Bent push rod causes oil leak

[MooneyBob]

I always found few drops of oil under the plane after flight. I was told it is normal and it is oil blown from the breather. It really annoyed me. I have removed the cowling few weeks ago for the first time as I have no experiences with the planes engine or mechanics at all.

I noticed that there is an oil stain on the top of the cylinder. Not a big deal, I was told.

I didn't feel like flying today so I removed the cowling again and took a closer look. It looked like the tube that houses the push rod is kind of loose or somethIng as it was really easy to spin it around. And it looked like the oil is coming from the spot where the tube enters the head of the cylinder. So as I am turning the tube a little more I have noticed that is bent. Since it's bent it is shorter and that's why it doesn't sit properly, seal is all messed up and tune oil leaks from the cylinder head.

I was wondering what could cause the tube bent like that. I called my mechanic and he said that pushrods is bent too and it happens when the exhaust valve (on cylinder 4 ) gets stuck. So I took it apart and I pulled the pushrods that is really bent and is rubbing against the tube inside. Pretty scary to me.

I have this plane for 8 months ( my first plane ever) and I put 120 hours on it. It had new engine with 485 hours but it was flown very little last 10 years.

I have to say that I never noticed any performance issues or change. No clicking or strange sounds, performance very close or right on the numbers according to POH. I have no idea when it could happen. Maybe very first time the plane was started after sitting long time? I don't know.

Before I removed the push rod I have turned the prop few times around to see that the valve is working properly. It looked like it travels freely all the way up and down.

My questions:

1.What causes the valve gets stuck? Again, it is exhaust valve on #4 cylinder.

2. What would be the concern after I replace the push rod and tube? Should we take a closer look at the valve or take the top apart to see any possible damage?

[carusoam]

My experience...

When a valve sticks closed you notice it immediately.... Significant loss of hp occurs if it stays closed.

If it sticks open, the piston may come in contact with the valve...

When the valve is stuck up it has the opportunity to bend the valve's push rod...

On subsequent flights the valve may be trying to operate normally. With a bent rod, it may be difficult discern a difference.

Valve tap is pretty evident with an O360. When you hear three taps of one kind and a fourth of another, you have something to point at when talking to your mechanic... Somewhat noticeable during start and warm-up.

My experience came within a handful of flights after I purchased a languishing M20C...

The cost of this experience... A new to me cylinder assembly, plus install...

A stethoscope could probably help identify which cylinder has a bent rod, on the other hand a bent tube and leaking oil probably is a tell.

The cause is typically oil that gets cooked under the high temperature of the exhaust valve area.

The solution is typically called the rope trick. Sending a flexible sanding tool down the valve guide to remove the build up...

Keep in mind a C runs much higher CHTs that increases the ability to cook oil on the valve guides.

My plane flew on for a decade after that with minimal difficulties...

Based on your description... I would be thinking to send a camera to look at the piston and valve. If there is a mark from the valve on the piston, check on the price of a cylinder assembly....

Then consider what to do for the other three. Cleaning the valve guides is an ordinary maintenance event.

Good luck,

-a-

[MooneyBob]

My experience...

When a valve sticks closed you notice it immediately.... Significant loss of hp occurs if it stays closed.

If it sticks open, the piston may come in contact with the valve...

When the valve is stuck up it has the opportunity to bend the valve's push rod...

On subsequent flights the valve may be trying to operate normally. With a bent rod, it may be difficult discern a difference.

Valve tap is pretty evident with an O360. When you hear three taps of one kind and a fourth of another, you have something to point at when talking to your mechanic... Somewhat noticeable during start and warm-up.

My experience came within a handful of flights after I purchased a languishing M20C...

The cost of this experience... A new to me cylinder assembly, plus install...

A stethoscope could probably help identify which cylinder has a bent rod, on the other hand a bent tube and leaking oil probably is a tell.

The cause is typically oil that gets cooked under the high temperature of the exhaust valve area.

The solution is typically called the rope trick. Sending a flexible sanding tool down the valve guide to remove the build up...

Keep in mind a C runs much higher CHTs that increases the ability to cook oil on the valve guides.

My plane flew on for a decade after that with minimal difficulties...

Based on your description... I would be thinking to send a camera to look at the piston and valve. If there is a mark from the valve on the piston, check on the price of a cylinder assembly....

Then consider what to do for the other three. Cleaning the valve guides is an ordinary maintenance event.

Good luck,

-a-

Thanks Anthony

[Guest]

Look at Lycoming SB388 for guidance on valve and valve guide inspection.

Clarence

[carusoam]

Thank you Clarence!

Best regards,

-a-

[triple8s]

If your tube is bent and rod is bent then the valve stuck a bit if the valve is stuck it can probably be freed up replace the push rod and tube then you should be good. I would definitely check to see if the valve touched the piston if so it could be bent and that will mean pull a cylinder. I have been advised over and over again by my mechanic who is a beech owner/ROP old school guy to run MMO in the oil and the fuel. I hate putting anything in the engine that the manufacturer doesn't call for but he swears by it.........thoughts? MMO? I did buy a big bottle to leave setting around so he'd leave me alone, but I have yet to crack the seal on it.

[Bob - S50]

I think I read from either John Deakins or Mike Busch that a plane with a sticky exhaust valve may develop 'morning sickness'.  That is, it runs a little rough when it first starts until it warms up then runs fine.  This is usually caused by a sticky exhaust valve which you say you may have.  We had that too.  We had an A&P ream the guides.  That involves removing the valve and letting it sit in the cylinder while they ream the guide to remove all deposits, then put the valve back in.  Takes a couple hours.  It wasn't too expensive.  If the morning sickness is not cured it can result in bigger problems as mentioned by carusoam.

 

The article I read attributed the problem to carbon deposits from running excessively rich, especially at low power settings (during ground ops for example).  Under those conditions, unburned hydro-carbons get deposited on the valve stem as they exit the cylinder.  When the valve closes, it takes those deposits up into the valve guide and some of them get deposited there.  After enough time they become a significant deposit.  When the engine is cold the deposits make the valve stick.  As the engine warms everything expands allowing more room and less sticking.

 

Their solution is to brutally lean on the ground.  Lean until you see a rise in the RPM and it just starts to drop again.  For our plane that turns out to be about 1.8 - 2.0 GPH.  If you lean it enough, you may not be able to advance the power to taxi or perform your runnup without enriching the mixture.  Whatever you do, be sure to go full rich before takeoff.  My way of doing that is to use 1, 2, 3, 4 before I take the runway: 1 on the floor (proper fuel tank selected), 2 on the pedestal (trim and flaps set), 3 at the power quadrant (mixture full rich, prop full forward, cowl flaps open), and 4 sets of switches (lights, pitot heat, boost pump, elevator trim; as required).

 

Good luck,

 

Bob

[Guest]

I meant to mention that in the worst case of valve sticking or morning sickness I've seen, the valve stuck enough to bend the pushrod which cracked the valve follower leading to engine removal, split and repair. Very costly outcome.

Clarence