Differential pressure test trouble shooting

I concur with RW. Seaform isn't approved by Rotax, so why cut corners with dubious processes. I also concur with RW's listening process, and that 30 min is nothing to resolve this. If you had said 30 flight hours, then sure. RW's process is spot on for what a quality Rotax HM would advise. 

Nicholas, RW,

You are thinking I only ran it 30 minutes to get to my conclusion. You may have missed this secondary information so I added it to my first post.

"To eliminate the posibility of the rings being lined up I did 3 separate runs on the ramp, and a 30 minute flight. I tested leakdown on all cylinders after each one with no change. I have since flown 10 flights acumulating 8 hours, testing afterwards again with no difference".

Thanks Walt, yes I missed that, sorry.  This brings me to then think that jug should come off to inspect the rings.  Check the ring gap, that will tell you if there is wear.  Carbon can bind up the ring lands even with auto fuels.  This would depend on how rich the mixture is and how hard the engine is running.  When you remove the cylinder check the ring end gap alignment.  If the rings happen to be aligned, rather than staggered, it would account for a lower pressure.  Other than that it may be a valve not seating well enough.  A valve lap is not difficult and can make a big difference.  

Cheers

Hi Guys,

Food for thought,

Usually when I see a lower than normal compression test on a single cylinder I don't worry just then because I know the ring alignment may be the issue. I finish my Annual inspection and usually do the carb sync last. Running the engine for this time period seems to have always corrected the mis-aligned ring set and when I re-do the one cylinder the compression test has come back to normal. I know this isn't the case for everyone because another issue may be in play. I brought this up because you have run it numerous times and the issue isn't corrected so it's time to look at other items in the cylinder as RW mentioned.

Great info. Generally speaking, is there greater chance of the rings sticking with carb verses fuel injection? 100LL verses autogas?