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Could it be safer to *not* replace Rotax hoses after five years and/or overhaul at 2000 hours?


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Yep, spacey, I have done exactly that with fan belts. You take off the old one to replace it with a new one and then you wonder how long the old one  would have gone for...  possibly years. So instead of putting it in the bin you carry it as a spare.

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Beware of statistics. Not doing replacement as being safer is ridiculous. Things used to be test flown. Cost has stopped that. IF a maintenance process can cause a safety concern adjust the process to

While I agree that the chances of powerplant problems increase after maintenance, it is also a comparable point that rubber components have a higher failure rate after a few years.   Rubber

come on 5 years or 2000 hours isnt much to ask.  

17 minutes ago, Bruce Tuncks said:

Yep, spacey, I have done exactly that with fan belts. You take off the old one to replace it with a new one and then you wonder how long the old one  would have gone for...  possibly years. So instead of putting it in the bin you carry it as a spare.

As a lone expedition 4x4 traveller for nearly all my life, I always did scheduled repairs to major drive line components that if they failed, would leave me stranded.

Other parts I considered as consumables were replaced based on time/mileage.

My schedule has worked for over 50 years.   But then I have always owned electrically prehistoric vehicles 🙂

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I agree  !.

BUT

l did all that, then had a front C V joint went at the top of Australia, 

Too much sand getting over those dunes to the East coast beach,

Great fun !. New replacement at Bamiga.

spacesailor

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You have to remember that Waddingtons maintenance re-jigging to improve reliability, was done during WW2. And the major problem he found, was that the planned maintenance schedules as laid out by the aircraft manufacturer, were causing a lowering of reliability and more downtime.

 

This was simply due to the fact that during WW2, many components had to be dismantled to inspect their condition - despite the component still performing admirably and showing minimal wear when dismantled.

 

As a result, this unnecessary regular dismantling led to an increase in component failures - largely due to them being disturbed, and no doubt also due to the pressure of wartime causing assembly errors.

Assembly procedures in WW2 were also not as refined as they are today, with a lot of haphazard work being carried out with a lack of regulated procedures - and also aircraft being cannibalised for parts.

 

As a result, "on-condition" became the byword for many aircraft components. If it was working well and hadn't done huge hours, it was better to leave it alone.

Today, we have a lot more refined testing and checking techniques available to us to keep an eye on component condition. 

 

I don't have a problem with regular rubber component replacement on aircraft. One, it's cheap to do so, and just may save your skin. Two, rubber components are generally easy to get at and replace, it's not like they're buried inside the engine. And three - rubber components are the fastest degrading item in the power unit, and they suffer adversely from heat and cold cycles, exposure to UV light and ozone, and chemicals in the cooling system (if the engine is water-cooled).

 

Even in a road vehicle, a ruptured hose can result in catastrophic engine damage if the driver isn't right on the ball - and even then, good drivers still get caught with cooked engines, and blown head gaskets, and cracked/warped cylinder heads - and "dusted" engines.

 

https://blog.aopa.org/aopa/2014/01/14/the-waddington-effect/

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It's not quite that simple Onetrack. Waddington's stuff was top secret, and it was the 1970's fuel crisis which led to the rediscovery of reliability centered maintenance. This rediscovery was quite independent of Waddington. I would guess that his work is still unknown to our airforce.

But I do have to say that in looking through the Jabiru maintenance schedules, I cannot find much unnecessary stuff, and this supports your argument. Maybe replacement of filters and spark plugs, but as stated earlier, the factory has little choice but to assume the worst possible operating conditions.

Getting back to rubber hoses,  I personally have replaced them as per the official schedule, but I do think this is too often as there has never been any sign of deterioration in the old ones. 4 years is considered "often" for automotive stuff, which usually lasts ten years.    The same goes for the filters and spark plugs. Jabiru do give a warning about getting oil on the new hose-joint and thus making the new hose more likely to blow off.  Yes this stuff is cheap for Jabirus, but costs thousands for Rotaxes.

There was a car ( I think a mini ) that had a warning light for oil-filter replacement. This light was controlled by a differential pressure switch and the filters lasted years and years. My guess is that the filter-makers persuaded the carmakers to stop fitting this warning light.

 

 

 

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Aero parts are not made oversize or they would be too heavy. Very few war time planes did high  hours nor did the pilots Military rated engines had much lower service lives than much the same motor in a civvie plane as it was de re-rated considerably. Nev

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I remember the English railway, going ' maitainance free ' only doing ' oil testing ' .

After which !, who knows what they did.

spcesailor

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Wow spacey, those railway guys took it too far I reckon.  But oil-testing is an example of how the newer maintenance systems are just as rigorous as the old ideas were. Mike Busch uses oil analysis to detect aero engine problems a long time before any symptoms show up say on a leakdown test.

Alas, Jabiru engines do not have the database to use oil analysis, or so I have been told.

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In my limited understanding of automotive "oil analysis" it is probably more about building a "picture" over time, than a one off diagnostic health check. By this I mean - the analysis must become a routine part of the service of the machine. A history  can then be reviewed at each analysis and 'wear" & contamination trends established. Over time it may be possible to advise for shorter/longer oil service intervals and also to project forward (given a consistent duty pattern) when the machine should be removed from service for either replacement or reconditioning.

 

I would guess that the greatest benefit is where a fleet of machines is being so monitored - giving a true picture of normal wear/tear and the abnormal signs of impending failure.

 

Oil analysis, by a reputable service provider, is not cheap so most of us go with the manufactures service intervals and estimated in service/duty span for components and total life.

 

If concerned - a cheap reassurance is to halve the manufactures oil service interval. eg Rotax 100 hr oil change, for engines run on ULP, can be reduced to 50 hrs - no need to change oil filter at 50 hrs. (this is what I do)

Edited by skippydiesel
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I had a BMW HP2 Enduro motorcycle and some had rear drive bearing failures with sometimes catastrophic results.  I used Hastings Deering oil analysis service and sampled every 3000km.  There reports used to include information from previous testing so you got an indication if something was going downhill.

https://sos.hastingsdeering.com.au/oil/HDLabServices/OilAnalysis.html

 

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OIL Analysis.

the public ' buyer,s of second parts were up in arms over that idea, as there were No chance of having a reasonable chance of a GOOD buy from them.

Every thing was a disaster at the immediate future. not just a strip and rebuild but whole engine replacement.  Nothing to save as it was worn completely out.

Train engines are run at optimal efficiency and can drop their oil on the go whilst replenishing at the same time. ( nope don,t know how, but oil on the tracks helps keep weeds down).

spacesailor

Edited by spacesailor
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On 27/06/2021 at 4:13 PM, spacesailor said:

Maintenance! .

The 4X4 clubs tell everyone to carry spare parts AND to replace parts before going on long offroad trips.

My thought is, if replacing perfectly good parts, why not csrry them as spares, after all they were good Before having to remove them. 

spacesailor

Extra weight. 

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On 27/06/2021 at 2:40 PM, facthunter said:

Just read carefully what I say thanks and don't put words into my mouth. Of course the first  flight after a plane has been on the ground a long while is often quite dangerous because the system checks are not adequate. Sub assemblies should be bench tested not tested on the plane. IF corners are cut there will be plenty of unreliability.. and there often is due to being pressured into getting the plane back in the air and pirating bits off other planes or a quick fix..  with a swapped bit that looks ok.

  Many of these "revelations "  may make good reading but a few I've read are pretty questionable. and I've had inflight failures I didn't cause and done test flying where things failed. IF better maintenance had been done they would not have failed, but it's It's a quantum leap of misplaced logic to take that as do less maintenance and you have less failures. You fix your maintenance set ups faults, like documentation and shift change over procedures and account for every tool used and part installed and removed.. Nev

I don’t think that anyone is putting words in your mouth. Another way of looking at it is that engines are so reliable that any maintenance you do might be crap maintenance, because it increases risk. When you work on an engine, you you have A, B and C sign off? 

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Things DO fatigue the more they are used. I know of a racing VW that replaced the crank every 6 SIX hours. A firm I  worked for( and drove the car once) was rallying one and broke about 3 cranks over  a few years. I could list about 5 other crank failures .  Nev

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Just now, facthunter said:

Things DO fatigue the more they are used. I know of a racing VW that replaced the crank every 6 SIX hours. A firm I  worked for( and drove the car once) was rallying one and broke about 3 cranks over  a few years. I could list about 5 other crank failures .  Nev

I don’t think anyone is actually arguing against maintenance. Just playing with ideas. 

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