Leaking intake valve 912ULS

Thank you for your answer.

The engine has always run on auto fuel octane 95 or higher, not sure if octane in Denmark corresponds to the same in US but it is according to the user manual.

I have now spent a few evenings in the workshop and have cleaned and lapped all valves and lapped the cylinder heads. now they just have to be installed. 

Based on the colors of the cylinder heads, are they running too lean or?

/Thomas

Very nice piece of work! Valves and surfaces look like new, excellent.

hi Thomas, looks great.  I dont think you were lean.  Carbon, assuming that was what was the problem, is more the creation of a rich mixture.  If you have EGT gauges check to see if you are running the recommended temps at normal RPMs.  The leanest burn will tend to be at 5000 approximatly, depending on your prop loading.  (pitch) 

Cheers

The 3 heads shown in the original post all have the valve seat leak at the same location eg right at the closest distance from the EX valve. For 3 valves to have carbon or other deposit at exactly the same location is nearly impossible (buy a lotto ticket)!

A more plausible reason is a slight distortion of the valve seat through overheating. Both rear cylinders (#3 & #4) are worse than #1 and #2 seems to be unaffected. This suggest some cooling issues as the actual cause.

The colours on the EX valve #3 and #3 & #4 heads also indicate a less that rich mixture (white deposit) compared to #1 (no white deposit). This is quite typical for the 912 due to the sharper bend in the intake manifold for the rear cylinders (making the mixture of the front cylinders slightly richer compared to the rear cylinders). A lean mixture would also add to increased temps.

Yes, there are many possibilities what can cause it and I haven't found a 100% answer yet.
Thomas@ I also think that the cause may be due to a slight overheating, but why on the intake and not on the exhaust valves, which are always hotter than the intake valves?
I am now ready to mount the cylinder heads and do a test run and I will continuously do a leak down test every 25 hours for the next 100 hours to observe any leaks on the valves.

I will come back with a status when the engine has been running for the first 25 hours after the repair.