Rolled Thread Engine Through Bolts Available as alternative

[turboplanner]

That's right Nev, I've seen Lycoming connecting-rod end bolts built like that.Here's something I found hard to understand... when the bolts are clamping something much stiffer than the bolts themselves, there is NO extra load put into the bolt until the forces are enough to open the clamped joint. So there should be no fatigue on those bolts if there is no opening of the joint.

But when you have aluminium clamped with steel bolts then the temperature effects will cause fatigue as I found once.

 

Now what torque should the new bolts have? The latest maintenance manual says 30 ft-lb, but my old Tech manual says 35.

 

I'm inclined to go for 35 because of the clamping theory and because the bolts are stronger.

 

cheers, Bruce

I'd check with Jabiru Bruce, the tension may have been reduced as a way of reducing the numbers of fractures in the field.

 

 

[Bruce Tuncks]

Thanks Chris, any information you can gather will sure be of interest. I'd like to get to one of those courses someday myself.

 

..Bruce

 

 

[facthunter]

Bruce, Sorry about the time elapsed. I agree with your general logic re fixed lengths etc. I think some funny things are happening with the crankcases. Jabiru have alluded to detonation and that makes sense. It can impose enormous loads in engines. Nev

 

 

[jetboy]

My original manual from 2003 states 30 ft-lbs for the thru bolts. Maybe you are mixing with NM?

 

Ralph

 

That's right Nev, I've seen Lycoming connecting-rod end bolts built like that.Here's something I found hard to understand... when the bolts are clamping something much stiffer than the bolts themselves, there is NO extra load put into the bolt until the forces are enough to open the clamped joint. So there should be no fatigue on those bolts if there is no opening of the joint.

But when you have aluminium clamped with steel bolts then the temperature effects will cause fatigue as I found once.

 

Now what torque should the new bolts have? The latest maintenance manual says 30 ft-lb, but my old Tech manual says 35.

 

I'm inclined to go for 35 because of the clamping theory and because the bolts are stronger.

 

cheers, Bruce

[Bruce Tuncks]

My manual is older than yours Ralph, on page 74, issue no. 1, date 010596 it has Table 9.0 "Torque specifications"

 

"Crankcase main studs" are listed at 47 nm or 35 ft-lbs.

 

So it looks like the change down to 30 ft-lbs was quite some time ago, between '96 and '03

 

.....Bruce

 

 

[Wayne T Mathews]

Good news Forumites.Finally i have been able to source an alternative to the standard Machined Thread Engine Through Bolts supplied by Jabiru. To go along with the ARP Nuts (rolled thread) that are supplied now as the fix for the failing through bolt (machined thread) issues we all know about, i have spoken at length with a manufacturer in Western Australia and he has imported in the correct thread dies to be able to manufacture a complete set of new Rolled Thread Through Bolts. There are 10 long studs and 4 short studs to make up a complete set. They are made out of 4140 round bar and will have a much higher strength due to the rolling process than the standard 4140 machined threads that are the only option out there at the moment. He is producing the first 10 sets for me tomorrow and will hopefully post them over to me early next week. They will be the slightly longer length so that you will still have a couple of threads protruding out of the new 12 point ARP nuts. The cost of these sets are currently around the $120 mark plus postage which is a great price. The more orders he recieves the cheaper he will be able to manufacture them for as he can buy in more material at a bulk discount.

 

For those of you that are in need of replacing the engine through bolt and would like a set to match the new ARP nuts i have included the manufacturers details and you can deal straight with the Director of the Company.

 

TL Adlard - 0430135816

 

Alliance Fasteners

 

8 Coolibah Way

 

Bibra Lake

 

Perth, WA 6163

 

I must stress that i have no interest in this company and i am not interested in becoming a supplier of these bolts but i thought that i would pass on the information for those of you who would like to eliminate the potential of the through bolts failing once and for all. I am not the first to use the rolled thread through bolts and, as i have always tried to do, i am just trying to find ways to improve the reliability of this jabiru motor.

 

I hope this can be of help to you and if you have any questions just ask.

 

Regards

 

Andrew

I have just read through this entire thread, and I have to say that I believe all of the contributers need to be congratulated... Well done men. Especially Andrew... But (there's always a "but" after a start like that), have there been anymore developements/results etc since October?

 

 

[JabSP6]

Wayne

 

The first bolts i asked TJ over in W.A. to make up were made the same diameter all the way to the rolled threaded section. As i said in earlier posts they were failing on the bolt side of the nut in the thread section between 55 & 65 ft/lb.

 

I took on board the info other people had mentioned about waisting the bolt to give you a specific area that the bolt will fail and asked TJ to machine a waisted section into each end of the bolt the same as the standard jabiru bolt. He then supplied a few more bolts for me to test and the results again where much better than the standard Machined through bolts from Jabiru. They were now breaking at the waisted section of the bolt and not in the threaded section however the tension required for this to happen has drop marginally to betwenn just under 50ft/lb and 55ft/lb. So the range of failure is more consistant by waisting the bolt but just marginally lower.

 

I think overall for piece of mind those of you who are looking at performing any maintenance on your engine or looking at doing the service bulletin and don't want to go to the trouble or expense of splitting the cases and upgrading to the 7/16" through bolts then the 3/8" Rolled thread through bolts are a much better option than the standard through bolt.

 

It is entirley up to you if you choose to give TJ a call or not. You can do your own testing to give you piece of mind.

 

Allianc Fasteners over in W.A are an altenative supplier of a bolt that gives a higher failure point than the standard bolt that jabiru make. They have all the latest equipment to ensure quality control of each and every bolt they supply to a very large range of industries.

 

I am in no way connected to TJ or involved in his buisness and i am not interested in making any money by becoming a supplier of this bolt.

 

I would ask you all, if you are interested, to contact him directly on the numbers i included in earlier threads.

 

I know there are some of you that have concerns about certified aircraft and not using a bolt that is not certified.

 

This is a valid point when it comes to Legal issues and Insurances. I am not suggesting for a minute to compromise this.

 

All i am saying is all aircraft bolts that you buy are Rolled Thread which is why they are stronger and more expensive than the standard off the self machined bolt.

 

I fly a 19 build aircraft which is Experimental so it is not a concern for me to use these bolts and it is my choice to improve anything that we come across on this forum that can be improved to give me piece of mind when i start up the motor and taxi out for a weekly round trip of 410nm to go to work.

 

I am a big believer of sharing knowledge and experiences and this is what i have been doing since i started flying my SP6 2 1/2 yeras ago.

 

For me it is all about improving the reliability and on a lesser note the economy of these great motors that jabiru are using to ensure i get home safely to my wife and kids each and every week.

 

Fell free to give me a call or PM me if you have any more questions or suggests of things we can look at to achieve this goal.

 

Safe Flying

 

Andrew (JabSP6)

 

 

[facthunter]

What you have done is a good thing. The installation of the ( bolts) Studs should provide a higher margin of strength and reduce the chances of failure. With the apparent increasing use of mogas and the suggested ignition retarding, obviously there is some question of detonation, (as there has always been) being the root cause of these failures and crankcase fretting incidents. Mogas doesn't have any real quality assurance in this critical application. Nev

 

 

[Bruce Tuncks]

I second those comments Nev. Well my set has been ordered, why would you not lessen a known risk?

 

It is interesting that the early engines (up to 22A serial number 1700 or so) were not included in the directive. They certainly have the same bolts.

 

I was told that the early engines didn't have this problem, does anyone know why this should be so? Could it be that the 32mm carby gave a lower risk of detonation?

 

When we were told of power increases with engine upgrades, my reaction was to say that I didn't want more power, I wanted more reliability. Not that I had ever had any problems, but you can never have too much reliability.

 

Anyway, thanks Andrew for a job well done.

 

cheers, Bruce

 

 

[Clive J]

This is great info and effort, thanks. I recently asked Jabiru to supply me with the material spec so I could have some rolled thread through bolts manufactured.

 

They wouldn't suply the info and also stated that they wouldn't approve the fitting of any bolts that were supplied by others that is not Jabiru. A slight misunderstanding as I'm not the individual who was going to make the bolts but I think it is clear what their position is, here is Susan's reply:

 

Hi Clive

 

Please contact Dave at Skycraft for the supply of the crankcase dowels and the longer through bolts and 12 point nuts and information regarding the service bulletin JSB031-1. We cannot endorse individuals making their own parts for Jabiru engines.

 

Regards

 

Sue Woods

 

So I would love to fit a set of these new bolts but we need to get approval of either Jabiru or the LAA (assuming I can get it from them without Jabiru beiing involved).

 

Firstly I think this info needs passing on to The LAA (I'm in UK) as I'm finally beginning to understand the issues.

 

I certainly won't buy bolts from the company that supplied the originals that are faulty and failing.

 

A business principle of mine, no company should make money from me out of their poor service.

 

Regards, Clive

 

3300 #1460

 

2200 # 596

 

 

[dazza 38]

Hi Clive, I think Sue left a sentence out in her reply mate. Quote- We cannot endorse indivduals making their own parts for jabiru engines.I would have added-

 

 

 

 

 

 

 

 

Even if those individuals are making our product alot more reliable.

 

 

 

 

 

 

 

 

 

[facthunter]

Well, they cannot admit the need as some of the engines are certified. Getting too far away from the original is not the go ( generally) but here we have a Work In Progress with an engine that has problems with failure of the particular item. The cause of that failure has been put down to (possible) detonation, so this should be investigated, but UNLESS the fitting of stronger stude can cause problems, Why not take advantage of it? ( I would, because it has been worked through fairly thoroughly. I wouldn't NECESSARILY recommend a big increase in the torquing down figures though, without further investigation. Nev

 

 

[Dieselten]

Reading this thread - even with the large amount of good, sound technical knowledge and sheer practical common sense it contains - seems to me rather like arguing about how many angels can dance on the head of a pin. Dogma and doctrine, argued with the ferocity of wizened old clerics haggling over abstruse point of canon law.

 

What I am not seeing - anywhere - is any suggestion that the torque on Jabiru through-bolts be periodically re-checked! Perhaps I am excessively stupid, naieve or just plain thick, but if these can loosen and cycle until they break, then checking them seems the blindingly obvious thing to do. And yet no-one appears to think this is worthwhile, least of all the factory that makes the thing in the first place. They tell us it is buttoned up and will run 2000 hours. Well, there is a steadily growing list of failures which constitutes evidence to the contrary. Do we have to lose lives before someone decides this might be a good idea?

 

If the cause of through-bolt breakage is nuts loosening, allowing the bolts to begin cycling until they ultimately suffer a fatigue-fracture, then surely it makes perfect sense to re-check torque at regular intervals?

 

Yet no-one seems to have suggested this. Jabiru glue the nuts on both ends with Loctite 620 and there is nothing in the service manual about re-checking the torque - ever. If the torque Jabiru uses is correct, then why glue both nuts on any given through-bolt? Are they holding the engine together with a torqued nut (and the pre-loaded through-bolt) or are they holding the engine together with Loctite 620? If the torque is correct then no adhesive should be required on one of the two nuts on any given through-bolt. If the torque is not correct then the Loctite 620 is merely masking the problem.

 

Maybe Jabiru have to bite the bullet and introduce a timed through-bolt torque-check. Even the time and effort in removing the cylinder-heads and checking the torque on the lower through-bolts is far less than the inconvenience and expense of having an engine re-build. I have had so much grief from their engine on my aircraft that I will be getting a LAME to re-check the torque at 500 hours when I replace all the exhaust-valves (they won't even do 1000 hours).

 

I'm a pragmatist. I need an engine that runs reliably, not one that breaks at random intervals because a bolt fails when the failure could be prevented by an extra bit of preventative maintenance which the manufacturer claims is not necessary.

 

Theories about why these things fail is all very well. I want results. I've had a belly-full of the theory!

 

 

[facthunter]

We know you are not happy Diesel10.

 

You've got a lot of "IF's" in your post so I can't deal with things that are not proven.

 

I also don't agree that things are happening the way you suggest they "might" be.

 

IF studs are found" loose", would it be OK to just retension them? I DON'T THINK SO, because some damage would have been done by then. Same as I don't believe that when one breaks it would be OK to just replace it and see if the engine works .

 

I can't object to the idea of checking the tension, but how often would you do it?

 

Would it guarantee that one couldn't break a short time after it had been checked? I suggest NO.

 

I don't like the idea of Loctite. The Continentals used to use a palnut ( extra nut as a lock nut) but don't (need/use) it on the later engines. (at least the 0-200's)

 

I believe the engine would require a strip and inspection. IF the case has been fretting, the tunnels that the mainbearings are located in would be suspect also, and the "crush" on the bearing shells would have changed.

 

The cases would require crack testing and re machining to get the original sizes/fits back. Every one of those studs is necessary to be in place and tensioned correctly for the engines structural integrity and for it to be able to run on full power.

 

When they fail the engine usually lets you know (I believe)

 

Regarding the exhaust valves, 1,000 hours would be a good life (realistically) I would think. They are not dear and you get what you pay for.

 

I doubt that many Gypsy Majors ran much more than that, or even that much, without a "top". .

 

PS I put my reputation on the line when I comment about matters as serious as these. I regret I can't provide you ( or anyone else) with a magic silver bullet solution, but let's not rush to an unproven "fix".. Nev

 

 

[jetjr]

A core issue here is we are addressing the outcome not the problem. I doubt Jabiru know if the through bolt replacement will fix the problem, sure is an expensive experiment.

 

IF we/they are combating detonation then it isnt likely to be this easy to fix

 

Can detonation be caused by uneven fuel distribution?

 

The problem with retensioning through bolts is that is is a BIG job, whole intake/exhaust has to be removed (at least)and the existing bolts, as discussed here are very close to stripping limits. Plenty of LAME or L2 would prefer to replace them than run the risk of over tensioning and stripping threads. Id estimate theres potential for even more mistakes is this level of work is required every 500hrs as many would try to do it themselves, over stretch a few threads and CAUSE a bolt failure.

 

If the bolts are upgraded, as per this thread, then maybe retensioning is an option, still an involved job beyond many owner maintainers Id guess

 

 

[facthunter]

Can detonation be caused by uneven fuel distribution?

 

It can be caused by lean mixtures so if one cylinder is too lean yes.

 

Clearly Jabiru are grappling with this problem. ( detonation). They have lowered the compression and retarded the ignition, so they are acknowledging it.

 

A hot running exhaust valve or plug of the wrong heat range or a loose plug or a build up of carbon that can incandesce. can cause it as well as wrong fuel stale fuel or carbon/ dust combination build up. If you are in a dusty area the dust will combine with the carbon.

 

The style of piston used may run hotter than a non slipper type, so if the piston crown gets too hot it wil have a similar effect to the head being too hot.

 

I think if the engine is running happilly the bolts should not need retensioning.

 

Proper procedures should be observed when replacing Studs or the mainbearing shells may move. As you say more problems can be created by people trying to do these things by themselves.

 

I can understand Diesel10's frustration, and I really sympathise with him, but the cause has to be eliminated, not the effect, as you say, jetjr Nev

 

 

[Dieselten]

I will replace exhaust valves on my 2200B Jabiru engine every 500 hours. Actually, there's quite a bit I will be doing every 500 hours.

 

Removing all the cylinder-heads is a very easy job...especially if your engine has the hollow push-rods. A good valve-spring compressor-tool and a calibrated torque-wrench are the only specialist tools you need.

 

At 500 hours a new set of exhaust valves, inspection and decarbonisation of heads and pistons, bore inspection, through-bolt torque-check, checking of hydraulic-lifters, valve-guides and rocker-bushes, re-assembly and return to service doesn't seem too onerous to me. I'd rather do that twice in 1000 hours than send the engine back to Bundaberg for a rebuild because it broke a through-bolt. If it came down to it, whilst the heads were off, I'd even contemplate a new set of through-bolts and nuts for the cylinders as well, if that would give me reliability.

 

I'd have the aircraft off-hire for less time and it would cost me less money - and I could watch as the LAME/L2 did the work. Because of broken through-bolts and consequential issues, my aircraft was off-hire for three days short of a calendar-year (23rd Dec 2010 to 20 Dec 2011). This will not happen again.

 

I am not unhappy as people seem to assume. That is far too "perfumed" a term for my feelings. However, my aircraft is now back on-hire, performing well (the propeller probably would benefit from a dynamic re-balance) and now has a chance to pay me back the money and lost income I have suffered as a result of the original problem.

 

In my view, the Jabiru engines are the most maintenance-intensive light-aircraft engines ever made. You are forever putting the spanners to them for one thing or another. A four-stroke engine with two-stroke reliability. A uniquely Australian achievement.

 

Such a great airframe deserves a far, far better engine.

 

 

[Relfy]

Yet my flight school J170 engine went 1200hrs before going in for the upper section rebuild. The engine was run solely on avgas and ran extremely well throughout its time. My reco 2200 in my 120 is going in for the through bolts and nuts to be replaced on the 9th Jan after 200hrs without a problem albeit slightly down compressions at the previous 100hrly. We will query this with the leak downs at the 200hrly, also being done by Jabiru at the same time. Strange how some have dramas and others run well but ultimately I still think about the through bolt issue when I'm over water or tiger country!

 

 

[jetjr]

Diesel10, I feel for your problems and your not alone.

 

For my interest what historically are your temps across the engine, CHT and EGT?

 

One of your key issues seems to be valves related, do you feel this is related to through bolts somehow?

 

 

[Jaba-who]

Sorry to talk theory again diesel10 but in this area theory is about all we have.

 

One of the problems of retourquing bolts is that they are stretched each time you retorque them. The bolt then gets stretched to a breakpoint. That's what happens when you over torque it to fracture point but it can also occur with incremental retorquing by small amounts. For thar reason many bolts in the automotive industry are now considered single use items.

 

So a bolt that is retorqued may be broken by the act of retorquing. Or if it goes loose and moves then it may break.

 

Opposite causes same outcome.

 

 

[rogerpl88]

Finally i have been able to source an alternative to the standard Machined Thread Engine Through Bolts supplied by Jabiru. To go along with the ARP Nuts (rolled thread) that are supplied now as the fix for the failing through bolt (machined thread) issues we all know about, i have spoken at length with a manufacturer in Western Australia and he has imported in the correct thread dies to be able to manufacture a complete set of new Rolled Thread Through Bolts. There are 10 long studs and 4 short studs to make up a complete set. They are made out of 4140 round bar and will have a much higher strength due to the rolling process than the standard 4140 machined threads that are the only option out there at the moment. He is producing the first 10 sets for me tomorrow and will hopefully post them over to me early next week. They will be the slightly longer length so that you will still have a couple of threads protruding out of the new 12 point ARP nuts. The cost of these sets are currently around the $120 mark plus postage which is a great price. The more orders he recieves the cheaper he will be able to manufacture them for as he can buy in more material at a bulk discount.For those of you that are in need of replacing the engine through bolt and would like a set to match the new ARP nuts i have included the manufacturers details and you can deal straight with the Director of the Company.

TL Adlard - 0430135816

 

Alliance Fasteners

 

8 Coolibah Way

 

Bibra Lake

 

Perth, WA 6163

 

I must stress that i have no interest in this company and i am not interested in becoming a supplier of these bolts but i thought that i would pass on the information for those of you who would like to eliminate the potential of the through bolts failing once and for all. I am not the first to use the rolled thread through bolts and, as i have always tried to do, i am just trying to find ways to improve the reliability of this jabiru motor.

 

I hope this can be of help to you and if you have any questions just ask.

 

Regards

 

Andrew

Andrew,

 

With reference to your post above.

 

I am new to this forum and joined having read your contributions on the subject. Until recently, I have been overhauling and servicing all the marks of engines in the UK with the earliest being serial no 24. I have learnt that it is always best to read between the lines when looking at a JSB and the one concerning the through bolts is worth looking at in detail.

 

Certainly there are problems with the threads failing and the JSB gives a number of contributory factors as to why. All quite plausible but the logic fails when the remedial action is applicable only to engines post 2200A1707 and 3300A6637. Why are engines 2200A1706 and earlier immune? I have stripped down and rebuilt scores of engines and never had a problem with the older through bolt threads failing.

 

Measure the OD of a pre and post thread and you will find that the later batch of bolts have undersized thread diameters. The worst case I measured was 10 thou undersized when compared to an equivalent AN6 bolt. Run a plain UNF nut up the thread and the play will be un-acceptable. in addition,inspection of the used MS nut threads and witness marks shows that a fraction of the nut thread is holding down the 30 ft lb torque. The MS nut is slight oval at the top to provide the 'self locking' feature and, in worst cases, the grip is only where the ID thread is smallest. That they are holding in the first place is testament to the inherent strength of the nut.

 

When you appreciate the above, you understand the rationale behind the JSB's use of a plain 12 point nut and locktite 620.

 

The proper solution is what you are doing and that is getting a set of through bolts made to the correct specification. If they are, you can revert back to the original MS nut or 12 point self gripping nut with no locktite. I would steer well clear of using locktite 620. It is was unnecessary before when the threads were to the correct spec. The use of locktite prevents the correct assembly of the barrels where the gradual torque down sequence and intermediate checks are essential. Knowing that incorrect torquing can distort the barrels when they get hot, I always use a hot air gun to gently heat the barrels and check for increased friction as I progressively torque down. Sometimes it can take 2 or 3 attempts.

 

I always thought that the original threads were rolled but had my doubts with the new batch because the threads were failing. A second opinion from a local engineering company say the are rolled. Certainly the thread quality of the earlier batch of bolts were acceptable and never showed any signs of failing when removed from 2000 hr engines.

 

Thanks for your work and offering us another source of through bolts.

 

 

[Dieselten]

Jetjr:-

 

Jabiru's valves at 500hrs were showing pitting and gas-cutting so I replaced them. Conclusion: Jabiru valves won't make 1000hrs. They will make 500.

 

CHT 220-250F max. No EGT monitoring is fitted to this engine.

 

General comment:-

 

One thing which hasn't been mentioned is when Jabiru changed from solid-lifters to hydraulic, does this cause a completely different set of resonances and harmonic vibrations to be established in the valve-train/cylinder/cylinder-head and crankcase areas, causing through-bolts to be stressed in a way they were never stressed in solid-lifter engines? Was any vibrational analysis done when this change was made, and was there any vibrational analysis of the solid-lifter engine to use as a benchmark? (I think I know the answers to both questions already.)

 

 

[jetjr]

After some discussions they have "never" had a through bolt break on a solid lifter engine, the JSB was extended back into Solid type to be sure they were all covered.

 

There are a lot of things here which dont make sense regarding the JSB unless there was a quality porblem with some bolts OR the problem relates to hydraulic changeover

 

With respect to your issue D10, EGT variation in some engines is absurdly high, this problem has plauged designers since the start and still theres no solutions except minimizing the problem and there are some simple ways to do this like vanes and jetting. Id strongly suggest fitting a monitor device for each cylinder and spending time (money) getting EGT sorted. Could explain pitting and failure?

 

Some can log too making diagnosis much less guesswork.

 

Valve guide wear has been a problem overseas and there are a few who claim to have the answer - From South Africa look for Kotze whos done something to drain oil correctly from heads. Also does more balance and machining work too. Some French work has seen other guides etc used.

 

There was long discussion from "Rootec" and Youtube vids regarding spring bind which was good info for hyd lifter engines too

 

No one knows why but plenty do go to 1000hr and beyond, however with parts being fairly cheap heads off at 500hr might be cheap insurance. These new bolts sure seem to be a good step and cheaper than Jabiru too I think.

 

 

[dazza 38]

I just received the latest Flight Safety Mag in the mail.It is reported that a 2200 had - Two crank case throught bolts broken. Time since New - 21 hours.

 

 

[Clive J]

Guys, there is a lo of info in this thread which is causing confusion, just what Jabiru intended when they added a lot of issues into the SB that aren't relevant to the problem. All the stuff about fuel and detonation and other guff is rubbish added to ensure we miss the point. The bolts are undersized and the nuts then slip on them as there isn't full contact on the thread. Read Roger's posting above.

 

As the nuts are moving on the thread they are loosening off, this is causing problems that CAN be associated with loads of issues but the associated issues aren't the root cause. As Roger says above, early engines didn't have the problems they didn' have undersized bolts.

 

As I understand it the newer bolts being manufactured by Jabiru are still not to an acceptable spec. I asked the question of Susan and she wouldn't answer, neither would the UK agent.

 

Andrew has the solution with properly sized bolts and I'd like a set for my 3300 (#1460).

 

Properly sized bolts won't need loctite.

 

Properly sized bolts can be used with MS nuts.

 

Properly sized boths can be retorqued if barrel heating shows tightness.

 

They won't slip and lose tension so won't need rechecking.

 

Lets concentrate on the issue that this thread was started for and not succumb to suggestion of contributory issues that have been added to hide the fundamental issue:

 

Jabiru have manufacted a load of undersized bolts and don't want to admit it.

 

Regards, Clive

 

3300 #1460, 39 hrs

 

2200 #596, 1300hrs