Rotax 912 ULS Cross threaded sparkplug

Ever since I started building RV's I've always been very careful to install sparkplugs with my fingers so I wouldn't cross thread them. Today though, I stuck a plug in my socket and started twisting. Right away the plug stopped turning and I knew I had a problem.

Now I guess it's time to learn all about installing a heli coil. I've read numerous posts on this subject and there are some good suggestions like using shaving cream to catch the bits of aluminum from the tap that would otherwise end up inside the cylinder. What I haven't seen though is anyone having this problem with the Rotax 912 engine. So, what size heli coil would be appropriate in this case? And, more to the point, is this something Rotax allows or will I need a new cylinder?

Also, I have a rather unusual situation with the hydraulic valve lifters on my engine; when the engine is shut down after running it up to 122 degrees, the rocker arms are very firm, with virtually no clearance between the valve and rocker. But when the engine cools down, the rocker arms on cylinder #3 have an excessive gap (more than the .020" in the specs)

I tried re purging the oil system with no results. I spoke with the Lockwood tech folks and they've never heard of loose rocker arms when the engine cools down. Common sense tell me the engine should be ok as long as the lifters are pumped up when flying. But I could be wrong. Any insight into this situation?

Thanks,

Walt Shipley

I would think a thread chaser would be the first thing to try. If not, hopefully the offending threads are bottom of cylinder. You can purge air in the top plug hole at a good rate to blow any debris out through the tap flutes. I think it would work from bottom up also. I have an adapter used to pressurize cylinders to check valves that would work. I know nothing about Rotax engines. Off subject/The wife and I are coming to Hensley in November to check out available lots for a possible purchase. May see you then?

Walt, this just happened to another member on the form a few days back. Read this thread at this link and all your questions will be answered.


http://www.vansairforce.com/community/showthread.php?t=117309&page=2

Hi Walt,

Left you some info on this on the Rotax Owner forum.
Follow JetGuy's link for more info right here on Vans.