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Recurring O-360 exhaust valve woes


DXB

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My plane's Lycoming O-360-A1D with 1st run Millenium cylinders on it was at 600 hrs SMOH when I bought it 3 years ago. At prebuy, #1 had a burned exhaust valve and was IRAN'd by Gann Aviation - new guide, exhaust valve, rings, rehoned barrel.  Last year I had to do the same for #2 with my local shop (burned exhaust valve)  as well as #3 (continuously oil-fouled bottom plug combined with high oil consumption, but excess slop in the exhaust guide was also found).  I've flown this bird now for >300 hrs. I was feeling pretty worry free about the engine at this point when I took my plane into annual.  

Then shop calls and says my #1 is at 40/80 and has a big exhaust leak that didn't improve after staking the valve and ground running extensively. I was incredulous that  #1 needed to get pulled again, and so I came over to take a look.  I had just borescoped it 30hrs ago personally when I cleaned and rotated my plugs - the valves looked fine. But sure enough there is a faint new crescent at the edge of the #1 exhaust, and it flunks the wobble test :angry:. The valve face is much easier to see after pulling the cylinder (below).

I have a good engine monitor and watch my CHTs religiously.  In cruise, I have to run a bit richer in the summer to keep my hottest #2 in the 380s, but I think my doghouse baffling is as good as it's gonna get.  #1 actually runs the coolest in cruise - Is it normal to see a cylinder go bad again this quickly after being IRAN'd by a reputable shop? Also is there any danger with reworking this cylinder a second time?  I wonder if my running richer to keep #2 in check makes my #1 (perhaps the richest) particularly susceptible to deposits.

image.png.89e77f23b930a35a3e19b9cab3b4db24.png

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I pulled a cylinder, had it IRANd, pulled it again 40 hours later. The price delta isn't horrible between IRAN and new so I just buy new these days given how much work is involved to pull a cylinder on the C.

Make sure pushrods are properly sized and your rocker arms are good as well. I'm no A&P/IA/etc, but I think there's probably a 'right' size that makes this work best. Everything that moves wears something.

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Make sure the rocker hits the valve stem all the way across the stem .  Prussian blue can be used to check it. Otherwise it can side load the guide and wear it out very soon. 

IMG_1297.PNG

Edited by jetdriven
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8 minutes ago, jetdriven said:

Make sure the rocker hits the valve stem all the way across the stem .  Prussian blue can be used to check it. Otherwise it can side load the guide and wear it out very soon. 

 

Excellent, thank you Byron! I will ask them to check that for sure.

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Just finished my annual a couple of weeks ago. My 67C has 1300 hours on a factory remanufactured engine but showed poor compression on #3 and an obvious exhaust leak. Borescope showed a badly burned valve. My IA indicated I had an induction leak in #3 which probably resulted in running lean. Interestingly enough I did not notice any signs of an induction leak. No popping sounds at idle or anything obvious. Cylinder replaced.

 

 

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16 hours ago, DXB said:

My plane's Lycoming O-360-A1D with 1st run Millenium cylinders on it was at 600 hrs SMOH when I bought it 3 years ago. At prebuy, #1 had a burned exhaust valve and was IRAN'd by Gann Aviation - new guide, exhaust valve, rings, rehoned barrel.  Last year I had to do the same for #2 with my local shop (burned exhaust valve)  as well as #3 (continuously oil-fouled bottom plug combined with high oil consumption, but excess slop in the exhaust guide was also found).  I've flown this bird now for >300 hrs. I was feeling pretty worry free about the engine at this point when I took my plane into annual.  

Then shop calls and says my #1 is at 40/80 and has a big exhaust leak that didn't improve after staking the valve and ground running extensively. I was incredulous that  #1 needed to get pulled again, and so I came over to take a look.  I had just borescoped it 30hrs ago personally when I cleaned and rotated my plugs - the valves looked fine. But sure enough there is a faint new crescent at the edge of the #1 exhaust, and it flunks the wobble test :angry:. The valve face is much easier to see after pulling the cylinder (below).

I have a good engine monitor and watch my CHTs religiously.  In cruise, I have to run a bit richer in the summer to keep my hottest #2 in the 380s, but I think my doghouse baffling is as good as it's gonna get.  #1 actually runs the coolest in cruise - Is it normal to see a cylinder go bad again this quickly after being IRAN'd by a reputable shop? Also is there any danger with reworking this cylinder a second time?  I wonder if my running richer to keep #2 in check makes my #1 (perhaps the richest) particularly susceptible to deposits.

image.png.89e77f23b930a35a3e19b9cab3b4db24.png

What are your typical power settings in cruise?  And are you operating ROP?

did you operate any certain way to break in the new cylinders?

Just curious. 

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25 minutes ago, Browncbr1 said:

What are your typical power settings in cruise?  And are you operating ROP?

did you operate any certain way to break in the new cylinders?

Just curious. 

Up high (6500 or higher) I run 2500, WOT typically.  Down low (3500 or less) I run 23-squared for traveling, 20-squared occasionally for sightseeing. At intermediate altitudes, I run 2400 and set MAP to give power of around 65%.   

I've broken in 3 IRAN'd cylinders now using 24-squared at 4500 or below for 5-10 hours, with only modest leaning in order to keep the new cylinder cool.   These steel cylinders seem to break in very easily - within just 1-2 hours of doing this, they start operating cooler and oil consumption drops off nicely. 

ROP/LOP not so relevant since it's carbed- below 70% power, but I lean as much as I can in normal operation.  In the winter it ends up being basically the equivalent of "lean to roughness, then push knob back in a bit" though I use the monitor - doing this typically puts the leanest cylinder around stiochiometric.   In the summer I can't go that far and run about 1.0 richer to keep hottest CHT in the 380s.  The problem cylinder here (#1) has always been the coolest though and I suspect always runs well ROP.

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Cylinder break-in is usually a full power, full rich affair... full rpm to go with that...

Down low for good MP and air cooling...

This makes the piston and rings go to the extremes of mechanical Travel...

Check with your mechanic for his details.

PP thoughts only. Not a mechanic...

Best regards,

-a-

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On 10/26/2017 at 3:50 PM, carusoam said:

Cylinder break-in is usually a full power, full rich affair... full rpm to go with that...

Down low for good MP and air cooling...

This makes the piston and rings go to the extremes of mechanical Travel...

Check with your mechanic for his details.

PP thoughts only. Not a mechanic...

Best regards,

-a-

Or as I was told - full out - fly it like ya stole it.  full power, full rich,  2600 rpm nothing over 2500 agl - never had so much fun.  I go 20 hours and add half a quart. 

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So...this Millenium cylinder with the exhaust valve leak and bad guide also shows a small crack by a spark plug hole that only became evident after bead blasting it.  Pretty crappy durability - 900 hrs :angry:. Will post pix when I get it back.  Going with new over IRAN makes sense to me going forward. Also I wonder if any of the other 3 have such hidden issues not evident on visual exam and borescope :blink:.

 

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