Rolled Thread Engine Through Bolts Available as alternative

[JabSP6]

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

 

 

[Guest JRMobile]

Hi Andrew

 

Thanks for the heads up and info on these bolts. I beleive that the rolled threads are many times stronger than the machined threads. Did Alliance Fasteners indicate how much stronger these rolled thrads are.

 

Cheers

 

 

[facthunter]

Is the design like the originals otherwise? They need to be wasted and have accurately ground sections to align the cases. Nev

 

 

[Thirsty]

I was speaking to someone at Natfly about this and he reckons Rod Stiff told him the thru bolts supplied by Jabiru ARE rolled thread! Anyone know for sure? I'm no machinest but the standard Jab thru bolts threads appear to be cut to me.

 

 

[Thirsty]

And another point - why would Jab not supply rolled thread thru bolts if they really are that much stronger? Is it a question of cost maybe?

 

 

[JabSP6]

JR Mobile.

 

Alliance Fasteners are saying that they will be up to 3 times the strength of the machined thread. The standard Bolts are only grade 5 4140 where as the rolled threads will also be using grade 8 4140 round bar.

 

Facehunter/ Thirsty

 

The Standard Long through bolts are just 10mm round bar with the ends machined down and a the 3/8" UNF thread on either end. The Short bolts have a 10 x 1.5mm thread on the case side and 3/8" UNF on the Barrel side. They are made at Camet on a CnC lath so, NO they are not a rolled thread. The new 12 point nuts (ARP) are a Rolled Thread. That is why i thought it would be better to have both the bolt and nut rolled thread also to improve the contact between the nut and bolt in the thread.

 

When I first went searching for companies that could roll threads in the size required i couldn't locate any in Australia that had 3/8" UNF dies. I contacted ARP to supply but they wanted up around $500 for the set and had to be specially made and imported from USA. TJ actually imported the dies in to do this job for me at his cost.

 

When i asked the factory why they under cut the section of bolt before the thread instead of leaving it at 10mm all the way to the thread and having a small radius just before the thread the only response i got was to improve the strength of the bolt??? I'm no engineer but i don't understand the logic in this. Anyway. Moving on.

 

From what i understand the cases are dowelled and the bolt does not play any part in aligning the cases. It simply clamps them together. I know of 10mm bar with metric threads being used with no undercut section to clamp the cases together and it works. The only thing that had to be done was the holes in the barrels had to be drilled out slightly to give clearance for the slightly bigger thread. (10mm instead of 3/8")

 

I believe that the reason Jabiru have not used rolled thread is exactly as you say Thirsty, COST. They can be turned out on a CNC quite cheaply in Bundy which would help keep the overall cost of the engine down.

 

I, on the other hand, don't mind paying a bit extra for a few components to have an overall superior product. Its all about improving the reliability for me.

 

Regards

 

Andrew

 

 

[facthunter]

SP6, It's extremely important that the studs be wasted to a diameter smaller than the thread root diameter and that it have radius's, and a smooth finish, otherwise the load (actually it's a strain) will be taken by the short threaded portions below the nuts predominantly, and they ( the studs),will fail . There may also be a consideration of the centrality of the thread with the rolled process. The threads are rolled hot and may end up not running as true as the machined bar process. This could put uneven loads on the cylinder flange.. This could exist if the nut faces ar not true to its thread axis too. The effect would be similar . None of this matters in the normal auto situation but aero engines do not carry much extra metal anywhere to cope with variations of dimensions..Nev

 

 

[Guest Maj Millard]

Your standard grade AN aviation bolts are rolled threads. They are much stronger because of the nice round 'valley' at the bottom of each thread cut, instead of the sharp 'V' cut at the bottom of a 'cut' thread, which is an inherant weakness waiting to crack.

 

If you go back to my past threads on through bolt dramas, you will find that this is what I have been suggesting all along. It is nice to see that somebody (but probabily not the Jab factory) at last is listening to what really is basic aeronautical hardware knowledge!.............................Maj....

 

 

[turboplanner]

Grade 8 bolts are what we use to bolt truck chassis together, nothing to write home about.

 

While this might look good, for aircraft use where lives are at stake, this is only step 1.

 

The next step is fail testing of a representative batch before getting too excited.

 

"Waisted" Facthunter, but what you are talking about is what I would expect to see.

 

 

[JabSP6]

Maj

 

As you mentioned, this has been discussed several times before and i have taken all this info on board and decided to find an Australian Company to source the components for us.

 

This is a well know company and produces rolled threads in many different sizes and has their own specialised machines that do Quality Assurance Testing of the threads which will pick up any problems such as the things Facehunter has rightly mentioned.

 

Turboplanner. I plan on having these bolts tested to see what tension either the bolts fail or the nuts fail. The old standard components have been tested and have failed anywhere from 28ft/lb to 35ft/lb. Some ARP 10mm metric studs the same length have been tested and failed just under 60ft/lb.

 

I will let you know what we get out of these studs once i receive them.

 

I also plan on taking a set into Rod to see if he is at all interested in the idea and will pass on the supplier details if he is.

 

Hope this helps and will keep you posted.

 

Regards

 

Andrew

 

 

[turboplanner]

JabSP6 you are to be commended for your efforts, so please take the following comments as constructive.

 

In referring to lb/ft you seem to be talking about a torquing test where the nut is screwed until failure occurs.

 

I would normally expect a test in a jig with a straight pull, and believe this would be a more accurate comparison.

 

I'd suggest a talk with a Metallurgic test company who could produce accurate and acceptable data to take to Rod.

 

I'm not a Metallurgist, so I'm subject to correction on this, but my understanding is that you use waisting to provide a very consistent fail point in tension (the constant smaller diameter untouched material well away from the thread area and well blow any fail points in the thread area caused by machine activity.

 

What I find very interesting from my own experience is that at around 28 lb/ft failure point it would be very easy to overtighten bolts almost to the failure point without a very accurate torque wrench, and careful attention to the nut faces. That's not a lot of torque to someone with a spanner in his hand.

 

 

[Thirsty]

I thought these through bolts were failing because they were loosening off thus allowing lateral movement which then fatigued the bolt - is that not correct?

 

 

[JabSP6]

Turboplanner

 

I welcome all comments especially the ones that raise question because that is the whole point of this forum. To use the vast wealth of knowledge that is available within this group to come up with the best solution.

 

As i have said i am only new to the aviation industry and respect the opinions of those who have alot more expertise than i do in this field.

 

The way i initially tested the old standard bolt was i made up a jig that replicated the engine case and barrels. I fitted a nut to either end of the thread and then slowly applied tension to them to see whether they would achieve a particular tension. Some made it to the required 30ft/lb and some wouldn't even do that. My understanding of the failures is similar to Thirsty's. The threads are not holding the required tension (especially when thermal expansion could increase this load) and therfore allow movement of the through bolts ultimately ending in the bolt failure. I think a straight pull test will definately indicate the strength of the bolt itself which i would expect to be higher than the standard bolt simply because we are using Grade 8 instead of Grade 5 and also the Rolled process. I will seek out somewhere to have this test performed so if anyone can help out with this please PM me so we can share the results with everyone.

 

I have a good friend that spent 5 years working at Camet assembling these motors and he has said that it was quite normal to be tensioning up a set of barrels and find the nuts would not reach the specified tension and they would replace the nut and bolt and go again. They were not allowed to change things because they were supplying a product to the Jabiru specifications.

 

So i believe (like many of you do) that by improving the strength of the thread in both the Nut (ARP nuts have done) and the studs (Rolled threads will do) this should put an end to the problems once and for all.

 

I will get some testing done to confirm this and see how it all turns out.

 

Regards

 

Andrew

 

 

[Guest Maj Millard]

JabSP6, Your efforts and interest in this area are to be commended , you are on the right track, and I believe your testing efforts will bear fruit. I would agree that Turbos suggestion Re: straight pull testing, is probabily a better testing method, however what you are doing with the torque testing should give a valuable comparison if conducted consistantly.

 

Turboplanner, I don't understand your negative implications in post #11, obviously jabSP6, is spending his good time in an effort to solve a problem, which needs to be solved. He is doing a lot more that the factory themselves are doing, as I see it. His efforts deserve our support................................................................Maj...

 

 

[turboplanner]

In the first para, I commended him.

 

The next part you and I agree on

 

Then I suggested if he's going to see Rod, he goes with some figures - any manufacturer would sit up and take notice with firm figures

 

I started to talk about waisting and lost my way. Where I was going was - say a 10 mm bolt has the necessary fail point at the thread, it's possible to lighten the bolt by waisting, not terribly relevant I know.

 

The last para to me gives some idea of how some bolts could have failed.

 

I didn't see anything negative there. He is suggesting someone put these bolts into an aircraft where an engine failure could result in a forced landing, so it is best to dot the i's and cross the t's with as much provable data as possible.

 

 

[Guest JRMobile]

JabSP6, Your efforts and interest in this area are to be commended , you are on the right track, and I believe your testing efforts will bear fruit. I would agree that Turbos suggestion Re: straight pull testing, is probabily a better testing method, however what you are doing with the torque testing should give a valuable comparison if conducted consistantly. His efforts deserve our support................................................................Maj...

Maj, Can I second these comments! :thumb_up:

 

 

[Guest Maj Millard]

All good Turbo. Putting a new part into their aircraft and causing an engine failure and forced landing would be no different to what they have been experiencing for a bit, with the factory parts.

 

I would also expect Rod Stiff to sit up and take notice of any good new data if presented to him. This remains to be seen however, and I do expect that JabSP6 will kept us up to developments there......................Maj...

 

 

[Guest Maj Millard]

Thank You JR.................................................................................Maj...

 

 

[Thirsty]

I also wish to provide my support and best wishes to Andrew. You are to be congratulated for trying to improve what could be a GREAT aussie product!

 

 

[facthunter]

Please don't take my input as criticism of what you are doing. IF these bolts fail with torquing to 35 ft/lbs they would be seriously deficient, in strength. Some bolts are single use. Torque to permanent stretch. I have never understood the logic of this. The metal has gone beyond the yield point. I would think that a bolt should carry well in excess of the manufacturers torque figure. The torque figure should impose enough force on the cases to keep them where they should be. Together and in alignment, plus a margin in normal operation

 

Jabiru suggest that detonation features as a cause of these failures.. Serious detonation imposes very large loads on the engine components often enough to destroy them. You practically cannot build an engine strong enough to guarantee it surviving strong detonation. Having stronger bolts is a good move but removing the cause is the most important thing to do. I believe an engine that has broken a through bolt/stud should be stripped and fully inspected before being put back in service. Nev

 

 

[JabSP6]

Guys

 

As i have said earlier I don't take any of your comments negatively. They are all constructive the way i see, to arrive at the most desirable goal, and that is making these motor as safe as possible. I agree Nev that we should be focusing on the cause of the problem which is why when i broke an exhaust valve off, the first thing i did after the rebuild was to fit the MGL EGT & CHT sensors to every cylinder. It was only then that i realised that i was running too hot and too lean. I didn't jump up and down complaining to Jabiru that the motor was no good. I found the cause and rectified the problem. I improved the airflow to the heads, fitted fine finned heads, added in some ceramic coating, which together reduced head temps dramatically. I then richened up the mixtures but as a secondary measure i also installed 1 piece valves and fitted the K Liner Inserts so that no mater what happened to the motor in the future i should not be left in a situation where a valve head could break off. We have all found issues with these Through Bolts so i figured the best thing to do here to help with the safety and reliability of the motor is to eliminate the problem with the Rolled Thread alternative which was suggested by you all on the forum.

 

I will carry out testing on the bolts so this info can be passed on to all including Rod so if anyone out there can help out with a contact for the straight pull test that Turboplanner has suggested i will forward some bolts. I will also carry out the test procedure that i have done to see how they compare and let you know. I am a firm believer of trying to improve if a problem has been identified rather than turn a blind eye and wait for it to eventually happen to me.

 

Regards

 

Andrew

 

 

[winsor68]

This is what experimental aviation is all about...

 

 

[Guest Maj Millard]

Well said Facthunter, And also spot-on JabSP6,......I would agree 100% with what you suggest. These engines do indeed have great potential as an Aussie product. However several inherent serious problems have to be ironed out firstly. Hopefully by airing constructive discussion and valid critism, the factory will be forced to take a serious look at problems, and develope solutions, or at least take notice from those users who are doing their work for them in the field.

 

As I've said previous, the first thing an aero-engine must be is reliable..You don't get that if the engine has built-in design flaws, that aren't corrected by the manufacturers................................Maj...

 

 

[stanzahero]

Some bolts are single use. Torque to permanent stretch.

It's more like 'torqued to a maximum elasticity'.

A lot of the European engine rebuild kits are now including head bolt kits.

 

It's a way of guaranteeing that an engine will not have a head bolt / head gasket failure due to over stressed bolts that go back into service.

 

It also gives the product a service life.

 

When I built diesels, the big end bolts were changed before the final assembly because each bolt was limited to the number of times it could be torqued.

 

 

[Thirsty]

Andrew have you done anything with the locating dowels in your engine? When ordering dowels from Jab now you have to provide the diameter of the holes so they can supply matched dowels. I believe the dowels supplied will be virtually an interference fit (which is going to make them very hard to get out again!) which is supposed to stop the movement of the case halves which is what ultimately causes the bolt breakage.