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Where do we land with lubricant on threads for torque spec? I know you recommend anti seize on Ti, but is that a dissimilar metals issue? I’m just looking at consistent specs. Conventional knowledge says put a little dab of grease on clean threads. But should I then compensate up or down on the torque spec? I only ask because I want to start playing with some chassis torque specs on my bike to see what it does with flex, so I want to make sure I’m accurate one way or the other.
did the factory torque spec call out a thread lubricant or loctite? if so they most likely factored the torque differences over using a dry bolt.
in most cases the factor is around 30% for lubricated bolts, meaning that it takes 30% less torque to achieve adequate amount of "tightness" due to less friction.
However this number can also vary based on the type of coating on a fastener, the 30% value is mostly based on a non coated bolt.
* Torque is irrelevant. What we actually care about is the bolt tension (clamping force). Unfortunately, it's not easy to measure that tension directly, so we use applied torque to make an educated guess at what that bolt tension is. Too little bolt tension and the bolt comes loose and the joint is no longer doing its job; things can come apart in a bad way. Too much bolt tension and the bolt is at a higher state of stress than it should be. If an external load comes around that's big enough, the bolt can fail making the assembly come apart in spectacular fashion (which is my best guess as to why we have this thread in the first place).
* That educated guess would be very accurate if it weren't due to friction and the unknowns that surround it. There are A LOT of factors at play when it comes to friction - bolt coatings, "nut" coatings (in the case of the clamps here, the threaded aluminum hole), lubrication applied, thread lockers, how many times the bolt has bee reused, etc.
* The vast majority of the torque you apply to a bolt is eaten up by overcoming friction rather than actually tensioning the bolt. It varies based on the conditions (lubricant, bolt size, etc.), but in the case of a steel bolt installed in aluminum triple clamps without lubricant (typical of a stock callout), only 6% of the input torque is actually tensioning the bolt. 40% of that input torque is used to overcome the friction at the threads and 54% is used to overcome the friction under the bolt head.
* The amount of friction present is directly related to the amount of tension in the bolt after torqueing it to a specific amount. Two bolted joints that are torqued to the same amount, but one dry and one with lubricant will have wildly different tensions.
* The only way to really know the difference in the torque-tension relationship between a dry bolt and the same bolt with a particular lubricant applied is to test it. In general rough numbers, though, it's a 30-40% difference in friction between the two.
* So, in the case above of two bolts torqued to the same amount, one dry and one lubricated, one of those bolts could have 40% more tension than the other. Depending on the external loading applied and the material of the bolt, that can easily mean the difference between having a great day at the track or bolt failure and a trip to the hospital!
* A correct bolted joint will not have any relative movement between parts of that assembly. So long as that is the case, changing the torque 5% or 10% (or whatever, really), will NOT change the overall stiffness of the assembly. Or in other words, there is no one in the world who can feel the difference after reducing the bolt tension of their engine mounts 5%. The difference just isn't there.
* Unless, of course, the torque is so low that the parts have relative movement between them. But that would be a very bad thing (and would also be considered a failure of the bolted joint).
Most all of our products use titanium bolts threaded into aluminum holes. We typically specify using anti seize for all of these bolts (because titanium in aluminum dry is a bad thing and it can seize up due to galling), both on the threads and under the bolt head. This creates a torque-tension relationship that's different than the typical steel bolt without any lubricant; and it's about 40% less torque to create the same bolt tension. Using anti-seize also creates a much more repeatable torque-tension relationship when reusing the bolt multiple times.
The downside of using anti-seize is that the torque spec is different from stock. It's easy to over-tension these bolts if you're doing it just by feel. The bolts are also more likely to come loose, since there's less friction to hold it in place.
In general, we believe the downsides of using anti-seize are outweighed by the upsides, and we try to mitigate the downsides by including the correct anti-seize with our products, including the correct instructions for installing the bolts with anti-seize with torque specs in our product instructions (with warnings that they must be followed), and engraving those torque specs on our parts directly. There are still mistakes made, despite that. And as we've seen, they can lead to some ugly situations.
So to answer your question more directly:
If you're using a torque wrench and will be checking torque often, use some grease on the bolt threads and under the bolt head. This will allow for much more consistent and repeatable torque-tension relationship. Reduce the applied torque from what is specified for a dry bolt by 30% to compensate for the lubricant. I would recommend using a paint marker to mark the bolts so you can quickly look at them to see if they're coming loose.
If you're more of a torque it and forget about it type, using a thread locker is a good idea (and the paint pen idea above is still good too). We recommend Loctite 243 (medium strength, primerless) for most bolts M6 and larger on the bike. If you apply a lot of Loctite (if it's oozing all over, on the threads and under the bolt head), reduce your torque by up to 20%. If only using a few drops (typically all that's necessary), then use the same torque as a dry bolt. For bolts that you really don't want coming loose (sprocket bolts, etc.), use Loctite 263 (high strength, primerless). Do not reduce your torque specs with 263, it doesn't have any significant lubricative properties.
Be careful reusing a bolt that has had Loctite applied earlier. The dry Loctite on the bolt and in the nut will add friction and throw off your torque-tension. You should thoroughly clean everything, then re-apply the Loctite, and torque appropriately.
The only difference is they will trust the certification, whereas we would have them lab tested because the budget is there to do it.
Pogipolini Ti bolts are off the shelf, its an expensive shelf, but you can get them .
I am notgoing to repeat what Luxon has said in a great post about bolt materials, and locking and lubricants.. He is selling stuff,and understands what matters.
I am constantly amazed by people who will spend $$$ on Cerakote and dont replace cheap OEM bolts .
We will leave the Hard Anodising discussion for another day..
Two one thousands is proper tight.
Works for very fastener!
The engine hanger opinions have merit, but missing the fact that when you only have one bolt it's tough to prevent rotation in the axis of the bolt. You could probably get similar results from adding lube under the bolt head and around the threaded hole as you can with reduced torque.
The clamp bolt in question here is not in a typical bolted joint configuration. The two faying surfaces never touch which makes the joint 100% dependent on the strength of the bolt. Ti bolts are cool but the strength and brittleness are inferior to a good 160ksi A286 bolt (grade 8 and up). Aluminum threads are a weak point but can be fixed with a stainless helicoil.
edit: another branch on a failure analysis fishbone would be raw billet quality. For example we frequently find vendors falsify their material certs. Also is it ultrasonic scanned for internal defects.
Pit Row
You have 8 pinch bolts between upper and lower clamps. Why wouldn't the clamp bolts be enough to hold things together? The fork legs are typically a pretty snug fit in the clamps, then you add in the 8 pinch bolts and even if you left out the upper bolt I don't see why it would be a problem.
Again, me being stupid probably but I just can't wrap my head around this bolt being a big deal.
the same way that an o ring failure doomed the Challenger in 1986.
When one small part gives way, the rest of the house of cards falls soon after.
In this case majority of the bike was still in tact. Approx 1/4 of the bike was not in- tact.
Just sayin......
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