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

A

ao.frog

Well Known Member
Hi gang.

Today, the wifey and me loaded up the -7 for a 3-day trip to Sweden, but we didn't get far: start, runup and takeoff-roll normal but at 500', we both felt a slight vibration and I noticed the EGT on #2 was approx 650*F.
CHT on #2 where at the same level as the others: about 400*F.

I turned back towards the field and entered downwind.

The vibration got slightly worse when reducing power to about 15'MAP on downwind.
The #2 EGT continued to show beetween 600 and 650, varying slightly with power.

There where also a few pops heard, and to me they seemed to come from the exhaust system.

The pops continued during base and final, both on low powersetting (15 MAP) and idle.

After taxi inn, I tried to do a mag check but the engine sounded rough when I advanced power from idle, so I only did a quick mag check at 1500 RPM before shutting down.
The roughness where present at both mags, when tested separately, as well as on "both".

After shutdown, I pulled the cowl and checked the P-mag timing: both bang on.

Then it was time to call it a day, accept the fact that the great weather forcast for the next few days, where not to be spent flying in Sweden.

My plan is to check the compression as the next step. I'm thinking that this must have something to do with cyl 2. Maybe sticky valves?

The engine has about 41 hrs TT, I'm still using mineral oil and running it hard.

I'm certainly no engine expert so I'm wondering if anyone have some advice regarding what to check to determine the cause?
 
Check the easy stuff first. Carefully check the spark plug leads and plug boots. Make sure nothing is loose. Then pull the plugs and check or replace them. With a 650 degree EGT I think that cylinder had gone cold and the CHT did not have time to start dropping. If no ignition issues then check the injector for a clog. After that start getting into the harder stuff.

George
 
hlangebro said:
Check for induction leaks on the intake tubes, both the hose and the upper clamp
Click to expand...

...and that one of the little hex-head plugs threaded into the intake port hasn't fallen out (on the lower side of the cylinder head, where a fuel primer line would screw into if you had a primer). Had that happen on a friend's Piper Cherokee who'd just got a freshly overhauled engine installed... the engine shop forgot to tighten those plugs, the primer was only connected to two of the cylinders, and the other two cylinders had plugs. After landing we found one remaining plug only finger tight and the other plug fell out sometime during the first test flight, making a huge intake leak and it ran very rough and backfired a lot.

Also, if you happen to have one of those mechanical push-pump type fuel primers, and if it happens to be only connected to that one cylinder, make sure the primer knob is fully in and locked or else it will run super rich as it's allowed to freely suck all the fuel it can thru the primer line and pretty much kill off any power that cylinder would've been making and foul the spark plugs. Don't ask me how I learned that one :eek:
 
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I will be interested in what you find because I have had the same thing happen to my Superior IO-360 on several occasions. #2 cylinder drops to 650 degrees and it runs rough. Mine has occurred during LOP operation and once when I cut the throttle abruptly while in cruise flight. I switched the plugs with the #4 cylinder and still had it happen. No sign of intake leak. Slick mags timing is good and no obvious problem with the wiring. Mine is intermittent and usually only for 15 seconds or so. I have performed the ignition system stress test (LOP in cruise and switch off one mag, then the other) and nothing obvious on the graph to indicate a problem. Maybe the exhaust valve is hanging up?
 
brad walton said:
I will be interested in what you find because I have had the same thing happen to my Superior IO-360 on several occasions. #2 cylinder drops to 650 degrees and it runs rough. Mine has occurred during LOP operation and once when I cut the throttle abruptly while in cruise flight. I switched the plugs with the #4 cylinder and still had it happen. No sign of intake leak. Slick mags timing is good and no obvious problem with the wiring. Mine is intermittent and usually only for 15 seconds or so. I have performed the ignition system stress test (LOP in cruise and switch off one mag, then the other) and nothing obvious on the graph to indicate a problem. Maybe the exhaust valve is hanging up?
Click to expand...


I have had the same thing happen when descending LOP. What is happening is the mixture gets leaner as you descend and you reach the point where that cylinder can't ignite the fuel charge. Next time it happens richen the mixture without touching anything else and I think you will find it goes away instantly. It's normal and nothing is wrong.
 
Sounds a little like a stuck exhaust valve to me. Had it happen on a PA28 many moons ago.
 
The most likely cause is an induction leak as mentioned already. Hose clamps, sump joint or the gasket under the head.

Primer plug is another sneaky gotcha but not as common.

To get an EGT back down at 650dF you must have a very big leak otherwise the EGT would be high.

You may have a fuel nozzle blockage. And it is running so lean of peak it is almost shut down. Do not rule that out.
 
If everything else has been ruled out and the engine happens to be an older Superior 360 with roller cam, then it could be a stuck lifter (note that in this case it'll be an automotive roller lifter, not a Lycoming type with removable plunger). This happened to me, and it was not easy to diagnose. Much time spent staring at engine monitor datalogs.
 
Problem found?

Today, my plan was to do a start-up and check the engine instruments right after startup. I was thinking that if a cylinder had gone cold on me, I thought I wouldn't see any temp increase on either CHT or EGT.

Before I climbed in, I took another close look at the engine, shaking alittle on intake-tubes and exhaust tubes.
When grabbing hold of the exhaust tube for cyl #2, the tube felt loose.
I took a closer look and sure enough: the tube had broken off just below the flange.

Here's a pic:

28arwu8.jpg





Here's a closer look:

2rcs9hl.jpg







Here's a closer look from the other (aft) side:

dmcv93.jpg


There can be seen vertical crack too.




On the spark plug booth, the sparkplug and on the nearby area, there's residue from an exhaust leak.
My guess is that there was a small leak for a while, and then during takeoff yesterday, the tube broke off and resulted in a larger leak.

x1cyzr.jpg



PS: on the above pics, I've pulled the tube downwards slightly to expose the broken area. Without downwards pressure, the break was almost not visible.



Now the big question is this: can this exhaust leak result in vibrations and a 650*F EGT on full power?

Obvioussly the EGT probably would be somewhat lower than the usual 1400 on takeoff power, but all the way down to 650??

In either case; I've contacted Vans since I bought the FF-kit from them but they told me to contact Larry Wetterman directly, which I just have done.

I'll report back how it goes.
 
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Ralph Inkster said:
Also check for broken exhaust flange, would cause low EGT & near immediate fouling of plugs.
Click to expand...

OK, so Ralph is the winner and the normal CHT with low EGT makes perfect sense here. I can see that exhaust escapes on blowdown then the pulse pulls in fresh air to cool the EGT.

What I don't understand is why the plug will foul. Please help me understand why this would occur.
 
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Might consider replacing the spark spark plug and wire that have been exposed to 1200 degree F plus exhaust gasses. They are cheap and might be a problem later.

Lucky the engine was clean and there was no fire as sometimes happens if a pipe cracks fully off like that.
 
By the way how does a crack like that even happen in the first place? This is fairly new engine right, and I assume new exhaust? Doesn't appear to have cracked at the welds.
 
Exhaust pipe crack

Alf--Just confirming, are your exhaust pipes supported flexibly at the other end to allow for engine movement? This is a puzzling failure if so.
LeRoy Johnston RV-6A Esperanza
 
miyu1975 said:
By the way how does a crack like that even happen in the first place? This is fairly new engine right, and I assume new exhaust? Doesn't appear to have cracked at the welds.
Click to expand...

I suspect that the crack did start at the weld. The area adjacent to where the joint was welded is called the "heat affected zone". This area can be problematic for strength issues. If the welding process, material selection or heat treatment are incorrect this area is notorious for cracking.

Given Larry's years of experience manufacturing exhaust systems I suspect that the culprit is more likely the massive structure of the flange and weld verses the relatively delicate tube. The tube shakes and acts like a long lever applying a massive force (on a PSI level) to the inflexible area next to the weld. Cracking is going to be the result. The exhaust system must move with the engine and also be prevented from oscillation.

Diagnosing the reason for this failure is likely to be an interesting adventure. I'm glad you found the crack before it caused other problems!

David
 
I've had that happen twice on my no.2 cylinder. Both times repaired by Clint at Vetterman's.

The longer term fix is to add gussets fore and aft on the weld joint. Some Vetterman exhausts include them anyway.

I agree that it's a low cycle fatigue starting in the heat affected zone of the weld.
 
We brush spark plug anti-seize solution on the exhaust ball joints every time the cowling is off. Seems to help keep the joint flexible.

LeRoy Johnston RV-6A Esperanza
 
Low cycle fatigue??

Mark Albery said:
I've had that happen twice on my no.2 cylinder. Both times repaired by Clint at Vetterman's.

The longer term fix is to add gussets fore and aft on the weld joint. Some Vetterman exhausts include them anyway.

I agree that it's a low cycle fatigue starting in the heat affected zone of the weld.
Click to expand...

Isn't this the bird that is for sale and has 150 hours? At 2700 rpm and this hours the #2 cylinder had experienced 12 million firing cycles, and 24 million piston reversals (side loading on cylinder). Low cycle fatigue?

Regardless, the very best people will fix it.
 
Perhaps the sliding joint under the engine (the crossover) is stuck. Those pipes want to get a lot longer when hot. I see an amazing amount of motion of these joints (as evidenced by the scoring).
 
Exhaust leaks

A relative of mine was flying right seat in a Bellanca over the Florida panhandle. An exhaust leak caused a fire and they made a controlled landing in trees. Both survived, but it pointed out to me the importance of those pipes. My relative's cell phone call from the plane was pretty dramatic, and the event changed the direction of his life.

John
 
Mine cracked twice. Larry fixed it the second time by adding a slip joint. He told me that he thought he had fixed all of them but mine slipped through. Those guys really do give great support.

Mine blew the spark plug boot off both times when it cracked so my run-ups failed.

I am also a believer in Moose Milk now. That is the only stuff that keeps the joints free.
 
"I can see that exhaust escapes on blowdown then the pulse pulls in fresh air to cool the EGT.

What I don't understand is why the plug will foul. Please help me understand why this would occur."

A friend had an exh flange brake loose on the way to OSH one year, after the repair he still had a rough running engine so amongst other things, pulled the plugs & found them totally fouled, cleaned them up & everything good after that. Later at OSH he happened by the Champion booth & asked why the plugs would foul like that. Their explaination reasoned that the heat retention normal in the exhaust port would be purged thru the open pipe causing the cylinder area around the exh port to cool enough to foul with lead (maybe similar to cold start / rich taxi plug fouling).
 
Typically the first indication of a crack is the exhaust deposits on the plug or other surrounding areas. Often visible long before the crack, especially a crack that starts behind the pipe.
 
Exhaust

Welding straight around a tube is considered a cardinal sin in aircraft welding. Many of the exhaust manufacturers get away with it but that doesn't make it right.
The proper term for reinforcement would be doubler, very different from a gusset. The doublers would be V shaped, 30 degree angle to flange, and located between the attach holes so as not to compromise ability to get a wrench on the fasteners.
For a repair I would grind away the original weld so the doubler fits tight against the flange, then weld all around the doubler.
 
From Vetterman Exhaust..

HI Everyone, here is some thoughts on this broken exhaust:
When an exhaust breaks at 42 (I think) hours, there is ALWAYS an explanation. A rough running engine, mag issue, out of balance prop are all good places to start. However, the #1 reason we usually see is when the tailpipes aren't hung properly. Usually the hanger brackets need to be further aft. They need to be within a few inches from the firewall to support the tailpipes properly. Another issue we see here and there is a heat shield or hose clamp over the female portion of a slip joint. As the exhaust goes through heat/cool cycles the hose clamp compresses the slip joint until it seizes up, and typically causes a break at the flange.
Alf is sending pics of his pipe hanging installation and we will either repair or replace whatever is necessary to get him repaired and flying again ASAP.
If anyone has questions about anything exhaust related we are more then happy to answer them. Clint Busenitz Vetterman Exhaust (605) 891-1290
 
Ralph Inkster said:
"I can see that exhaust escapes on blowdown then the pulse pulls in fresh air to cool the EGT.

What I don't understand is why the plug will foul. Please help me understand why this would occur."

A friend had an exh flange brake loose on the way to OSH one year, after the repair he still had a rough running engine so amongst other things, pulled the plugs & found them totally fouled, cleaned them up & everything good after that. Later at OSH he happened by the Champion booth & asked why the plugs would foul like that. Their explaination reasoned that the heat retention normal in the exhaust port would be purged thru the open pipe causing the cylinder area around the exh port to cool enough to foul with lead (maybe similar to cold start / rich taxi plug fouling).
Click to expand...


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

Bill
 
BillL said:
Isn't this the bird that is for sale and has 150 hours? At 2700 rpm and this hours the #2 cylinder had experienced 12 million firing cycles, and 24 million piston reversals (side loading on cylinder). Low cycle fatigue?
Click to expand...

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.
 
Clint B said:
... hose clamp over the female portion of a slip joint.
Click to expand...
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?
 
Mark Albery said:
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.
Click to expand...

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.
 
Exhaust Preventive Maintenance

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.
 
Cause found...

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.

qrx4pc.jpg


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... :D
 
Bill Dicus said:
Bill - What was the anti-seize? Do you have a source? Thanks in advance...
Click to expand...

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 :D
 
Running W/O Exhaust

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

Bill
Click to expand...

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
 
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repair plans

I just wanted you all to know that I've heard from both Larry Vetterman and Clint by now. I even got their replies on a SATURDAY! Impressive!
Both of them where very helpful and gave me very valuable info.

Clint sent me detalied instructions about how to weld the broken pipe.
I'm going to contact a certified aircraft welding shop in my local area and see if they can weld the pipe according to Clint's instructions.
If not, I'll send the pipe to Clint for the repair.

He promised a quick repair and he even offered to pay the return shipping. VERY NICE customer care!

I'll let you know how it turns out and ofcourse how the testflight goes, once the repair is done.

So far, I'm very happy with the service I've gotten from both Clint and Larry. (the latter is retired, but he still took the time to answer me. Good guy!)
 
Doug said:
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?
Click to expand...

The hose clamps on the EGT probes are normal. Unless your EGT probes are more than 4 inches below the flange, they will be above the slip joints on all of the systems we manufacture. Putting a hose clamp over a slip joint will compress them over time and cause the slip joint to seize up.
Anti seize works well but won't creep into a slip joint or ball joint the way mouse milk will. Mouse milk was originally designed as a turbo charger waste gate lubricant and will help dissolve carbon residue, helping to keep ball and slip joints free.
 
Update

Here's an update of the repair-process:

The Norwegian Airplane repair shop in our local area didn't have the correct welding rods or the correct material.
Therefore, I shipped the pipe on Friday the 5th of Sept to Clint in the US.

He got the pipe on Saturday the 20th and yesterday (Mon 22nd), the welded pipe was out of the door again and on it's way back to Norway.
That sure was a speedy repair! And even during a weekend! Impressive!

Not only did Clint do the repair for free, but he also covered the return shipping.

This is VERY nicely done of him and I'm very impressed with his willingness to stand behind their product!
It's good to know that there's help out there when you need it!

So right now, I'm eagerly waiting for the pipe to get here, probably in a couple of weeks.
I'll post another update when it's here and the -7 is back in the air.

So far: WELL DONE Cint!
 
Problem solved

Here's an update and hopefully the cause of the problem:

I received the repaired exhaust pipe a few weeks ago, and the repair-work done by Clint was very nicely done:

jq5f2v.jpg


14mzzvp.jpg







The reason WHY the little tab (LV-706) failed in the first place, has worried me quite alot, and finally I think I found the answer, and the fault was mine:
I had installed the two support pipes with too little spacing, so my guess is that the rubber-hose didn't absorb the vibrations the way it was supposed to.

24mia11.jpg


I contaced Clint again, and he said that the ideal spacing beetween the pipe-ends would be 1/2 inch.
As you can see on the pic above, my spacing was alot less.






After cutting off alittle on one end on both starboard and port sides, the result was this:

23mjvpg.jpg


After this pic was taken, I adjusted the angle of the starboard support-rod so it ran in a straight line from the 706 tab to the exhaust pipe.
(as you can see on the pic, it's alittle curve on the support-rod)

I've flown about 7 hrs since the repair, and so far everything is back to normal. :)
 
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Superior XP-360 engine issue (Roller Lifter)

Lars said:
If everything else has been ruled out and the engine happens to be an older Superior 360 with roller cam, then it could be a stuck lifter (note that in this case it'll be an automotive roller lifter, not a Lycoming type with removable plunger). This happened to me, and it was not easy to diagnose. Much time spent staring at engine monitor datalogs.
Click to expand...

Lars, I believe I'm experiencing an issue with a roller lifer in an early Superior IO-360 engine (500 hrs.). What did you end up doing to resolve the issue considering the Superior SV72800 Roller Lifter is no longer available? I really do not want to split my engine case!!
 
brad walton said:
I will be interested in what you find because I have had the same thing happen to my Superior IO-360 on several occasions. #2 cylinder drops to 650 degrees and it runs rough. Mine has occurred during LOP operation and once when I cut the throttle abruptly while in cruise flight. I switched the plugs with the #4 cylinder and still had it happen. No sign of intake leak. Slick mags timing is good and no obvious problem with the wiring. Mine is intermittent and usually only for 15 seconds or so. I have performed the ignition system stress test (LOP in cruise and switch off one mag, then the other) and nothing obvious on the graph to indicate a problem. Maybe the exhaust valve is hanging up?
Click to expand...

Check your p-lead on you mags and confirm everything is tight. I experienced similar intermittent problems and discovered my p-lead ground that screws into the left mag was loose. Once tightened problem disappeared.
 
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