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possible morning sickness?

Lars

Well Known Member
Sponsor
I have a parallel valve Superior IO-360 in my RV-7. Vertical draft P/A Silverhawk fuel injection, 8.5:1 (180HP) pistons, dual Light Speed Plasma III ignitions, auto plugs (currently NGK BR8EIX), roller cam. Delivered new to me with 1 hour of dyno time in January, 2007. Sat pickled until first start in early June, this year.

The engine has always started easily, idles smoothly, with no signs of roughness on the ground other than the initial 1-2 seconds after it catches. Has only been run on 100LL. About 50 hours TTSN as of yesterday, oil changed regularly, burning about 1 quart in 25 hours now.

At about 5 hours of flight time, I was cruising at 6500', approximately 24 squared, leaned somewhat, when suddenly the engine started missing badly. After the initial panic and 180? turn back towards the airport (I was maybe 15 nm away at that point, airport is at sealevel) I noticed that CHT and EGT on #2 cylinder were dropping way off- it had gone completely cold. It was obvious that I was going to make the field, so I continued. Suddenly the cylinder came to life, as if nothing had ever happened. The symptoms reappeared as I was on downwind, but disappeared again by the time I was halfway through a 180 to final. Ran fine on the ground. My first thought was clogged injector, so I removed the line and the injector, checked for contamination. Found nothing. Reassembled, test flew, everything seemed fine.

A few hours of flight time later the problem reappeared, #2 cylinder again, once again it was only after I'd been flying for at least 15 minutes. Warm day, probably 80 degrees at altitude, but not scorching hot. That time it was intermittently less severe, but the cylinder eventually dropped off. During a beeline back to the airport it once again cured itself. Maddening, the worst type of problem to troubleshoot. This time I removed all the injectors, and, after calling Precision Airmotive, disassembled the flow divider to check for contamination. Found nothing. Ran fuel through the system with nozzles in glass jars which confirmed even flow. Swapped injector nozzles between #2 & #4 just in case, to rule that out. Reassembled, test-flew, everything was fine.

Yesterday, 35 hours after the last incident, the problem reappeared, intermittent in the air as always. Once again I returned to the airport and landed, only this time the problem continued intermittently on the ground. I ran it up to about 1500 rpm and watched the engine monitor. #2 would intermittently cut out (every few seconds) and when it did the EGT would drop precipitously. Once again I disassembled the fuel system from the flow divider on, but once again found nothing. I buttoned it up and test-ran it last night but didn't fly- it started and ran fine, all temps came up evenly.

Now I'm thinking about morning sickness, but I'm not sure what the symptoms are. It never happens at first start or when the engine is cold, but maybe that doesn't matter. What would one expect to see on an engine monitor? For what it's worth, I've checked compression, it's consistently 80/77 all around with a warm engine. Checked plugs, they looked fine everywhere yesterday. If an exhaust valve is sticking open, wouldn't EGTs go up instead of down?

I've spoken to a few local mechanics, but they don't have any ideas. I'm new to aircraft engines, but I've been working on ground-based engines my entire life, so I'm comfortable turning wrenches. I've read the description of the "rope trick" and I'm happy to do that if it makes sense.

Thanks in advance for any input!
 
Have you tried replacing the plug on that cylinder? A bad plug can look fine. If that isn't the issue, try replacing the plug lead. If you're getting fuel and air into the cylinder, then it's gotta be the "fire".
 
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50 hours is way too early to have valve sticking, unless there is something really odd. I'd look closely at the induction pipes. Could one of the rubber covered junctions be intermittantly opening up, leading to too lean misfire?
 
I wouldn't think of morning sickness. People often use that to describe when a cold engine is roughly running when started, but starts to smooth out. It's Lycoming's way of telling you to check the valve guides. If I've got the history of your engine correctly, and given the sudden on / off of the fault, it would seem very unlikely. I'd probably put that idea on the back burner.

Have you checked spark plugs & ignition leads? You might start by rotating the spark plugs to see what happens. It would be possible that you currently have two that are bad in the same cylinder. When you do a mag check they seem fine; yet when you push some power, at some point they break down (I've had this happen). That could explain why EGT is dropping - normally when one plug goes off and the other is still firing, EGT on the cylinder would rise.

You could also check the resistance of the ignition leads to see if there's some problem there.

Dan
 
I wouldn't think of morning sickness. People often use that to describe when a cold engine is roughly running when started, but starts to smooth out. It's Lycoming's way of telling you to check the valve guides. If I've got the history of your engine correctly, and given the sudden on / off of the fault, it would seem very unlikely. I'd probably put that idea on the back burner.

Have you checked spark plugs & ignition leads? You might start by rotating the spark plugs to see what happens. It would be possible that you currently have two that are bad in the same cylinder. When you do a mag check they seem fine; yet when you push some power, at some point they break down (I've had this happen). That could explain why EGT is dropping - normally when one plug goes off and the other is still firing, EGT on the cylinder would rise.

You could also check the resistance of the ignition leads to see if there's some problem there.

Dan

Thanks for the reply. Morning sickness seemed sort of unlikely to me, too, based on the descriptions I read. Especially considering the first time was at 5 hours.

I've checked plug leads, replaced plugs, etc. EGT always drops when this happens, along with CHT. In lockstep.

Also, a little more clarification: for anyone who isn't familiar, the Light Speed ignition systems are a "wasted" spark design" which means the plug fires on every rotation of the crankshaft. Each plug is fired from a coil that's shared with the plug on another cylinder, which means that if a coil goes bad it manifests itself as a misfire on both cylinders served by that coil.

Could be both plugs or leads going dead at the same time, which would mean that it's as you described, Dan, but since fuel would still be sprayed at that cylinder, wouldn't I expect a rise in EGT rather than a drop, and/or a big backfire when the raw gas ignited on its way out the exhaust valve?
 
50 hours is way too early to have valve sticking, unless there is something really odd. I'd look closely at the induction pipes. Could one of the rubber covered junctions be intermittantly opening up, leading to too lean misfire?

Yep, checked for that. All tight, in good condition :( Including nuts & gaskets at the cylinder head.
 
During your troubleshooting, be sure to check the quality of your connections to the LSE coils. I was doing a run-up earlier this year after flying the day before with no issues and when I turned off the mag, the RPMs dropped off drastically and one of the cylinders' temps dropped as well.

It turned out that the wire to one coil had broken from vibration where it attached to the connector. I replaced the connector (and reinforced the wires to prevent vibration) and figured that, if one wire was broken, the other one might be ready to break. Sure enough, all I did was touch it and it broke!

Just something to check.
 
Call Bart at Aerosport Power

Bart should be able to help with the diagnosis. He has been very helpful even though I didn't purchase my Superior IO-360 from him. Give him a call.
 
I don't see any reason to discount valve sticking.

Agreed. Unlikely maybe, but definitely not off my list. But, do my symptoms point in that direction? That's part of the problem: there's plenty of information that vaguely describes the missing, and what it looks like after the valve spring has been removed, but nothing I could find that mentions what one might see on an engine monitor.

I agree.. find a local mechanic that can perform this Lycoming SB 388 -

http://www.caa.si/fileadmin/user_upload/pageuploads/AD-NOTE/AD-2006/093_sb_SB388C.pdf

Have read that. If I pull the rocker cover I'm inclined to go ahead with valve spring removal and checking both valves for slop or lack of same. Here's an article I found, which refers to the Lycoming bulletins and offers some DIY advice: http://www.theleftseat.net/stickyvalvereaming.html
 
Lars, back in my old race engine days, we'd go wires, plugs, valve train. Sounds like you have covered the ignition and fuel side of things pretty well, so Dan and Gil may be on to something with a valve stem/guide clearance issue. Sounds wierd I know, but pulling the rocker covers and taking a look is certainly warranted. My .02 worth.
Tom
 
If you use the Lycoming tool for the SB 388 test you don't have to remove the valve springs. The tool pushes down on the spring retainer so you can take the wobble measurement. It's pretty non-invasive...:)
 
If you use the Lycoming tool for the SB 388 test you don't have to remove the valve springs. The tool pushes down on the spring retainer so you can take the wobble measurement. It's pretty non-invasive...:)

Interesting. Where would one buy the tool? I ask because I'm betting that the tool is probably the same price as I'd have to pay for a mechanic to do the job, and if I have the tool I can do it more than once. Etc, etc.
 
Agreed. Unlikely maybe, but definitely not off my list. But, do my symptoms point in that direction? That's part of the problem: there's plenty of information that vaguely describes the missing, and what it looks like after the valve spring has been removed, but nothing I could find that mentions what one might see on an engine monitor.



Have read that. If I pull the rocker cover I'm inclined to go ahead with valve spring removal and checking both valves for slop or lack of same. Here's an article I found, which refers to the Lycoming bulletins and offers some DIY advice: http://www.theleftseat.net/stickyvalvereaming.html

I know of one brand new Lycoming purchased through Vans installed in a RV-7A that had a stuck #4 exhaust valve before first flight. The cylinder was removed an returned to the factory.

It happens.
 
Lars - did you go full rich when the symptom occured in flight? I had a sticking valve on #2 cylinder, not nearly as frequent of an issue as yours and after about 400 hours. It would always clear when the mixture was enrichened.
Also, a compression check revealed some leaking around the exhaust valve but it was always cured by staking, leading me to believe a piece of carbon got under the valve, which was not the case. It turned out to be a slightly sticky valve that would act up on occasion.
This led to several other symptoms at idle. Lower than normal EGT's on that cylinder when cold and difficulty setting idle mixture.
I chased the problem for quite some time.
Bart reconditioned the cylinder and all was good.
 
Lars - did you go full rich when the symptom occured in flight? I had a sticking valve on #2 cylinder, not nearly as frequent of an issue as yours and after about 400 hours. It would always clear when the mixture was enrichened.
Also, a compression check revealed some leaking around the exhaust valve but it was always cured by staking, leading me to believe a piece of carbon got under the valve, which was not the case. It turned out to be a slightly sticky valve that would act up on occasion.
This led to several other symptoms at idle. Lower than normal EGT's on that cylinder when cold and difficulty setting idle mixture.
I chased the problem for quite some time.
Bart reconditioned the cylinder and all was good.

Jon, thanks for the reply. Yep, tried full rich and everything else in between. Maddening that it happened the first time with only 5 hours, but the more I ponder this the more I think it's time to check the valves on that cylinder.

Lycoming lists several valve guide IDs in SB388C. My cylinders (and the rest of the engine) are actually from Superior but presumably the same numbers apply. I understand that valve stems are nominally .5000" diameter- are valves and guides specified as matched sets with some variation? I ask because if I do need a reamer, it would be nice to have it on hand in advance. Maybe I need several?
 
Interesting. Where would one buy the tool? I ask because I'm betting that the tool is probably the same price as I'd have to pay for a mechanic to do the job, and if I have the tool I can do it more than once. Etc, etc.

I believe Lycoming has a tool rental program...
 
Any comments on what I could expect to see on an engine monitor with a stuck exhaust valve? I've seen a couple of posts that imply that EGT would fall, which seems strange to me since fuel is presumably still being burned. Could a really stuck exhaust valve cause the CHT and EGT on the offending cylinder to fall to near ambient temperature levels, as I experienced?
 
If the exhaust valve sticks open, then what happens is that on the intake stroke you don't pull in much fresh fuel/air mixture. Instead, you pull the burned exhaust back in (the pressure in the exhaust pipe right there is probably higher than the less-than atmospheric pressure in the intake manifold). Of course the exhaust won't ignite and burn at all, so EGT and CHT fall rapidly toward ambient temperatures.

I don't know anything about the electronic ignition, but you stated that the plugs in another cylinder fire (during exhaust stroke) off the same coil. Is there any failure mechanism (such as the plugs in that other cylinder having much smaller gaps?) than can make the other cylinder hog all the available electrical energy? In an intermittent way?
 
If the exhaust valve sticks open, then what happens is that on the intake stroke you don't pull in much fresh fuel/air mixture. Instead, you pull the burned exhaust back in (the pressure in the exhaust pipe right there is probably higher than the less-than atmospheric pressure in the intake manifold). Of course the exhaust won't ignite and burn at all, so EGT and CHT fall rapidly toward ambient temperatures.

I don't know anything about the electronic ignition, but you stated that the plugs in another cylinder fire (during exhaust stroke) off the same coil. Is there any failure mechanism (such as the plugs in that other cylinder having much smaller gaps?) than can make the other cylinder hog all the available electrical energy? In an intermittent way?

That explanation makes sense, thanks.

The type of ignition coil, and for that matter the wasted spark system used by Light Speed is actually pretty common, both on motorcycles and late model autos with distributorless ignitions (nearly all of them, these days). A bad or mis-gapped plug won't affect the other cylinder served by the same coil.
 
As to your other question, to the best of my knowledge valves and guides are not sold as matched sets, and I think in general there is only one ID specified. It used to be, at least for TCM guides, that the installer reamed them to final fit, don't know if that's still standard practice or not. Guides can be bought with the OD oversize, since they are interference fit into cylinders and if you need to replace the guide you usually have to go one size up from the old one.

Keep us informed, I'm very curious about this.
 
As to your other question, to the best of my knowledge valves and guides are not sold as matched sets, and I think in general there is only one ID specified. It used to be, at least for TCM guides, that the installer reamed them to final fit, don't know if that's still standard practice or not. Guides can be bought with the OD oversize, since they are interference fit into cylinders and if you need to replace the guide you usually have to go one size up from the old one.

Keep us informed, I'm very curious about this.

Will update as I figure this out. Doesn't seem right to ping the forum for help and then not share the knowledge. I have learned a lot today already.
 
Pulled the valve cover and rockers this evening. Everything looks normal, pushrods are both arrow-straight. Don't have the Lycoming wobble test tools or a spring compressor (yet), so that was as far as I could go. It's reassuringly simple in there, even moreso than inside the rocker covers of my BMW motorcycle.

Given what happened to Greg Arehart a few years ago I paid particular attention to any evidence of cracking on the rocker shaft bosses, but all looked good.
 
I'm still thinking there is a problem with the ignition lead to that cylinder. I know you tested the leads, but the symptoms are intermittant, so cant yet rule it out completely. Can you swap the lead with a different cylinder and see if you can get the problem to move, hopefully while on the ground? Simple and cheap to try at least.

Erich
 
troubleshooting

From what you've described, I too would suspect a sticking valve. You might take the rocker cover off and pull out the pushrods and look for any sign of a bent pushrod, or hammering on either end of the pushrods. A simple thing to do that won't take much time, but might confirm a suspicion. Good luck.
 
Would have to have both leads/plugs bad?

I'm still thinking there is a problem with the ignition lead to that cylinder. I know you tested the leads, but the symptoms are intermittant, so cant yet rule it out completely. Can you swap the lead with a different cylinder and see if you can get the problem to move, hopefully while on the ground? Simple and cheap to try at least.

Erich

seems like if one of the leads was bad, you might get some mis-fire, but then the temps would go up just like on a mag check. It would take both plugs or both leads to be bad to get the non-firing cool-down that Lars is seeing. Is there any common point of failure to both ignitions? Does the hall-effect/crank sensor trigger for each cylinder? I think the crank sensor just has two triggers (two magnets), so if a magnet fell out or a sensor failed, you would get two cylinders non-firing. Thats part of the virtue of the wasted spark design. What else though?
 
Try two Magneto's!

We have seen several Lightspeed issues lately in my part of the world.....and the returned parts failed 15 hours later. Story from Lightspeed, found nothing wrong but did an upgrade free of charge. Yeah right!

So far in my opinion, there has not been a really good EI, suitable for the task at hand. There is promise, but so far nothing for sale. Topic for another day.

If you can try two mags, borrow some, give it a try. You are running short of options.
 
The ignitions are fully independent. Only common point of failure is the battery, which is in good shape and in any case the system was showing 13.9 volts during the flight, as it always does- the ignitions will continue to function down to 10 volts or so. More importantly, logically there is no possible way that the dual Light Speed ignition arrangement itself can cause one cylinder to drop out completely- whether that was an intentional part of the design or otherwise. I can explain the system in detail for those that may be curious, but it's really a topic for another thread.

I won't attempt to defend the choice of electronic ignition- there will always be detractors- in this case though they are certainly not the issue, regardless of any other problems they may or may not cause in the future.

Last night I pulled the cowl and removed the #2 rocker cover and rockers. Got as far as I could into it without either Lycoming's inspection fixture or a spring compressor to remove valve springs. The pushrods were arrow-straight, the rotator cap was intact on the top of the exhaust valve stem. No strange witness marks on either pushrod. At this point I think I'll pull the springs, since it's trivial, and I want to feel how the valves move in their bores. I like the tactile experience. It has been suggested to me that it could be an intermittently collapsing lifter. I hope not- I don't believe those are serviceable without splitting the case.

I'll keep reporting on what I find, thanks for all the interest!
 
It has been suggested to me that it could be an intermittently collapsing lifter. I hope not- I don't believe those are serviceable without splitting the case.

I'll keep reporting on what I find, thanks for all the interest!

You can pull the lifter right out with a dental tool and take it apart to inspect it. You will need to do this anyway as once you take the push rods out you then need to drain the oil out of the lifter to allow it to compress again for reassembly.
 
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I'll keep reporting on what I find, thanks for all the interest!

I wager one fly-in beer on a tight intake valve ;)

BTW, a collapsed lifter won't kill the cylinder. The valve just has less lift with the lifter collapsed, so the cylinder is down on power, not dead.
 
You can pull the lifter right out with a dental tool and take it apart to inspect it. You will need to do this anyway as once you take the push rods out you then need to drain the oil out of the lifter to allow it to compress again for reassembly.

Thanks for the tip. Hopefully the Superior roller lifter is the same.
 
You can pull the lifter right out with a dental tool and take it apart to inspect it. You will need to do this anyway as once you take the push rods out you then need to drain the oil out of the lifter to allow it to compress again for reassembly.

Cleaning the lifters is also a part of SB 388C..
 
I wager one fly-in beer on a tight intake valve ;)

BTW, a collapsed lifter won't kill the cylinder. The valve just has less lift with the lifter collapsed, so the cylinder is down on power, not dead.

:)

Dan, if you make it to NorCal, beer is on me. Heck, if I make it to Wetumpka, I'll buy anyway.

I'm thinking the same thing. Springs are coming off as soon as I can get my hands on a spring compressor. Unfortunately the one I used to swap springs on my small block Ford a couple of weeks ago doesn't work on a parallel valve Lycoming head...
 
seems like if one of the leads was bad, you might get some mis-fire, but then the temps would go up just like on a mag check. It would take both plugs or both leads to be bad to get the non-firing cool-down that Lars is seeing. Is there any common point of failure to both ignitions? Does the hall-effect/crank sensor trigger for each cylinder? I think the crank sensor just has two triggers (two magnets), so if a magnet fell out or a sensor failed, you would get two cylinders non-firing. Thats part of the virtue of the wasted spark design. What else though?

I've had these same symptoms exactly. My setup was a standard mag and electronic ignition to each cylinder. On run up I did my mag check and when I turned off the EI, my engine got very rough at 2k rpm. I lost about 400 rpm and got backfires along with a cold cylinder. The problem was a bad ignition lead. Replaced and all checked good. Another data point for you guys anyway...
 
IGNITION PROBLEMS

Hello Lars

Your problem is d?finitly ignition related.

I've had the exact same problems with the exact same symtoms you're seeing on my RV-4 with an 0-320 with an Ellison TBI and dual LSI with Hall Effect sensors a couple years ago.

If you have Hall Effects sensors installed, your problems is with the DSUB connectors to the Hall Effects.

I called Klaus when I encountered that problem on the road and his reply was ''Remove the connectors, clean them with contact cleaner and re-install''

I did just that and Bingo, never had that problem ever since..This is now a twice annual recurrent event..

I had replaced the coils (had a spare ) and all the plugs prior to that and it didn't cured the problem, cleaning the DSUBs did the job..

You could call Klaus to confirm but he will tell you the same thing

Best of luck

Bruno
[email protected]
 
I wager one fly-in beer on a tight intake valve ;)

BTW, a collapsed lifter won't kill the cylinder. The valve just has less lift with the lifter collapsed, so the cylinder is down on power, not dead.

Ok, I bet it's an exhaust...
 
Lightspeed

If you have a lightspeed Ig, check the spade connectors on the coils. I had an intermittent problem like this that plagued me for over a year, finally tracking it down to a wobbley spade connector on the ig. coil for one half the engine....
Jim Frisbie
RV-9A
N571DF 250+ Hrs.
 
[QUOTE="DanH, post: 702159, member: 2320"]I wager one fly-in beer on a tight intake valve ;)

I wager one fly-in beer on a tight intake valve ;)

BTW, a collapsed lifter won't kill the cylinder. The valve just has less lift with the lifter collapsed, so the cylinder is down on power, not dead.

Aloha folks, just a quick note as i was over at Lars hanger tonight to see what's up and it looks like Dan H wins a beer!..
Stuck Intake valve #2 ...but i'll let Lars add the photos and comments for all;)
 
I wager one fly-in beer on a tight intake valve ;

Dan, you may be right. We found a circumferential scratch or nick on the intake valve stem last night. It raised enough of a burr that the stem wouldn't enter the guide past that point. Reinstalled the rocker and pushrod without the spring. One of my friends (yep, I have a few- thanks Lee and Mark) pulled the prop through while I held the valve against the rocker. The valve started hanging up in the guide just before the rocker reached full travel. We dressed out the scratch until the valve no longer hung up, then reassembled everything.

Later I started the engine and ran it up. All CHTs and EGTs looked normal, but then they have many times before. Can't prove a negative, so don't know if this was the issue, but I'm glad I found it.

I contacted Superior and emailed photos. The opinion there was that it's not an issue now that the scratch is dressed out, go ahead and fly. But I will report back any additional responses from them, and anything else I learn.

Photo of the scratch on the intake valve stem before dressing it out, below.

i-WCKz6cQ-XL.jpg
 
Well done. Glad I didn't bet Dan, but I know better than that. I would buy him a beer anyway.
I would be pretty confident you found the issue.
 
Slight update...

Flew to SoCal last weekend from my NorCal base, the first real cross country flight in N718WG. No issues on the way down (which we did in 2 hours, compared to the usual 7 hour drive- a happy reminder of why I built this thing) but on the way home #2 started dropping off again after a steady climb from sea level to 8500'. Felt the airframe shake and saw #2 CHT & EGT start falling. Before it had a chance to get really obvious, and frightening my wife, I thought to grab the red knob. Leaned it way out till the engine started to die (thus scaring her anyway) then back to about where I expected best power to be. Stopped the problem in its tracks- #2's numbers came back up to join the others, and it behaved itself all the way home.

So the issue doesn't seem to be related to #2 intake, which I sorta suspected, despite the finding of the scratched valve.

Time to take some advice and make some measurements- Gil's advice in this case. I bought Aircraft Spruce's version of the Lycoming wobble test tool. That means removing the exhaust valve spring since (as Gil noted in another thread somewhere, the ACS version requires that, unlike the official Lycoming tool) but that's no big deal with shop air and a spring compressor. The measurement is somewhat subjective, since none of the structure is terribly stiff. Push hard enough and you can grow the measurement quite a bit.

Rocking the valve back and forth firmly without manhandling it like I was trying to break it off, I got .012-.013" of movement. Went off to drain some of the coffee I'd borrowed earlier, then tried again and got the same thing. Per Lycoming SB388C, the acceptable range is .015 to .030", so this was slightly under. The valve was not stuck, however. It slid back and forth in the guide smoothly, likewise with rotation.

I miked the guide at ?.4995", then ran a reamer of that size through it. Found some gray/black crud on the blades. The stem was a bit varnished- cleaned it up with a scotchbrite pad, then reassembled. The result was .015" of wobble, at the low end, but in spec.

I ran out of time so I haven't had time to fly, but assuming it runs fine I'll know that I might have taken care of it. I hate troubleshooting intermittent problems,
 
The (exhaust) valve was not stuck, however. It slid back and forth in the guide smoothly, likewise with rotation. I miked the guide at ?.4995", then ran a reamer of that size through it. Found some gray/black crud on the blades. The stem was a bit varnished- cleaned it up with a scotchbrite pad, then reassembled.

Might want to go back and size the intake valve guide too. The intake valve had a burr resulting in zero clearance when cold. ("The valve started hanging up in the guide just before the rocker reached full travel.") I know you dressed out the burr on the stem, but some galling on the ID of the guide is to be expected....and new clearance is what, 0.001" to 0.003?
 
Lar's, sorry your symptoms still exist. I thought you had it licked. Chasing intermittent problems is no fun. At least you know what cylinder it is. I would consider pulling that jug and have it gone through. It takes about two hours to get it out of there, the biggest time sucker is the baffling.
My engine builder did it for free, and included all of the gaskets and expendibles, and that was after 400 hours and four years of use.
Something to think about.
 
I'm a bit late to this thread, but the symptoms in your last update sound sorta familiar... a few years ago I had an almost identical issue. Climbing out from a lunch stop (wife in the back too, that's gotta be the problem!), leveled off, got rough, #2 low EGT/CHT, wiggle some knobs, smoothed out, flew home.

Troubleshooting with a compression check showed a stuck exhaust valve, I could hear the air blowing out the exhaust pipe. I towed it downfield to an engine shop to let them have at it... they worked their magic, broke it loose, cleaned, lapped, wobble checked, closed it up. What they found with the wobble check was there was some play there, within tolerance, but enough to allow carbon and crud to build up on the stem and guide, eventually seizing it up. The grizzled old mechanic made a suggestion: Marvel Mystery Oil. He said to burn it in the fuel and it'll help keep the valves clean to keep 'em from sticking again.

Maybe it's just an old wives tale; is it a solvent or a light oil, is it the mint scent or the animal fat (so I've read) that is the Mystery... I dunno, but the stuff seems to work. Every other top-off I add 8 oz to one 21 gal tank and the sticky valve has not reappeared. The initial episode was at 300 hrs or so; right now I'm at 965 hrs and it's running well. I probably oughta get another wobble check done though. It might or might not solve your trouble, but it's a cheap and easy experiment!
 
Might want to go back and size the intake valve guide too. The intake valve had a burr resulting in zero clearance when cold. ("The valve started hanging up in the guide just before the rocker reached full travel.") I know you dressed out the burr on the stem, but some galling on the ID of the guide is to be expected....and new clearance is what, 0.001" to 0.003?

Good point Dan, and actually I was concerned about that. Not mentioned in my previous verbose posts was that I pushed the intake valve into the guide a ways (gotta love those magnets on a stick) and twirled a .4040 reamer in it. There was a witness mark, presumably caused by the burr, but it couldn't be felt with a fingernail test, and in any case it only went about 1/16" into the bore.

Drove to the airport at lunchtime and fired it up. It's still decowled so I didn't fly, but I can say it hasn't started that smoothly in a long time. Like the proverbial car engine. Previously it started like it wasn't running on all four, then smoothed out after a second or three. One cold start isn't enough data to draw any conclusions, so you'll find me at the airport again after work adding to the database :)

Lar's, sorry your symptoms still exist. I thought you had it licked. Chasing intermittent problems is no fun. At least you know what cylinder it is. I would consider pulling that jug and have it gone through. It takes about two hours to get it out of there, the biggest time sucker is the baffling.
My engine builder did it for free, and included all of the gaskets and expendibles, and that was after 400 hours and four years of use.
Something to think about.

Point well taken. If this thing gives me any more trouble it's coming off. The remover will be me though, since the engine builder (Superior) is in Texas and the warranty disappeared with the bankruptcy :( Fortunately there are a couple of experienced A&Ps in my neighborhood that have been a great help during this. Have learned a lot. I'm (re)discovering that I really like working on engines.
 
Good point Dan, and actually I was concerned about that. Not mentioned in my previous verbose posts was that I pushed the intake valve into the guide a ways (gotta love those magnets on a stick) and twirled a .4040 reamer in it. There was a witness mark, presumably caused by the burr, but it couldn't be felt with a fingernail test, and in any case it only went about 1/16" into the bore.

Drove to the airport at lunchtime and fired it up. It's still decowled so I didn't fly, but I can say it hasn't started that smoothly in a long time. Like the proverbial car engine. Previously it started like it wasn't running on all four, then smoothed out after a second or three. One cold start isn't enough data to draw any conclusions, so you'll find me at the airport again after work adding to the database :)



Point well taken. If this thing gives me any more trouble it's coming off. The remover will be me though, since the engine builder (Superior) is in Texas and the warranty disappeared with the bankruptcy :( Fortunately there are a couple of experienced A&Ps in my neighborhood that have been a great help during this. Have learned a lot. I'm (re)discovering that I really like working on engines.
I should have been more clear. I removed the jug and sent it to the manufacturer. First time I ever pulled one and it was quite simple. They reconditioned it for free. Best of luck.
 
I should have been more clear. I removed the jug and sent it to the manufacturer. First time I ever pulled one and it was quite simple. They reconditioned it for free. Best of luck.

Ah. If it comes to that, I'll channel your good karma and hope for free, too :)
 
conclusion, maybe...

I was gently reminded that, since I started this thread, updates are a good thing. Some 10-odd hours after reaming the exhaust valve on the offending cylinder (that would be #2 for those just joining in), I have experienced no symptoms of morning sickness or inflight cylinder drop-outs. My airplane seems to be very happy cruising at 165 KTAS burning around 8.8 gph.

I've been a little reluctant to declare victory since after the first couple of occurrences, the problem "fixed itself" for over 30 hours of flight time before it reappeared- and it's not easy to prove a negative. Still, it instantly disappeared after the guide reaming, and I've done several flights involving abrupt power changes since then, with no issues.

For those new to Lycoming "morning sickness" and intimidated by doing the "rope trick to drop the exhaust valve for guide reaming, I can say that it's a non-issue. It may sound sorta crazy, but at this point I could probably do the whole thing including cowl r&r in an hour, given the tools.
 
And the final answer is...

Resurrecting an old thread.

Not long after my last post, #2 cylinder started dropping out in flight, again. As usual, both CHT and EGT would drop- the latter precipitously, especially at high power settings (that was a clue, though I didn't know it at the time).

Through all of this I had been in touch with Superior Air Parts. Despite my warranty having been invalidated by the Theilert bankruptcy debacle, they have been stellar to work with. In the Fall of last year they sent me a complete new flow divider, four new injector nozzles and new stainless tubes to try, free of charge. That didn't solve the problem, obviously. After the work I described in my last post didn't work, they offered to go through the cylinder, in case it was a valve problem. I pulled the jug and shipped it to them. They checked the guides, cleaned them, then installed new valves and springs, and turned it around in one day, all on their nickel.

After reinstalling the cylinder, I had one brief incident where I thought it recurred (November of 2012) but it was so brief that I was never sure. Flew again until late October, some 50 hours of flight time, without incident. Then it happened. Again. Only it was much less transient.

Short version of the story... a datalog off my GRT EFIS, plotted at savvyanalysis.com, pointed to a stuck lifter plunger. My lifters are early Superior rollers, and completely different than anything on the market. They are essentially a GM roller lifter adapted to the engine. Plunger design is totally different, retained with snap rings as on GM V8s (among others). They also have much more stroke than a Lycoming plunger (valve clearance with lifter collapsed is much greater). A PITA to get the plungers out, but once done the intake plunger showed some deep axial score marks- as if metallic debris had gotten into it (I wasn't able to find any using no-lint cotton swabs). Superior was once again stellar to work with; got help from VPs of engineering and marketing, as well as the tech who built my engine originally. New lifter plungers sent on their nickel. Now 10 hours into it and all seems well. In fact cylinder now runs about 5-7 degrees warmer at usual power settings than it did before.

If someone wants details of the troubleshooting process I'll share. It's not something you might figure out unless you'd also dealt with a similar scenario on an automotive engine. The datalog was the key. I have pix of the lifter plungers but they don't show the score marks- too much reflection.
 
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