Leaking intake valve 912ULS

I had a previous 912UL where one of the inlet valves failed in such a way that the sealing surface of the valve had worn away. It looked like the metal had lost its hardness. I fitted another valve and the problem was solved. What do your valves look like? Are the stems OK and are they sticking?

All valves are fine and all measurements are within tolerances as described in MAINTENANCE HEAVY MANUAL and no sticking valves.

/Thomas

Hi Thomas

What fuel are you running?  This is normally from carbon, or lead, trapped between the valve face and the seat.  

As for the problem Kevin had with the cupped inlets these are signs of detonation.  This happens on the inlet in that the inlet valve is not as hard as the exhaust, it is stainless but without the hardened face like an exhaust valve.  The larger surface area under some detonation will cup.  In turbo engines the exhaust can cup also and even burn a notch into the valve face and destroy the seat also.  If you have used a lot of auto fuel it may be low octane and not giving you the protection you need. 

Cheers

It looks like it's some lead deposits on your valve seats. If the valve seats are fine then all you need to do is lap the valves in.

I had this happen several times on a couple of my 912ULS and the first time it happened I pulled the head a lapped the valve back in.

I then tried the shade tree task. While the air was on the cylinder, I could hear it coming out the carb. I took a rubber hammer and tapped the intake valve a couple of times (just enough to pop it off the seat). The air leak went away and it went from 80/62 to 80/79. Problem solved!

I've had good success with the above on several occasions and each engine went on to run another 1,000+ hours trouble free and still counting.

Hi Glenn, yup that is called "spike the valve" and is a common practice on aviation engines, especially when running leaded fuels.  This can also happen on a piece of carbon as well but not as likely.  

The procedure is actually in both the type 915 and 916 manuals, perhaps they will update the others in the future.

For reference I have included a few of the pages for you.

Cheers