Johann Posted July 13, 2012 Share Posted July 13, 2012 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. 1 Link to comment Share on other sites More sharing options...
Pilot Pete Posted July 13, 2012 Share Posted July 13, 2012 Welcome Johann to the best Recreational Fliers Forum on the planet.(i'm a little biased here) I'm sure that given a little time and reserch of previous posts and members input you will hopefully find a solution to your problem. Link to comment Share on other sites More sharing options...
kaz3g Posted July 13, 2012 Share Posted July 13, 2012 Hi, I live in Iceland and fly the Zenith 701 with a Rotax 912 ul 80 hp. engine.... Hell Johann and welcome. When I saw your topic heading I thought you must have been a fellow Victorian (south-east corner of Australia)! I was speaking to two people just the other day who are heading to Iceland on holidays. They are really keen and said it is a very popular tourist destination now. Anyway, you are very welcome here and I hope you enjoy the camaraderie of a whole bunch of flying fanatics. Kaz 1 Link to comment Share on other sites More sharing options...
Herm Posted July 13, 2012 Share Posted July 13, 2012 Welcome! I would love to be flying around your part of the world. Was high up in the arctic circle last year. Loved the cold and the views were out of this world. Not to mention the aurora that I went thier to see. I am sure you have the same sort of thing where you are located... Took some nice pictures and placed them on my Astro Web Site http://www.scopepics.wordpress.com Regards Mardy Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted July 13, 2012 Share Posted July 13, 2012 Hi johann, Welcome to the forum. Nice looking aircraft you have there, must be very scenic to fly around Iceland between Volcanic eruptions and ash events..! I do a lot of maintenance on 912s....what is the nature of your problem ?........................................................Cheers ............................Maj... Link to comment Share on other sites More sharing options...
Johann Posted July 13, 2012 Author Share Posted July 13, 2012 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. 1 Link to comment Share on other sites More sharing options...
eightyknots Posted July 24, 2012 Share Posted July 24, 2012 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. Welcome to the forum. It will be nice to hear of your flying experiences. Perhaps you have some nice photos of Iceland from the air? Link to comment Share on other sites More sharing options...
Flying Librarian Posted July 25, 2012 Share Posted July 25, 2012 G'day Johann, Welcome to the site.This website http://www.homebuiltairplanes.com/forums/general-experimental-aviation-questions/5292-help-vibration.html suggests that it could be a spark plug issue. I have no experience with Rotax, but my old falcon ute had problems that I was sure was carb related. Turned out to be high tension leads. Hope you get to the bottom of the problem. Flying Librarian Link to comment Share on other sites More sharing options...
Kyle Communications Posted July 25, 2012 Share Posted July 25, 2012 Has the prop been balanced?...if not a vibration can come in at a specific rpm range Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted July 25, 2012 Share Posted July 25, 2012 Johann, Don't know how many hours on your friends 912ul, or if it has been involved in a prop-strike or crash. Vibrations in the rev area you mention are not common, and many possible causes come to mind. If there has been a prop-strike or crash, you may want to remove the foward gear-box casing and check the large cog for any tooth damage. Whilst in there you could feel for damage to the fwd engine bearing, and prop shaft bearing. The fwd Gbox casing is a very tight fit, and there is a Rotax puller for removing it. You can do it without the puller, but you must be very carefull not to damage the mating surfaces. Is his prop balanced and tracked ?......Has he got the little rubber O-rings on top of the jet needle clip, in the carbs, they are required........Has he got a non-standard carb equilazation-tube set up, on the carbs, the little clear plastic tubes that are tucked under the float-bowl clips....Has he double checked that his mechanical adjustments are by the book on each carb.......has he checked his carb-mount rubbers for cracks ?..inside and out....is he running his elect fuel-boost pump 100% of the time, and over-pressurizing his carbs in flight (max pres 5.8 psi)....are his spark-plugs gapped correctly (.024 thou is good)....has he tried a new set of plugs to see if the problem remains ?...are both his carbs mounted perfectly vertical (when viewed from front) as per Rotax manual....are the air inlets (filters) the same set-up on each carb........are both his throttle cables running freely throughout their full movement.....are both carb supply fuel-lines the same lenght after they split at the T ?......The carb equalization clear tubes out the side of the carbs cause a lot of dramas if they are not standard, and especially if they are Td together and routed overboard (neg pressure)...also check that the carb main jets are nice and tight, and that fuel bowl cork gasket is seated in it's groove correctly....ensure visually that the chokes (enrichers) are coming all the way off..........Also pop off each valve cover and check all collets on top of valve springs for cracks, there was an AD pertaining to the earlier collets on the early 80 hp engines, and they needed to be upgraded......................................good hunting !...................................................Cheers Maj.... Link to comment Share on other sites More sharing options...
J170 Owner Posted July 25, 2012 Share Posted July 25, 2012 If we get the long hot dry summer that has been suggested then move over, because I'll be heading your way Johann. Link to comment Share on other sites More sharing options...
Old Koreelah Posted July 26, 2012 Share Posted July 26, 2012 A belated welcome, Johann. There seem to be quite a few intrepid aviators in your country. I read of a bunch of home-built Jodels being flown from Iceland to Oshkosh, presumably via Greenland and Labrador. Makes crossing the Tasman Sea to NZ look like a short hop! 2 Link to comment Share on other sites More sharing options...
Johann Posted July 29, 2012 Author Share Posted July 29, 2012 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. Link to comment Share on other sites More sharing options...
Johann Posted July 29, 2012 Author Share Posted July 29, 2012 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/ 1 Link to comment Share on other sites More sharing options...
Johann Posted July 29, 2012 Author Share Posted July 29, 2012 If we get the long hot dry summer that has been suggested then move over, because I'll be heading your way Johann. 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. Link to comment Share on other sites More sharing options...
Johann Posted July 29, 2012 Author Share Posted July 29, 2012 Has the prop been balanced?...if not a vibration can come in at a specific rpm range 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, Link to comment Share on other sites More sharing options...
Old Koreelah Posted July 30, 2012 Share Posted July 30, 2012 http://mbl.is/frettir/innlent/2012/07/28/bjorgudu_hvolum_sem_satu_fastir/ Thanks for the link, Johann. They look like pilot whales. Its a mystery why they beach. In 1980 I helped save about 43 of them in Macquarie Harbour, Tasmania. Beautiful animals. They have the teeth and tail strength to do real damage, yet these wild animals were so gentle to us humans climbing all over them in the shallow water. We eventually found that if a key member of the pod was harnessed and towed out to sea, a co-ordinated effort could get the others to follow. A few which were too exhausted to follow were put out of their misery so they would not call the others back to the beach. Link to comment Share on other sites More sharing options...
Johann Posted August 2, 2012 Author Share Posted August 2, 2012 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. 3 Link to comment Share on other sites More sharing options...
Johann Posted August 2, 2012 Author Share Posted August 2, 2012 Johann, Don't know how many hours on your friends 912ul, or if it has been involved in a prop-strike or crash. Vibrations in the rev area you mention are not common, and many possible causes come to mind. If there has been a prop-strike or crash, you may want to remove the foward gear-box casing and check the large cog for any tooth damage. Whilst in there you could feel for damage to the fwd engine bearing, and prop shaft bearing. The fwd Gbox casing is a very tight fit, and there is a Rotax puller for removing it. You can do it without the puller, but you must be very carefull not to damage the mating surfaces.Is his prop balanced and tracked ?......Has he got the little rubber O-rings on top of the jet needle clip, in the carbs, they are required........Has he got a non-standard carb equilazation-tube set up, on the carbs, the little clear plastic tubes that are tucked under the float-bowl clips....Has he double checked that his mechanical adjustments are by the book on each carb.......has he checked his carb-mount rubbers for cracks ?..inside and out....is he running his elect fuel-boost pump 100% of the time, and over-pressurizing his carbs in flight (max pres 5.8 psi)....are his spark-plugs gapped correctly (.024 thou is good)....has he tried a new set of plugs to see if the problem remains ?...are both his carbs mounted perfectly vertical (when viewed from front) as per Rotax manual....are the air inlets (filters) the same set-up on each carb........are both his throttle cables running freely throughout their full movement.....are both carb supply fuel-lines the same lenght after they split at the T ?......The carb equalization clear tubes out the side of the carbs cause a lot of dramas if they are not standard, and especially if they are Td together and routed overboard (neg pressure)...also check that the carb main jets are nice and tight, and that fuel bowl cork gasket is seated in it's groove correctly....ensure visually that the chokes (enrichers) are coming all the way off..........Also pop off each valve cover and check all collets on top of valve springs for cracks, there was an AD pertaining to the earlier collets on the early 80 hp engines, and they needed to be upgraded......................................good hunting !...................................................Cheers Maj.... 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. Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted August 2, 2012 Share Posted August 2, 2012 You mentioned earlier that it appeared the engine had had a prop strike ?.....from your work in the gearbox. Sounding to me like there could be crankshaft damage (bent/damaged) or even possibly a bent rod or two. Being that your ignition rotor is attached to the rear of the crank, there may be a runout problem there, which may effect the air gap on the ign triggers, causing a problem at a particular rpm. To check for bent rods you'll need to somehow rig up a dial-indicator into a spark-plug hole, down onto the piston at absolute top dead center. The distance to the top of all the pistons should all be pretty much the same. A major difference may indicate a bent rod. Either of these problems also indicate serious internal problems which could effect bearings etc., and may be reason enough to remove the engine from service...this falls into the catogory of unusual damage relating to the prop-strike..........................................................................Maj... Link to comment Share on other sites More sharing options...
Johann Posted August 2, 2012 Author Share Posted August 2, 2012 You mentioned earlier that it appeared the engine had had a prop strike ?.....from your work in the gearbox. Sounding to me like there could be crankshaft damage (bent/damaged) or even possibly a bent rod or two. Being that your ignition rotor is attached to the rear of the crank, there may be a runout problem there, which may effect the air gap on the ign triggers, causing a problem at a particular rpm. To check for bent rods you'll need to somehow rig up a dial-indicator into a spark-plug hole, down onto the piston at absolute top dead center. The distance to the top of all the pistons should all be pretty much the same. A major difference may indicate a bent rod.Either of these problems also indicate serious internal problems which could effect bearings etc., and may be reason enough to remove the engine from service...this falls into the catogory of unusual damage relating to the prop-strike..........................................................................Maj... 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. Link to comment Share on other sites More sharing options...
Old Koreelah Posted August 2, 2012 Share Posted August 2, 2012 What puzzles us is that sometimes everything seems to be working fine, and then suddenly we are back to the same problem. Johann G. Just a thought, Johann, could there be something loose in the driveline? I have a large home-made spinner. I installed a length of chrome-moly tubing through the prop centre and out through the tip to keep it centred. When having my prop dynamically balanced last year the job took much longer than expected. It turns out that this length of steel tubing had worn the holes larger and was moving about 1 mm off centre, causing variable vibration. Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted August 2, 2012 Share Posted August 2, 2012 Johann, Yes I'm sort of thinking something may be amiss back in the ignition area somehow, have you checked all the airgaps on the pickups as per Rotax ?..........................................................................Maj... Link to comment Share on other sites More sharing options...
Johann Posted August 3, 2012 Author Share Posted August 3, 2012 Just a thought, Johann, could there be something loose in the driveline?I have a large home-made spinner. I installed a length of chrome-moly tubing through the prop centre and out through the tip to keep it centred. When having my prop dynamically balanced last year the job took much longer than expected. It turns out that this length of steel tubing had worn the holes larger and was moving about 1 mm off centre, causing variable vibration. 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. Link to comment Share on other sites More sharing options...
Johann Posted August 3, 2012 Author Share Posted August 3, 2012 Johann, Yes I'm sort of thinking something may be amiss back in the ignition area somehow, have you checked all the airgaps on the pickups as per Rotax ?..........................................................................Maj... 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. Link to comment Share on other sites More sharing options...
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