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Discussion Starter · #1 ·
I bet this is an original thread.

Does anyone have a few used 6.0 head bolts from an original OE engine, ones tightened at the factory? I'd pay the postage.
 

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I can't wait for the results on this one. What are you testing this time?
 

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Discussion Starter · #3 · (Edited)
Just a curiosity.

I have a set of brand new bolts, and I have the set I removed from my Ford reman when I took it apart. I haven't gone through all of them, but I do not see any diameter change between the sets. It's like they were never taken to TTY. Which considering the other work done to this motor may very well be.

You can't really check them for length as they were not machined to a consistent length as some other head bolts are. But in a yielded state, the diameter will change ..... somewhere if they are yielded.

It might be my resolution is not small enough, or the diameter change is too small due to it being spread over a large area so that you can't. But I need another example to see if this can be measured in the field at all. Lengthwise, a 200mm long head bolt might change in length by a certain amount and still be acceptable. Some manufacturers have that limitation when they torque close to the proof load, just under yield. Over my life, I've checked for that only a few times, but I've never checked diameter. It's slightly yielded, like being slightly pregnant.

This is not about If a TTY can be reused; I'd never tell someone to do that. You don't know where on the curve the engineer has yielded the bolt to, how close to the ultimate strength.

Edited, sentence structure.
 

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Discussion Starter · #4 ·
Here's an example of an engine manufacturer that has a Go / No Go value for using head bolts since I brought it up.

775642
 

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The results will be interesting -- of all the engines I have done over the years, I don't remember measuring bolt diameter -- there was a specified length that was used tho -- as long as the bolts fell into that length we re-used them, unless it was specified by warranty

Maybe the engines I was working on were more accepting of the engineered tolerances than the Ford engine
 

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Discussion Starter · #6 · (Edited)
Some manufacturers don't go fully into the yield point; they bring it higher than the standard clamp load up to the proof load to get the most out of a fastener. But with the wide friction spread using torque, you can easily get to yield. Then the only way to know that is to check the length. If it's too long, it yielded.

The diameter values may be too small to measure. I'm trying to figure out where the movement is. I can go down to 0.0001", but it may be smaller than that. This may be a total waste of time.

Both the factory 6.0 and 6.4 bolts were thread rolled to alter the stretch, the 6.4 bolts, while shorter, are threaded a longer distance. The thread engagement into the block is 11 threads, so there are playing with lengths, altering the stretch zone. It's not as well-engineered as an aerospace or rod TTY, where the threads are stronger than the shank.

I just thought of another way; tomorrow, I'll see if there is any change to the thread pitch. Interesting that the flange under the head is thicker, but the tension may be higher. While it's a larger diameter, they don't wind the bolt (technically a screw) into the block as far.

775650


775651
775652
 
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Discussion Starter · #7 · (Edited)
The bolts were yielded! The damn fools did something correctly. Not the best image trying to do this in front of the screen with only two hands.

The thread pitch is changed down the length; the used bolt pitch is longer than the 2mm new bolt. This is because they are using the rolled thread area to control the yield, the thread extends much longer than it needs to be. Bad image; I was trying to capture two things at once.

775659


With the thread engagement area in the block, there is no deformation.

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Once you go out of the area, the thread pitch changes.

775661


It's better seen in the entirety of the rolled thread. Going through all the bolts, they have been rolled exactly the same amount; the threads are degreed the same.

No longer a 2mm pitch down the length once yielded. But the shanks measure exactly the same length from the flange to the first/last thread, depending on your frame of reference.

775662



They used the rolled thread area to control how much yield they wanted in the bolts, and the 6.4 bolts have a longer yield length (orange) despite being a shorter bolt overall. The shank and the rolled threads become two springs in tension. Block thread engagement appears to be the same.

775663
 

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I find this fascinating even though I have absolutely no idea what you are talking about or describing lol. Feel like I'm taking a 500 level class in college without taking the 101 haha.
 

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Discussion Starter · #9 · (Edited)
I'm going down to rabbit hole level 10 - I try to understand why things are done when I see something altered.

If they just went from 14 to 16mm bolts, OK. But there are other changes, and what first got my attention was why to thread such a long distance that is never engaged. The threaded area is longer by 4mm and the shank is reduced by 21mm. That along with the different tightening specs alters the design; it's not just clamping load.

My first employment was with a company working with carbon fiber; they were moving into automotive from sporting goods. Two engineers came from General Dynamics, where they designed and built the cargo doors for the space shuttles. Since some of our components were bolted together, we got into aerospace fasteners' discussions, where TTY is commonplace. They are highly engineered designs, not your common 'calculate the clamping load you need and size a bolt that has the load at the "clamping load" value,' a percentage of yield so you can use the bolt over and over while allowing for the inaccuracies of using torque as your method of control. You can use the Torque-Angle method on any bolt, not just a TTY - it's more precise than Torque, no matter the lubrication used.

Due to friction, Torque control has a +/- of 25%; add the 2 to 4% variance onto that for torque wrenches. You can tighten that up a few percent with the type of lubricant (ARP Lube), but it's still not as precise as Torque-Angle. And there are more precise means to ensure proper torque, used mostly in the structural or pipefitting industry. Bolt elongation is so much of an improvement, TTY. But they also hydraulicly stretch the bolt, then lock it down with the nut. Truck frames use those swaged on nuts onto elongated bolts.

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While ARP uses a graph to show consistency with ARP lube (there's much more to the story of those graphs when what ARP marketing is using them for - another discussion), there is variation in clamping force.

Oil, Moly, Detroit #2, and ARP Lube. ARP lube is better than those lubricants but better than TTY????

775665


I'll leave thread polishing out of the discussion.

I've listened through about 2 dozen videos on studs and TTY, and more published stories in the trade journals. I feel like the woman in the ad where everyone is missing the point. The design of head bolts is much more than just clamping load, especially due to the gasket, and more than I've capable of answering. Fastening is a specialized field.

But the primary reason for TTY is the consistency of clamping load across the entire surface, in this case, the heads, using the angle to determine elongation. You stretch into the flatter yielding area where rotational variance does not develop as much of a Delta bolt to bolt or stud to stud. It is tension limiting is another way of thinking of it.

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The issue for me is ARP goes back to using the less precise Torque, which is probably because they don't have the ability to understand the gasket crush; they are just giving a value to the same clamping load design using a fastener (stud) that has different properties.

I found one video demonstrating the issue, even though I don't think that was the overall intention. And another thread source where I have issues with what they say, being in touch with my feminine side. But it's a good demonstration where using the ARP specified torque while using the ARP lube does not get you the proper elongation with an ARP 2000 fastener. We can't do that when using the ARP head bolts, so the question becomes how consistent and how well are we achieving the proper tension with the ARP studs due to using the poorer technique of using torque? And is that why some people like KDD are starting to recommend using 625 studs, but for the wrong reason.


 

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