Another through Bolt gone

[turboplanner]

Following on from Vev.....

 

Or if you are recommending, on Recflying, to gullible people, lubricants not on the manufacturer's approved list, be prepared to take the financial responsibility for any failures.

 

This particularly applies to experience with one engine, or in one application, or if you "read it somewhere" or if someone "told you".

 

An oil needs to be dyno tested over thousands of hours, with strip downs at fixed intervals before it can be approved with confidence.

 

There may be engine design issues, such as galleries too small from some viscosities, locations where the heat factor exceeds the breakdown of the oil etc.

 

The engine failure rate in recreational aviation is of serious concern.

 

 

[Camel]

Following on from Vev.....Or if you are recommending, on Recflying, to gullible people lubricants not on the manufacturers approved list, be prepared to take the financial responsibility for any failures.

This particularly applies to experience with one engine, or in one application or if you 'read it somewhere' or if someone told you.

 

An oil needs to be dyno tested over thousands of hours, with strip downs at fixed intervals before it can be approved with confidence.

 

There may be engine design issues, such as galleries too small from some viscosities, locations where the heat factor exceeds the breakdown of the oil etc.

 

The engine failure rate in recreational aviation is of serious concern.

You are absolutely correct and it reminds me of the Lycoming O320 H2AD story, it was a lemon but with Lycoming they developed an additive which helped, and this additive is what is in the W100 Plus product, now there are other mods for the H2Ad, T mod an oil galley mod and improved valve train gear i.e roller rockers. I had one of these engines and spoke to many Lame's of problems, armed with the right info and using tested and manufacturer recommended products I had no problems with my engine, thankfully everyone was working to a solution but with Jabiru through bolts it seem not much participation from Jabiru as if they were they would be reading this and talking to Motz right now. In case other don't know lycoming used Ford automotive Hydraulic lifters in their engine on this model and the cam follower Hydralic lifters are originally designed to slowly rotate to share the wear but in this case they did not rotate due to the angle or location the cam touched causing excessive wear and pitting on the lifters and camshaft reducing engine life dramatically with the additive alone engines could possibly make TBO and with the mods it was a good engine and do TBO.

 

Quote , One friggin engine major - you need that to happen on a hundred before getting excited....Oh and 180 trouble free hours?

 

Very fair comment turbo, I hope one day the right advice is offered by the right sources to be part of the solution not adding to the problem.

 

 

[Head in the clouds]

I've followed this whole thread with great interest but never had or operated a Jab engine although I have had many c/l split crankcase engines and never had any problems with them except oil leaks on some, particularly where they're metal to metal and not gasketed.

 

Just a couple of thoughts - no-one's actually said where or how these through bolts break so I'm just guessing that it's at the beginning of the thread, the thread root diameter probably being the place of smallest cross-section? So if the weakest part of the bolts just aren't strong enough is there room to bore out the holes for larger diameter bolts? I'm not suggesting that anyone do that themselves, just curious why the factory hasn't done it. From what I can see in the picture in post #47 there would appear to be heaps of room.

 

Another post mentioned 'fretting' (galling?) on the case halves' faces, that means lateral movement must be taking place. Are these case halves not dowelled? If they're not, and they're relying on the bolts to prevent lateral motion I would say that the bolts could develop harmonic vibrations because they're not a reamed and tight fit I imagine (?) and if they're vibrating and high tensile that'll be a likely reason for them to fatigue and snap even if they're well enough sized to satisfy the initial bolting forces required.

 

I also read comment about the hydraulic lifters maybe being a cause. I can't see why unless they were to pump up and become jammed and also, in that fully extended condition the valve springs would have to be fully compressed so as to cause a lock-up which might be trying to push the two case halves apart. But as long as there was still valve spring motion available then a hydraulic lifter becoming jammed or not relaxing for some reason should only mean that a valve wouldn't be closing and that would show as a cylinder not firing.

 

Just thoughts.

 

 

[turboplanner]

Just a couple of thoughts - no-one's actually said where or how these through bolts break

Yes they have in the many earlier posts, and there's not a consistent point. Agree with the rest of your post.

 

 

[Head in the clouds]

Yes they have in the many earlier posts, and there's not a consistent point. Agree with the rest of your post.

I just scanned the whole thread again, no description of a failed bolt at all so I guess you mean it was described on earlier threads rather than posts? If so could someone enlighten me please. If 'there's not a consistent point' does that mean the bolts were breaking anywhere? Not always at the thread root? If a shanked bolt breaks somewhere along the shank and not always at the smallest cross-section then I'd say it has to be a fatigue issue from vibration rather than a tensile failure in which case changing almost anything could be a possible fix i.e. bolt diameter, material (titanium?), grade (higher or lower tensile), surface finish...

 

Come to that has anyone had a broken bolt properly examined? Any good metallurgy lab will be able to report on the failure mode and cause.

 

 

[turboplanner]

Sorry, I should have said threads.

 

The frustrating part of the discussions are that the people who have the failures seem to be allergic to metallurgists

 

 

[Head in the clouds]

Sorry, I should have said threads.The frustrating part of the discussions are that the people who have the failures seem to be allergic to metallurgists

Yes, well metallurgists are about the only ones who will be able to give a definitive answer.

 

However the factories can sometimes be the problem too. When I bought my Drifter it was the first certified one that Austflight sold and after a few hundred hours the crank broke (this was before the ramp dog or slipper clutch) and so I returned the plane to them for a new crank, when it was fixed they wanted about $900 IIRC. They said it was an engine problem and so not covered under their airframe warranty. They were a Rotax supplier under OEM so could get the engine warranty but didn't want to go through the hassle I suppose. I agreed to pay but only when they gave me the broken crank so that I could make my own claim. They said they'd sent the crank back to Rotax for inspection but couldn't or wouldn't supply me with any documentation to confirm it. I took my aircraft and gave them a promisory note for payment on delivery of my crank. I never heard any more but about a year later I was at the Drifter factory and there was a pile of broken cranks under the engine bench...

 

So, I'm guessing the Jab factory always want the broken bolts returned for 'inspection' and that means the owners don't have them to be able to get them tested?

 

.

 

 

[turboplanner]

No, I think they are being genuine in getting the cranks back to look at, but whether they bother reading our posts or whether they get metallurgical tests done, we just don't know.

 

However, owners should be aware of their statutory warranty rights beyond the small print and beyond the laziness of dealers.

 

 

[Guest Maj Millard]

Head in the clouds, Some time back, (I'd be guessing 2 yrs) there was a thread or two on broken through studs. The NZ tech man at the time gave a good deal of input, as they has suffered a couple of failurers in trainers over there. might be worth going back and reading through those threads...they may be under Jabiru.

 

I bought up the suggestion at the time that they needed to have 'rolled threads', insteads of 'cut threads' (standard engine practise) to eliminate that weakness, from the equasion. Aircraft AN airframe bolts for instance have rolled threads for a reason.

 

Anyway not long after, Jab came out with a replacement through-bolt, which I assumed had the rolled threads. (real silly if they didn't, but that's jab for you !) As you may or may not know, most engines and particulaly aircraft engines rely on the through-bolt to hold the whole mess together, and they are also 'working' bolts, that have to absorb heat and constant pulses as the engine operates.

 

It is the 'new' throughbolt that is still failing, so obviously they need to upgrade to stronger still !...can someone out there confirm that jab did go to rolled threads on the 'new' replacement threads ?. Also the securing nut/washer assy has to also be as strong as the stud itself, and I'm not sure if this is the case either. Believe me, I don't go to bed reading Jab service bulletins so excuse me for my lack of up to date knowledge...................................Maj...

 

 

[geoffreywh]

" Earlier post From VEV......................You really need to be careful when comparing Aviation octanes to Mogas ... Mogas measured differently to aviation fuels. " I was under the impression that as the minimum quoted octane rating for my engine (87) was lower than 91 (Shell unleaded) Then I would be OK using the 91........BUT someone told me very rightly last week that I was WRONG! .... The tests are different for cars and aviation...So the test that gives 91 octane for mogas is different than the test for Avgas............... 91 mogas equals 84 for avgas! Although I have used 91 unleaded for some years with no ill efects I'll stop doing it now and use 98!.....Just goes to show that not everything is as it seems...

 

 

[Head in the clouds]

Thanks for the info Maj.

 

I had a look at some of the conversation in older threads.

 

All graded production bolts have rolled threads, it's the fastest way to make them, only ungraded cheap rubbish bolts for garden fences and the like have cut threads, and cheap versions of threaded rod do too. But AN, Grade 5, Grade 8, Class 8.8/s and socket head cap screws (SHCS) always have rolled threads, as do the nuts associated with them, the nuts' threads are formed with a 'rollform' tool which looks like a triangular section tap but isn't sharp, it sort of smears the threads into shape.

 

In the case of the Jab bolts, were they actually making their own bolts? That would be plain crazy unless they had a need for some weird shaped stud and even then it'd be better to get a fastener maker to produce them.

 

I saw that some people were talking about up-sizing their bolts to 7/16 from the original 3/8. Can that be done without boring the holes for the larger bolts?

 

I also read that someone who had considered just replacing the nuts with the long series 12 siders decided instead to also replace the bolts with the longer ones, because the threads had deformed 'like a christmas tree'. Thread failure of that nature indicates very poor manufacturing QA because the thread rolling die must have been very much out of adjustment, and that indicates that the bolts were from a very poor quality supplier. For aircraft engine use there is absolutely no excuse for not using individually tested bolts, they don't cost very much more than the cheap ones.

 

Without doubt the best value tested bolts are made by Unbrako and their strength is far superior to almost anything else on the market. Their surface finish is also tested individually to ensure that they don't have any sharp microscopic flaws which could act as a stress riser, eventually resulting in cracking.

 

American Grade 5 bolts have a tensile strength of about 120,000 psi which is similar to metric Class 8.8/s structural bolts. American Grade 8s are about 150,000 psi tensile and Unbrakos test out at between 180,000 and 190,000 psi, so you can see they are significantly stronger and also tested against flaws. Yield strengths are about 75% of the tensiles mentioned.

 

I guess only privately operated Jabs could run the better bolts, flying schools would have to stick with the manufacturer's supply...?

 

 

[Guest Error404]

It's pretty simple really, the bolts only rarely broke for many years and now they break quite frequently it would seem. Sounds like the latest bolts might not be up to scratch doesn't it?

 

Sounds like the dodgey valves they used to use, they knew about them for a long time but because they bought 40,000 of them at once they wanted to use them all up first before buying new ones, I was led to believe by numerous sources.

 

 

[Camel]

If your interested in fuel octane description and comparison then this may be of interest. http://en.wikipedia.org/wiki/Octane_rating and http://en.wikipedia.org/wiki/Avgas

 

 

[M61A1]

If your interested in fuel octane description and comparison then this may be of interest. http://en.wikipedia.org/wiki/Octane_rating and http://en.wikipedia.org/wiki/Avgas

Also... http://en.wikipedia.org/wiki/Avgas Down the page a bit explains the vapour pressure issue.

[biggles5128]

Just throwing this into the mix.. I used Shell 100 oil as recommended by the factory through the run in period and then went onto Shell W100, I discovered that my engine oil temps were on the hot side through most phases of flight. I changed over to Exxon Elite about 2 years ago and interestingly have seen constant lower oil temps. Spoke with a number of users and maintainers about this, one theory was that as the Jabiru motor has extremely tight tolerances, one brand of oil may behave differently to another given the same quoted properties. The Elite oil is a multigrade semi synthetic 20W 50W (I think).

 

I don't profess to know aircraft engines in detail like some others here but proof of the pudding is in the tasting..... Now to get my CHT's down a bit and I'm laughing.

 

Further to this, I would like to see actual figures on Jabiru engine failures with a break down of type of fuel used, type of oil used etc.

 

 

[fly_tornado]

the viscosity of the lighter oil helps dissipate the heat. I can't understand why Jabiru are recommending 100 weight oil, its got to create a massive amount of problems with oil starvation on startup.

 

 

[turboplanner]

Further to this, I would like to see actual figures on Jabiru engine failures with a break down of type of fuel used, type of oil used etc.

It beggars belief for aviation operations, but you aren't going to get it because there is no detailed investigation of forced landings, which as we know are an aerial form of Russian roulette.

 

 

[vk3awa]

"Another post mentioned 'fretting' (galling?) on the case halves' faces, that means lateral movement must be taking place. Are these case halves not dowelled? If they're not, and they're relying on the bolts to prevent lateral motion I would say that the bolts could develop harmonic vibrations because they're not a reamed and tight fit I imagine (?) and if they're vibrating and high tensile be a likely reason for them to fatigue and snap even if they're well enough sized to satisfy the initial bolting forces required."

 

I think you are on the money.

 

1. It was a rare event for solid lifter engines to break through bolts or fret crankcase halves.

 

2. With the introduction of hydraulic lifter engines, through bolts were breaking and crankcase halves were fretting with some regularity. (Usually after 300+ hours of operation (first generation hyd. engines))

 

Jabiru have done a great job in developing a fantastic Australian product. I'm sure they have the best intention when making changes in both airframe & engine in the name of developing a better product.

 

They don't have a sqillion dollars to spend on development and at times have released a product out into the wide world, that with time, has proved to be not as good as they had predicted.

 

Welcome to the R&D department.

 

PS the crankcase halves are dowelled but much more attention is given during engine rebuilds (and I would expect new engines) in having a closer tolerance fit.

 

 

[biggles5128]

It beggars belief for aviation operations, but you aren't going to get it because there is no detailed investigation of forced landings, which as we know are an aerial form of Russian roulette.

Maybe our RAAUS organisation should start forcing the hand as they collectively would carry more clout than an individual banging his or her head against the wall. If there really is an issue, as I have said before why is CASA allowing these engines to continue to run off the production line. As with all matters legal, as soon as you make an individual or an organisation accountable for their actions or inactions as the case maybe, they tend to cover their respective butts very quickly.

I am not ignorant to the fact that there seems to be an over representation of Jabiru engines that are giving pilots a closer look at paddocks than expected, I own one and will do what ever I can to ensure that it is maintained to the highest standard and flown with due consideration to operating parameters. If there is an identified problem lets find out what it is and start a fix, I think most owners would pay for the fix rather than take a chance on it letting go one day.

 

The only engine that has ever given me trouble was a Lycoming which blew to bits at night, but thats another story.

 

On a positive note in regards to the Jabiru, if you have an engine out at least you have a very very good chance of surviving the sudden stop due to the exceptional airframe, not every aircraft can give you that chance.

 

 

[boingk]

I have read a few articles on the evils of mogas, most of them speak of the poor quality control, but I think the main advantage of avgas is that it is designed not to cause vapour lock at altitude (something to do with vapour pressure). Since I tend to stay under 5000' amsl, I don't think too much of it. As for the oil, if it works in my aircooled bike, in traffic, with no cooling airflow, I am prepared to run it (I do tend to avoid diesel oils in petrol engines though).I agree with boink about most aviation products, there is much better out there, aviation just hasn't kept up. An example that comes to mind are the 2 greases used on the Bell 206, there are many better lubricants than them in general industry. I have also had a major oil company rep recommend(for a particular application) and sell grease that was totally inappropriate and caused a lot of bearing failures. If I wanted to find out the best oils, I'd talk to one of their chemists.

Highly agree with you on the motorcycle test. Loving my motorcycles shift feel and general smooth running on Dello 400 / GW Top Dog. I'm speaking about a little CBR125R and a VTR1000F here, too; engines producing about 120hp/litre at an operational redline of 10,000rpm in each case. The compression ratios are in the order of 11:1 and the crankcase also shares its oil with the transmission. Both are regularly ridden hard and for extended periods of time, the little 125 especially. Its rarely below 75% throttle and generally at maximum under acceleration as its a hoot to ride and won't see you exceed the freeway speed limit without a hill and tucking in race-style.

 

You cannot imagine a harsher environment for a lubricant than a motorcycle, and yet there is widespread evidence that diesel oil is about the best stuff you can get for this environment. Diesel oils 'dieselness' is essentially in its high quality base stock oil and antiwear compounds, namely molybdenum sulphide and zinc diphosphorous. These compounds help with any metal-to-metal contact (shouldn't happen but will negate any damage by forming a last barrier if it does) and also reduce engine friction. The amount of ZDP is limited to about 2.5% as it will cause plug fouling in excess of that fairly quickly - most manufacturers cap at 1.2~2% or so. Diesel oil is also able to withstand a huge range of temperatures while still conforming to its stated levels of protection, generally as a result of high quality base stock and superior methods of refinement.

 

Compare this to an 'ashless dispersent 100wt mineral oil' as is used in aircraft and we're talking about 50 years of evolution. It simply boggles the mind once you have the facts - the difference is night and day.

 

Cheers - boingk

 

 

[Guest Error404]

I was told that RAA have a collection of Jabiru engine parts in the office and some have been forwarded onto CASA. I expect we will hear more about that if we ever get a new technical manager again.

 

 

[Phil Perry]

Guys,

As for using automotive engine lubes or additive packs ... There is so much complex chemistry behind designing an engine lube, you will be playing Russian roulette by departing from the manufactures spec. .. Just don't do it.

 

If a major oil company recommends a product you can be assured its has been carefully designed and tested to do the job and meet all the OEM performance specs.

 

Cheers

 

Vev

Oh Really ???? ( Devil's advocate for just a moment here Vev. . . I don't know you personally, and therefore have no intention of trying to make your assertions in any way too trusting of the corporate giants. . . . .)

 

Sorry mate, but in MY industry, I get all sorts of RECOMMENDATIONS from major manufacturers AND suppliers of whatever product. . . . that it has been researched and designed to meet certain specifications, only to find out not too far along the timeline that this was sometimes not QUITE factual when compared to mine ( and others' ) experiences of long term use of such products . . . , and in some cases, what appears, in actual operation to be covered by a range of statements, from being slightly economical with the truth regarding the "Research results" quoted to what amounts to be (apparently ) either seriously flawed in it's conclusions or just downright sales - driven bull$hit.

 

Lots of new products come along all the time. . . , some of which are better, some are not, . . . . . but technology DOES advance, in all fields, and, reading comments on this thread ( and elsewhere ) from people who use OTHER lubricants for OTHER high energy purposes, and appear, on the surface to know what they are talking about, which must be backed up by use of said products for some time to produce their resulting comments and suggestions, . . . . I would think, that on a balance of probabilities, that just because "we have traditionally used Brand X for years, as it was researched and designed by a Well Known major manufacturer . . . and therefore it would be plain stupid to try anything else" that strict adherence to that philosophy would, in short order,. . . prevent the advancement of, not just aviation powerplant lubrication technology, but most other things as well. ??

 

Following 40 years or so of using similarly RECOMMENDED products, I have yet to find a manufacturer / suppllier who EVER ADMITTED . . . that they might have made any errors, however minor, in their original calculations. ASSURED ? . . . . If you are happy to accept manufacturers' specs FOREVER, THEN AT LEAST AFFORD YOURSELF THE LUXURY OF ASKING THE QUESTION : Assured by what or Whom exactly ?????

 

****** Edited to add. . . . have you ever tried to sue a manufacturer because their specs didn't come up to expectations and cost you a lot of money ? * * * * * *

 

Just a thought mate . . . . ( and no offence whatsoever intended )

 

Phil ( Now returning to Non-DA mode. . . )

 

 

[facthunter]

A few years back quite a few synthetics did not meet performance expectations and were withdrawn from the market ( as they should have been) Shell and Mobil were some of them and they are significant players in developing oil technology.

 

There is no "best oil" out there. The specs vary depending on the application and what the market will pay. It is more a question of what is suitable for the application. ED (extended drain) oils have more additives to go the longer distance. They are not necessarily "better" oils.

 

I don't accept that motorcycles are hard to lubricate or a particularly severe application as even on a racetrack they are only flat out for short periods. You keep part power only on corners and when you are braking you have none.

 

Not every manufacturer of oils makes an aero engine oil. The "green slime" by Penrite was taken off the market as a consequence of a court action. but that is a two stroke oil.

 

On the subject of two stroke oils I have only seen two who will label them as " suitable for aircraft use" and that are SHELL and Penzoil (US).

 

Vev may choose NOT to respond, but I would suggest NO-ONE here knows what he knows about oils. Every -one has their favourite "antisqueek" but few of our examples and experiments are very scientific.

 

Aero engine 4 stroke oils are the only ones formulated to run "leaded" fuel. The other thing you want to watch out for is where the oil lubricated drive gears as well, as many engine oils don't get close there.

 

IF you don't stick to maker's recommendations you run a risk if something goes wrong, of not being insured.

 

Thick oils need to be warmed up as per the makers oil temp figures. Nev

 

 

[Sapphire]

The first criteria of a company in recommending a product is profit. The financial industry is full of this. Before the big bust, some American companies would promote sale of a financial product then secretly hedge on it's failure. Consumers are taken for a ride every minute of the day on everything from soap to spaceships.

 

 

[Phil Perry]

SILKOLENE COMP-2 PREMIX ( UK ) has always been labelled ( for around 25 years ) as suitable for use in aircraft using two stroke engines. Anyway, must go home now as security want to lock up the airfield, and the missus won't accept another excuse of being locked in. . . . . .

 

Thanks Nev, your comments are always appreciated, even if I don't totally agree with the point you are trying to make.

 

Kind regards,

 

Phil