Check those exhausts regularly...

After spending a considerable amount of time inspecting the exhaust system during the condition inspection (right before launching for OSH), you can imagine why my eyes popped out when I saw this after uncowling the plane to change oil upon my return...
Let's be regular about checking these things...I believe I was moments away from very bad things happening...



Shot with DSC-P32 at 2007-08-02

And then yer eyeballs fell out?

Bob and I have spoken about this a bit. My theory is the slip joints (the end of the pipe to the right of the pic is a slip joint I believe) are binding up and the resulting thermal expansion increases the length of the pipe.

If the slip joints don't slip (i.e are bottomed out, or pre-stressed at installation) the lengthening has nowhere to go so it flexes the pipe and it cracks.

Either that or its fatigue due to not being supported correctly, but my money is on that thermal expansion having now seen the crack.

Comments?

Frank

Changing your oil often is the key...

to long life, for both you and the engine Not only is it the single most beneficial thing you can do to keep your engine running longer but you also have a chance to find things like this before they become a serious problem. I know folks who push oil changes to the limits because they don't like taking the cowl off . Finding this before it failed completely is a perfect example of what good maintenance practices will do for you. Good job Bob! This also looks like an unusual failure as most of the time it's just at the weld where the failure occurs (you should inspect the full circumference of every weld everytime the cowl is off). How old are these pipes and who's are they just out of curiosity?

The pipes had 110 hrs on them (at the time I spotted this)...but could have failed at 85+ hrs, since that's when the oil was changed last (I've sheperded a couple of engines to TBO on 25 hr <or 4 months> oil changes, I figure it's cheap maintenance). This is a Vetterman system. There was about 1/2" of steel left between the crack on the right side in the photo and the crack that wrapped around the joined tube...

Bob,

Were you using the Vetterman exhaust hangers on the rear of the pipes? Were they intact when you discovered the crack?

Was there ever any anti-seize put on the ball socket upon installation? It doesn?t look like that joint has ever moved. I read that along with my exhaust it required that and I suspect to prevent this from happening. May not be the case here but you never know.

-Jeff

Too hot

RV_7A said:

Was there ever any anti-seize put on the ball socket upon installation? It doesn?t look like that joint has ever moved. I read that along with my exhaust it required that and I suspect to prevent this from happening. May not be the case here but you never know.

-Jeff

Click to expand...

Jeff.... does anti-seize hang around at the near red-hot temperatures of an exhaust system?

I would think the temperatures involved would be above the rating of any added chemicals...

gil A

Good catch Bob

Diligent maintenance paid off this time.

To answer a few questions...
The exhaust was the stock Vetterman setup, with hangars aft of this ball joint. NeverSeize was applied to all slip joints and ball joints at installation...in addition, all the ball joints were "exercised" on the bench prior to installation to insure they moved and that there was an even coverage of NeverSeize.

In conversation with Vetterman's, they indicated that the ball joints were to facilitate installation...that from a practical standpoint, they should be considered "solid joints" after a period of use because the NeverSeize wouldn't hang around at those temps. They recommended putting "Mouse Milk" on the slip and ball joints every time the cowl is off. Any play or movement in the system is supposed to be taken up by the exhaust hangar system (the stainless steel tube/fuel hose setup).

The other recommendation by Vetterman's was to install the hangar as far aft as possible (as close to the firewall as possible). My setup (remember, this is an -A model) had the center of the brackets positioned 6" forward of the firewall. When this is all reinstalled, I'll try to move the hangars further aft down the pipe. This will entail installing longer bolts (3" or so?) in the hangar setup to clear the nose gear tube on the engine mount.

I forgot to answer John's question about the ring of the exhaust hanger being intact. The ring was fine, as was the condition of the tube/fuel line hanger and the other side of the exhaust supports on cyls #1&3.

This cracking occurred at the junction of tubing from cyls #3&4. Before I removed the pipes, you could grab the discharge end of the pipes and flex them...which opened up the crack to about 3/8" (only apparent with the cowl off). I suppose that is an excellent pre-flight item (to try to flex the pipes)...but it wouldn't necessarily alert you to the fact that there was a crack upstream if you couldn't visually examine the exhaust while you were checking the pipes for movement.

This is the same thing that happened to my exhaust. Total airtime was 120 hours.

For what its worth I found the problem from watching my engine monitor. Typically my EGTs differ by 25-20 degrees (EGT Span on EIS). One day I noticed the EGT span was 110. Sure enough the front right (cyl #1) EGT was 100 cooler on average than the rest. Did the inspection and found a nice crack about 2/3 circumference of the pipe. Mine seemed to start at the slip joint and additional stress in the area was casued from the EGT probe itself since the crack followed the band around the pipe. I ended up moving the EGT probe 1/2" further away from the joint.

Steve
RV7A

Help out an old jet guy with little experience in pistons. What do you think would have happened if the pipes had completely separated in flight? Thanks.

-John

Bob Brown said:

After spending a considerable amount of time inspecting the exhaust system during the condition inspection (right before launching for OSH), you can imagine why my eyes popped out when I saw this after uncowling the plane to change oil upon my return...
Let's be regular about checking these things...I believe I was moments away from very bad things happening...

Click to expand...

Here's where mine broke around 125 hours:

Vetterman fixed it no charge. Solid since. I always check it at oil changes and specifically pay close attention to the hangers and cross brace between the hangers.

If these had separated, they would probably have only partially separated, since the exhaust hanger system was intact. So the exhause gases would probably have been deflected in other directions...at least initially. There's a fuel line coming through the firewall 4" above and 3" to the right of this pipe junction. There's also flammable material (wiring insulation, a battery and the cowling itself) within a few inches in any direction of this junction. I'm not saying you'd go flaming out of the sky...but it's just never good to have unrestrained exhaust gas loose in your cowl...no good can come of it.

Permatex Anti-seize is good up to 1600 degrees so yes it does hang around at these temps.

Right off Permatex website.

Permatex? - Anti-Seize Lubricant - NFPA Fire Code 30B Level 3
A heavy duty blend of aluminum, copper and graphite lubricants in a petroleum base. Use during assembly to prevent galling, corrosion and seizing and to assure easier disassembly. Inert, will not evaporate or harden in extreme temperatures. Salt, corrosion and moisture resistant. Temperature range -60?F to 1600?F (-51?C to 871?C). Non-aerosol version meets Mil Spec A-907. Suggested Applications: Boiler and oven parts, gears, chains, cables, sprockets, levers, pivots, rollers, valve stems, jet engines, industrial turbines.

They have obviously gone to a different spring loaded type of ball joint for what I assume would be to eliminate these type problems from happening.

Shown here
http://www.vansairforce.net/vetterman/VettermanExhaust.htm


-Jeff

Bob Brown said:

I suppose that is an excellent pre-flight item (to try to flex the pipes)...but it wouldn't necessarily alert you to the fact that there was a crack upstream if you couldn't visually examine the exhaust while you were checking the pipes for movement.

Click to expand...

I make this a part of every preflight for the spam cans I rent. About a year ago I was finishing up my inspection of the cowl and I randomly gave the exhaust pipe a wiggle, and it came off in my hand. This was on a Katana DA-20 and the weld was completely broken where the exhaust pipe exits the muffle.

Definitely something you want to find out about on the ground.

Bottom Line...

The bottom line here is that there are more RV's flying with Vetterman exhausts than any other brand out there. Larry has done a great job of innovating and evolving exhaust systems to the benefit of us all. He's a multiple RV builder and a strong supporter of this group.

When I brought this up here in the forums, the idea was to encourage everyone to LOOK at what's going on under your cowl. Don't assume that because everything was OK 25 hours ago, it's OK now. That's the important thing.

Larry Vetterman wanted all the facts here...made pertinent recommendations to my particular installation, and fixed the pipe immediately...no questions asked. I don't know how any of us could ask for more.

Mine cracked also at around 100 hrs and Larry Vetterman fixed it without question or fee, he was great to deal with and stands by his product. you can't go wrong with customer service like that.

John

Mine also cracked at around 185 hrs. I bought it around 1998 or 99 and don't remember any mention of anti-seize... so obviously never used any.

Sent it back and it was repaired fairly quickly but I was charged $20 plus $8 for a new exhaust clamp that had broken. I think that price is more than fair but I'm curious why I was charged and others weren't?

Karl