I think this issue arose in its entirety over the last few hours only. I spoke to the US engine shop and they don’t think it is possible to get such rapid wear, even if there was no lube, and there was lube allright; the pushrod was covered in oil. What I don’t know is whether oil was being pumped through the middle of the pushrod.
I have decided this engine cannot be used unless we positively prove that oil is being sprayed onto the exhaust valve stem.
It turns out there are two types of rocker arms. They look almost the same. Both types get oil in via the hole inside the pushrod
and both have oil exiting in the bushing, to lube the bearing, via the visible hole above. Only the exhaust rocker has an extra hole where shown, which gets oil (via a groove in the outside of the bronze bushing) and this oil sprays onto the exhaust valve stem.
To make life more interesting, Lyco made a large batch of rocker arms with the extra hole and used them for the inlet valve also, but the bushing didn’t have the groove so the hole has no oil coming out of it, so the inlet valve stem doesn’t get the spray, and this is apparently intended. I have this…
I need to do a test, where we will wash the area with avgas to get all the oil off, replace the rocker cover, run the engine for a minute, remove the rocker cover, and see where there is oil. Also, extract the pushrod and make sure it is full of oil inside.
If this cannot be proven, the engine will be shipped to be stripped.
Peter,
Are you certain the pushrod has been worn shorter? There are at least a couple of lenghts available. Also, it is not unusual for stuck valves to result in slightly bent pushrods. Did you verify yours for straightness?
I doubt it is worn. We didn’t check the clearance with the pre-repair cylinder. It could simply be that the repaired cylinder has the exhaust valve sitting further in (not sure how that’s possible; any machining of the seat would make it sit further out).
Or a wrong pushrod may have been fitted originally. The engine had some weird issues, starting with various oil leaks, suggesting less than great hygiene on the crankcase mating. You need only one slightly careless person…
I will check the pushrod part numbers and measure them; then I will know. One can buy them longer in steps of 0.030", apparently.
I am informed one can spin the engine with the starter (with the bottom plugs out and all 12 ignition leads removed) and there should be enough oil pressure to pump oil down the pushrods. Safer than starting it up.
What’s annoying is that this simple check could have been done when we reinstalled the cylinder. We did a run with the cowlings off. Now we have to spend a couple of hours at least… I wish I knew yesterday what I know today.
Peter wrote:
I wish I knew yesterday what I know today.
Best aviation quote ever
Did they not use a new valve seat? If so, an increased clearance is to be expected.
Even if not , an increased clearance within limits is not cause for concern, as long as oil passages in the rocker and pushrod have been verified (easy enough with a squirter) , and that the pushrod is straight.
Peter wrote:
The engine had some weird issues, starting with various oil leaks, suggesting less than great hygiene on the crankcase matingNow you are getting a bit paranoid over it…probably the same oil leaks you had prior to the cylinder issue. Some minor oil leaks are usual…what’s important is that you know the source and all mechanical aspects are addressed.
Your crankcases were mated by a good shop. You can retorque the crankcase bolts to ensure proper spec and no fretting being caused by a loose bolt. All your throughbolts are torque-sealed. The two throughbolts in your newly installed #2 cylinder have been torqued while holding the nuts on the opposite side, on cyl #3, and all nuts torquesealed. If that’s done, the main thing you would have to worry about a minor case parting surface leak is a case crack.
That in itself is much less worrying than the other aforementioned items and has almost never caused an engine to stop in flight, but you would anyway find those easily by cleaning and using a developer or talcum powder.
I agree that knowing all of the possible lycosaurus engine failure modes can be worrying…but in the end with the average precautions (much more with the ones being discussed here) they last around 10 overhaul cycles before letting you down in flight…you have eight more to go with standard precautions, more like 16 in your case!
A stuck Lycoming exhaust valve is a known issue and well done for catching and correcting it , but is not cause for a teardown a fifth of the way to OH.
The valve seat was re-machined.
I will know more today 
BTW I heard from one TIO-550 owner that he gets all his valve guides reamed at every annual, using the “old rope trick”, as a precaution. Takes about 45 mins per cylinder, apparently.
but is not cause for a teardown a fifth of the way to OH.
It certainly is if there is no oil coming up through the pushrod
Did that oil flow check today.
It is harder than you would expect.
Firstly, spinning the engine with the starter produces almost no oil, even after minutes. The starter can do it for ages; the current draw (with bottom spark plugs removed, and obviously all ignition leads disconnected) is very low. The battery voltage is 22.5V during operation and that suggests a current draw of max 20A. It barely gets warm.
Even idling the engine produces minimal oil through the pushrod.
There are two oil paths to the cylinder head. One is through a gallery here
which also floods the hydraulic tappet, and the other is via the tappet which then goes up the middle of the pushrod.
After much work we proved, to my satisfaction, that oil is entering the pushrod and passing through the rocker arm. But at 1200rpm – the highest you can do with somebody standing next to #2 cylinder and looking for oil – there is really no visible oil dripping out of that special hole in the rocker arm. The only way to verify it is to dismantle it all after a few mins’ run and then – having washed the parts in avgas and blown them out with compressed air – you can see fresh oil there. We did it with the parts, one by one. Not obvious but I am happy with it.
In retrospect it is obvious there can’t be much oil coming into the cylinder head because the drain pipe
is way too small to drain more than a trickle. If the cylinder head filled right up with oil, you would have major problems with the mechanism operating.
I did a 1.5hr flight, to the Lyco protocol and all was good.
The CHT at 75% power (about 24/2400/16GPH) steadily dropped from 340 to 330 over that flight which is what one would expect. It will continue to drop.
There is no wear on the pushrod ends. They are different part numbers and differ in length by about 1mm.
A lot of effort Peter but you should feel very lucky to have the required combination of time, mechanic, and opportunity to investigate this to your own satisfaction.
Well done.
When can I bring the Cessna down for you to look it over for me ;-)
Good job! Keep monitoring and you should be good.
Antonio
