914 Case Fretting

Dear Richard,

i have no experience with 914, only with 912 UL 80 hp. My former engine had the SN. 4407214 maybe build in 2004 or 2005.

At my former engine a high friction torque at the crancshaft was not shown on the cold engine. Not by turning by hand and not by measuring. The engine runs smuth and had good performance. The high friction occours at the hot engine direct after engine shut down: After landing (normal engine running and taxiing) i could turn the propeller after shut off the hot engine only with extreme force. Starting the engine with the electric starter was not possible, to much friction. 1/2 h later after the engine was a little bit cooler everything was normal, not problems, easy to start. After I recognised this first, I flew the engine for further more 6 month without any problems.

So the procedure to measure the friction torque is useful like rotax explains at the cold engine but it is more important at the hot engine.

So perform the friction test at the cold and direct at the hot engine and keep an eye at the propeller pitch/max rpm which was setted at the past.

Yes, the crancase was changes in the meanwhile to impove this well known problem but first it is important how the engine was operated in the past. Not every engine was operated at to low rpm at WOT.

The reason for my case fretting which leads to the high friction torque was the to high pitch of the propeller, so the max. rpm at WOT was approx. at 4800 (approx. 4600 at take off). This leads to high forces at the cylinder walls and vibrations of the crankchase. This low rpm was given by the manufacturer of the plane for noise reasons.

Greetings

Thank You for the reply and information. Do you recall the number of hours on your engine when you first found the problem?

All Rotax engines made before 2006 were subject to this issue.  The 914 more than the 912 series.  Most of those occur under heavy load, such as over-pitch of the engines, and around 800 plus hours.  

Cheers

Dear Richard,

I bought the plane with its origin engine at approx 1650 h (operation h clock). But i guess in total it must be 1800+ h by later checking the documentation and the flight log. It was my first ROTAX so had no experience for this engine before. I knew for the 1200h TBO for this engine but many of us had the opinion this engine runs 2000 h and more.

I recognised the problem at approx 1750 h on the clock. In my oppinion, the hight friction at the hot engine must be ovious (its a slow moving prozess) at approx. 1500 h. For me it was not easy to find this out because the high friction was only if the engine was hot. So after landing there was no reason for a restart. I noted this first by turning the propeller a little bit for using the front fork to stear the plane after a flight into the hangar. But first i was not really afraid of it because i was not experienced.

Later at a regular checkflight with a FI he shut off the engine in flight for precisition landing. Perfect landing to full stop. Then i want to restart the engine at the middle of the runway for taxiing. The electric strater moved only a little bit like no battery power, so we pulled the plane by hand back to the hanger and wondered why the battery could run out so quickly for the few minutes into the pattern. 1/2h later i had full electric power means full starter rpm and the engine runs like before.

So i recognised i have a serious problem and I was deceived by the former owner.

6 Month later i installed a brand new engine and now i am happy because the plane itself was my dream and with a heard transplantation it is like new - only the bank account and the trust in sellers has been compromised.

Greetings

Thank You for taking the time to reply. Very much appreciated. This helps me decide what to.