Lycoming cam wear power loss

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Vigilant1

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I just had to overhaul my o-320. It had pretty severe inlet cam wear which impacts 2 of the 4 cylinders. I measured that it lost 0.15 inches. It felt very low on takeoff performance, and highish fuel burn (9.5 vs 8).

What would you estimate my power loss would have been?
I can understand the power loss if an intake valve isn't being sufficiently opened, but what's the reason for the higher fuel burn? If a valve isn't opening right, then presumably less air and fuel gets drawn into that cylinder, but the fuel efficiency wouldn't seem to be diminished. Is it just that the resultant amount of fuel/air charge in that jug is so low that it produces even less power than would be expected from the fuel used? (Behaving like a cylinder with a very low compression ratio)
 

TFF

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I figure on the shared lobes, one side is intake, one side is exhaust. Extra mixture is diverted into good cylinders so they are richer. The bad cylinder with low exhaust lift can’t get rid of fuel while the other is weaker and throttled back.
The shared lobe does not get a break like the lobes that only wrk one valve. The single valve gets time to cool with oil and no pressure. The shared lobe comes off one valve and right on to the opposite side opening that valve. There is an STC cam mod where oiling holes are added to the lobe to hit the lifer with extra oil before it actuates.
Lycoming cams and lifters rust where they contact, when the engine stops and sits for a long time. Oil runs off over time, contaminated oil with acids from combustion with the water vapor. Every lobe will; the lobe that starts to rust on the tip of the lobe is the winner. Rust pit is a great cutting tool for the lifter. Once it starts hitting the lifter with the valve spring pressure, it will wear away. The lifter rusts the same and crunch crunch over time. Wider lobe design helps, flying the engine weekly helps, oil changes helps. Roller lifters helps with the shared lobe too.
 

speedracer

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Lycoming long had cam problems. I think the cams themselves might have been carburized and case-hardened, and once corrosion sets in on the lifter and cam, the metal disappears quickly. That skinny little line of contact between the cam and lifter face is under terrific pressure, and is probably the most highly loaded surface in the entire engine.
Both times my cam lobes went flat I had to rebuild the engine due to all that metal going through it even with a good oil filter. My present Long EZ has an O360 which I purchased with 129 hours TTSN. I rebuilt it with lots of performance upgrades (porting, 10-1 pistons, balancing, hot rod camshaft, and maybe most importantly, Ney nozzles. They're (Lycoming blessed) inserts into an oil galley in the case that squirt oil on the cam lobes starting at the first blade.
 

proppastie

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when putting a dial indicator on the rocker and measurement of the relative lift what might be a number to look for as regards time to tear down the engine.....as regards a constant speed prop static rpm is not a specification?
 

TFF

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A slight guess but probably in the area of .4 difference between valve all the way closed and all the way open directly over the pushrod. There is one issue, hydraulic lifters can have some movement internally when the engine is not running. You don’t know if it has leaked down any to be precise. But should work for general health. To do it precise you pull the pushrod tubes and pull the hydraulic center out of the lifter and with a homemade pushrod inside the lifter housing, you can be very accurate. Lycomings have hydraulic lifters unless it’s a O-235 or 290D. The 290D2 went hydraulic and it’s been the standard since.
 

proppastie

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.4 difference
that is over 3/8 inch ( .375) so you must be talking travel.....I was thinking the travel of each valve and the difference between all of them.....perhaps if it is different greater than the service limit on the cam lobe? I can not image the engine would run if one valve was about 3/8 inch travel less than the rest.
 

TFF

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A couple of cylinders would be deader. Throttled back essentially. Top fuel dragster cam about .7”. The problem is oil can squeeze out of the lifter when not running and give an error valve to valve. You can probably get a consensus of wear, but measuring it at just the lifter body on the cam, I would think under .005 difference would be right. And that would be a limit. They are made to probably.0005” out of the machine At the valve you technically would take the rocker ratio in account. Once you loose the surface, it’s just a cutting tool on a lathe. 50-100 hours and it’s flat.
 

karmarepair

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Volvos, otherwise known for the durability of a Wilton vise (our $100 122 wagon had a burnt valve and a broken ring, that cylinder honed out and took standard pistons and rings), had a run of bad cams. Our 164 had a weird miss we couldn't figure out, took it to the dealer, they go "oh yeah, give us two hours and $800". ONE lobe was ROUND.
 

Dan Thomas

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Volvos, otherwise known for the durability of a Wilton vise (our $100 122 wagon had a burnt valve and a broken ring, that cylinder honed out and took standard pistons and rings), had a run of bad cams. Our 164 had a weird miss we couldn't figure out, took it to the dealer, they go "oh yeah, give us two hours and $800". ONE lobe was ROUND.
GM had a whole bunch of cam wear problems in their small-block V-8s many years ago. Not uncommon at all. Looking at the loads on a cam, it's a wonder it lasts as long as it does.
 

TFF

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In the car world, cams are like avionics to airplanes. Everyone is chasing the newest grind hoping to get something better. You can watch on YouTube people gutting the engine to change one for the next race. Different attitude with the same part.
 

PiperCruisin

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.15 inches is huge, and would be an alarming account of metal flakes in the oil chewing up other parts of the engine... hard to imagine it not being caught sooner. That sounds like years of undetected wear. Are you sure it wasn't .015?
Yes. 0.15 inches gone. You read that right. Didn't see anything alarming in the filter. This was a new to me airplane, but never felt right.
 

PiperCruisin

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Here's a pic. of one of two cams I've personally flattened out. They both soldier on now as towel racks in my shop. When the first one was happening I noticed a distinct loss of power but didn't know why. The engine was running smoothly so I kept on flying trying to figure out what the problem was. The longer I flew the greater the power loss, a noticeable difference in only 30 minutes. The second time it happened I caught it much sooner. And yes, both times the two lobes were the shared ones which makes perfect sense. Also, both cams are O290 "narrow lobe" cams.
Mine looks almost exactly like that... but not red. Maybe I should gold plate mine.
 

aeromomentum

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I assume everyone here has read the Lycoming operators manual and knows that all ground operations are at 1000 to 1200 rpm.

Yes, you can make your Lycoming idle much lower. Don't. Unless you like losing power and replacing cams.
 

PiperCruisin

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I assume everyone here has read the Lycoming operators manual and knows that all ground operations are at 1000 to 1200 rpm.

Yes, you can make your Lycoming idle much lower. Don't. Unless you like losing power and replacing cams.
Don't assume... I tend to run in that range to keep the battery charged. Had no idea I would be mucking up my engine's innards.
 

Dan Thomas

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I assume everyone here has read the Lycoming operators manual and knows that all ground operations are at 1000 to 1200 rpm.

Yes, you can make your Lycoming idle much lower. Don't. Unless you like losing power and replacing cams.
Baloney. I looked after seven Lycomings in the flight school, idling them at 650-700 all the time, and every engine went to TBO with no cam problems. Seven airplanes, with multiple engine replacements while I was there, maybe a total of 35,000 hours or more, and no cam failures despite low idle. At 650 RPM there is still lots of centrifugal force to throw oil off the crank at the cams. The Operator's Manuals tell you to warm up a cold engine at 1000-1200 RPM. They don't tell you to idle it there all the time. If 1000 RPM was necessary, the maintenance manuals would tell the mechanic to set the idle at 1000. They don't.

Always operating at 1000 on the ground while taxiing will burn out your brakes. And the discs. That drag on the tires wears them out faster, too.

It's corrosion that does most of the cam/lifter damage, and the guys that ground-run their engines "to circulate the oil" and then put it away are asking for lots of corrosion. Fly it or leave it alone.
 
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dog

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I have heard that the best and simplest way of
keeping an engine good is to pull the prop through one cylinder every time you go by.
Mags off ,as there are some motors that will
demonstrate there willingness to start on the
slightest pretext.
And oil that smells bad,is bad,and probably corosive.And something to consider along
those lines is that the electrolite used in many
batteries,including phones and laptops,uses is
in fact a flamible liquid hydrocarbon.
Add the disimilar metal in a motor and you
do have a battery,a realy lousy one in the worst possible place.
 

Dana

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Actually, Lycoming recommends 1000-1200 "when possible" to prevent lead fouling.

I have heard that the best and simplest way ofk eeping an engine good is to pull the prop through one cylinder every time you go by.
Nope, it's best to not move the prop. Moving it without actually running can scrape off any oil film that's on the surfaces.
 
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