mch

Finally engine checked, one general advice for MOGAS users Hi all, thanks for all the suggestions. I feel I should post the result of the engine check I did with a "real" aviation mechanic yesterday. About one month ago I flew the jab back to my home strip on a very warm day. This was the first flight after the reported problem (enigine loosing power and shaking rather violently) and during that flight the engine made no trouble. The check yesterday revealed two potential problem areas: 1. Compression on one cyl. (No.1 ) was sub par on leakage test. The cylinder blows slightly into the oil and also into the exhaust. The drop is not serious now but must be watched for further degradation. I have a hydraulic lifter engine and the lifters were OK. 2. I loose some oil in the right distributor. The leak is very small, so I did not see excessive oil consumption nor traces outside the distributor housing. I will have replaced the gasket. The oil leak could account for one ignition circuit failure if getting more serios. So since we did not find a real explanation I tend to accept the carb ice theory by now. After all I expected carb ice anyway and should have used carb heating in advance, not waiting for the symptom. All spark plugs (iridium type) were in very good order after 250+ hours, no signs of wrong mixture or lead dendrites. We replaced them anyway. One suggestion for MOGAS users as as side remark: I used a paper fuel filter. Since I plan to run on MOGAS again (last 25h AVGAS) the mechanic suggested strongly to replace it by a filter with a solid mesh. The reason he gave is this: If one gets by accident wet fuel one may not be able to drain it if the MOGAS has ethanol in it. The ethanol can absorb quite some water. That I knew. But the paper filter can get clogged by the water up to a point where it will starve the engine. This I did NOT know. We replaced the filter. Regards to all, Mike

Hi Andy and Jabby, I would also be very interested in the exact Matco part numbers. As for my experience, I can only speak for the 2 caliper solution. It does work well enough for me at the moment. However, I have the fortune of a 870 m asphalt home strip and when I go abroad I also select long asphalt strips. So I can let the Jab bleed off speed by air braking and the wheel brakes don't get much stress. But this summer (here it is summer) I would like to go to places with shorter grass strips and I suspect I will have to use the brakes more than in the past. Quite frankly I also have more confidence in the wheel assy from Matco than the original Jab ones. The previous owner has had a flat foot, I keep hearing that flat tyres are not that uncommon on Jabs. So if I replace the whole assy (beginning with the axle stub) with a Matco solution I think I'd feel somewhat better. But I also have to say that up to now I have had NO brake or tyre failure. Mike J400

Hi Alf & jetr, the carb icing was my first thought as well, but I did not realize it could build up without symptoms and then break loose like hell. If it has been so it will be difficult to proove. Yet it looks like a plausible explanation. In hindsight I should not have been prepared for icing, as I was, but used carb heat well in advance. The low rev of 2400 was due to an economy flight, I must someday change my needle to one that allows me to use more power at reasonable fuel flow.It's on the agenda. About rain & prop: Everytime I cross rain I check the prop afterwards for damage. None yet. Of course I do not look out for rain :) I'm living in the most rainy corner of Germany and it is quite frequent that we have local drizzle or showers here, but after 30 min of flight you are out of the bad weather. jetr: What do you mean by "the J400 leak in flight a bit"? Do you mean water can get into the tanks or something else? Anyway, since the engine ran smooth on the ground again I suspect that at least at the moment the prop is still OK (balance) and all cylinders are firing. But I have left the aircraft there without any checks, I will do all checks next week when I'm there again. Dexter & peterm: You both suggest carbon at the valve stems. I have never heard of that, I have heard of lead (AVGAS) at the valve stems, though. Since I am no motor expert, can you tell me more about how the carbon could have got there? The compression check is a good idea, I would have missed that! Mike

Hi all, on my last flight I encountered a serious engine problem. I was flying for 3h at that time without problems but mayby an anomaly. Since I don't know much about the different modes of failure I'd like to ask if anyone recognizes the symptoms. I was flying for 3h in moist air (but no rain). Almost all the time at about 2400 rpm, AVGAS, EGT at 680. Oil temp/press all the time 69/2.9, CHT about 120-130. I noticed at times that all of a sudden the EGT started to change in weird way. One side would go up (720+), the other down (630-). That resulted in a difference of 100 degrees while no other parameter changed. Lits/h the same, rpm the same, CHT and oil the same. This happened 3-4 times. I applied carb heat + some throttle play and everytime managed to get it back to both sides equal again at 680 EGT. Then, after 3h I started to get into rain. No problem, I flew the aircraft in rain, and heavier one, before. Temp was +10 degrees so I would not have been surprised about carb ice, I actually was prepared for that. Nothing happened for a while, though. Then, really ALL OF A SUDDEN, the engine began not only to run rough but began to shake violently and lost all power. I applied carb heat at once and the shaking would stop after some time (maybe 10s), so I thought, well, that was quick ice. But after some more seconds the same happened again, though of course carb heat was on still. The engine was close on stopping again, with some throttle play I got it running again. Since I did not know the cause of the problem I made an immediate safety landing. On the ground the engine ran again quite normal. I have not been at the aircraft again until now, since the airfield is 150km from my home base and I had to leave it there (in a hangar) to get back to work the next day. Now I'm wondering what could have happened and where to look for problems. Normally with carb ice the engine starts to loose power and begins to run rough in a more gentle manner, at least this is my experience with a C172. Carb heat removes the problem as long as it is applied (in icing condition). Here the drop and shake was absolutely sudden and really frigthening - I even thought of a missing propeller tip and an unbalanced momentum. I also do not understand why the problem reoccured with carb heat on. In the meantime I have thought about water in the fuel. I had drained before and no problems for 3h. I will check for water once I am at the aircraft again. Does anybody recognize this symptoms? What should I look for? Any explanation for the EGT mismatch, which I also encountered the first time at that flight? Maybe the same cause? Mike J400, Germany

Hi Diablo, you have do dismount the carb. The idle system consists of several very small boreholes in the main housing. These bypass the main air duct. The most effective way to clean these was for us this procedure: We removed the screw #7 (number of the screw in the explosion drawing of the carb). It is located on the bottom of the housing, very easy to find - made of brass. We found quite some dirt already there. Furthermore you can now easily check airflow in the idle system, because the boreholes pass the opening below that screw. Pour in some aceton or similar and then blow air into the opening. This presses the aceton through the boreholes and expels the dirt in there. For us that worked fine. We did have a compressor, which eased the task :) Before cleaning there was almost no airflow through the boreholes, afterwards one could blow through happily. But I think you can do the same with "mouth air pressure" also, it will probably take longer. I hope this solves your problem. Mike

Hi Ross and Lowflyer, at least for me that is true. I have used Mogas with up to 7.5% Ethanol (at least according to the fuel station at our field). There was no visible debris in the bowl, that one was perfectly clean. The material that blockes the idle system appeared to be some sort of mud. Of course it takes not a lot of a mud film with these tiny orifices to block them. Maybe the ethanol has washed out something from the fuel lines like water dissolves chalk. In that liquid form it could have passed the filted. Later, maybe when the engine is resting for days or a week, fuel evaporates in the idle sytem leaving that mud film. Like a coffee machine. But I don't know for sure. I'm going back to Avgas, anyway. Mike

Hi, took Geoff's advice and cleaned the carburetor today. The idle system was almost completely blocked. It was not a single piece of debris but sort of a greyish/white "mud". The other systems (choke and main) were clean. It will take some time until I can flytest the "new" carburetor again but I think this looks like a plausible reason. Will post one more reply when I know for sure that this was the cause. Mike

Hello all, it's me again (simply because I'm still on the learning curve with my J400). I seem to have a problem with my engine setup. This is what I can reproduce rather reliably: Procedure: 1. Engine running at some speed above idle (say 1000 RPM) 2. Plane moving at more than 10 kts 3. Throttle back to idle 4. Decelerate the plane rapidly Result: Engine experineces a serious RPM drop below normal idle, this can even stop the engine. I have first encounteres this behaviour when I decelerated from a speed taxi on the RWY (to get it cleared for the next plane). Today I experienced the same when I went to idle after the round out while landing. So this was a glider landing with the prop nicely but stationary in front of me :) My stationary idle is set at 900 RPM and there is no (real) way to overcome the idle stop, you would literally have to break something. Also the fuel pump was on while landing and carb heat applied until in final. I do not think that the engine starved for fuel, had icing in the carb or that I closed the throttle beyond the stop. Something else must happen systematically. I presume that the problem is that the prop acts as a "brake" when the plane decelerates quickly. This could force the engine below the "normal" RPM mark for a given power setting. The strange thing is that this *never* happened during my "GA career" with a C172. Has anybody experienced the same? Can I do something to avoid that by a carb setting? Of course I could learn to decelerate more slowly :) The engine restarts immediately (with the starter, of cousre), with NO change in power setting. This also indicates that it is not an idle throttle problem. Mike

Hi thebun 88, I was referring to Tomo, because he wrote: "which jabs do have a tendency sometimes on finals!!" So he thinks that the 3300 in the J400 discriminates indeed when deciding to stop. There could have been reasons for that, but I did not find evidence. I did read, however, in another thread about engines stopping when idling after landing. I think I must have at least some basic trust in an engine that it will run. I do go on top sometimes, I have been over the ocean with no land in gliding distance, I do cross mountaineous areas where finding an emergency spot for landing is sometimes a matter of luck and I have been flying in the night (the last one not in the J400). My current decision to go in low is a tradeoff. In HL I get everytime to the field an have, based on my current limited experience on the J400, a chance to produce a bad landing there. In LL I produce a gentle landing everytime but have a chance (engine!) not to get to the field. I see, however, that most of you here use the HL style with the Jab and with obviously no ill effects. So I may start to rework my technique once I feel more confident that I can handle the Jab in any configuration from almost empty to MTOW and from zero to full flaps. Mike

Hi Bruce, true enough. For me it's a risk trade-off. If I'm a mediocre HL (and I think, I am), I will one day misjudge the round out and do a hard landing. Not happened yet, but I feel I have potential there :/ So I trade off the risk of a worse than necessary landing against the risk of an engine failure on final. Mike

Hi Tomo, yes, those are the advantages of HL. I've not heard of engines stopping on final yet. In an older thread I have read about engines stopping when they should idle, but on final I'n not on idle yet. On the flare it would not matter much, except the embarrassement that you could not leave the RWY as fast as expected (when one has to track back). I'm not sure about the turbulence advantage, that probably depends on what the ground looks like. In my experience it is sometimes the other way round, especially a rougher wind can be quite calm once getting closer to the ground. I do understand the visibility advantage, but have a remark: 5cm of additional height on the seat made a WORLD of difference for me. I can now really float in the flare seeing the complete RWY. Only on touchdown, when the nose really goes up for a few seconds I'm out of sight, but this is a very short time. I then lower the nose again until I can see enough again or until the nose wheel slightly touches the RWY. I would not have thought before that 5cm would make such a difference. Mike

Hi all, since the thread about take off has evolved to landing, I'd like to ask for opinions on that as well. After all, my takeoff improved by your input. In my experience there are basically two approach styles which I'll call "highlanders" HL and "lowlanders" LL. Actually, the HL would be better called "steep descent lander" and the LL "flat descent lander", but HL and LL just sounds so nicely Scottish :). Anyway, a typical HL does this: - remain in circuit altitude up until the end of downwind - bleed off speed for first level of flaps until end of DW - set first stage on base, but basically keep altitude - set second stage on final, set approach speed, let the engine idle - therefore come in rather steeply - round out and by that loose 10-15 kts, now beeing at almost stall - let her sit down after only a very short remaining flare A LL is of this type: - prepare almost everything on the second half of DW - start to loose altitude when turning base, set second stage in base already - turn into final at not much more than 2/3 of circuit altitude - come in at about 3 degrees at approach speed, this requires some power left - round out and by that loose not enough speed to let her sit down immediately - let the engine idle while flaring at about 1-3 feet above the RWY - wait...stick back...wait...stick back...wait - let her sit down when speed has bled off with stick full back I have tried both and I feel a lot more comfortable as a LL. Of course I also have that habitude from the C172. Initially I had been warned that the J400 has a very long flare and therefore I expected to become a HL, but with full flaps at least my plane also bleeds of speed quite nicely in the flare. I do appreciate that the HL technique has a lot of advantages, like more obstacle clearance, secure landing even if the engine fails on final and a potentially shorter flare. However, I also feel that with a light aircraft you have to get that round out from steep descent to almost sit down at exactly the correct altitude. If you do it too late, well, you sit down harder that you planned. If you do it too early you end up in the air at 5 feet with no speed left - might also result in a harder than planned landing. The LL round out is, for me, much more relaxed. I usually reduce the remaining power not before I'm beginning the round out, sometimes even a bit later, i.e. when beginning the flare. Any opinions? Have some of you started out as LL and, when becoming more familiar with the J400, gone to HL style? Mike

Full trim back: same here with only the front seats loaded. To remain within W/B limits I have about 15kg in the "baggage compartment" behind the rear seats. In that configuration full back trim results in the approach you describe. However, for me that type of approach feels to steep, remember, I come from the tin GA planes. So I prefer a 3 degrees descent which requires some power on the final, let's say something in the order of 1400 rpm. I just feel better with that type of approach as the round out is very smooth then with less change of attitude. When the flare peters out she just sits down on the mains gently. It will take more runway, I concede. Here in Germany we have a lot of tarmac runways, usually in the 700m+ category, so this is no problem. With a 500m or less strip your steeper approach technique is probably better and also with obstacles in the final. Mike

Much better now Thanks to all, all of you have advised to lessen pressure on the nosewheel during takeoff and today I tried that. The takeoff run is much better now, in fact, there is no "nervousness" left now. I still don't lift off the nosewheel ASAP because I feel that the aircraft has not enough speed at that point to be fully controlled by the rudder. I tried that also in calm wind condition and control was too soft for me initially and my limited experience. With more wind or a sudden gust it might be hard to keep her on track. However, with now neutral trim and almost no elevator input she lifts the nose at about 45 and then flies off gently at 55 or so while still accelerating fast. Computed stall speed in this configuration is about 43. There is no jitter in the wheel left (at least I could not feel it) and I feel quite happy now. Thanks a lot! Mike