facthunter Posted September 18, 2015 Share Posted September 18, 2015 Over the years everything possible has been tried with valve seat inserts. They threaded them, cast them in, rolled an extension into a recess. etc. The bronze heads on the DH Gipsy 1 series were considered unsafe to insert when I was involved with them, but I think are done satisfactorily now. The biggest improve as far as I can see is the newer seat alloys that don't shrink with heat as much as the older ones did. What keeps them in is the interference fit and that needs good strong metal around the seat for support, not some soft stuff, like your head becomes once it goes over about 220degrees C. . The best way to put the inserts in is cryogenic (Very cool to shrink metal) Liquid nitrogen, with the right interference and good finish so the heat transfers out of the seat. The seat shouldn't be too thick or it's too rigid to compress a bit, which helps it stay there. It's a process that needs good quality control , or you will have failures..Nev 1 Link to comment Share on other sites More sharing options...
Oscar Posted September 18, 2015 Share Posted September 18, 2015 Oscar, I don't agree. Harmonics is length and mass to stiffness considerations, None of which you are correcting or measuring. It's not practical to rule out individual component balance. I did say if everything runs true. Balancing an assembly means you must continue to do it that way. as only the final outcome is assessed. Any change to the position of components with your method is bound to result in an unbalance.(in principle) Nev Nev - it's length/mass/stiffness and excitation. The swinging crankshaft counterweights on Lycomings/Continentals ( I am not sufficiently conversant with either of them to know) are intended to negate the harmonics problems. If it were as simple as just getting all the bits hanging off the crankshaft within a close tolerance weight, the swinging balance weights would not be necessary. Link to comment Share on other sites More sharing options...
facthunter Posted September 18, 2015 Share Posted September 18, 2015 Another factor entirely. The excitation problem is the harmonic frequency that becomes critical when undamped.. Neither your method or my suggestion address harmonics which are a totally different consideration. You are unlikely to feel harmonics as a vibration as it's a twisting of the crankshaft/drive assembly, and it may impose failure loads on the parts affected if operated at the critical RPM's..You will feel out of balance on any rotating parts not balanced and the engine may shake but it doesn't load up the internals significantly, as the unbalance forces are of a low order compared with the size of the forces occurring with the operating loads internally. Nev Link to comment Share on other sites More sharing options...
deadstick Posted September 18, 2015 Share Posted September 18, 2015 Based on my experience balancing helicopter rotor heads and my Uni days, a harmonics in reference to balance is represented as an integer of that being referenced. For example a vibration/ balance run would involve me setting up the Vibro gear to measure a spectrum spread from the slowest rotational frequency to the fastest. The rotor head would spin at 203 rpm of which being the reference it's called a 1R or 1 per Revolution the next harmonic from that reference would be 406 RPM and be a 2R or 2 per revolution and so on and so on. A print out of the complete spectrum would show differing harmonics of all rotating components, say for instance I had an IPS spike at a set frequency, a quick glance at the known rotating speed chart of components allows you to ID the failing component. A few data inputs and you could accurately predict which blades required a track adjustment to effect a better balance solution. Link to comment Share on other sites More sharing options...
deadstick Posted September 18, 2015 Share Posted September 18, 2015 Awe aren't confusing harmonics with resonant frequency here are we? Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 18, 2015 Share Posted September 18, 2015 ...The best way to put the inserts in is cryogenic (Very cool to shrink metal) Liquid nitrogen, with the right interference and good finish so the heat transfers out of the seat. The seat shouldn't be too thick or it's too rigid to compress a bit, which helps it stay there. It's a process that needs good quality control , or you will have failures..Nev This level of engineering is beyond my ken, but it fascinates me; I feel compelled to tell of a related experience. In 1975 a valve guide failed on my Ducati as we rode into Melbourne. I kept going until we got to my brother's place. (The resulting smoke plume caused traffic chaos.) I purchased a new valve guide and seal, which we put in the freezer. We had a beer or three while we assessed the situation. Using only the standard Ducati tools I removed the head (no head gasket). We put it in the oven. After another beer or two we removed the old guide, tapped in the new (cold) one and fitted the oil seal. After reassembling the valve gear, big brother used toothpaste to lap in the valve. Compression tested at 175psi and it ran like a locomotive for years thereafter. 5 Link to comment Share on other sites More sharing options...
facthunter Posted September 18, 2015 Share Posted September 18, 2015 What it goes Toot Toot and steam comes out every where? Nev 1 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 18, 2015 Share Posted September 18, 2015 Only when I flog it on a cold morning. 1 Link to comment Share on other sites More sharing options...
facthunter Posted September 18, 2015 Share Posted September 18, 2015 Then it's an Icycle. Nev Link to comment Share on other sites More sharing options...
fly_tornado Posted October 25, 2015 Share Posted October 25, 2015 another Jabiru powered Tornado bite the dust: from Tim on the Tornado list. I had another in-flight Jabiru engine failure (my second Jab) which put me and my plane up against a prison fence last week. No injuries except my feelings. The first engine that failed only had 275 hours on it and this latest one had only 118 hours. Both ingested an intake valve in flight. Needless to say, I am finished with Jabiru engines forever. My plane sustained substantial damage and I'm not going to repair it. 1 Link to comment Share on other sites More sharing options...
facthunter Posted October 25, 2015 Share Posted October 25, 2015 Who has ever recommended a Jabiru engine in a pusher aircraft? Nev 1 Link to comment Share on other sites More sharing options...
Nobody Posted October 25, 2015 Share Posted October 25, 2015 Who has ever recommended a Jabiru engine in a pusher aircraft? Nev Jabiru do. See here: http://jabiru.net.au/engines Link to comment Share on other sites More sharing options...
facthunter Posted October 25, 2015 Share Posted October 25, 2015 Yes a reference to ducts being available for pusher installations. I wouldn't see that as a "real" recommendation as to it's suitability, since it has cooling problems with many tractor installations. Nev Link to comment Share on other sites More sharing options...
fly_tornado Posted October 25, 2015 Share Posted October 25, 2015 there doesn't appear to be any issue with the Jabiru overheating in the Tornado, as long as you don't do any extended ground running its all good. Link to comment Share on other sites More sharing options...
facthunter Posted October 26, 2015 Share Posted October 26, 2015 Be the only engine that ever cooled better in a pusher. VERY unlikely I would think. Need some temps to prove it. Nev Link to comment Share on other sites More sharing options...
Russ Posted October 26, 2015 Share Posted October 26, 2015 500+ hrs in me jab...( hyd 2200 ) hasn't even sneezed. Done many extended trips, stinking hot ambients at times ( 40+ ) monitor CHT, fly accordingly......( step climb etc ) Run avgas, dosed with Moreys, modify lower engine cowl lip. Just these 3 things seem to aid matters.....IMHO.........BUT, waiting, waiting, for a CAE cert engine. Link to comment Share on other sites More sharing options...
fly_tornado Posted October 26, 2015 Share Posted October 26, 2015 he has had two of them fail, I warned him after the first one. 1 Link to comment Share on other sites More sharing options...
deadstick Posted October 26, 2015 Share Posted October 26, 2015 Sounds like heat related, are jabiru offering any warranty? Link to comment Share on other sites More sharing options...
chippy061 Posted October 26, 2015 Share Posted October 26, 2015 I hope you buy that fella at Bordertown a drink Bruce:wink: I know this post is below the belt and is not really decent but I do have a weird sense of humour (some people say I have no sense of humour, actually some say I have no sense!) I really am a friendly person and all my digging is meant to be friendly ribbing, I have friends that own jabs. Also I don't want to stop people posting about problems so please don't take this too much to heart. I had a through bolt failure on my 914 that I posted about on here, so we aren't perfect either. Anyway so you get the point I sort of feel a little guilty about this post but I just couldn't resist. Link to comment Share on other sites More sharing options...
chippy061 Posted October 26, 2015 Share Posted October 26, 2015 the Jabiru hits the magic 500 hour mark and automatically wants to migrate to bundaberg for a 3 week holiday 1 Link to comment Share on other sites More sharing options...
fly_tornado Posted October 26, 2015 Share Posted October 26, 2015 Tim has cut his losses with the Jabiru due to writing off his airframe. Link to comment Share on other sites More sharing options...
chippy061 Posted October 26, 2015 Share Posted October 26, 2015 L Link to comment Share on other sites More sharing options...
jetjr Posted October 26, 2015 Share Posted October 26, 2015 What temps did his monitoring system indicate? What model engine? Sure sounds like an install issue with two similar failures in the one airframe 1 1 Link to comment Share on other sites More sharing options...
Dieselten Posted October 26, 2015 Share Posted October 26, 2015 Jabiru specifically advise against the use of any upper cylinder lubricant in their engines. If your engine is under warranty, use of an UCL would most likely allow Jabiru to avoid and responsibiilty under that warranty should it be invoked. If you are flying a 19-registered Jabiru-powered airframe, do what you like, run it on what you like and live with the consequences - unless your engine is still under Jabiru's warranty, in which case you have to stick to what Jabiru recommend. But if you fly a Jabiru-engined 24-registered aircraft, you are bound to follow Jabiru's recommendations - and prohibitions - to the letter, regardless of whether you think they are the right thing to do or not. There is no choice. I know there are people out there who probably know more about Jabiru engines than Jabiru do themselves, but legally you must stick with what the manufacturer says you can do or use - and nothing else. Otherwise you have become an unpaid test-pilot. Link to comment Share on other sites More sharing options...
facthunter Posted October 26, 2015 Share Posted October 26, 2015 If some people know more about engines (Jabiru is an engine) than Jabiru you might be less of a test pilot,( Or more at risk pilot,) than doing only what they allow. That's about certification and factory warrantee, Safety is another matter. If people fiddle they should make sure they.know what they are doing. Jabiru have little control over how their engines are operated, and installed. Nev 2 Link to comment Share on other sites More sharing options...
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