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Lycoming Carbureted O-290-D2 EGT out of Family

snopercod

Well Known Member
Something went amiss two days go on a 1 hr. cross country flight at 7,500' and I'm searching for ideas. Perhaps someone here can point me in the right direction. My normal routine when reaching cruise is to pull out the mixture control maybe 1", let things stabilize for a couple minutes as the speed builds up, then start the leaning process with my JPI EDM-700. I usually lean to peak and leave it there unless the engine is running rough. In that case, I enrichen 50 degrees. My four bar EGT display usually isn't quite level, so I adjust the throttle a tiny bit until all four EGTs are a straight line on display. The throttle butterfly works magic to even up my fuel distribution.

So on this flight, EGT 1 (red line) was way low (230F), and EGT 2 (green line) was also low (150F). No matter how I fiddled with the mixture and the throttle, I couldn't get that nice straight line. The engine wasn't running rough, but I could feel an unusual vibration. My airspeed was normal, so I kept on to my destination. (My runup had been completely normal with equal mag drop on both mags.)

The return trip was the same. I really didn't realized how messed up the EGT/CHTs were until I got home and dumped the data. The #1 CHT was way low as well. (#1 is red, #2 is green) Just look at this mess:

MO4oZL.jpg


My first thought was spark plugs (which really wasn't right), so the next day I pulled the #1 plugs. The top plug was sooty, the bottom plug was a nice tan color. The resistance checked good on both plugs (after I used emery cloth on the electrode to get a good connection).

Then I panicked, thinking that if both #1 and #2 were messed up, that it had to be the common intake lobe for #1 and #2 going bad on me. This possibility is always in the back of my mind since my engine sat for several years during my build. My engine analyses have always been good, but today I removed the oil filter, cut it open, and removed the pleats. I held them open as my lovely wife poured MEK over them into a coffee filter. (The MEK ruined her nail polish, but she forgives me.) Thankfully, there was no significant debris found, and almost nothing magnetic.

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So tomorrow I'm going to change both plugs "just because", even though a fouled plug should have made the EGT go UP, not DOWN, I believe. After warming up the engine, I'll do a compression check.

I also intend to remove the carburetor and make sure my 2-piece venturi is still intact, and that nothing else is wrong in there. I recently installed a carb temperature gauge, so I need to insure the probe (on the cyl 1 and 2 side) is still intact.

Other than that, the only thing I can think of to check are the plug wires to #1, but that wouldn't account for the low EGT on #2. Maybe something in the mag?

I'm down to grasping at straws here, so any SWAGs would be greatly appreciated.

P.S. I do have a traditional primer going to cylinder #1, but thought I had that fixed. If push comes to shove I could cap it off as a test.
 
I always thought that running an engine at peak EGT was the worst place to run it. 50 degrees on either lean or rich side is supposedly better? :confused:
 
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Give how low those EGT reading are and that the engine is running more or less smoothly, I'd entertain the possibility of instrument error. Maybe a bad ground or kinked lead wire to those sensors? Do you have enough wire to swap the probes between the "good" and "bad" cylinders to see if the problem stays with the cylinder or moves with the probe?
 
I'd entertain the possibility of instrument error.
That's certainly a possibility, but as an instrumentation engineer in a former life, the possibility seems remote to me. It's been my experience that thermocouples don't ever "read wrong", they mostly just fail open. I do have a spare EGT probe, though, so I'll put it on my list of things to check.

After tossing and turning all night, my current thinking is that a fouled plug or bad mag would have caused the EGT(s) to rise, not fall (somebody correct me if I'm mistaken). When we do a mag check during runup, we expect to see an even rise in EGTs, right? So if the problem isn't the cam, and isn't the ignition, then it has to be a rich mixture in cyl #1 and, to a lesser extent, #2. I recently battled what I thought was a leaking primer (see this thread, which I just re-read) If the primer were the problem, though, it would only effect cylinder #1 and would show itself at idle, not cruise power.

So if the problem isn't ignition-related, isn't cam related, and isn't primer-related, then something has to be going on inside the carburetor barrel to mess up the fuel distribution to the front two cylinders (unless you guys can come up with something else). There are several opportunities there. Let me think out loud for a minute:

Several years ago I had my way with my main fuel nozzle. I drilled it out to obtain more fuel flow on takeoff and, for better fuel distribution, I also drilled four tiny #57 aeration holes on the back side of the nozzle to direct more fuel toward the rear two cylinders. Marbel-Shebler came out with this "fix" after they went to the one-piece venturis, but my carb is so old they didn't bother producing a "peppermill" nozzle for my model. The homemade aeration holes have been working just fine up until now but what if they have become clogged? That seems unlikely since my carb inlet screen was clean when I checked it last month. Could clogged aeration nozzles cause these symptoms? Maybe...

Secondly, I still have the two-piece venturi and the AD requires me to check it's integrity every 100 hours. I did that just last month, but will certainly have to check it again now.

Thirdly, not long ago I added a carburetor temperature probe in the front side of the carburetor barrel (toward cyls 1 & 2), so I'll need to check that as well. The probe came with my $13 digital display that I bought on Amazon and I glued it in place with J-B Weld, so I really need to check it.

Fifthly, two months I also added a 1/16" phenolic spacer and extra gasket between my carb and oil sump to mitigate a heat-soak problem I was having (see O-290-D2/MA-3SPA Dies when heat soaked. That (and doing some other things) fixed the heat-soak problem, but maybe I introduced another problem? But the EGT/CHTs have been fine for months, to that's probably not it, unless something broke loose?

Before I go through the painful process of removing the carburetor for inspection, I guess I need to do the easy thing first and check the compression. It was 78/80 or better on all cylinders only a month ago, but spit happens... I guess I can put the old plugs back in temporarily to warm up the engine.

Wish me luck...

(It just occurred to me that I really need some kind of inspection port in my airbox so I could inspect the carburetor internals with a borescope rather than removing the darn thing.)
 
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Assuming you weren't dumping a bunch of extra fuel into those two cylinders and you don't believe that you are having misses, the most likely culprit is a reduced power output in those cylinders. The first thing that I would do is check compression in those cylinders. A leak (broken ring, sticking valve, debris preventing valve from closing, etc.) will reduce the energy produced from the common air/fuel charge and will reduce CHT and EGT.

I can't see it as an ignition issue. When the ignition is too weak to light, you will get either a dead cylinder or misses. Also, running on one plug should increase EGT, not reduce it.

What is odd is that it is happening to two cylinders, not something I would expect for a compression issue (low odds for two cylinders to do this at the same time, unless a detonation event was encountered). I would also be checking the valve lift on those cylinders. A worn lobe that impacts both cylinders seems to be the high probability cause (reduced lift reduces the amount of air/fuel that can enter the cylinder and you see a smooth reduction in power output and commensurate reduction in CHT/EGT). You can easily check the valve lift on those cylinders and compare to the good cylinders. Significant lobe wear can occur for reasons other than corrosion based spalling. Remember, that lobe gets twice the wear, due to interfacing with two lifters. Given that it just happened, I would not expect to see much in the filter yet. Some destructive cam wear patterns result in very rapid wearing of the lobe. IMO, the lack of metal in the filter is not a definitive sign that you have not worn off a lobe, given how recently the problem appeared.

Larry
 
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you might consider returning the engine to the previous config to understand if the changes are causing the issue.
 
IMO, the lack of metal in the filter is not a definitive sign that you have not worn off a lobe, given how recently the problem appeared.
Trying to cheer me up? :( I'm new to this stuff, but I'm having trouble understanding where the metal from a worn cam would go if not into the filter. I haven't pulled the screen in the oil sump yet. As soon as the test kit arrives, I'll do another oil analysis. Maybe that will show something. Here's what I did today:

I reinstalled the old plugs and warmed up the engine so I could do a compression test like you suggested. I did my usual runup at 1,800 RPM and everything was normal as far as I could tell. I got an "equal" rise on all EGTs using the "normalize" mode on my JPI, which is much more sensitive than the way I had been doing it. Reading the data the rise was 100,80,76,129 on one mag and 145,127, 119, 158 on the other. I wouldn't read too much into the higher readings on the second mag because I wasn't being very precise; I was just looking at the bars on my EDM-700.

Back in the hangar and after removing the top plugs, the compression test was good - 78/80 or better on all (Cermichrome) cylinders just like it was last month and has been every time prior for the last 180 hrs. Next I unbolted the air box and pushed it aside so I could see up inside the throat of the carburetor. Everything seemed just fine in there. The two-piece venturi was still secure and the temperature probe was still there. This all looks normal to me:

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Better view of the carb temp probe:
n2KGau.jpg


The carb heat mechanism was intact and operating properly.

Hopefully the new plugs will arrive this afternoon. If so, I'll install those tomorrow and put everything back together. Oh yes, before I do that I'll check the insulation resistance on my #1 plug wires with the conductance function on my Fluke 87V-II. That's all I know to do so if nothing else turns up I guess I'll go flying and see if the problem has gone away by magic.

You mentioned checking the tappet clearance. I have a dial indicator, but am unfamiliar with the procedure. Anybody?
 
I'm with Steve

Pull that carb temp probe and see what happens.

Cheers, David
RV-6A 0-360 A&P
 
+1, pull the carb temp probe.
The close the throttle a bit trick is a good one, for evening up the mixture distribution. But your goal should not be that all EGTs are the same; the goal should be that all cylinders reach peak EGT at the same setting. e.g., after slightly closing the throttle, enrichen and then re-lean, see if they all peak at or closer to the same setting.
To check the tappet clearance:
Start with, say cylinder #1. Turn the prop so the intake valve is open. Let it sit for several minutes for the oil to drain out of the lifter (the cam will be putting pressure on it). Carefully turn the prop, while pushing hard on the rocker arm (push rod end) to not let the tappet re-expand, until you are at TDC. There should now be a gap between the rocker arm and the end of the intake valve. Use a feeler gauge to measure it (don't release the pressure on the push rod end of the rocker!), compare to specifications. Repeat for exhaust valve. Repeat for other cylinders.
 
That temp probe in the carb is just asking for trouble......it probably is creating havoc with air flow and if it ever came loose....
 
polish

pull the carb sensor and try it again.

from and old cub driver.... polish the carb venturi and get an 1 HP, polish the venturi supports and get another 1 HP, polish everything in the carb and get another 1 HP. then somehow +3 then become +5 HP. he will put his hand on the Bible. who knows for sure?
 
you might consider returning the engine to the previous config to understand if the changes are causing the issue.
Those are words to live by but, in this case, I haven't changed anything lately. Here's my JPI data from a flight only five days ago. This is how it's supposed to look as I lean:

U3nn14.jpg
 
I have never seen a carb temp probe that installs that way.
That's very true; Mine is a one of a kind ($13 vs. $1,000 for a "certified" unit), but I have a couple of questions: Many carbureted aircraft have temperature probes in the barrel with no problems reported. Mine is 1/4" diameter vs. the usual 1/8", so it probably disturbs the air flow more than an FAA-approved probe. But if the probe was disturbing the air flow, why wasn't it doing the same thing five days ago (see data just posted)?

I installed that probe as part of my quest to find out why my engine was quitting at idle when hot - and also to learn whether I really need to pull carburetor heat on final. The first question has been answered (heat soak from the oil sump) and the second question has been partially answered (not even close to icing at summer temperatures). I would really like to leave the probe in there for the upcoming cold weather but, after that, I could remove it.
 
Trying to cheer me up? :( I'm new to this stuff, but I'm having trouble understanding where the metal from a worn cam would go if not into the filter. I haven't pulled the screen in the oil sump yet. As soon as the test kit arrives, I'll do another oil analysis. Maybe that will show something. Here's what I did today:

As the metal comes off, it falls into the oil sump and will typically sink to the bottom pretty quickly (bigger pieces sink quickly and smaller pieces more likely to stay in suspension). It takes a while for the circulating oil to pick up the shavings and hold them in suspension so that they make it to the filter. Given that this problem appeared within the last two hours, I just don't believe many of the shavings would make it to the filter that fast. Further, this would have to be a more catastrophic type failure to literally appear overnight. Those type of failures create larger chunks and the larger pieces take longer to get picked up of the bottom and sent to the filter.

I certainly hope this isn't your problem, but I struggle to come up with something other than compression and air flow that would cause a 250 drop in EGT without out missing, other than flooding it with excess fuel (it can't be 250 lean of peak). So, the likely scenarios are 1) running 250 ROP or 2) power production is down, bringing down the EGT adn CHT. If you have a dial micrometer ($15 at harbor freight), it shouldn't take but an hour to rule out a valve train issue. You can put the plunger right on the valve spring cap and observe the total movement. Do this for the intakes on a bad and a good cylinder.

I also don't believe that a 1/4" tube in the carb throat, post-venturi, can cause the variability in mixture you are seeing. I would believe it if it happened to all four barrels, but don't see how something upstream of the throttle plate can impact only some cylinders at the magnitude you are seeing. For example, would you expect a restricted air filter to only impact the flow to two of your cylinders? You can confirm, but my read from your posts indicate that your engine ran normal and fine after installing the probe and the recent problems did not appear immediately after installing the probe. If that is not the case, then removing the probe would be the first thing I did.

Intake leaks, unless severe, tend not to create serious problems at WOT. They usually produce noticeable symptoms at lower MAP/higher vacuum levels.

Larry
 
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That's very true; Mine is a one of a kind ($13 vs. $1,000 for a "certified" unit), but I have a couple of questions: Many carbureted aircraft have temperature probes in the barrel with no problems reported. Mine is 1/4" diameter vs. the usual 1/8", so it probably disturbs the air flow more than an FAA-approved probe. But if the probe was disturbing the air flow, why wasn't it doing the same thing five days ago (see data just posted)?

To each his own, but since these aren't certificated aircraft you don't need a certified unit (even if you did they can be bought for a fraction of $1000).

By "Many carbureted aircraft have temperature probes in the barrel" I assume you mean within the airflow bore of the carb.?
I have never seen that.
The standard practice is a threaded 1/4-28 sensor that threads into a port on the front of the carb. body with only a very small tip of the probe actually protruding into the airflow path.

Whether your non standard home grown sensor is causing your problem or not, I think you are taking a huge risk with what you have.
Airplanes have made forced landings from just the accelerator pump nozzle tube coming loose and lodging in the small venturi. If your sensor ever comes loose I imagine the outcome wont be much different.
 
As the metal comes off, it falls into the oil sump and will typically sink to the bottom pretty quickly...
So then I need to drain the oil and remove/inspect the bottom of the sump and the screen. I think I'll fly one more time before I do that. Today won't be that day, though, because FedEx/ACS hosed me on shipping my new plugs; They won't arrive until tomorrow. It's so frustrating that it takes three frikkin' days to ship something less than 200 miles.

One other question. If my cam lobe is severely damaged, how could my runup at 1800 RPM be so normal?
 
If your sensor ever comes loose I imagine the outcome wont be much different.
If it makes you feel any better, that sensor consists of an aluminum tube about 1-1/2" long with only the tip protruding into the barrel. Most of it is outside the carb. It's bonded in place with epoxy and can't really fall into the airflow path. It could come loose, but the external wiring would prevent it from protruding much further into the barrel. It could break apart, but that seems unlikely. I appreciate your words of caution, though.
 
So then I need to drain the oil and remove/inspect the bottom of the sump and the screen. I think I'll fly one more time before I do that. Today won't be that day, though, because FedEx/ACS hosed me on shipping my new plugs; They won't arrive until tomorrow. It's so frustrating that it takes three frikkin' days to ship something less than 200 miles.

One other question. If my cam lobe is severely damaged, how could my runup at 1800 RPM be so normal?

I wouldn't change the oil. Just confirm the valve travel on the affected cylinders. That will provide a definitive diagnosis. I didn't mean to imply that the lobe is severely damaged, only that some wear damage takes many 10's of hours to wear down the lobe. Other types wear it very fast. The latter tends to produce larger debris.

Please define "normal" for runup. I would argue that your current condition is not all that far from normal. At cruise, your producing near full power, no serious roughness, etc. I would expect the symptoms to be less noticeable at runup RPMs, escpecially given the limited time spent at runup. Do you have a graph of EGT/CHT for your runup?

Larry
 
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Just confirm the valve travel on the affected cylinders...
I don't know how to do that properly, but I pulled the rocker covers from #1, #2, and #3 cylinders and used my dial indicator to check the intake valve lift. I'm not sure I learned anything because the #1 tappet was bleeding down and I couldn't get a constant reading. Curiously, the other two gave me steady readings. Could a leaking ball check be the problem? The lifts were as follows: #1 - 0.365" to 0.385" (variable): #2 - .410"; #3 - 0.430" (sorry for the crappy cell phone photos)

kNzgao.jpg


oGRJJD.jpg


To do this correctly I'm led to believe that I need to release the pressure from the plunger by somehow depressing the ball check valve. Frankly, I don't even know how to get my push rod shroud tubes off because they don't have a "keeper" on the cylinder head end. The Overhaul manual doesn't offer any knowledge...

I usually see a 140 RPM drop on either mag and roughly a 100 F EGT rise during the mag check. I write the RPM drop down on my checklist every flight so I can go back and see if there is a trend.

UPDATE: My two new UREM38F spark plugs and my oil analysis kit arrived in the mail. I'll be sending off an oil sample for analysis on Monday. If the cam is wearing, that should certainly show up. I also found an AvWeb article Power Deficient Engines which advises checking the cam lift exactly like I did it. They say:
How do you determine whether you’ve got a badly worn cam, without taking the engine apart? Basically, you remove all rocker covers and put a dial indicator, one by one, on each rocker, so that you can swing the prop and note the rocker or valve travel for each valve.

The total throw should be very nearly identical for each valve. A flat lobe will be immediately obvious, because you’ll have a rocker that barely moves.

Clearly my plunger was collapsing on cyl #1. I don't see how I can get a reliable dial indicator reading if that's the case. Anybody?
 
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Here's a pertinent comment from the EAA forum regarding suspected camshaft problems:
As an A&P and first hand knowledge, best take a look.
Last annual on my O-360 A4M, I discovered a cracked head.
I pulled #4 cly. Piston skirt was impregnated w/sparkly stuff.
Took a peek at the cam.....SHOT!!!!!
I change oil at 50hr intervals, have a oil filter that is opened and inspected at every oil change and the screen is also always removed and checked for fodder.
NO SIGNS OF IMMINENT DANGER!
When I dismantled the engine, in the bottom of the oil sump (left rear) were the remains (Grindings) of the cam and lifters!
The way the oil sump is designed with the bottom mounted Carburetor, there are webs that are just high enough to prevent the last 1/8 inch oil in that corner of the sump from making it to the oil pump intake port. HMMMMMM.
Lots of stuff sitting in the 1/8" of oil!
Again, IF YOU REALLY WANT TO KNOW, Pull#4 and either #1 or #2 and visually inspect the cam.
If you don't find anything amiss, Great!! You will now feel safe flying behind that engine.
If the cam shows wear and / or the pistons have a little sparkle on the skirts, IT IS TIME TO TAKE THINGS APART.
The parts requiring replacement from pulling the Clys. is a small price to pay for the knowledge gained.
It seems like when changing the oil, it might be smart to rig up a strong magnet on a flexible shaft and swipe around the bottom of the oil sump.
 
I don't know how to do that properly, but I pulled the rocker covers from #1, #2, and #3 cylinders and used my dial indicator to check the intake valve lift. I'm not sure I learned anything because the #1 tappet was bleeding down and I couldn't get a constant reading. Curiously, the other two gave me steady readings. Could a leaking ball check be the problem? The lifts were as follows: #1 - 0.365" to 0.385" (variable): #2 - .410"; #3 - 0.430" (sorry for the crappy cell phone photos)

Yes, an improperly sealing lifter (plunger assy in Lyco terms) will reduce your lift. As you saw on #2 and #3, they should not leak down much with just valve spring pressure. When I want to install a rocker, I need serious leverage and force, well beyond valve spring pressure to get it to leak down. .040" - .070" is a decent amount of lift to lose (20% reduction in open valve area). Not sure it would be enough to manifest in the symptoms you see, but it is getting there. I would bet that once the oil is thinner at operating temp as well as hot metal and the engine spinning 2700 RPM that the lifters are compressing more than you are seeing here.

The lifter will only bleed down so far, so you will always have some lift, even when they are shot. I am guessing your#1 is fully bleeding down while running and reducing the lift by 30% or so.

EDIT: The plunger will only compress to whatever you set your cold lash at. That can be as much as .08" - .100" after wear. This is about 25% of your valve lift (25% reduction in area for air fuel to flow into cylinder) and is likely to produce the reduction in power that you are seeing in #1.

I suggest you buy a new plunger assy (only $50) for #1 and see if your problem goes away. I suspect it will. You only need to pull the rocker, pushrod and shroud tube. You can pull the plunger out with a dental pick. Don't use a magnet.

You can also disassemble and test the plunger assy before buying new. Sometimes debris can block the ball. However, it is more likely that the metal has worn. That said, the sudden onset of the issue ups the odds that it is debris blocking the ball. The two parts have a VERY tight tolerance to hold the oil in them. Call me if you want instructions for disassembly and testing of the plunger.

If the new plunger puts the lift back in line with the others, you can conclude that your cam is fine and jug removal should be unnecessary.

Larry
 
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Here's a pertinent comment from the EAA forum regarding suspected camshaft problems:
It seems like when changing the oil, it might be smart to rig up a strong magnet on a flexible shaft and swipe around the bottom of the oil sump.

This gentleman's experience is consistent with my thinking on the lycomings. While metal in the oil filter is conclusive evidence of a problem. Lack of metal in the filter is NOT conclusive evidence that a problem doesn't exist. I observed the same design issues in the sump when I rebuilt my 320.

Same philosophy should be applied to oil testing. Many of the particles in significant wear events are too large to be picked up by the spectrographic equipment used and will provide a false sense of security. WHen my engine was eating up the piston pin caps, I found large amounts of debris in the filter, yet the oil analysis was showing excellent results. Needless to say, I don't waste money on oil analysis anymore.

Larry
 
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It seems like when changing the oil, it might be smart to rig up a strong magnet on a flexible shaft and swipe around the bottom of the oil sump.

A magnet in the pan is a better idea. Aerosplat sell a nice unit that uses one of your drain holes. You would pull it at each oil change and look for debris.

Larry
 
Larry just described the process to change out a plunger. While the push rod & tube are removed, you will have access to the top of the tappet body. Then you can measure the true lift of the cam lobe.

My son Peter installed a Christen Oil System on his RV-4, so He had to remove the sump to work on it. This was a good running O-320 about 1/3 TBO & about 10 years since.
The inside was full of muck. The bottom of the sump casting is kind of rough, like it was designed to catch and hold the junk that falls into it.
We were left with the feeling that removing the sump a couple of times in the life of an engine (between overhaul) might be a good idea, just to clean it out and see what's in there.
Fortunately it's not too hard.
 
Thanks

Scott and Larry--

Thank you both so much for your expertise on this problem. Another A&P friend advised me to crank the engine with the starter and see if that pumps up the plunger assembly in order to redo the test. I'll try that tomorrow.

I'm still searching for instructions on how to remove my push rod shroud tubes. According to my ancient parts manual, the tubes are 65006 and the seals are 60053 (new P/N LW18661?). The tubes seem to be captive between the cylinder head and the crankcase.

If I do figure out how to remove them, Wilco on the NO MAGNETS to remove the plunger assembly.
 
Scott and Larry--

Thank you both so much for your expertise on this problem. Another A&P friend advised me to crank the engine with the starter and see if that pumps up the plunger assembly in order to redo the test. I'll try that tomorrow.

I'm still searching for instructions on how to remove my push rod shroud tubes. According to my ancient parts manual, the tubes are 65006 and the seals are 60053 (new P/N LW18661?). The tubes seem to be captive between the cylinder head and the crankcase.

If I do figure out how to remove them, Wilco on the NO MAGNETS to remove the plunger assembly.

No need to crank the engine to pump up the lifter. You have identified a bad part (the plunger) and it needs to be replaced or cleaned and tested. Once it is replaced you will be able to determine if the lobe is still providing the proper lift. You have already confirmed that the plunger is not holding, like the good ones, and it needs to go.

You can follow shipchief's advice to measure the lift via the lifter body. However, be advised that the lift will not match what you found in your other tests. What you measure on the lifter body is the actual lobe lift. What you measured on the the valve spring cap is the valve lift. The valve lift is greater, as the rocker creates leverage (probably about 1.4:1) due to the offset center. If you follow this method, you don't have gravity pushing on the lifter body and the dial micrometers spring won't be strong enough. You'll need to apply some pressure to the lifter body on the down stroke.

The actual lobe lift could be compared against the spec, but I don't believe that Lycoming publishes it, though I am sure the aircraft machine shops know it for testing. I have a cam with pitting but no wear on the bench. I could mic it and let you know the lift number. Or you could compare it to another lobe. Just don't compare it to another cylinders valve lift.

Given what you have found so far, the odds are high that your cam is fine and you just have dirty plunger assy.

Larry
 
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I'm still searching for instructions on how to remove my push rod shroud tubes. According to my ancient parts manual, the tubes are 65006 and the seals are 60053 (new P/N LW18661?). The tubes seem to be captive between the cylinder head and the crankcase.

Pull the rocker cover. Partially pess out the rocker shaft to release the rocker arm. It is not a tight fit, but the pressure from the lifter pushing on the rocker makes it a bit snug. take out the pushrod. You will find a spring type piece of metal that captures 1/3 of of the edge of each pushrod tube and it held to the cylinder head via a nut. Remove that nut and the metal piece. The tube can now be pulled out. It is a bit snug due to the oring and green rubber gasket.

You will then find a cap in the top of the lifter body that the pushrod mates with. Pull that out. You will now see the plunger body. It is loose and you just need something to grab onto it with. You can easily get behind the plunger top as it does not extend to the edge and the shaft below it is thin.

PM and I give you my number. I'll walk you through tear down and testing of the plunger before you order a new one.

Good luck,

Larry
 
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PM sent

PM sent. A couple of other possibilities I have thought of. While researching part numbers, I found that the plunger assemblies come in two versions: fast leakdown (72876) and slow leakdown (76290). I have no idea which ones I have and why one would be used over the other. I can only hope the part number is etched on the assembly since they all need to be the same. That got me to thinking about "valve float". I cruise at high RPM - usually around 2,750 RPM (my motor is rated at 2,800). If I had a limp plunger assembly or weak valve spring, could that cause the low EGT problem? It would explain why I see nothing abnormal at 1800 RPM. I really never wanted to learn all this stuff :confused:
 
O-290

I believe the pushrod tubes are captured by the cylinders on the 290 similar to the Continentals. If this is the case the tubes can't be removed without pulling each respective cylinder.
You may still be able to fish the the plunger assembly and socket out through the pushrod tube at the head. This most likely would require a MAGNET but if your DISPOSING the plunger and socket anyway should be okay.
I have a supply of used Lycoming parts and would be happy to give you another plunger and socket if you pick up the shipping.
 
PM sent. A couple of other possibilities I have thought of. While researching part numbers, I found that the plunger assemblies come in two versions: fast leakdown (72876) and slow leakdown (76290). I have no idea which ones I have and why one would be used over the other. I can only hope the part number is etched on the assembly since they all need to be the same. That got me to thinking about "valve float". I cruise at high RPM - usually around 2,750 RPM (my motor is rated at 2,800). If I had a limp plunger assembly or weak valve spring, could that cause the low EGT problem? It would explain why I see nothing abnormal at 1800 RPM. I really never wanted to learn all this stuff :confused:

Valve float only occurs due to weak springs with excessive RPM. It is rare to see it appear out of nowhere unless the valve spring cracked. Also it will not restricte air flow, but enhance it. Though it typically reduces compression
 
I believe the pushrod tubes are captured by the cylinders on the 290 similar to the Continentals.
That seems to be the case. Look at this...the shroud protrudes right into the cylinder head.

CvmDDc.jpg


That's very kind of you to offer to send me a used plunger. I'll let you know in a few days. I have a tape head de-magnetizer and it seems like that would work to de-magnetize the old one if I pulled it out with a magnet.

What I did today was crank the engine for 10 seconds with the top plugs out. That pumped up the plunger on #1, but the hardness only lasted about 20 seconds and then it got squishy again - .040" squishy. The #3 intake stayed hard for several minutes and eventually got to .020" squishy. I also re-measured the #1 valve loft and it was 0.365" - still somewhat less than the others.

I also checked the ignition wires with my Fluke and they all read 6 nS (167 Megohms) so I'm calling that good.
 
Dry Tappet Clearance

Turn the prop so the intake valve is open. Let it sit for several minutes for the oil to drain out of the lifter (the cam will be putting pressure on it). Carefully turn the prop, while pushing hard on the rocker arm (push rod end) to not let the tappet re-expand, until you are at TDC. There should now be a gap between the rocker arm and the end of the intake valve. Use a feeler gauge to measure it (don't release the pressure on the push rod end of the rocker!), compare to specifications. Repeat for exhaust valve. Repeat for other cylinders.
Somehow I missed your important suggestion earlier. I'll do that today before I put everything back together. My Direct Drive Overhaul Manual says the Dry Tappet Clearance between the rocker and valve should be .028-.080 (Ref. No. 681).
 
Carb airflow

One quick test to see if the carb heat probe might be part of the issue. While in cruise, move the throttle off the wide open stop and vary carb heat to see if that induces change is the EGTs.

I use carb heat and throttle position to "steer"airflow and mixture to balance CHTs and vary EGTs for LOP ops with my O-320.

It is cheap, easy and non-invasive. A good thing for for engine checks, IRS audits, and medical procedures......

Good luck!
 
Dry Tappet Clearance

Here's what I found today using BobTurner's procedure:

#1 Intake - .080"
#1 Exhaust - .030"

#2 Intake - .052"
#2 Exhaust - .072"

#3 Intake - .032"
#3 Exhaust - .052"

#4 Intake - .040"
#4 Exhaust - .072"

So the #1 intake is right at the upper limit. I put the rocker covers back on and torqued the screws.
 
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Two years ago I rolled my plane over to the shop at AVL to have them check for a suspected sticking intake valve on #1. That turned out not to be the case, but they pulled both intake and exhaust push rods. Since the intake clearance is now at the top end of the service limit and the exhaust is at the bottom end, I'm wondering if they swapped push rods when they put them back . (I know they didn't keep the valve spring keepers separate because I watched them toss them all in a cup.) I'm also wondering if I should buy a longer push rod for the #1 intake. The P/N on mine is 73413 which was superseded by 15F19957-13. Anyway, I'm putting everything back together this morning and "letting things develop" since I never found a smoking gun. Thanks for all the suggestions, everybody.
 
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I've missed a whole week of great flying weather so today I installed two new plugs in Cyl #1, capped off the primer line (in the cockpit), put the cowling back on and went flying. The engine seemed to run just fine with no vibration like before, but the #1 EGT was still a little bit low at cruise, depending upon how much rich of peak I was. I fiddled with the mixture and throttle position during this sequence and when it was lean enough that the engine started to run rough (at the beginning and end of the run), the EGTs were almost flat (within 50F). When I richened the mixture to 80 ROP (that dip in the middle), the spread increased to 150F. It's pretty clear that cylinders 1 &2 are running richer than 3 &4, but why? Is it that temperature probe after all? Is it possible that the accelerator pump outlet check valve is leaking and would that cause this problem? The discharge nozzle is aimed toward cyls 1 & 2. But at this point I have to ask myself, "Does this even matter?" For decades I flew C-172s with no EGT/CHT instrumentation and would never have known.

l0BVrE.jpg
 
moving on

To close out this thread, I got my oil analysis back today and it was completely normal. The Fe was even lower than usual. Maybe oil analysis gives a false sense of security as several of you have posted, but I'm going to keep doing it. I'm funny that way. I did find this, though, at Reliability Web. It may explain why oil analysis works sometimes but not others:
Most people rely on the elemental analysis test to determine when a machine is starting to wear so they can take corrective action. However, depending on wear mode, this test can lead to a false sense of security. The issue lies in the fundamental test methodology used to determine wear debris, known as inductively coupled plasma (ICP). Specifically, ICP instruments lack sensitivity to particles below three microns, so depending on wear mode, this test can be misleading. While elemental analysis can be an excellent test for revealing slow incipient wear or wear modes that create small particles (<3 um in size), such as corrosive wear, it can completely miss wear modes that generate larger particles greater than 5 um, such as adhesive wear in gearboxes or fatigue wear in rolling contacts. Instead, ICP should be complemented by large particle detection tests, such as particle counting, particle quantifier (PQ) or ferrous density.
I'll have to ask Lab One Aviation which process they use.

Since I capped and plugged the primer line to cyl #1, I'm not seeing excessively low EGTs in that cylinder. So I have concluded that must have been the problem and it must have been intermittent. Although my EGTs aren't almost equal like before, they're well within the "normal" range according to my JPI EDM-700 Pilot's Guide:
the normal EGT spread for a carburated engine is 120-150F and 70-90F for fuel injected
I'm well within that range now, so I'm going to quit obsessing. I've done every reasonable thing that I can think of doing so I'm just going to press on. It does bother me that the EGT spread used to be only 30F but, even after fixing the leaky primer, is now in the 50-100 range. Maybe I should be asking why it was so low before :rolleyes:

Thanks again to everybody for the helpful suggestions.
 
Glad to hear...

Hi Snopercod,

Glad to hear that it appears your cam is sound! :) Thanks for the interesting post. I appreciate the updates and feedback. Learning a lot.

I'm curious tho why you chose to ignore your findings on that more than normal leaky plunger?
Was it from unsure test results and the learning curve?

Anyway here's a quote from an article I believe that was discussing valve guide wear problems. But very much included useful information and a bit of history and design.

"Bleed down rate is nothing more than the speed at which oil can leak between the plunger and plunger cylinder under valve opening loads. If this speed is too fast, valve timing is harmed. In such a situation, the valves open too late, close too soon, and do not achieve the full amount of lift that the cam is intended to provide. The engine is thus unable to "breathe" efficiently, robbing it of power. Additionally, an excessively fast bleed down rate allows the lash, which is ideally held to zero (but never is in the real world) to increase beyond limits, causing components in the valve train to hammer into each other instead of operating smoothly. This wreaks havoc with the longevity of parts. On the other hand, if the bleed down rate is too slow, the valve is held open when it shouldn't be, causing compression (and therefore power) loss, as well as possible valve face erosion. Bleed down and bleed down rate are essential ingredients of all hydraulic lifters regardless of application or manufacturer."

The bleed down also influences how much oil is supplied downwind...

To read the full article go HERE.

Best regards,
 
I'm curious tho why you chose to ignore your findings on that more than normal leaky plunger?
I wasn't able to get to the plunger without pulling a jug, and I wasn't going to risk fishing it out with a long wire. You really have to wonder what Lycoming was thinking when they made those pushrod shroud tubes captive, but my engine was mabnufactured in 1946 so who knows? I figured the risk of pulling a jug was greater than flying as is. The Overhaul Manual states that if you pull a jug, you're supposed to replace (not re-use) the cylinder through-bolts. Since Lycoming doesn't support the O-290-D2 any more, those bolts are unavailable (AFAIK). The bottom line is that I've only got a few good flying years left and I don't want to spend them tearing down an engine. I'll keep a close eye on my engine monitor.

The only other thing I could do is call Don George, the guy who rebuilt the engine in 1991. Maybe I should do that.

That link you posted had lots of valuable information. Thanks.
 
... You really have to wonder what Lycoming was thinking when they made those pushrod shroud tubes captive.

...and having to split the case for a tappet? :mad: I understand you.

Hey, you keeping your crankcase oil temps 180degrees and above now days with the drop in ambient temps?:)

I was a bit upset when you described that A&P mixing up your parts.
I thought according to the manual all valve train parts should be identified and kept separated during teardown. Thinking that perhaps the wear patterns could cause some issues... That said I've also seen where owners are swapping their push rods around for the best lash...? So after all the work of getting the perfect gaps, maybe that's why they want you to keep em separated. ;)

Keep her flying!
 
...and having to split the case for a tappet?
Not split the case, just back off the cylinder(s) enough to pull the shoud tubes out. Maybe I used the wrong terminology (case through bolts), but some of those cylinder bolts are supposed to be replaced. My Overhaul Manual is at the hangar so I can't look it up.

Yeah, I cringed as well when the A&Ps tossed all the keepers into the same cup, but what could I do? I've wondered the same about swapping or replacing pushrods. If they're so sensitive to being worn in, then what happens when you put a new pushrod in between the old rocker arm and socket in the tappets? There's a lot I don't know here...
 
same assembly different part...

I was referring too the mushroomed part of the hydraulic tappet assembly.:)

Here's a nice pic...

kf1j6f.jpg


Rides right on the cam.




As far as removing the cylinder, the only thing I remember seeing about the studs, where that they needed to be re-torqued.

But you actually get to get a look at the cam with the cylinder pulled.



Hey here's a nice webinar that addresses a few things, including those oil analyses and indication of metal damage as previously discussed.

Watch here...


The presenter is a little heavy on Continentals and Cam Guard, but still a good watch.


Regards,
 
Hey here's a nice webinar that addresses a few things, including those oil analyses and indication of metal damage as previously discussed.
That was absolutely worth an hour-and-a-half to listen to. Busch answered every single one of my questions. I especially liked his comment at 57 minutes: "Cam and lifter spalling is not a safety of flight item". I'll just keep on flying, but I'll certainly be changing and inspecting the oil filter every 25 hours along with the oil. Hopefully I will wear out before the cam does. Thanks so much for the link!

P.S. Now I understand what you meant about splitting the case for the lifters, not the plunger assembly. Doh!
 
As far as removing the cylinder, the only thing I remember seeing about the studs, where that they needed to be re-torqued.


Ahhhhh, this is what it was...


"At any time a cylinder is replaced, it is necessary to re-torque the thru-studs on the cylinder on the opposite side of the engine."

Lycoming Manual

Page 5-7


Glad you got some piece of mind with the webinar.:) Did you run out and purchase some Cam-Guard?

...Just a safety WALLET issue! Lol....classic.
 
Did you run out and purchase some Cam-Guard?
I've used Cam-Guard since my first flight in 2014, but doing so is probably like closing the barn door after the cows escaped. I was a fool not to pickle the engine when I moved from FL to NC but I just couldn't admit to myself that it would be years before I started the engine again. Now I'm having to live with the uncertainty.
 
I haven't made any changes at all, but this data from my last flight is looking good. The EGT spread after leaning was less than 30 degrees and it's hard to beat that in a carbureted engine. It's obvious that full rich, WOT on climbout, the rear cylinders are getting too much fuel. That may well be due to those "aeration holes" I drilled in the carburetor nozzle...I dunno'. Maybe I could even the 120 deg. spread by leaning slightly on climbout, but do I really care? 120 degrees really isn't that bad. (I was at 6000' in cruise.)

6jnoPq.jpg
 
Perhaps a true purrfectionist would finish drilling out the other 5 holes...

800px-IMG_20141111_123854.jpg


And/or pull back that huge carb temp sensor to flush with the inside casting. One can't always tell...:rolleyes:


Best regards,
 
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