Dead Cylinder AFTER Repair

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Russnrenea
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Dead Cylinder AFTER Repair

Post by Russnrenea »

So had a 0 compression cylinder at annual. Removed sent for repair, had a crack so the shop built me a serviceable cylinder, ground valves, new guides, honed barrell, new rings, cleaned piston.

Reinstalled cylinder, relieved hydraulic tappets, changes one pushrod to get proper valve clearance per Lycoming manual. Ran aircraft and cylinder is dead, cool to touch after running, others hot. Normal Mag drop, but rough running since one cylinder is out.

Checked spark by removing plugs on all cylinders and holding lead against baffle and spinning with starter, got spark on top and bottom plugs. Removed intake and checked for obstructions none, found. Compression 78/80, rotated prop through full range to check for early/late valve opening, all normal.

Reassembled, flew it for 10 minutes at high power hoping to "bring it to life" no luck. Plugs appear wet (looks like fuel not oil) after the flight.

Mechanics and I are scratching our heads? Thinking about sending the mags out for testing, but it was running fine before the cylinder change, unless with 0 compression I couldn't tell that the cylinder was dead. Only have the one CHT.

Any Thoughts?

Russ

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Russnrenea
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Post by Russnrenea »

Carburetor Equipped 4 Cylinder Lyc.

Russ

Mr. Ed

dead jug

Post by Mr. Ed »

My guess is that the intake valve isn't opening. I'm sure you pulled the prop through and watched the valve movement but do it again and see if the valve actually moves. If you relieved the hydraulic tappet and the push rod is the correct length and the valve is opening fully and you have spark and you've checked that the intake manifold is connected and seated properly and the plugs are good and nothing is out of whack, then I'm stumped.

Just pulled, repaired and re-installed #1 jug on my O360. So far so good. So, you flew this thing around on 3 jugs? :shock: I bet that took a little runway.

Good luck!

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crbnunit
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Post by crbnunit »

Plugs are wet so I assume they are wet with fuel. You have compression so the only thing left is spark or timing. I doubt the timing is off too far or it wouldn't run at all, let alone well. I'd suspect an ignition problem. Sometimes the ignintion will fire just fine without a load but add compression and it craps out. Have you tried new plugs in that jug? Check the wires and mag contacts. Pretty unlikely both mags would fail at the same time on one cylinder though. Flat cam lobe? Are the valves actually opening and closing? Just throwing ideas now.
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Russnrenea
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Post by Russnrenea »

Keep the idea's coming. We did pull the prop through and watch the valve, then went a step further and put pressure on the cylinder moved the prop until the intake valve opened and then back the other way until the exhaust valve opened, did this with only about 40 psi in the jug.

Checked timing of Mag to engine, it's right on and other cylinders running great. The idea of the ignition under a load not working has come up, but for both to be out, none of us can believe that, BUT at this point anything is possible.

Going to borrow a friends mags and harness off his airplane, same motor, put new plugs on it and test it. That will eliminate ignition system.

Have to work this weekend, so can't get to it until next week, I hate leaving an airplane torn apart!!

Russell

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maules.com
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Post by maules.com »

How about spark plug breakdown when under pressure.
Perform a resistance check on the two plugs in that cylinder.
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riverbuggy
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Post by riverbuggy »

Sounds like an induction system air leak to me. The cyl. could also be pumping oil, and drowning out the plugs. Were the new rings installed rightside up? Is the repaired cyl. chrome or steel?
Ray
1970 M4-220C N2056U

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Russnrenea
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Post by Russnrenea »

Tried two new plugs early in the attempt to solve this.

As for the induction leak that is a possibility, any great ideas on the best way to pressurize the intake system to check it? I have the old air filter so I was thinking of fitting it to the output of the shop vac and blowing air through the intake and doing a bubble check.

Russell

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Russnrenea
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Post by Russnrenea »

The rings where installed by the cylinder shop onto the pistons, the barrels are chrome. Not sure they were checked for proper installation prior to being fitted into the cylider. I know the rings were "clocked" before install. Can rings be put in backwards?

Russell

benflyn
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Post by benflyn »

Suck, sqeeuze, bang, blow

Suck,
Intake valve opening and closing at proper time and lift? Spray starting fluid around intake connections with engine running and note any change in rpm.

Squeeze,
Static compression ok, maybe a auto compression (dymanic) check.

Bang,
Ignition, if we have proper air/fuel mixture and spark we should get a bang. A bad mag would affect all cylinders, ignition leads and spark plugs would affect that cylinder. Is there a primer on this cylinder, if so with engine running lean mixture until rough and administer a shot of primer and note rpm change, does it start banging on the missing cylinder.

Blow,
Exhaust valve opening and closing at proper time and lift?
Exhaust pipe restriction?

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aero101
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Post by aero101 »

Chrome Cylinder? Thought they quit building those years ago? No way both mags would quit one cylinder same time! Harnesses on that cylinder rubbing and worn somewhere? Wires crossed somewhere in firing order?
Jim
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riverbuggy
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Post by riverbuggy »

The top ring is a champhered ring. It needs to be installed champhered side up. Although this is really not very likely; it can be installed upside down. A compression check would still test good, but in operation it would not seal well, and pump oil. Sometimes chrome cyls. will just pump oil with no obvious cause. Clean the plugs real good, and try it again. Beyond that with everything else checking out good; we are back at the induction leak scenario.
Ray
1970 M4-220C N2056U

Mountain Doctor
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Post by Mountain Doctor »

I hope you have this fixed soon.

It's not compression, you're 78/80.

I still can be spark. You can have spark at atmospheric pressure but not under compression. Swap the plugs with another pair and see what happens.

Oil vs. gas on the plugs should be easy to tell by feel and by smell.

Can't be timing, all the jugs are the same.

BTW, nothing personal, but NO WAY would I FLY a 3 cylinder airplane!!!!
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Russnrenea
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Post by Russnrenea »

ALL FIXED!!!

BTW this is not my airplane, don't want anyone thinking my Maule is less than perfect! ;-)

Was having a hard time sleeping and was thinking about my buddies problem. I asked myself what has change, what simple problem could cause this? The discussion of intake leak really made sense, then it hit me IS THE PRIMER PLUG INSTALLED? Well the cylider shop didn't install it and it got missed during the install.

All better now. It's funny how it can be staring you right in the face and three of us missed it.

Thanks for all the input guys!!

Russell

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Post by Mountain Doctor »

Glad you fixed it and it was cheap!

Still, I don't quite get it. How could the jug make compression with the primer plug out? Doesn't it srew into the head past the intake valve?

Also wouldn't you have heard it hiss when turning the prop on while on the compression tester?

Glad it's fixed but I am missing some tidbit of mechanical knowledge.
I am an AME in Richland, Washington. Please call for an appointment!

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