Valve wobble test out of spec.

[flysrv10]

Originally Posted by DanBaier

From what I recall in the Lycoming engine school, when the valve opens / closes, it doesn't move in a straight line; rather there is a little side action to it and if you were to watch it close you'd see it kind of snap into position as it closes. As the engine ages, excessive valve guide wear could cause the valve to seat incorrectly leading to the valve failing.

In this case, I'd suggest a look at the valves with a borescope to see if there are any telltale heat issues. AOPA has a good chart with illustrations at https://www.aopa.org/-/media/files/a...inal.pdf?la=en . If you see any evidence of green tint to the valve or if the heat signature is obviously uneven, then the risk of a valve failure is very high, and I wouldn't fly the airplane in that condition as I expect the valve would probably fail sometime in the next 8 - 10 hours.

Dan

Thanks for the info. I have checked the valve pics and compared with AOPA's article. My valves look good for now when viewed form inside of the cylinders.

In addition too this forum, I am planning on calling Lycoming to see if they have anything else to add.

[turbo]

Originally Posted by flysrv10

Hey Turbo, You have recommendation in SE FL to replace valve guides?

no recommandations here.

[jrs14855]

I have seen posts from people who like the shop in Sebring. When Cessna resumed production on piston single's they plumbed the oil pressure line to the front of the gallery on the right side. This will result in a reading 10# lower that at the normal position for the oil pressure line. The oil pressure relief valve is then set to read middle green or higher. So 70# is now really 80#. There are experts who believe that this is very beneficial to the valve train, especially the guides.

[Gusmax]

How old is the engine? Old exhaust valves can have corrosion issues.

[rag]

I would call Continental/Titan James Ball or Mark Cummins. They have been very helpful to me.

[Walt]

Originally Posted by flysrv10

This is music to my ears. What is your recommendation based on? Thanks.

Nothing scientific, just experience. As has been mentioned the test is mostly to spot stuck valves, as long as the valve faces don't show any signs of distress I'd keep running it.

[rv6agrbk]

For what it's worth in your decision making, I recently had a momentary power loss over some very inhospitable terrain in the Coast Mountains. As oil consumption had also started to increase recently, I had a mechanic help me with an inspection of the engine (Lycoming O-360 with about 1400 hours on the cylinders). When I pulled the bottom number 2 sparkplug, you could pour oil off it. Further inspection revealed that there was very excessive wobble in the exhaust valves of two of the cylinders (we didn't have the official tool to measure, but it was very obvious). The other two cylinders were questionable as well. Compressions at the most recent annual about 50 hours earlier had been good. We sent all four cylinders to the engine shop and they replaced all exhaust valve guides and two exhaust valves. While it might be early to consider pulling the cylinder, I would definitely monitor for awhile to determine if it is getting worse.

Rob
RV6A C-GRBK

[scsmith]

Originally Posted by lr172

While I have no first hand experience, given the horizontal orientation of the valve and the anemic oil flow to the rocker box, I doubt that worn guides would show noticable increased oil consumption like they would on most auto engines.

Larry

Physical orientation (horizontal vs vertical) will have far less effect on oil consumption through the intake valve guides than the pressure differential that exists (primarily on intake stroke at low manifold pressure) between the ambient pressure in the rocker box and the intake chamber.

Not clear to me what mechanism would promote oil consumption through the exhaust valve, since the chamber around the valve stem is normally higher than ambient.

It seems to me that if the guides are worn enough to cause seating errors that might risk breaking a valve, it would show up in a compression test.

[gasman]

Originally Posted by scsmith

Physical orientation (horizontal vs vertical) will have far less effect on oil consumption through the intake valve guides than the pressure differential that exists (primarily on intake stroke at low manifold pressure) between the ambient pressure in the rocker box and the intake chamber.

Not clear to me what mechanism would promote oil consumption through the exhaust valve, since the chamber around the valve stem is normally higher than ambient.

It seems to me that if the guides are worn enough to cause seating errors that might risk breaking a valve, it would show up in a compression test.

During a differential pressure test, the valve is seated slowly as the motor is turned by hand. The valve will almost always seat. Running at 2300 rpm the valve has many opportunities to hit off center and fail. All prior DP tests were normal.

I lost an exhaust valve at night...... the motor does not run smooth (shakes like he**) on three cylinders. What saved me was the fact that 1/3 of the head stayed with the stem and the other 2/3 broke in two pieces and was pushed out the exhaust port.

I would not mess with a sloppy exhaust valve.

[scsmith]

Originally Posted by gasman

During a differential pressure test, the valve is seated slowly as the motor is turned by hand. The valve will almost always seat. Running at 2300 rpm the valve has many opportunities to hit off center and fail. All prior DP tests were normal.

I lost an exhaust valve at night...... the motor does not run smooth (shakes like he**) on three cylinders. What saved me was the fact that 1/3 of the head stayed with the stem and the other 2/3 broke in two pieces and was pushed out the exhaust port.

I would not mess with a sloppy exhaust valve.

Point taken. It just seems like 0.050" of misalignment on seating is not enough to create a significant moment, and is more likely to just guide the valve into its seat. But I suppose if it did it the same a bunch of times, it could fatigue the valve stem and fail. And of course, "a bunch of times" can happen pretty quickly at 2300 rpm.