other than ordering a new exhaust, is there something else I should consider doing instead?
2. if I order a new exhaust, is Vetterman still the best bet, or is there another supplier I should look at?
3. if Mouse Milk the best anti-seize for the ball joints, or is a better product?
4. has anyone else had recurring exhaust system issues? If so, did you manage to resolve them?

[C-FAH Q]

Kevin,
Check your PM's

[DEWATSON]

Kevin,

This may be a stretch for you, but I promise it is the truth.

I had a Continental 90 horsepower engine on a Smith Miniplane years ago and it broke the #3 exhaust pipe flange three different times. I was at my wits end trying to figure it out. The engine ran beautifully......never a problem except the exhaust pipe. After I fixed it the third time, I cranked it with the cowling off and ran it a few minutes after I washed the engine. I stood off from it a distance and watched it run. I noticed that the rocker arm cover on the #3 cylinder appeared to be moving (I say again that the engine ran great). Sure enough........the head was loose on the barrel. I pulled it off and replaced the cylinder and the exhaust flange never broke again.

David Watson

[az_gila]

Kevin,

Isn't Mouse Milk more of a penetrant than a lubricant?

The certified PowerFlow exhaust system had similar problems and now specify an anti-seize at each joint.

Try some of this 1800 F stuff on the slip and ball joints next time it's off -

http://www.permatex.com/component/vi...bricant-detail

Update. This 2400 F one would be better for SS parts -

http://www.permatex.com/products/pro...t-77124-detail

[Kevin Horton]

Originally Posted by az_gila

Kevin,

Isn't Mouse Milk more of a penetrant than a lubricant?

The certified PowerFlow exhaust system had similar problems and now specify an anti-seize at each joint.

Thanks for the comments Gil. I'll look for a supplier for that 2400 deg F stuff.

Mouse Milk is what Vetterman recommends. But, I agree that it isn't obvious why it is the right choice. It does penetrate well to help free a seized joint, but I'm not sure it really does much to prevent the joint from seizing again.

Does anyone know which anti-seize PowerFlow recommends?

[az_gila]

Originally Posted by Kevin Horton

Thanks for the comments Gil. I'll look for a supplier for that 2400 deg F stuff.

Mouse Milk is what Vetterman recommends. But, I agree that it isn't obvious why it is the right choice. It does penetrate well to help free a seized joint, but I'm not sure it really does much to prevent the joint from seizing again.

Does anyone know which anti-seize PowerFlow recommends?

PowerFlow isn't very specific.

I just chose the nickel stuff since it is the highest temp. product from Permatex and is designed for SS.

It was in stock in a few of the local Tucson car supply places.

[DanH]

Slip joints are easy enough, but how does one get paste anti-seize into a ball joint? Install a grease fitting?

Hmmm. That's actually a pretty good idea.

[YellowPeril]

Holy Smokes Kevin!

I've got the same Vetterman exhaust purchased around the same time hanging off'n an Aerosport Power O-360-A1A (you may recall flying in my -8 at the Oswego RV Builders Forum a long time ago).

1,000 hours with the pipes hanging off the mount (never liked the arrangement, but couldn't come up with anything better), and nary a problem other than a leaking gasket or breaking one of the hangers. The ball joints have remained loose without use of a lubricant, too...

The the exhaust for the aspirated engine the same as the FI version?

I gotta go find some wood to knock on.

[Russ McCutcheon]

Lee, the fellow that built my RV-4 said he could not keep the exhaust on tell he got a decent prop=less vibration, I bet you have a good prop already though, has it been dynamically balanced?

Next idea, once when flying formation with a local RV driver, taking a look at his belly revealed his exhaust stacks vibrating in a circle about twice the size of the pipe, told him about it and had him raise and also lower his RPM, 50 RPM either side would result in rock steady pipes. You could try running at a different RPM.

[David-aviator]

Kevin,

The pipes were 10 years old when the problem started and are now 12 years old. That's pretty good service, it's time to replace 'em. Nothing lasts forever and they live in a tough environment