Titan 0-340 Burnt Intake Valves

[rocketbob]

Originally Posted by Full Throttle

So if one was to use roller rockers on a Lycoming engine, all the valves would have a good chance of burning. Is that correct?

Not if they are made correctly. I have had rocker arms custom made and offset the valve stem slightly. As long as the pushing force is off to one side they will rotate.

[Full Throttle]

A roller rocker has a small roller that rolls over the end of the valve stem. This virtually eliminates side load on the stem and greatly reduces wear. How does it rotate the valve.

[lr172]

Originally Posted by Full Throttle

A roller rocker has a small roller that rolls over the end of the valve stem. This virtually eliminates side load on the stem and greatly reduces wear. How does it rotate the valve.

side loading is mostly a function of angles/geometry and not friction. The roller is still a static plane, just like the flat surface of the old rockers. Change the angle of the bearing shaft from parallel to the valve stem face plane and you still get side load. There can be different side loads happening, not just the side load introduced when the rocker face is not operating exactly in plane with the valve stem, as it does through most of it's travel. Yes, in that particular case, friction is driving much of the side load in a flat faced rocker. I believe Bob is referring do a different type of side load, introduced by tilting the rocker shaft plane a small amount from the valve stem face plane.

[rocketbob]

Originally Posted by Full Throttle

A roller rocker has a small roller that rolls over the end of the valve stem. This virtually eliminates side load on the stem and greatly reduces wear. How does it rotate the valve.

The roller rockers I made are simply offset a slight amount, just as are stock rockers. There is just enough sideloading to cause the valve, springs, keepers, and the spring seats to rotate. That is why the spring seat bottoms appear highly polished when removed.

[theduff]

I’m a Lycoming guy and I question some of this. On Parallel Valve cylinders the exhaust valve has a rotator cap which actually releases the valve keepers as the rocker depresses the valve allowing valve rotation. The intake valves have no such device. On Angle valve cylinders many have rotator caps on the Intake valves as well allowing them to rotate. Rocket Bob May be right about the whole assembly ie springs,keepers,retainer and valve on the intake side rotating in the head but why doesn’t Lycoming simply put rotator caps on the intake valves like they do on some Angle valve engines ? I’ve noticed all the turbocharged angle valve engines use rotators on the intakes if that’s a reference point.

I would love to see something definitive in a Lycoming publication on the subject.

On the Titan 340 cylinders, they are unique and only work with the Titan 340 crank and rods. There is no equivalent in the Lycoming world.

[rocketbob]

The rotator cap is used on sodium-filled exhaust valves. I believe the reason is the weld that closes off the sodium chamber is not hard and would quickly wear without it. The rotator caps are stellite coated for hardness but they do wear. I'm not sure if it actually aids in rotation.

Here's a youtube I stumbled across (albeit a Continental) that shows the rotation.

https://www.youtube.com/watch?v=_UUvIDaWChA

The other possibility for the valve not rotating would be incorrect angles on the seat and/or valve face. The OH manual specifies a desired 1 degree included angle. If the angle goes the wrong way the valve can wedge in the seat and not rotate.

[brown bear]

I was hoping someone would post on the cylinder barrow difference in the 0320 and titan X340 engine . Continental list the exp titan X340 as 32.27 wide , same as the 0320 . So not sure the X340 dose not use same barrow as 0320 ? They list the 0360 as 33.41 wide .

[Full Throttle]

I think the valve spring itself creates most of the rotation of the valve. When the spring compresses and returns to normal, it has torsional movement that rotates the retainer, the keepers, and the valve. The valve spring itself may rotate slightly because of the inertia of the rest of the moving parts. Its really a random amount of movement that would be hard to regulate. No two valves rotate at the same speed. At least we can all agree that they do indeed rotate.

A good thing.

[BillL]

Originally Posted by Full Throttle

I think the valve spring itself creates most of the rotation of the valve. When the spring compresses and returns to normal, it has torsional movement that rotates the retainer, the keepers, and the valve. The valve spring itself may rotate slightly because of the inertia of the rest of the moving parts. Its really a random amount of movement that would be hard to regulate. No two valves rotate at the same speed. At least we can all agree that they do indeed rotate.

A good thing.

You need to look up the mechanism of how the positive rotators actually work. There are different designs and do not randomly rotate, they always rotate and a fixed amount. With NO rotator, the rotation is random and may not even occur, thus the reason for having positive rotators. Light duty engine seldom have positive rotators. Heavy duty always have them for predictable (longer) life. Aircraft propulsion is a heavy duty application.

I should have stated that, as Bob has mentioned, exhaust are the first to need rotators, then intake. Typically not on the intake esp. for NA engines. Since all are burning, it is like some design issue that could well be overcome with rotators. Many factors come into play for the determination from a design standpoint.

[Full Throttle]

[quote=theduff;1456859]I’m a Lycoming guy and I question some of this. On Parallel Valve cylinders the exhaust valve has a rotator cap which actually releases the valve keepers as the rocker depresses the valve allowing valve rotation. The intake valves have no such device. On Angle valve cylinders many have rotator caps on the Intake valves as well allowing them to rotate. Rocket Bob May be right about the whole assembly ie springs,keepers,retainer and valve on the intake side rotating in the head but why doesn’t Lycoming simply put rotator caps on the intake valves like they do on some Angle valve engines ? I’ve noticed all the turbocharged angle valve engines use rotators on the intakes if that’s a reference point.

Not all Lycoming valves have a rotator cap.