Rotax 912 valve spring retainers failing

[Jerrytex]

I don't understand why Rotax has not addressed this? I guess I am going to do the lifter air check that Dave mentioned and hope that Rotax comes out with a SB soon.

[Dusty]

I wasn't aware of the bank / pitch limitation, but air in the 912 is a problem.

I only have experience with one retainer failure but have seen plenty of valve damage, usually related to air leaks in the suction side of the oil system or improper oil change procedure such as starter cranking to get pressure after opening the system.

Hand prime only, preferably with the filter slightly loose to effectively bleed any air before it gets into the pressure systym.

My theory, for what is worth , is that air will gravitate upwards toward the crank journals and only oil, free of air will flow down hill to the cam and lifters.

Starter cranking just feeds foamy oil everywhere due to the speed.
Run the engine up to temp with the cooler covered if necessary then do the rocker test (the "o" rings unless very old will go again)

[Slyfox]

ok I give, what is the rocker test. I'm thinking take the cover off and push on the rocker for air in the lifter. dah I don't know. help me out. When I change my oil I never take any hose off, I remove the tank cover and suck out the fluid. I have the new filter sitting on the floor and fill with new oil, sometimes takes a couple times, oil soaks into the filter. I remove the old filter and immediately put on the new filter. takes very little to purge the system. that's my oil change procedure.

[Shadowrider]

Can a rotax not run on 3 cylinders. If you lose a cylinder it will bring the engine down? Seems like if you lost a valve on on cylinder it should keep running?

[Jerrytex]

The Rocker test:

https://www.youtube.com/watch?v=UwARvpIP9-k&t=266s

About the 9:00 mark he talks about checking for trapped air.

The crazy part is.....if there is air, the fix to "untrap" thee air is to run the engine.....

[Dave S]

Jerry.

One of the comments in the report you posted from the NTSB was that a test was performed to see how long the engine had to run to bleed the air - something like a bit over 6 minutes at idle for that experiment. This is empirical information we don't normally see.

One of the problems with bleeding lifters on a boxer engine like the rotax - the lifters are laying on their sides in the bores. On engines with the lifters oriented upwards the trapped air exits up through the metering valve feeding the pushrod pretty well. With a horizontally oriented lifter, some of the air is above the lifter metering valve and its only way out is between the lifter piston and lifter body which is machined to incredibly close tolerances. Warming up the engine/oil at idle speeds facilitates the bleed rate between the lifter piston and lifter body and is likely the route the remaining air has to go. Thick cold oil does not flow as well. Rotax fit and finish of the engine parts is extremely close compared to many other engines.

Dusty's comments about air up, oil down and easy does it is golden. I guess we are more like plumbers than a person might think!

There is probably quite a difference in hammering stress on the affected parts between idle speed and running at 5000+ rpm. How many of these instances occurred at cruise RPM vs idle - pretty much all and none as well as I can tell?

I think there is a lot more to find out about this - the NTSB report is a good start. I am still not convinced air in the lifters alone is the only factor.

[avidflyer]

Can a rotax not run on 3 cylinders. If you lose a cylinder it will bring the engine down? Seems like if you lost a valve on on cylinder it should keep running?

Running on three cylinders is not so bad, vibrations and such, but if the valve shatters the piston, and the connecting rod bends, ect, ect then the engine probably wont keep the plane in the air