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2/22/2014
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Warwick, NY
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With the alum frames and the different engine mounts available ( stock, carbon,thicker,thinner and drilled) it was never really a thought to me on tightening the mounts after a rebuild. I'm coming from steel frame everything from the 80"s era. I would just tighten the hell out of them and go ride. The way I see how ea team now plays with the mounts for rider "feel" is now looking like a MUST DO for proper torque on these . Using stock Yamaha mounts
Currently doing a 18 yz250f.
Curious for feedback on everyone's thoughts .
Currently doing a 18 yz250f.
Curious for feedback on everyone's thoughts .
It’s very important and something over looked by many.
The placebo effect is strong. When someone makes a change like this it can absolutely make a difference mentally, but I guarantee it won't make a measurable difference in how the components deflect. Changing your tire pressure 0.1 psi will be a far greater change than changing your engine mount bolt torque by 10%.
My oh my.... I doubt they used a torque wrench when doing the hasty engine swap on Barcia's bike a few weeks ago. I have no idea how he was able to race a Pro SX with un-torqued engine mounts. [/sarcasm]
I got another one for you. My buddy actually worked on the assembly line in Japan. If you think the factory even follows the torque "specs"...well......
The Shop
Down in Baja, I rode 2 Honda 450X back to back. All stock, clickers the same, and very close on hours. The only change was engine mount bolt torque and swing arm torque. The different in feel was very obvious.
Lets be honest anyway, most torque wrenches arent accurate within 1lb-ft. Even snap ons have a % of error that worsens with higher torque levels. At 2% error, a 50lb-ft bolt can be 49 or 51 lb-ft because of error.
If Keefer was really on it he would tell us what thread lubricant he used and what the bolt's stretch as measured with a micrometer was to achieve the particular tension. He doesn't and it is highly likely that his comments are 100% subjective with no measurable way to evaluate.
Tension wrenches or 'Torque wrenches' can be easily checked for calibration using first principles- and probably should be annually. User technique issues probably account for much bigger errors than out of whack equipment.
Lastly, I make sure my chassis stuff is all to spec, I don't play with varying torque specs.
Just looking at the HRC vs Smart top bikes from the posted poll on here and you see the engine hanger difference between the two. Roczen uses steel with 1 small hole and Vince has a alum hanger with a larger hole. Fast Expert here in the D34 Northeast would always remove the upper hangers completely. He is a rocketship. Will track him down when we start the season and pick his brain on the contrast of running/not running the hanger
Beyond that, it's important to understand what bolt torque means and how it can vary. The bolt torque, by itself, is completely meaningless. The measure of interest is the tension in the bolted joint, e.g. what holds it all together. But measuring the tension in the bolt is not an easy task. It is easy, though, to measure the torque applied to the bolt, which is related to bolt tension, and that's why torque is always specified rather than bolt tension.
The bolt torque is related to bolt tension by some constant parameters such as bolt size, thread pitch, etc., but it's also related by friction, and that's a huge variable. For a steel M8 bolt threaded into aluminum and without lubricant (typical of a triple clamp bolt), 94% of the bolt torque is "used up" in overcoming the friction and only 6% of that torque actually tensions the bolt. If the friction changes some amount, then the tension can change a lot. A small amount of lubricant, a new bolt vs a used bolt, a zinc coated bolt vs a plain steel bolt, a bolt of different material, tolerance variation in bolt/nut manufacturing, and more, all change the friction value and the resulting bolt tension, even though they may all be torqued the same. Throw in the inaccuracy of your torque wrench and things become even more uncertain.
For the M8 bolt example above, if the bolt is torqued to 15 Nm and everything is dry, the resulting bolt tension is 4,143 N. If you take that exact same bolt and lubricate it, torque it to the same 15 Nm, then the resulting bolt tension jumps to 6,964 N. That's an increase of 68%!
For comparison, a lubricated M8 bolt torqued to 13.5 Nm (10% less torque) results in a tension of 6,268 N, which is about 11% less than when torqued to 15 Nm. But that's still 51% more tension than the dry bolt torqued to 15 Nm. The friction makes an enormous difference. If you're comparing the effects of bolt torque on feel, you're going to have a REALLY hard time doing an apples to apples test unless you can do it on a single bike (to isolate all other variables), with brand new bolts of the same manufacturing run, with identical lubrication, using the same torque wrench, and on the same day. And it still won't make a difference if the bolt tensions is high enough to hold everything together (as it should be) for reasons explained above.
BTW, if anyone wants to play with bolt torque/tension calculations our spreadsheet is available on the resources section of our website:
https://luxonmx.com/resources.html
Most riders can't detect detect variances in torque within +/- 10%, but I 100% believe that most riders could feel a slight difference in a bike that has had every bolt tightened with a clicker wrench vs. that same bike if a clicker wrench was not used at all.
My rule of thumb is to use a torque wrench on any joint that clamps something that is in motion.
Like the time he said “‘you’ might not notice the disc guard missing off the new Crf450, but I can”!
My question relating to above. How does Loctite effect torque? Blue seems to help them stay a little, Red does the trick much better. But then resetting the torque after replacing something the bolts obviously feel different. Even if you clean the bolt, the receiving part could be near impossible to clean. I've never really though about it much until I read what Luxon had to say about lubricated vs. dry tension. Those figures were substantially different and I'd think could be felt by the rider.
So, Luxon MX and mxtech1; what are your opinions, Lubricate or dry, (and keep tightening bolts every ride) or Loctite?
That said, if you don't get all the loctite cleaned off after you remove a bolt and then reinstall, I would argue that would change things. As you note, it's relatively easy to clean off the bolt, but difficult on a nut or internal threads. You can try chasing the threads with a tap to help out with that.
In general, I like to lubricate bolts as it keeps a more consistent torque to tension relationship and is just nicer to the threads and mating surfaces. Some of the bolts on my personal bikes are titanium, so I have to use anti-seize anyway. Some bolts, though, I prefer to use loctite on. Mostly bolts that see a lot of cyclic loading, tend to come loose, or are very important. Sprocket bolts are the classic example here on Vital, but engine mount bolts, shock bolts, etc. all fall into the category.
Check the actual loctite numbers, though, rather than simply relying on the color. There are multiple variants for the different colors. I like 243 (blue) for general applications, 222 (purple) for small bolts, and 271 (red) for things you don't want coming apart easily without heat. And then there's the 600 series of sleeve retainers which are very useful, particularly in repairing things, but they need to be mated to their particular application.
Pit Row
If the bolts are not being tightened to 75% of their tested yield strength they are not properly specced. It's easy to test this by turning a few lubed with your favourite stuff, to failure, and working back with the tightening torque.
Turn the nuts not the bolts to tighten as per aviation.
Commercial SHCS are the strongest bolts you can easily buy- an M8 SHCS has a recommended seating tension of 22 lb/ft
I’ve solved our issues with Loctite. I was asking Billy and mxtech1 for their opinion on torquing bolts with Loctite and even more so the possibility of changing torque values after these bolts have been removed and replaced.
Problem with the locking stuff when you get to the higher grades is they will often pull the female threads when being undone so often the manufacturers directly recommend against it's use.
On a similar assembly with the same issue we drill deeper into the casting and use a longer bolt of a higher grade.
Sounds like the KTM needs an engagement length increase so the bolt can be properly stretched.
On our main assembly lines at work, we will always specify whether a joint is dry or lubricated because it dictates the applied force.
A dry joint, using a normal zinc plated bolt is going to have a K factor of 0.19.
We classify the application of Loctite as a lubricated joint due to the fact that the lubricated joint K factor is effectively reduced to 0.15.
Since
T = K * F * D
and K (lubricated) 0.15 / K (dry) 0.19 = 0.789
Thus, a lubricated joint will only need 78.9% of the normal Force to achieve desired Tension.
Example would be a standard M10 hex head bolt. Dry torque nominal call-out is 73Nm while lubricated torque call-out is reduced to 58Nm.
The same principle applies when lubricating threads with oil. Lubricating the threads of a standard fastener that has an electroplated zinc or zinc/nickel/chromate surface changes the coefficient of friction classification from high to low. Again, the reduction in the coefficient of friction needs to be considered by reducing the applied force.
In general, don't use Loctite or oiled threads unless your manual tells you too. If the manual tells you to use Loctite, the torque callout in the manual will be adjusted for the thread lubricant.
If loctite curing is a chemical reaction, I would imagine it quickly looses lubrication as you torque the bolt causing heat and pressure that one would imagine increases the rate of curing?
I was able to find this paper, though, from Henkel Australia:
http://www.loctite-success.com.au/content/uag/oneloctite-campaign/austr…
This is a bit more scientific than the marketing documentation, and suggests that loctite does act as a lubricant "To accommodate a threadlocker in the test, the wet torque specification was selected.", which is consistent with MX Tech's findings. So it's probably wise to assume a lubricated condition if using standard "wet" style loctite.
Perhaps one of the more interesting points in the paper is that they test bolts of the same size from 5 different manufacturers. For the same applied torque, the resulting tension had a standard deviation of 21%, which is MASSIVE. They ran the same test with loctite on the bolts and the standard deviation dropped to 12%, which still seems high to me, but much more consistent.
Regardless, either standard deviation reported above just further goes to show that altering torque by small amounts (10% or so) on the engine mounts is going to be completely meaningless in relation to rider feeling as it's so variable and not terribly repeatable.
If you look at the clamp load values on the bart chart, you can see that in samples D & E that the clamp load nearly doubles between dry and lubricated. Samples A & C are more closely in line with the ~21% I posted above.
They specified that they used a calibrated torque wrench to apply 112 lbs/ft. It is well known within industry that a calibrated torque wrench in the hands of a certified operator is repeatable to +/- 15% of nominal (4% for the tool and 10-11% for the operator and materials variation). Sample B shows lubricated had a lower clamp load, but it is more likely that this sample is exemplifying the repeatability of the human-clicker wrench at +/-15%. A 30-piece study, standard in industry, would have flushed this out.
Now let's say you evaluate clamp loads of lubricated vs. dry at the + or - 15% of nominal applied force. Dry joint with an applied force of 95 lbs/ft will have a clamp load of only ~9,600 lbs vs. a lubricated joint with an applied force of 129 lbs will have a clamp load of ~16,500 lbs. That's a 171% difference in clamp load.....and significant enough that a hard joint will show differences in how it transmits vibration and possibly deflection. Again, could most people tell this during a ride...doubt it, but some can if they are sensitive enough.
https://tdsna.henkel.com/americas/na/adhesives/hnauttds.nsf/web/96FA02B…
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