Johann

Hello Maj, Yes, my friend removed the engine to inspect that area and clean all the oil residue and he inspected the gap. He tells me that it was according to Rotax specs. He did not check the rear crank for out of round measurement. We will do that after the weekend. Will keep you posted. Best regards, Johann G.

We do not think that anything could be out of the ordinary in the driveline. The prop is new and has been balanced and track checked. The gear box has now been inspected and the bearing replaced. The shims removed from the gearbox that should not have been there in the first place. If there would be any misbalance, it would show up sooner and extra vibration at full throttle. But the vibration seems to be within a certain rpm only??? Thank you for your input and advice. Best wishes, Johann G.

Thank you very much Maj, for your advice. This explanation and the possible cause to the problem is very good. I will have my friend do the measurement to the TDC. What puzzles us is that sometimes everything seems to be working fine, and then suddenly we are back to the same problem. He did a thorough measurement to the crankshaft when he removed the gear box. No damage there. I do remember when he received the plane, there was some oil contamination around the ignition rotor area. That could be the cause of a bent crank on that side and a damaged seal. Something to inspect also. We will do some work on these items and keep you advised. Thanks again. Best wishes, Johann G.

Hello Maj. My friend has been working on his engine problem and he has replace the bearing in the gearbox and inspected and measured everything. No change. I noticed this item in you letter: "are both carb supply fuel-lines the same lenght after they split at the T" ? This is not something we have checked and did not know if it mattered that much. The engine is running very smooth at idle and up to 3500-4000 rpm and then starts to shake everything or go out of balance. Then everything works fine around 5000 and up. Also when the throttle is reduced back through the 4000 range rpm, everything starts to shake and rattle. The magnetos have been run individually left only and right only an no change. If the triggers are the problem, they should be isolated on each side by changing magnetos, right???? Everything indicates that the jet needle and needle jet are the cause, but this has been inspected and checked and adjusted according to the Rotax manual. Even has replaced the carbs and still shaking at that rpm. Even so that the new carbs have overfilled, and not just on the right or left, but randomly, no consistency. If there is air in the fuel line, it should run rough all the time, not only around 4000 rpm. Grounding was one thing we thought of, but that seems to be working and should not only cause problems around 4000 rpm. Mag drops are the same on both magnetos, around 100 rpm. We would appreciate any help if you see something we are missing. I know it is difficult to cure a problem like this without inspecting and testing at the location, but anyone that has heard or knows of a situation like this could maybe share their knowledge. Best regards from Iceland.

Hello to all from Iceland. I wanted to shear with you some flying photos and videos from Iceland. This is a link to one of our ultralight members photo page. He has been taking photos and videos of Iceland from his ultralight. Hope you enjoy it.

Hello Kyle, the prop is new and has been balanced, tracked and tested. Runs great until this vibration starts at only around 4500 rpm. We are sure that it is only the gear box. Thank you for you input. Best regards,

Hello J170 owner. Let me know when you arrive. I will pick you up at the airport. Show you the sites in a Zenith 701.

I promised to send you some pictures from Iceland. Here is a photo of my friend in a Rans 10 overflying some whales that were seen just out of the coast of my town. Here is a link of the whales when they swam to the shore and people tried to help them out again. Sorry the story is in Icelandic. But you will see what i mean. http://mbl.is/frettir/innlent/2012/07/28/bjorgudu_hvolum_sem_satu_fastir/

Hello all and Maj, thank you for a very thorough list of things to check on the Rotax engine setup. My friend just tore up the gear box and it does show sings of a prop strike. The main bearing is worn and the bolts that hold the bearing have some extra shims under the bolts that are not supposed to be in a gear box. Other signs of a prop strike are visible. I have added two photos of the bolts and shims and the wearing of the "clutch". He will be replacing the bearing and removing the shims, using thread lock instead. He hopes to resolve the problem with a new bearing. All other items Maj has mentioned have been checked and replaced when needed. This is a three year process and we hope it is reaching its conclusion. I will keep you posted on the result.

Just bragging at an airshow in Reykjavik, Iceland.

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Hello all. Nice to receive such a warm welcome. Maj, the problem my friend has is very puzzling and has been around since he bought the plane three years ago. It is a vibration around the 4000-4500 rpm. We know it is the jet needle- needle jet region of the carbs, but all that has been thoroughly checked, adjusted and re-adjusted many times. Carbs balanced many times. Here is what has been done: Redone all the fuel system with a new fuel pump. Replaced the carbs, new prop installed and adjusted, tightened the motor mounts and shortened the spacers as recommended by Kitfox. Everything in the setup of the engine is according to Rotax instructions. The only thing we can think of next is to check if the engine has an out of place camshaft or a bad gearbox. After that we are out of ideas.

Hi, I live in Iceland and fly the Zenith 701 with a Rotax 912 ul 80 hp. engine. I have been building ultralights since 1994, not many only 3, and restored one. Built two Kolb Firestars II, rebuilt a Phantom ultralight and built the Zenith 701 called Joeing 701. Flew it first 2.july 2005. Have only flown 170 hrs. since then. It is a dream to fly and maybe that is the reason I have stopped building and enjoy the flying instead. Stumbled upon this site when trying to solve a vibration problem in a Rotax 912 ul which is mounted on a friends Kitfox. Hope to find some solution soon. Glad to be a part of this international community of recreational flyers. When it comes to Rotax maintenance, Iceland is very isolated place and all help must come from the internet. Hope I can contribute to the forum one day with my experience of problem solving and flying.