Sticky valve_Lycoming IO-360-A3B6D

[Jsavage3]

For the last several weeks and on the first-start-of-the-day engine starts only, I've been seeing a smooth running engine for 2-3 minutes, then it suddenly starts running rough.  It does this for about 30 seconds or so and then goes away.  During the event, the MP starts to climb (I've seen it go as high as 20") while the RPM decreases or stays fairly constant at 1000 or so.  Mixture rich or lean for taxi seems to have no affect.  Fuel boost pump on doesn't change anything either.  After a minute or so, it smooths out, the MP drops back down to 12" or so at 1000 rpm and all is well.  The following mag check is normal.  This situation doesn't show up on subsequent starts that day...just the first start of day and even then, not every time.  It feels like a fouled plug, but I cannot get it too clear up with the usual techniques of leaning her out.

 

I talked to my engine guy and he thought, based on my description, that I had a valve sticking.  So here I am 92 SMOH and I may have an engine issue.  Lovely!

 

My engine guy told me to look at the engine monitor next time and try to figure out which cylinder is running colder than the rest...he says that is the one with the sticky valve/tight valve guide.  He said once we determine which cylinder is having the issue, then he will take that cylinder off, mic the valve and guide and have the valve guide reamed a little, if needed.
 

My initial questions were (and answers in parenthesis):

1) Am I safe to keep operating it like this?  (NO...look into sticky-vs-stuck valve...if she sticks, you're a glider)

2) Will a tight valve guide "wear itself in" over time?  (NO, get it fixed.)

3) Is this common?  (It's not unheard of...Lyc felt it worthy of SB & SI...see below)

4) Marvel Mystery Oil?  (Might temporarily help the symptom, but won't fix the problem.  I elected not to try this option...)

 

It was at this point that I stumbled across Lycoming's Mandatory Service Bulletin 388C and Service Instruction 1425A...which finds/fixes a sticky valve and can fix it without removing the cylinder.  Lyc recommends we comply with this SB every 400 hours or sooner if one suspects a sticky valve.   Hmmmmm!  So, does Lyc consider this a common issue...IMHO, apparently so.

 

Considering possibilities of any future attempts to sell our Mooney and putting ourselves in the shoes of a potential buyer, we ended up taking her to Signature Engines in Cincinnati (my engine guy is great, but he's not an engine shop and I just didn't want to start by pulling off a jug).  I had the engine shop c/w Lyc SB 388C.  No issues with cylinders 1, 3 or 4.  However, the exhaust valve on cyl #2 was tight.  They reamed the guide IAW Lycoming's directions and she's been given a clean bill of health! 

 

I am relieved beyond words!!

 

A stuck valve is going to ruin your day (i.e. start looking for an emergency landing site) and hopefully this story will help a fellow Mooney Driver avoid having the displeasure of their day being ruined over a sticky/stuck valve...

 

Blue skies...

 

 

P.S. Here is an article found on AvWeb that seemed quite informative:

 

 

February 5, 1996

Dealing with Stuck Valves

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If your engine seems rough when first started, it might be giving you an early warning of a stuck valve. Failure to heed this warning and correct the situation promptly could cost you an engine teardown, or even result in a catastrophic engine failure and a forced landing. Here's the lowdown on why valves stick and what to do about it.

February 5, 1996

 

by John Schwaner
Copyright © 1995 by Sacramento Sky Ranch Inc. All rights reserved.

 

     

 

 

Each cylinder of your piston aircraft engine has two valves—intake and exhaust—that open and close by sliding in and out through a close-tolerance valve guide. A stuck valve is one that no longer slides readily in its guide. A stuck valve may refuse to open, or once open it may refuse to close. Either situation is quite serious.

Stuck valves are usually caused by a build-up of deposits and/or corrosion on the valve stem. Because the fit of the stem in the guide is so snug, it doesn't take much build-up on the valve stem to interfere with free movement of the valve within the guide.

"Morning sickness"

 

The clearance between the valve stem and its valve guide are at a minimum when the engine is cold. Consequently, the first sign of a stuck valve usually occurs when the engine is first started, and is often identified by an intermittent hesitation, or miss, in engine speed. We call this "morning sickness".

Morning sickness is a warning that should be heeded immediately. Sticky valves never get better by themselves...they always get worse, usually fairly quickly. Flying an airplane whose engine exhibits morning sickness increases the risk of serious engine damage and possibly in-flight engine failure. Hence, the aircraft should be downed for maintenance at the first hint of valve sticking.

 

What makes valves stick?

Valve sticking is influenced both by the design of the engine and the environment in which it is operated. Lycomings have more valve sticking problem than Continentals. Hot-running engines stick valves more often than cool-running ones. Valves are more likely to stick in hot summer weather than in cold winter months. The use of heavily-leaded fuels and inadequate leaning can lead to valve sticking, as can infrequent oil changes.

Heat is the primary cause of valve sticking. High temperatures in the exhaust valve guide oxidizes oil and forms carbon deposits on the valve guide, and these deposits can cause the valve to stick. The most frequent reason for elevated valve temperatures is valve leakage.

All of the combustion gas must pass around the valve face as it goes out the exhaust port. The large heat-absorbing surface of the exhaust valve face must conduct heat away from its surface. A valve that is not contacting its seat properly (i.e., is leaking) cannot conduct as much heat into the cylinder head as a valve with good seating.

 

Sticky Lycomings

Lycoming valve stems operate at higher temperatures than Continental valves stems. Continental engines use solid exhaust valves whereas Lycoming engines use sodium-cooled exhaust valves, which have hollow stems filled with metallic elemental sodium. The sodium in the Lycoming valve melts at 97.5°C and conducts heat from the valve head into the valve stem, where it is conducted through the valve guide into the cylinder head. The Lycoming valve stem normally operates 100°F hotter than the Continental valve stem. The higher valve stem temperatures in Lycomings make them more susceptible to valve sticking.

Most of the heat conducted from the head of the Lycoming exhaust valve goes out though the valve stem into the cylinder head fins. In addition, the Lycoming guide boss allows 5% of the guide to extend past the end of the boss and protrude into the exhaust port. The protruding guide absorbs heat from the flow of exhaust gas. Because of the high temperatures and combustion deposits on the exhaust valve stem, this area of the guide "bell mouths" or gets bigger. This increases the clearance between the guide and the stem and allows combustion products and heat to travel up the valve stem. These combustion products create lead deposits and acids which increase the corrosive environment.

Lycoming valves also stick because of corrosion buildup on the valve stem. Corrosion increases the diameter of the valve , thereby reducing the valve stem-to-guide clearance. The high stem temperatures, combined with a design which allows more combustion products into the guide bore, create a corrosive environment which is seldom seen on Continental engines.

Lycoming TIO-541 engines installed in the Beechcraft Duke use an oil-cooled exhaust guide. Cooling oil circulates in a groove between the exhaust guide and the guide boss. If this groove cokes up with oxidized oil and becomes blocked, the exhaust guide and valve overheat and stick. If you have a stuck exhaust guide on this engine, be sure to check the oil passage by blowing compressed air through the oil fitting in the cylinder head.

Continental engine design is more resistant to valve sticking. Big-bore Continentals rarely stick valves. We do see a tendency for intake valves to stick on Continental engines in the O-200, O-300 series. A stuck intake valve disrupts the breathing of the entire induction system. The power loss results in a forced landing.

 

Engine operating environment

Environmental influences that create valve sticking are: high temperatures, dirty oil, high-lead fuels, hot engine shut-downs, and poor engine baffling. Improper leaning can also be a culprit: an engine that is run excessively rich will build up carbon, lead, and other combusion-related deposits on exhaust valve stems more quickly. On the other hand, an engine that is leaned excessively during high-power operation will experience high valve temperatures, and this contributes to valve sticking.

Engine overhaul shops can't do much to prevent valve sticking. They cannot change the engineering of the engine, and have little control over its operating environment. About all they can do is to use the correct parts (valves, guides, seats, rotators, etc.), to dimensionally match the parts carefully, and to control the surface finish of the guide by careful reaming and honing.

Your regular maintenance shop can influence the operating environment by checking the engine's health regularly (via compression checks, oil analysis, filter inspection, etc.), by making sure the cooling baffles are in good shape and the magneto timing is correct, and by changing the oil frequently.

 

What happens whan a valve sticks?

When an engine has a stuck valve, one of five things can happen, each of which is bad news:

1. The pushrod bends.

2. The surface of the camshaft or cam follower fails.

3. The valve opens but won't close.

4. The rocker support breaks.

5. The valve rotator cap falls off the end of the valve stem. (Lycomings only.)

 

 

A valve that sticks closed will often result in serious and costly engine damage. Each time the cam-tappet-pushrod-rocker try to open that stuck valve, you risk catastrophic engine damage. With a stuck valve, the valve doesn't want to move. Tremendous valve train forces develop as the camshaft lobe tries to force the valve open. The camshaft follower and lobe are the most highly-stressed components of the engine even under normal conditions...the additional loading caused by a stuck valve may induce catastrophic failure of the rocker support, pushrod, cam follower, or cam lobe.

A damaged camshaft lobe requires complete engine removal and teardown. The same is true of a damaged cam follower if it is the mushroom-head variety used in many Lycoming engines.

Sometimes an exhaust valve that is stuck closed can cause the intake pushrod to bed or the intake rocker support boss to break. How can this happen? If the exhaust valve sticks closed, exhaust gases will not exit from the cylinder. Gas pressure within the cylinder then prevents the intake valve from opening. If this happens, something's gotta give. Either the pushrod bends or the rocker support breaks.

You might think that a valve that sticks open is a much less serious situation, but that's not necessarily so. If the valve is an intake valve, you lose power and will need to make a forced landing. If the valve is an exhaust valve, there will not be any compression on that cylinder.

In either case, if the valve spring can't close the valve, the entire valve train (cam follower, pushrod, and rocker arm) unloads. The end of the pushrod that rests in the socket in the cam follower may come out of the socket and fling around inside the tappet boss. If the pushrod ball does not locate itself back into the socket when the cam lobe comes around, it may jam against the tappet housing, usually causing crankcase damage.

The valve rotator cap on Lycoming engines is kept on the tip of the exhaust valve stem by the rocker arm. If the valve sticks open, the rocker may move far enough away to allow the rotator cap to fall off the valve stem tip. When this happens, not only is valve clearance excessive, but also the rocker face pounds into the spring seat. The rotator cap is too big to fall down the pushrod tubes. It just lays in the rocker box until you take the rocker box off. It then quietly falls unnoticed onto the hangar floor. If you notice a missing rotator cap, it is likely that the exhaust valve was stuck open in the past. Look in the rocker box or around the hangar floor and you might find it.

Engine damage does not always occur when the valve sticks, but the longer the engine operates in this condition, the greater the chances are that some damage will occur.

 

Remedial action

Repairing a stuck valve can be done without removing the cylinder from the engine. The procedure is described in Lycoming Service Instruction 1425 and consists of dropping the valve into the combustion chamber, reaming the guide, and then reinstalling the valve.

Another method is to tie dental floss to the end of the exhaust valve and lower it down into the cylinder. Ream the guide and then pull the valve back up into the guide.

If it's necessary to remove the cylinder, we recommend you inspect the condition of the camshaft lobes and the cam follower. You may want to review the operating environment of the engine. Pay particular attention to the oil change intervals, baffle condition, and operating techniques.

The procedure outlined in Lycoming Service Instruction 1425 and described here can also be used on Continental engines.

Do not use Marvel Mystery Oil or other solvents to un-stick a valve. Solvents may un-stick the valve in time but not immediately. Eventually the valve may un-stick, but not before your camshaft lobes have been damaged.

Solvent treatments dissolve the outer deposit layers in the guide boss and temporarily un-stick the valve. The remaining deposits push the valve over to the opposite side of the guide and cause rapid, uneven guide wear. The valve stem may stick or it may cause rapid guide wear where the stem is forced against the guide material opposite of the deposit buildup.

Edited January 12, 2016 by Jsavage3

[carusoam]

I had a stuck valve on the O360, in my C.

It stuck on T/O and removed the power needed to climb. Landed on the next available runway 90deg to the left.

I would not want to fly one like that again....

Just my experience,

-a-

[Dale Logsdon]

The valve guides can be reamed without removing the cylinder. Takes removing the valve spring and pushing the valves in to the cylinder with the piston all to way down. Ream the guide, then fish the valves back into the guides with a hooked wire and a magnet and putting the springs back on. Takes about 1 hour per cylinder. Lycoming says if you do it once you won't have to do it again.

[tony]

I had an experience similar to carusoam and I would totally agree with his assessment.  I don't think I would want to do that again.

 

 

Just about the same amount of hours as you too.  In my case it ended up being an exhaust valve on my IO-360-A1A.

[Skybrd]

One of my friends had a homebuilt that had valve sticking. He then started using Marvel Mystery Oil in his fuel. I used it in my Wittman Tailwind and VW Powered Green Hornet and never had valve sticking. What do you think can this help keep our valves from sticking?

[Jsavage3]

MMO is not an aviation/FAA approved product.  I've heard of many aircraft owners who swear by it, but...my tractor, no problem...my cars, no problem...currently, I won't be using it in my airplane.  

 

I've heard that folks are using MMO in their oil mainly and that it can be used in fuel too...

[N201MKTurbo]

If the cylinders are that low time I would just run it for a while. High time engines will stick from deposits on the valve stem, but yours should be pretty clean. I would wait for them to wear in.

 

What oil are you using?

[Jsavage3]

N201MKTurbo,

 

I understand your position and, initially, that is what I was thinking too.  Upon my learning the potential of a sticky valve taking the next step and actually sticking and the inevitable & catastrophic consequences that will follow, well, that is when I (as well as Lyc and the engine shop) felt something needed to be done.  That's where SB 388C fit the bill quite nicely.  Upon finding the exhaust valve guide on cyl #2 too tight, it was confirmed that, in my case anyway, allowing it to wear in would not have worked out well.  

I use Aeroshell 15W50 and CamGuard added at each oil change.

Edited January 12, 2016 by Jsavage3

[M016576]

N201MKTurbo,

 

I understand your position and, initially, that is what I was thinking too.  Upon my learning the potential of a sticky valve taking the next step and actually sticking and the inevitable & catastrophic consequences that will follow, well, that is when I (as well as Lyc and the engine shop) felt something needed to be done.  That's where SB 388C fit the bill quite nicely.  Upon finding the exhaust valve guide on cyl #2 too tight, it was confirmed that, in my case anyway, allowing it to wear in would not have worked out well.  Why was that valve guide too tight?  I suspect that the engine overhaul event would be the culprit, but this is just a hunch on my part...

 

I use Aeroshell 15W50 and CamGuard added at each oil change.

Just out of curiosity- where was the overhaul performed, or was it a factory reman?

[John Pleisse]

Valves can also be sticky in low time engines from disuse over a period of time. Pop the jug and send it out. Bore scope your top half while you have it off. This will tell much.

[bnicolette]

I get this same thing on every start up and honestly haven't thought much about it.  However, I will certainly query my engine shop to see what they have to say.  Here is a pic of what is happening:

 

What do you guys think?

 

The red EGT line that's dipping down is the #1 cylinder.  The yellow line is the manifold pressure.  This seems to be exactly what the OP was talking about.

[tony]

When your airplane talks to you, you really need to pay attention and listen.  Ignoring it and you're just asking for trouble. 

 

When I experience my stuck exhaust value, I found out that the piston came up and dinged the valve, the valve stem was deformed, and the push rod was bent.  It was all do to the valve guide being reamed out at the minimum tolerance instead of the nominal. 

 

I assumed you performed the wobble test and found out that your valve guide was too tight as well?

[N601RX]

Your also risking ruining a camshaft running the engine with a valve that is sticking.

[N201MKTurbo]

It usually just bends the push rod. Back in the 80s when Phillips XC came out there were a lot of stuck exhaust valves and a lot of bent pushrods. I had one that bent so bad it bent the tube and it was obvious without disassembling the engine.

It has to be traumatic on the valve train.

[Jsavage3]

Just out of curiosity- where was the overhaul performed, or was it a factory reman?

 

I had my A&P/IA do a field OH for me.  He's been maintaining my airplanes for 6 or 7 years and I trust him.  Of course, there's no warranty, but I've been very happy with this smooth-running OH'd engine.  He basically did the dis- & re-assembly as the case/crank/cylinders/etc were sent out to engine shops...

 

Would I do this again?  Probably would, especially if I was going to keep the airplane.  If I was looking at resale value, I'd probably go with a factory reman.

[Dale Logsdon]

Theory has it that... When new guides are installed the only thing holding them in place is the negative or press fit in the head. Over a few hundred hours of heat and cool cycles the metals equalizes their pressure against each other and  the head squeezes the guide to a smaller dia. Sometimes the guide wears enough to compensate for this decreased clearance but when it doesn't you get a sticking valve. This does not seem to be a reoccurring problem once you have your guides reamed and after you pass a few hundred hours your chances of having the problem go away.

 

If your airplane has the "Morning sickness" Have it looked at ASAP. This is the first sign of the doom to come.

 

As I posted earlier you don't have to remove the cylinders to ream the valve guides.

 

I believe the problem with Phillips X/C was the 2nd blend with a new additive that turned out not to be compatiable with aviation use. That blend was disscontinued back in the '80.

[bumper]

Theory has it that...  the head squeezes the guide to a smaller dia.

 

 

Theories notwithstanding, I would not buy into the idea an aluminum head is going to squeeze a relatively thick steel valve guide to a smaller diameter! I'm a hobby machinist and tool nut, have a full machine and welding shop in my hangar, so play with this stuff regularly. Aluminum flows under pressure, it can be easily extruded. Bolt together two pieces of aluminum and given enough pressure to properly stretch the fastener, the aluminum can flow and the bolt will thus loosen. This is not an issue with steel, much higher tensile strength than aluminum. 6061 T-6 has a yield tensile strength of >35,000 psi, 4130 steel is at least double that. Unlike aluminum, steel cannot be extruded unless at extreme temperatures.

 

I reamed a valve guide for a friend who had a stuck valve last year (used the old rope trick), gotta say that the varnish and carbon I removed from the guide with my reamer seemed almost as hard as steel. The ream removed all the crud and removed absolutely no metal in the process. 

 

bumper

[Piloto]

I had the same problem when I switched to Exxon Elite 20W50 oil. Switched back to AeroShell and problem solved.

 

José

[fantom]

I had the same problem when I switched to Exxon Elite 20W50 oil. Switched back to AeroShell and problem solved.

José

Interesting because for me it was just the opposite. Maybe you didn't 'stick' with Exxon Elite long enough.

[Alan Fox]

Signature is by far the best engine shop on the face of the planet... I can not elaborate more on that ....Secondly I think it is foolish to fly an engine with a sticky valve....(morning sickness) if it acts up on take off , or a go around you could be screwed .........Its telling you there is a problem.....They don't fix themselves....

[Jsavage3]

Joe at Signature Engines in KLUK is the man who (1) discussed my bird's condition with me and (2) then performed the SB work.  He's very knowledgeable about this and I'd strongly recommend giving him a call if you'd care for any sticky-valve specific details.

 

IMHO and along with N74795, I cannot say enough good things about Signature Engines!

 

Bottomline, if your bird is suffering from morning sickness, get it looked at ASAP!!!

[mcpilot]

Your also risking ruining a camshaft running the engine with a valve that is sticking.

 

 

Your also risking ruining a camshaft running the engine with a valve that is sticking.

Yes.. Why take the risk of ruining your new engine?  I would treat this aggressively..  Have the valve guides reamed and avoid an engine failure....  You are lucky to have noticed this symptom...  Don't ignore it...

[bnicolette]

I have grounded my airplane until further investigation.  Hopefully early this week.

 

Are most guys complying with the SB388C?  I had never heard of it before but it is now on my maintenance minder.

 

A big thank you to Jim for posting his experience.  One of the great things about this forum!

[bnicolette]

Finally got to tend to the airplane today.  Upon inspection of the exhaust valve in the #1 cylinder we found that it was in fact tight in spots and in order to get it completely out of the guide had to pound it out.  Lycomings tolerance for the guide is .4995 - .5005.  We reamed it to .5000 and got lots of carbon out of it.  Pic attached.  I had to leave but the shop is putting it back together tonight and hopefully I can run it tomorrow.

[N601RX]

How many hrs since your teardown?