Leaking exhaust valve

[bvolcko38]

30 hours on my aerovee and I have a leaking exhaust valve on number 3. What size valve do I need to order ?

[Outlaw6]

35.5 mm single groove stainless steel. Sonex sells a set of 4. If you're going to pull the head you might as well replace the #4 also. You'll need to regrind the valve seat if there is enough material left and lap the valve to the seat.
But first, you should borescope the cylinder and look at the valve face and mating surface, or if you haven't experienced lower than normal power you may want to fly the plane for another hour and redo the compression test. Compression tests are unreliable. Here's a good video of what you are looking for: https://www.youtube.com/watch?v=7R-dAmv9VZk. Just bought a borescope for this reason. If the mating surface isn't bad you can lap the valve without pulling the head.

Having said all that, last year (150 hours on Aerovee) my #3 exhaust valve failed a differential compression test so I pulled both heads so I could check them, all the exhaust valve mating surfaces and seats were cupped and the guides were sticking. A new head costs $125 more than having a shop repair the head so I just replaced both heads (thinking I might have the old ones reworked to have spares).

[bvolcko38]

Pulled the right head yesterday and found 2 leaking exhaust valves, one much worse than the other. Upon careful inspection we found the seats warped, valves were fine. A friend has a seat grinder and we trued the seats. Waiting for parts now.

[bvolcko38]

Before re-assembly and upon inspection, I found an exhaust valve pushrod with extreme wear especially for only 30 hrs TT.
One shows normal wear and the other is extreme. There is oil at that lifter. The worn end was on the lifter end. Improper heat treatment? Chinese quality? I don't recall but I think they were Empi.

[sonex1374]

Bill,

I had a similar experience years ago with my AeroVee where one pushrod tip was severely worn (ground down actually). After troubleshooting and giving it a good inspection I think there may have been something inside the pushrod that slightly restricted oil flow thru the tube. It wasn't completely blocked (just slightly obstructed), but it was enough to wear the tip. Maybe this just happened to coincide with a soft/bad tip, but replacing the old pushrod with an entirely new assembly solved that particular problem.

Jeff

[Area 51%]

Pulled the right head yesterday and found 2 leaking exhaust valves, one much worse than the other. Upon careful inspection we found the seats warped, valves were fine. A friend has a seat grinder and we trued the seats. Waiting for parts now.

Have you thoroughly examined the head? What looks like smoke around one of the stud holes might be coming from a crack. Or possibly gases getting by the head gasket.

A plugged pushrod tube might cause that type of damage at the rocker end, but it should be getting all the oil it needs at the lifter.
Throw the Empis away and get CB performance or some other high quality units.

[bvolcko38]

I thought there was an exhaust leak past the head gasket due to the "smoky" appearance. No leaks or cracks.
I know Empi is made in China and my faith in their quality control is low. What are the other choices? CB I am not familiar with, MOFOCO?
At this point I'm pretty sure this pushrod end was never hardened properly

[Spaceman]

Bill,

I had a similar experience years ago with my AeroVee where one pushrod tip was severely worn (ground down actually). After troubleshooting and giving it a good inspection I think there may have been something inside the pushrod that slightly restricted oil flow thru the tube. It wasn't completely blocked (just slightly obstructed), but it was enough to wear the tip. Maybe this just happened to coincide with a soft/bad tip, but replacing the old pushrod with an entirely new assembly solved that particular problem.

Jeff

Oh wow, I'm glad I saw this. I didn't know oil passed through the inside of the pushrods! I will have to go back and check mine. I bet some of them are clogged from when I beat the tips on.

[bvolcko38]

I bought a set of pushrods and tested a couple for hardness with a file. On the new pushrods a file pretty much just skates across the pushrod end without really cutting. On the worn pushrod,a file cuts right in. That problem is solved for now.

Now to the valve. After regrinding the valve seats and reassembling everything we had good compression by hand propping. So, I did 6 or 8 aborted takeoffs and noticed that the no. 3 egt was still high. Put the plane back in the hangar and did some hand propping and still have a weak cyl. Haven't got to the point of figuring out which one is weak but my money is on number 3. Could be valve lash is off a bit but i doubt it. Will do another leak down test.

At this point I feel more like a mechanic than a pilot.

[Onex107]

This is a stupid question but ----------- Did you cut the new push rod to the same length as the others?

Sorry, I am not questioning your abilities, but the research approach to a problem is to start with the most obvious questions. Hardness of the end nipples can be checked with a file, lubricating oil for the rocker arm does flow through the pushrod tube at very low pressure so it needs to be not restricted. The cylinder and head, with a new fire ring will move closer to the block with engine running and re-torque causing the push rod clearance to reduce or disappear. Even a new valve and seat regrind need to be lapped to be leak free. And, I never check compression cold. A short engine run to warm up the heads and block make the plugs come out easier and expands everything to a operating temp condition. Don't short change a compression test. You can even do a compression test on a removed head on the bench by bolting a plate and gasket over the head face using the head bolt holes. This can save you an installation if the valve is not seated and needs more lapping. Been there, done that.