Head Bolt Angle Tightening - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
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post #1 of 11 (permalink) Old 10-01-2019, 11:36 PM Thread Starter
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Head Bolt Angle Tightening

Guys, what's the idea behind tightening the head bolts on a 3.5 to a certain torque, and then having to finish with a certain ANGLE, in our engines case, 90 degrees. Then to check it, refer back to a certain torque, over 90 ft lbs, and if not, the bolt is considered bad.
Ok, I get the tightening sequence beginning at 45 ft lbs, then 65 ft lbs, then a re-torque and check at 65 ft lbs again, but then turn the bolts 90 degrees??? Which is supposed to put the bolts at something over 90 ft lbs., and if not, the bolt is bad?
WTF? First of all, I have new bolts in my gasket kit, which is why I bought it. Head bolts are a one time stretch, and should not be re-used, correct me if I'm wrong.
Second, why an angle and not just a torque spec??? And why check that angle with a torque spec as a method of determining whether the head bolt is bad??? Oh, and lubing the head bolts with oil??? Huh??? Shouldn't the head bolts be installed DRY? With the threads in the block and the bolts being thoroughly cleaned?
Supposedly the angle method is more accurate, but I don't see it at all. If using a torque wrench is so inaccurate, yet utilized for the initial tightening, then the angle tightening is simply tightening an inaccurately torqued bolt.
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post #2 of 11 (permalink) Old 10-02-2019, 01:47 AM
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A properly tightened head bolt acts like a spring (applying clamping force). You tighten close to or slightly into the point of yield (permanent deformation, i.e. elongation). The 90 beyond is guaranteeing yielding of the bolt. (It is calculated not to yield it too much, as going beyond initial yield just results in necking down and weakening that spring effect and concentrates it thru a smaller cross-section.)

(“Normal” bolt torque specs. are to some specified percentage of yield, for example to 75% of yield.)

Torque is not appreciably increasing thru that additional 90 (because the bolt is yielding), which is why the last bit of tightening is not by torque, but by distance (degrees). It is ensuring that you are into the maximum spring action that is needed for adequate clamping, but not into a neck-down on the way to “ultimate yield”, AKA, the breaking point.

I don’t claim to have perfect understanding of it, but that’s the best I can explain it. As an afterthought, I looked it up: https://en.m.wikipedia.org/wiki/Torq...yield_fastener

Regarding the lubing, any valid torque spec. should be with stated or assumed lubed or non-lubed thread. I believe in industry, unless otherwise stated, it is assumed that the threads are lightly lubed. The assumption may vary within specific industries. Torqueing wheel lug nuts is an exception - they are torqued to spec. dry unless otherwise stated.

Lubed or not lubed makes a difference. The real goal on any torque spec. is the resulting clamping force. That determines where you are (again, as percentage of yield) for the bolt’s material (including tempering) and cross-sectional area. If you lube a bolt for which the stated torque spec. is for non-lubed condition, you decrease the margin to the yield condition, or perhaps could yield and weaken it. Doing the opposite will result in lower clamping force, which could be a problem in critical applications (cylinder head).

In the case of torque-to-yield head bolts, for them to be specifying that it be lubed, apparently it was determined that the end effect (clamping force and being reliably close to the yield point) is more accurate and consistent with it lubed at a lower torque than lubed at some higher torque value that would in theory give the same clamping force.

BTW, with stainless steel fasteners, it is pretty much imperative that you use anti-seize on the threads. Stainless steel threads will gall (cold weld) without anti-seize - IOW, before you reach the specified torque value, the bolt and nut threads will be irreversibly fused together, and you’ll have to break or cut the bolt off and start over with new hardware. The anti-seize will have its own coefficient of friction different than oil, so that has to be taken into account in critical applications. Often where stainless steel fasteners are specified, the type of anti-seize will also be called out, and the specified torque value will have that taken into account.


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Last edited by peva; 10-02-2019 at 02:03 AM.
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post #3 of 11 (permalink) Old 10-02-2019, 04:36 PM Thread Starter
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Thanks a lot Peva, great explanation, I learned something. I've ordered an angle torque device, about $8 on ebay. Just attach a breaker bar and turn the bolt 90 degrees, can't miss. As far as oil on the bolts, I read it on fixya, seemed to be an opinion, so I'll check the FSM. Most of the head bolts came UP dry, or mostly dry, some had some oil on them, but oil does leak down into those bolt bores. I'll look again, but it seemed like they did have loctite on them. Again, I'll check the FSM.
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post #4 of 11 (permalink) Old 10-02-2019, 04:59 PM
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You’re welcome.

From the FSM in the head installation procedure:

“(4) Before installing the bolts, lubricate the threads with engine oil.”

What’s this angle torque device? You should be able to eyeball 90.

Last edited by peva; 10-02-2019 at 05:04 PM.
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post #5 of 11 (permalink) Old 10-02-2019, 10:38 PM Thread Starter
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Wow, ok, so the engineers calculated the hydraulic effect engine oil would have on the torque of the bolts, as you previously stated. Perhaps its to keep the metal of the bolts from fusing with the aluminum block.
Yeah, I agree, its easy to eyeball 90 degrees. I just want to be as accurate as possible, particularly if the only way the socket engages the bolt is askew from 12 or 6 o'clock after torquing to 65 ft lbs.
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post #6 of 11 (permalink) Old 10-03-2019, 02:16 AM
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post #7 of 11 (permalink) Old 10-03-2019, 04:50 AM
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Mark the bolt head and the cylinder head with a paint marker so that you know when the marks align.
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post #8 of 11 (permalink) Old 10-03-2019, 05:05 AM
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As far as the torque sequence, the idea is to evenly compress the gasket by starting at the lower torque, then torquing again at the higher torque, then making sure that all bolts are holding the same amount of torque (repeating the sequence at the higher torque value) before being turned to apply the final clamping force (as bolts are being tightened, the bolts that were tightened earlier in the sequence lose torque due to the gasket compressing).

For that same reason, it would be less accurate to give the final clamping force using a straight torque value as opposed to making sure that each bolt is holding an even force at a value that is lower than the yield point and then turning each bolt the same amount. In the case of torque to yield bolts, you could end up torquing to the yield point, have the gasket compress while torquing other bolts, and end up with some loose bolts. If you went back and retorqued them when they've already been stretched to the yield point, then they can become excessively stretched and fail.
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post #9 of 11 (permalink) Old 10-03-2019, 10:27 PM Thread Starter
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Another great explanation, much appreciated, I have learned much. Marking 90 degrees is a good idea, I may do both, use my new gauge and also mark the bolts. Marking the bolts also lets me keep track of which bolts have been tightened.
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post #10 of 11 (permalink) Old 10-03-2019, 10:49 PM
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Marking the bolts is pretty much an industry standard whether it is marking the bolts to know when they've been turned the correct amount or to show that they have been torqued and do not get missed.
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post #11 of 11 (permalink) Old 10-04-2019, 04:15 AM
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i have a ratcheting breaker i use for 90 eyeballed pulls. you can get it within a couple degrees of 90 to the block.
but i also have a degree meter i can put on for the odd angles, like 60 degrees.
meter can even pause between pulls to get better angles.

threads need to be oiled to prevent galling and seizing. only oiled threads provide true clamping force torque, as dry theads may increase turning torque without sufficient clamping force.
that's why there is pipe dope on pipe threads. it's main purpose is lubricant.

Last edited by yevrah; 10-04-2019 at 04:20 AM.
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