Topics

Loose cylinder !


Mick O'Connor
 

Maybe he didn’t measure the ‘stretch’ on his cylinder fixings ?


Jim Chuk
 

Thought those beemers were supposed to go forever...JImChuk


On Tue, Mar 23, 2021 at 2:49 PM Mick O'Connor via groups.io <mickoconnor909=btinternet.com@groups.io> wrote:
Maybe he didn’t measure the ‘stretch’  on his cylinder fixings ?







David Amsler
 

Probably followed Jabiru's "dry" torque procedure.

David A.

On Tue, Mar 23, 2021 at 3:49 PM Mick O'Connor via groups.io <mickoconnor909=btinternet.com@groups.io> wrote:
Maybe he didn’t measure the ‘stretch’  on his cylinder fixings ?







Mick O'Connor
 

Can anyone give an accurate, true and proven correct alternative ‘wet’ torque or bolt stretch ?

Mick


On 23 Mar 2021, at 22:05, David Amsler <EnergyHawk@...> wrote:

Probably followed Jabiru's "dry" torque procedure.

David A.

On Tue, Mar 23, 2021 at 3:49 PM Mick O'Connor via groups.io <mickoconnor909=btinternet.com@groups.io> wrote:
Maybe he didn’t measure the ‘stretch’  on his cylinder fixings ?







glen english LIST
 

I did for stretch. but Mick you didnt like it. :-)

Friday, I will measure the "onset of stretch" torque.
That is, the torque (with the fancy lube) where there is 0.1mm elongation (stretch).

That's where (I think) the crankcase has been compressed up.

Then it is a matter of going a specific rotation from there based on the thread pitch.

approximately. there may be some more crankcase squash, I dunno.

to be measured with other bolts nearby at or greater than onset=stretch torque

-glen

On 3/24/2021 9:18 AM, Mick O'Connor via groups.io wrote:
Can anyone give an accurate, true and proven correct alternative ‘wet’ torque or bolt stretch ?
Mick


Jay Scheevel
 

Hi Glen,

If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Tuesday, March 23, 2021 4:43 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

I did for stretch. but Mick you didnt like it. :-)

Friday, I will measure the "onset of stretch" torque.
That is, the torque (with the fancy lube) where there is 0.1mm elongation (stretch).

That's where (I think) the crankcase has been compressed up.

Then it is a matter of going a specific rotation from there based on the thread pitch.

approximately. there may be some more crankcase squash, I dunno.

to be measured with other bolts nearby at or greater than onset=stretch torque

-glen


On 3/24/2021 9:18 AM, Mick O'Connor via groups.io wrote:
Can anyone give an accurate, true and proven correct alternative ‘wet’
torque or bolt stretch ?

Mick


glen english LIST
 

Hi Jay
agreed.
On studs:
Once i know what the approx onset-of-stretch torque is for a specific nut-washer-thread-lube combination, then I would apply the stretch I want ( proportional to length of the stud) and go the rotation for that stretch. likely to be close enough for this work.
(in absence of an ultrasonic stuf tip tension measurement tool) .

On 3/24/2021 10:35 AM, Jay Scheevel wrote:
Hi Glen,
If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.


Mark Dunstone
 

These fancy tension washers would be nifty if they came in suitable sizes...but alas, I don’t think so. 

That Beemer....who said it stopped running?  


On Wed, 24 Mar 2021 at 11:19, glen english LIST <glenlist@...> wrote:
Hi Jay
agreed.
On studs:
Once i know what the approx onset-of-stretch torque is for a specific
nut-washer-thread-lube combination, then  I would apply the stretch I
want ( proportional to length of the stud) and go the rotation for that
stretch. likely to be close enough for this work.
(in absence of an ultrasonic stuf tip tension measurement tool) .



On 3/24/2021 10:35 AM, Jay Scheevel wrote:
> Hi Glen,
>
> If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.
>






Jay Scheevel
 

Pretty cool, Marc. That would really be the solution for a lot of applications. Too bad they are only for large fasteners.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Mark Dunstone
Sent: Tuesday, March 23, 2021 7:30 PM
To: main@jabcamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

These fancy tension washers would be nifty if they came in suitable sizes...but alas, I don’t think so. 

 

That Beemer....who said it stopped running?  

 

 

On Wed, 24 Mar 2021 at 11:19, glen english LIST <glenlist@...> wrote:

Hi Jay
agreed.
On studs:
Once i know what the approx onset-of-stretch torque is for a specific
nut-washer-thread-lube combination, then  I would apply the stretch I
want ( proportional to length of the stud) and go the rotation for that
stretch. likely to be close enough for this work.
(in absence of an ultrasonic stuf tip tension measurement tool) .



On 3/24/2021 10:35 AM, Jay Scheevel wrote:
> Hi Glen,
>
> If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.
>





Mick O'Connor
 

Glen,
I don’t remember saying I didn’t like it ?
Anyway, I know of only one through bolt failure in the U.K., so not really a major problem.

Would I implement a torquing method developed by an enthusiastic person, that is untested or the method developed by the engine manufacturer ?

I have to assume my engine was assembled by Jabiru using the ‘dry’ torque and it has covered a trouble free 900 hours. Aren't there 1000s of engines running fine with ‘dry’ torqued through bolts ?

On 23 Mar 2021, at 23:35, Jay Scheevel <jay@scheevel.com> wrote:

Hi Glen,

If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.

Jay
-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Tuesday, March 23, 2021 4:43 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

I did for stretch. but Mick you didnt like it. :-)

Friday, I will measure the "onset of stretch" torque.
That is, the torque (with the fancy lube) where there is 0.1mm elongation (stretch).

That's where (I think) the crankcase has been compressed up.

Then it is a matter of going a specific rotation from there based on the thread pitch.

approximately. there may be some more crankcase squash, I dunno.

to be measured with other bolts nearby at or greater than onset=stretch torque

-glen


On 3/24/2021 9:18 AM, Mick O'Connor via groups.io wrote:
Can anyone give an accurate, true and proven correct alternative ‘wet’
torque or bolt stretch ?

Mick











glen english LIST
 

Hi Mick

I beleive a real measurement. I have little faith in Jabiru to get it 100% right. Especially when dry / unprepared leaves such a critical tension to a rather wide variation result....and ignoring industry best practice, that is without question nor argument.

If that's the attitude of the manufacturer, I wonder just how many failures are due to factory assembly errors. IE just what technique was used to ensure the conrod screws and bolts are the correct tension etc.????

IE I dont like leaving things to chance. Bad things happen when good people do nothing.
and of course there have been hundreds of failures. Huge numbers.

I'm not being critical of the design . I am just highlighting possibilities.
Having said all that, at least the bottom end is reliable, I've never heard of the bottom end of the engines havinf trouble. I hear of a Jabiru engine failure about once a week or so locally..

On 3/24/2021 7:18 PM, Mick O'Connor via groups.io wrote:
Glen,
I don’t remember saying I didn’t like it ?
Anyway, I know of only one through bolt failure in the U.K., so not really a major problem.
Would I implement a torquing method developed by an enthusiastic person, that is untested or the method developed by the engine manufacturer ?
I have to assume my engine was assembled by Jabiru using the ‘dry’ torque and it has covered a trouble free 900 hours. Aren't there 1000s of engines running fine with ‘dry’ torqued through bolts ?

On 23 Mar 2021, at 23:35, Jay Scheevel <jay@scheevel.com> wrote:

Hi Glen,


jabcamit@...
 

You can easily work  out the  perfect torque  (or degrees of rotation)   by tensioning your old through bolts on  a simple jig  (see my previous posting number 14213 of Feb 18 2021) and plotting  torque against rotation.  Lube the bolt washer combination (thread and under the nut head) at one end - Nordloc specify a copper-ease type low friction paste on their bolt torquing recommendations ). Use jab lubrication instructions at the other end. Alternately tighten the nuts  say 30 degs at a time. You will finish up with 2 curves one for the dry nut the other for the lubed nut . For each curve the point where it starts to flatten is when the elastic limit has been exceeded for that lubrication combination. 

I think you want to tighten the bolts to 75% of the elastic limit tension.

Mick if you care to re-read my post of 18 Feb. I think your question will be fully answered

BobP


David Amsler
 

Mick,

This probably will not help you sleep nights, but many if not all Jabiru engines were assembled in CAMit's shop prior to CAMit marketing their own, and that continued for a while after that as well.  Ian used oil to torque his engines' through bolts.  I do not know what torque spec he used on Jabiru engines, but do know he had his own method for setting some other parts that were not per Jabiru's manual.

David A.

On Wed, Mar 24, 2021 at 4:18 AM Mick O'Connor via groups.io <mickoconnor909=btinternet.com@groups.io> wrote:
Glen,
I don’t remember saying I didn’t like it ?
Anyway, I know of only one through bolt failure in the U.K., so not really a major problem.

Would I implement a torquing method developed by an enthusiastic person, that is untested or the method developed by the engine manufacturer ?

I have to assume my engine was assembled by Jabiru using the ‘dry’ torque and it has covered a trouble free 900 hours. Aren't there 1000s of engines running fine with ‘dry’ torqued through bolts ?

> On 23 Mar 2021, at 23:35, Jay Scheevel <jay@...> wrote:
>
> Hi Glen,
>
> If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.
>
> Jay
> -----Original Message-----
> From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
> Sent: Tuesday, March 23, 2021 4:43 PM
> To: main@JabCamit.groups.io
> Subject: Re: [JabCamit] Loose cylinder !
>
> I did for stretch. but Mick you didnt like it. :-)
>
> Friday, I will measure the "onset of stretch" torque.
> That is, the torque (with the fancy lube)  where there is 0.1mm elongation (stretch).
>
> That's where (I think)  the crankcase has been compressed up.
>
> Then it is a matter of going  a specific rotation  from there based on the thread pitch.
>
> approximately.  there may be some more crankcase squash, I dunno.
>
> to be measured with other bolts nearby at or greater than onset=stretch torque
>
> -glen
>
>
>> On 3/24/2021 9:18 AM, Mick O'Connor via groups.io wrote:
>> Can anyone give an accurate, true and proven correct alternative ‘wet’
>> torque or bolt stretch ?
>>
>> Mick
>>
>
>
>
>
>
>
>
>
>
>
>
>







Mick O'Connor
 

David, I’m not too worried. I can just see the report after an engine failure “ so Mr O’Connor, your through bolts failed because you ignored the manufacturer’s advice and did the nuts up using advice from someone you don’t know on the internet ?, hmmm”

 

Mick

 

From: main@JabCamit.groups.io [mailto:main@JabCamit.groups.io] On Behalf Of David Amsler
Sent: 24 March 2021 14:13
To: main@jabcamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

Mick,

 

This probably will not help you sleep nights, but many if not all Jabiru engines were assembled in CAMit's shop prior to CAMit marketing their own, and that continued for a while after that as well.  Ian used oil to torque his engines' through bolts.  I do not know what torque spec he used on Jabiru engines, but do know he had his own method for setting some other parts that were not per Jabiru's manual.

 

David A.

 

On Wed, Mar 24, 2021 at 4:18 AM Mick O'Connor via groups.io <mickoconnor909=btinternet.com@groups.io> wrote:

Glen,
I don’t remember saying I didn’t like it ?
Anyway, I know of only one through bolt failure in the U.K., so not really a major problem.

Would I implement a torquing method developed by an enthusiastic person, that is untested or the method developed by the engine manufacturer ?

I have to assume my engine was assembled by Jabiru using the ‘dry’ torque and it has covered a trouble free 900 hours. Aren't there 1000s of engines running fine with ‘dry’ torqued through bolts ?

> On 23 Mar 2021, at 23:35, Jay Scheevel <jay@...> wrote:
>
> Hi Glen,
>
> If you measure stretch for each 10-20 degrees of rotation, then plot that up, you can find, graphically, the point at which the case becomes fully clamped. The fully clamped point is the place on the graph where stretch becomes linear with respect to rotation. I think you will find that the stretch versus rotation slope is slightly less than the thread pitch would dictate. This is because of the finite stiffness of the case which will also be linear in compression (subtractive). From these data you can compute the stiffness of the case and the stiffness of the bolt and compare to the theoretical study. Key practical item is to know the degrees of rotation that will achieve the linear stretch desired, then apply that rotation to all bolts. If the stretch versus rotation starts to deviate from linear at high stretch, then you have exceeded the plastic yield point of the bolt. Studs are another story altogether. I have not figured those out yet.
>
> Jay
> -----Original Message-----
> From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
> Sent: Tuesday, March 23, 2021 4:43 PM
> To: main@JabCamit.groups.io
> Subject: Re: [JabCamit] Loose cylinder !
>
> I did for stretch. but Mick you didnt like it. :-)
>
> Friday, I will measure the "onset of stretch" torque.
> That is, the torque (with the fancy lube)  where there is 0.1mm elongation (stretch).
>
> That's where (I think)  the crankcase has been compressed up.
>
> Then it is a matter of going  a specific rotation  from there based on the thread pitch.
>
> approximately.  there may be some more crankcase squash, I dunno.
>
> to be measured with other bolts nearby at or greater than onset=stretch torque
>
> -glen
>
>
>> On 3/24/2021 9:18 AM, Mick O'Connor via groups.io wrote:
>> Can anyone give an accurate, true and proven correct alternative ‘wet’
>> torque or bolt stretch ?
>>
>> Mick
>>
>
>
>
>
>
>
>
>
>
>
>
>






Mick O'Connor
 

Bob,

My old through bolts are a different design to my new ones

 

Mick

 

From: main@JabCamit.groups.io [mailto:main@JabCamit.groups.io] On Behalf Of jabcamit@...
Sent: 24 March 2021 12:35
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

You can easily work  out the  perfect torque  (or degrees of rotation)   by tensioning your old through bolts on  a simple jig  (see my previous posting number 14213 of Feb 18 2021) and plotting  torque against rotation.  Lube the bolt washer combination (thread and under the nut head) at one end - Nordloc specify a copper-ease type low friction paste on their bolt torquing recommendations ). Use jab lubrication instructions at the other end. Alternately tighten the nuts  say 30 degs at a time. You will finish up with 2 curves one for the dry nut the other for the lubed nut . For each curve the point where it starts to flatten is when the elastic limit has been exceeded for that lubrication combination. 

I think you want to tighten the bolts to 75% of the elastic limit tension.

Mick if you care to re-read my post of 18 Feb. I think your question will be fully answered

BobP


Jay Scheevel
 

I need to confirm (maybe someone on this group remembers), but I think that Jab’s recommendation with the longer/redesigned 3/8” through bolts and ARP nuts are to replace every 500 hours. I have an extra set so I will replace at 500 hours and that should get me to the 1000 hour TBO, when I will get the case machined to take the 7/16” bolts, provided the cylinders are still good. That is a long time down the road. Maybe we will all have fusion engines by then.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Mick O'Connor via groups.io
Sent: Wednesday, March 24, 2021 9:43 AM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

Bob,

My old through bolts are a different design to my new ones

 

Mick

 

From: main@JabCamit.groups.io [mailto:main@JabCamit.groups.io] On Behalf Of jabcamit@...
Sent: 24 March 2021 12:35
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

You can easily work  out the  perfect torque  (or degrees of rotation)   by tensioning your old through bolts on  a simple jig  (see my previous posting number 14213 of Feb 18 2021) and plotting  torque against rotation.  Lube the bolt washer combination (thread and under the nut head) at one end - Nordloc specify a copper-ease type low friction paste on their bolt torquing recommendations ). Use jab lubrication instructions at the other end. Alternately tighten the nuts  say 30 degs at a time. You will finish up with 2 curves one for the dry nut the other for the lubed nut . For each curve the point where it starts to flatten is when the elastic limit has been exceeded for that lubrication combination. 

I think you want to tighten the bolts to 75% of the elastic limit tension.

Mick if you care to re-read my post of 18 Feb. I think your question will be fully answered

BobP


Mark Dunstone
 

I thought the pie chart below might help people understand.  The objective of torquing a bolt is to set the tension of the bolt to within the paremeters tge designer/engineer have worked out.  

Because friction makes up such a large proportion of total torque, and because friction is highly variable, total torque as a technique of setting bolt tension will produce highly variable bolt tension....no matter how good the torque wrench or operator is.  Lube might decrease the spread or scatter a bit.  
For an operation like Jabiru, their use of consistent methods will probably reduce scatter to produce more consistent results but still highly variable.  Out in the field, various mechanics trying to reproduce the ‘in factory’ settings won’t achieve the same precision as the factory.  The question for Jabiru is how to get them (those mechanics...we call them ‘licensed aircraft maintenance engineers’) to get the least worse results given their real skills and knowledge, that doesn’t produce failures. Torquing the nuts with a calibrated torque wrench is likely to be it.  But this will still produce highly variable tensions.  Luckily the Jabiru cases and the 7/16 through bolts empirically show this works.

Jabiru could do what Glen or Bob suggest....use a specified lube and then torque, or light torque plus turn the nut X degrees, to reduce variability or scatter.  But would aircraft mechanics replicate this well given their skills and knowledge?  From my experience a significant proportion would not.

So, I’m with Mick.....stick with the manufacturer’s instructions, unless you have the confidence your alternative approach is better.  FWIW I would be unconcerned about using Jabiru’s recommended approach knowing the result is likely highly variable, except if I was using the 3/8 bolts in a 2200 hydraulic lifter motor, or re-torquing existing through bolts.  In the latter cases, I’m with Glen.  But I’d still like some added re-assurance that a long throughbolt extension of 0.4mm for the 7/16 bolts produces the desired tension in the bolt. What would it be for 3/8 bolts and for the shorter studs?






Jay Scheevel
 

Your points are valid, Mark. I would hope that a qualified rebuild technician would have the knowledge necessary to know how to do it by number of degrees rotation. Many auto engine manufacturers specify this method, so it is not unknown. With respect to torque, many are unaware that static friction and dynamic friction are different, and when the bulk of the friction is subject to static and or dynamic (dynamic being lower than static).  The nutface and thread friction you show below are subject to this transition and may even go stick-slip. So if the wrench stops moving during the torqueing process, everything goes static. Increasing the relative proportion of the thread extension torque is a good idea, because it is the only component of torque that you show below that does not experience any different torque whether static or dynamic is the extension torque.  May be academic at this point, as you point out. So many engines relatively few failures.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Mark Dunstone
Sent: Wednesday, March 24, 2021 6:11 PM
To: main@jabcamit.groups.io
Subject: Re: [JabCamit] Loose cylinder !

 

I thought the pie chart below might help people understand.  The objective of torquing a bolt is to set the tension of the bolt to within the paremeters tge designer/engineer have worked out.  

 

Because friction makes up such a large proportion of total torque, and because friction is highly variable, total torque as a technique of setting bolt tension will produce highly variable bolt tension....no matter how good the torque wrench or operator is.  Lube might decrease the spread or scatter a bit.  

For an operation like Jabiru, their use of consistent methods will probably reduce scatter to produce more consistent results but still highly variable.  Out in the field, various mechanics trying to reproduce the ‘in factory’ settings won’t achieve the same precision as the factory.  The question for Jabiru is how to get them (those mechanics...we call them ‘licensed aircraft maintenance engineers’) to get the least worse results given their real skills and knowledge, that doesn’t produce failures. Torquing the nuts with a calibrated torque wrench is likely to be it.  But this will still produce highly variable tensions.  Luckily the Jabiru cases and the 7/16 through bolts empirically show this works.

 

Jabiru could do what Glen or Bob suggest....use a specified lube and then torque, or light torque plus turn the nut X degrees, to reduce variability or scatter.  But would aircraft mechanics replicate this well given their skills and knowledge?  From my experience a significant proportion would not.

 

So, I’m with Mick.....stick with the manufacturer’s instructions, unless you have the confidence your alternative approach is better.  FWIW I would be unconcerned about using Jabiru’s recommended approach knowing the result is likely highly variable, except if I was using the 3/8 bolts in a 2200 hydraulic lifter motor, or re-torquing existing through bolts.  In the latter cases, I’m with Glen.  But I’d still like some added re-assurance that a long throughbolt extension of 0.4mm for the 7/16 bolts produces the desired tension in the bolt. What would it be for 3/8 bolts and for the shorter studs?

 

 

 

 

 


jabcamit@...
 

Mick, even though the through bolt profiles are different you can do  tests on your old bolts that will enable you to obtain more even tension on your engine through bolts.  

Alternately tightening (a few degrees at a time) lubricated and unlubricated nuts on opposite ends of the  bolt under test will tell you the (reduced)  torque to use if the threads are lubricated (but see picture in my earlier posting for important info in doing this).  Specialist lubricants on the threads and moving surfaces will be better for your engine as this will result in a more even tension across all bolts -the bigger the percentage of  the torque applied  that goes into stretching the bolt then the less the variation in tension resulting from inconsistent  thread and under-nut resistance. I suspect (experience, nothing I've read) that stiction will also be significantly lower when threads are lubricated with a high pressure lubricant. If so this will  further improve bolt tightening consistency. A copper based lubricant might be particularly good  at keeping friction levels down in the long term (when torque checking years into the future).

If the diameters of the  waisted section of your old and new bolts is the same, then the curve profile to determine the torque at which yield point will be reached will be the same shape (just a diffent number of nut flats).  So you can use this to work out the maximum safe torque to apply.  But you cant use the figures to calculate the number of flats to turn nuts to obtain the correct tension.

Mick if you wanted to send me a few of your old through bolts and nuts  I'd be happy to do a few tests on them and post my findings on this site.


BobP


Mick O'Connor
 

Glen,
I find your claim of 50 Jab failures per year locally is a tad hard to believe !

Mick

On 24 Mar 2021, at 08:35, glen english LIST <glenlist@cortexrf.com.au> wrote:

Hi Mick

I beleive a real measurement. I have little faith in Jabiru to get it 100% right. Especially when dry / unprepared leaves such a critical tension to a rather wide variation result....and ignoring industry best practice, that is without question nor argument.

If that's the attitude of the manufacturer, I wonder just how many failures are due to factory assembly errors. IE just what technique was used to ensure the conrod screws and bolts are the correct tension etc.????

IE I dont like leaving things to chance. Bad things happen when good people do nothing.
and of course there have been hundreds of failures. Huge numbers.

I'm not being critical of the design . I am just highlighting possibilities.
Having said all that, at least the bottom end is reliable, I've never heard of the bottom end of the engines havinf trouble. I hear of a Jabiru engine failure about once a week or so locally..


On 3/24/2021 7:18 PM, Mick O'Connor via groups.io wrote:
Glen,
I don’t remember saying I didn’t like it ?
Anyway, I know of only one through bolt failure in the U.K., so not really a major problem.
Would I implement a torquing method developed by an enthusiastic person, that is untested or the method developed by the engine manufacturer ?
I have to assume my engine was assembled by Jabiru using the ‘dry’ torque and it has covered a trouble free 900 hours. Aren't there 1000s of engines running fine with ‘dry’ torqued through bolts ?
On 23 Mar 2021, at 23:35, Jay Scheevel <jay@scheevel.com> wrote:

Hi Glen,