Bolt tightening procedure 1

[HenHen]

Hi!

Attachment is from a procedure regarding conrod bolts, torque to yield type.

My understanding of what's going on in this bolt tightening procedure:

The bolts are stretched a bit more in each step. After completing step 7, the clamping force is greater than after completing step 3, and after completing 11, the clamping force is greater than after step 7. The clamping force increases for each iteration. Agree? Any other reason for doing it like this?

Br
HH

 

[EdStainless]

That is the idea, also to take up any slack in the rest of the parts.
I have seen similar procedures that after the second round do not relax clear to zero.
My question is which rules, the torque or the rotation?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[HenHen]

Thank you for the reply! There's no compensation for rotation?;p

Follow up question!

How long is the engine going to last if only step 1-3 was performed?
S65 4L V8 with 8300RPM redline.. Current owner didn't read the entire procedure when installing new conrod bearings..

Told him not to drive the thing, but he won't listen...

 

[JohnRBaker]

It will probably be OK, for awhile at least ;-)

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[EdStainless]

If everything was seated and well positioned it is fine, if something was not quite right then who knows.
Of course it also depends on load/speed and what else have been modified in this engine.
It is a very robust platform, but build errors can kill anything.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[enginesrus]

Just wow. I was under the impression that most torque to yield fasteners would not do good exercising them and is why they are usually one time use. That is like a stretch and keep stretching procedure.

 

[HenHen]

Yep, first time I’ve seen it. Guess they save a few bucks on the bolts doing it like this..

 

[SwinnyGG]

My question is which rules, the torque or the rotation?

It's not one or the other- its one THEN the other.

1. Torque all bolts to 6 Nm

2. Torque all bolts to 20 Nm

3. Turn all bolts 130⁰

 

[GrouchyStressedTensePoor]

jgKRI,

In general or for this specific application?

Thanks

GSTP

Graduate Mechanical Design Engineer
UK

 

[JJPellin]

I am not familiar with the use of "torque to yield" fasteners. How is it that you know that this was the intention with these bolts? If I saw this procedure for connecting rod bolts on one of our compressors, I would assume a different purpose. I would assume that the intention was to alter the mating surfaces between the nut and bolt by subjecting them to a predefined stretch repeatedly. For new nuts and new bolts, I would expect this to change the surface finish of the mating surfaces slightly at each re-torque resulting in a more consistent stretch outcome. This could be demonstrated by the use of a stretch micrometer. If the bolt stretch increased with each repetition, it could suggest that the loading torque was resulting in slightly more stretch as the surfaces were smoothed. But, this should approach a consistent values as the process was repeated over and over. In other words, this would really only be beneficial on new nuts and bolts. And, if higher cost bolts with rolled threads were used, it might be completely unnecessary.

I will ask our reciprocating compressor program owner for his take on this.

If this procedure was really bringing the entire bolt to yield, it seems like a really bad idea to do that over and over.

Johnny Pellin

 

[SwinnyGG]

In general or for this specific application?

Most torque-to-yield fasteners use a similar scheme- where some low level of torque is applied, the purpose of which is just to seat the stack of components and ensure everything is in firm contact. The rotation component is then applied so that the fastener is put into the inelastic region in a controlled way.

If this procedure was really bringing the entire bolt to yield, it seems like a really bad idea to do that over and over.

Torque-to-yield bolts dont experience yield everywhere. They experience yield in one specific spot, which takes advantage of physics and results in very consistent bolt preload levels with simple installation tools and procedures.

They are designed per application- the rod bolts for the S65 are not some off-the-shelf part that was repurposed. They were designed specifically for this application and this installation procedure.

With regard to multiple tightening stages- the S65 uses rods with cracked caps. With that style of big-end assembly, it is CRITICAL that the caps are assembled correctly and perfectly aligned. I suspect the multiple stage process is designed to leave no doubt that the caps are properly seated before the work is finished.

 

[Tmoose]

I don't think it is a necessity that all angle tightened fasteners are torque to yield.

 

[SwinnyGG]

I would agree that seeing an angle step as part of a tightening procedure does not in itself indicate a torque-to-yield fastener.

 

[GrouchyStressedTensePoor]

Thanks jgKRI.

GSTP

Graduate Mechanical Design Engineer
UK