Greasing all bolts


23 replies to this topic
  • swatdoc

Posted April 26, 2007 - 01:05 PM

#1

I read an article in one or the current magazines where a professional mechanic says to grease all the bolts on your bikes.
For the past couple years I have actually been using blue loctite - and the past year or so I have really liked the blue loctite that is solid and comes in the twist up tubes like Chapstick.
A few years back I actually tried greasing the threads of some bolts - notably the motor mount bolts on my 99 YZ450F. Unfortunately, before I was close to the recommended torque, the threads in the frame totally stripped out, and I had to end up using Time-serts in the frame.
So, I'm concerned about repeating this horror on my new bike (07 450). Also a concern is the tendancy for 4 strokes to vibrate and loosen bolts, which I think would be even worse with grease instead of loctite.
What do you guys use - grease or loctite?

  • KJ790

Posted April 26, 2007 - 01:16 PM

#2

I always grease every bold on my bikes and have never had this problem. The grease helps hold them tight so none come loose too. I started doing it b/c my family has been in the mechanic business for almost 50 years and has had great success by greasing everything.

  • grayracer513

Posted April 26, 2007 - 01:39 PM

#3

The torque values written in the manual, except where specifically noted otherwise, are for clean, dry threads. Applying oil or grease, or even loc-tite to a bolt whose torque is given for dry threads will cause you to over torque those bolts if you use the published values.

When you use a torque wrench, you are measuring the twisting effort required to turn the bolt, but you are doing so to determine how much clamping tension is being applied to the threads and the bolt shank. Lubricating the threads makes the bolt easier to turn, which means you will turn it farther to get the same resistance to turning, and thus, you will have increased the clamping tension on the bolt by as much as 25% by the time you hit the same torque value.

Angle torquing is a way around this. Take the dry bolt and torque to a 1/4-1/3 of its published dry torque spec. Then, mark the bolt and the part, and torque to its full value. Note how far it has turned.

Now, with the lubed or Loc-Tited bolt, torque to the same 1/4-1/3 torque you used earlier, then tighten to the same angle of rotation as when it was dry.

  • PATHPOUNDER

Posted April 26, 2007 - 03:40 PM

#4

Everything get a little grease at re assembly for me...clean with gas and a wire brush and grease..I have never had any problems because of this..And when taking things back apart,no seizing..disassembles nicely

  • rbinstoon

Posted April 26, 2007 - 05:37 PM

#5

Putting lubricant can cause over torquing by far more than even the 25% that gray stated. Depending on the type of lubricant used, the torque required to achieve proper bolt stretch can be less than half of that which is needed on clean dry threads, which is what is always quoted unless specifically stated otherwise. So it is possible to put more than twice the intended force on the bolt, often stripping those that have been lubricated.

If you want to put in anti-seize to help with disassembly, it can be a hit-or-miss proposition getting the right torque. What I prefer to do if I want to make sure it won't vibrate loose is put blue loctite on the couple threads which will just enter what you are bolting to so it will also keep moisture from getting in and rusting the bolt while not affecting the friction between the threads greatly.

Another thing to be careful of is putting lubricant into the threads of a blind hole or on the end of a bolt. If you do this and the bolt comes close to the bottom of the hole, it is possible to create a great amount of hydraulic force at the end of the bolt and break whatever the bolt has threaded into, especially with thicker lubricants like grease, because it cannot escape back between the threads to release the pressure. So if you choose use lubricant only put it on the male threads and start it at least one thread from the end of the bolt.

  • BergArabia

Posted April 26, 2007 - 08:04 PM

#6

Very informative thread.
I like the idea of a little loctite at the top end of the bolt.
Seems to make sense to me..

  • grayracer513

Posted April 26, 2007 - 08:33 PM

#7

I almost never strip threads on anything, especially stuff I've done most or all of the work on, and I rarely use a torque wrench except on parts I consider critical, like cylinder heads and cam caps. I tighten stuff based on feel and according to angle of rotation after contact, and I hardly ever give a thought to it, other than whether it's tight enough. But I've had 35 years of professional experience, and 10 or so more outside of the trade working on this stuff to develop that skill.

rbinstoon's advice is good, especially that concerning blind holes. But if you're going to lube a bolt that has a torque spec for dry threads, the most reliable way to avoid trouble is the angle method I laid out. You'll see this method specified for the head bolts on the 450.

  • rbinstoon

Posted April 26, 2007 - 09:20 PM

#8

The angle method is the most accurate method of doing this, true, if you know enough about it or have specifications.

From my investigation of it (I'm a millwright, not just bored), about 85-90% of the torque applied to a fastener goes to overcoming friction, so only 10-15% is put towards stretching the bolt to get proper tension. With so little of the force applied to tensioning, that is why a little lube can make such a difference in bolt torquing(as can several other variables).

Even with clean, dry threads I usually go to about 75% of rated torque to start then go up in a couple steps after that and using feel while doing it to make sure it is still tightening, not stripping. If I can't get them completely clean I go to around 50% and use feel after that.

Anyway, what gray said was right, snugging a bolt to a specified point and then turning it a set amount is a much more accurate method of getting proper tension on a bolt if it can be done.

  • rbinstoon

Posted April 26, 2007 - 09:30 PM

#9

A little bit more to add to that: the angle tightening method relies on knowing the tensile strengths of the materials involved, so there is no one magic amount to turn a bolt. The grade of the bolt and nut, the material being threaded into(eg. aluminum) or even if you are using copper washers can all affect it, so unless you really know what you are doing or it is specified for you, it is not something most people can use.

  • Yamahafan

Posted April 27, 2007 - 05:55 AM

#10

When you say grease I assume you mean assembly lube?

I tighten all non-critical items that are removed frequently (seat, radiator shrouds, number plates, etc.) with a hand held nut driver. These are the bolts that are most subject to stripping, but it is hard to strip them when you hand tighten them.

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  • grayracer513

Posted April 27, 2007 - 05:59 AM

#11

That's why I posted the method the way that I did. It provides a real-world means of extrapolating an appropriate torque angle for any fastener you have a torque spec for. The low torque level base point gives a repeatable point of reference that is low enough not to be affected by the presence of lubricants to any great degree if you compare it to really clean, dry threads in good condition without using something more subjective, like, "just snug". Once you find the angle the bolt rotates to at its specified torque, you use that with a lubed fastener, instead of the torque value.

And you're right, you'd be amazed if you check it with a torque wrench at how much less toque you need to turn it farther.

  • MikeDD

Posted April 27, 2007 - 07:56 AM

#12

I have never heard of greasing the threads of a bolt. Working on aircraft, we would routinely grease the shaft of a bolt to provide some corrosion protection. This would also provide a barrier between the two parts and prevent corrosion from dissimilar metals. For the threads of a bolt we used threadlocker and that's it.

  • grayracer513

Posted April 27, 2007 - 09:49 AM

#13

IMO, most stuff on the bike should be assembled with the threads "clean and dry". This is how I do most of the off-engine bolts. When assembled that way, I find I don't need Loc-Tite for the most part. If I catch something loosening repetitively, or I consider the risk of a certain bolt too high to tolerate, I use it.

The cool thing about Loc-Tite is that it has enough residual effect to be reusable. It won't work as well when reused as it will on a fresh application, but it clearly works better than nothing.

  • rbinstoon

Posted April 27, 2007 - 10:23 AM

#14

I agree, I wouldn't lubricate any fasteners on my bike unless it said to or Loctite unless I need to. I use anti-sieze on equipment where I work, but that is in a very wet, dirty environment. I've never had trouble with corrosion on bolts on my bike and anyway, most of the critical ones are into aluminum which you need to be careful with anyway and are less susceptible to seizing with rust.

  • PATHPOUNDER

Posted April 27, 2007 - 03:48 PM

#15

When you say grease I assume you mean assembly lube?


Nope,just some red grease out of a grease gun..I just wipe a little on the threads and screw them in..Ive been wrenching on bike for 5 years now..Im a machinist by trade,so I understand threads..this just prevents corrosion and makes disassemby easier..I also rarely use a torque wrench..maybe on cam caps,triple clamps and cylinder or head bolts..I have a good feel for aluminum..I never strip out threads.

When I first started wrenching on my yammie all the factory tightened bolts had corrosion in the holes and bolts were a bear to get out..If I dont like the way threads look or the head of the bolt it gets replaced with socket head cap screws.

I dont use any locktite either..

  • gbalias

Posted April 27, 2007 - 08:07 PM

#16

The science behind the torque and lube goes a little like this (thanks from the rock crawling gurus)......just understand, this is given we know the actual specs and grade of the bolts we are using...


It mainly comes down to bolt preload/fastener tension. When you're applying torque to a fastener, you are essentially stretching or preloading the fastener. This is done to prevent the fastener from relaxing too much and the nut from coming loose - or even worse, falling off. The big question is “how much preload do I need?”

The basic rule we use is that for structural applications, the fastener preload should be 67% of the yield strength. This value was chosen because a fastener (i.e. bolt) has a proof load value for each grade and diameter. The proof load is usually 90 percent of the yield strength. The proof load guarantees that the fastener will not permanently yield or stretch. If it did, you will loose your preload and the fastener will eventually fail or fall out.

The coefficient of friction between a bolt and nut can vary tremendously. Fastener coefficients of friction vary as much as +/-20% of nominal. Therefore, if we used a value close to the proof load (i.e. 80%) and had a high variance in coefficient of friction (+18%) from our nominal calculation, we would end up going beyond the proof load and yielding the fastener, thus applying no preload.

The next thing you need to know is what value for the coefficient of friction you should use. If the fasteners are dry it can vary the coefficient of friction from 0.15 to 0.25. If either is lubed with some sort of lubricant (ie. dry film lube, WD-40), etc.), it changes the coefficient of friction quite a bit. We use 0.20 for the unlubed coefficient of friction and 0.09 for the lubed coefficient of friction. As you can see again, there is a pretty large difference, so please note if the fasteners you are about to put the torque wrench on are dry or lubed with any sort of lubricant.

Now you have all the tools to calculate the torque required, so here is the basic formula to use.

T = K x U x D x P where K is a constant that equals 1.33

U is the coefficient of friction

D is the basic diameter of the fastener

P is the preload you need

T is the torque required

Here's an example of where someone has a ½ inch diameter, unlubricated Grade 8 bolt and needs to calculate the torque setting.

D = 0.500 inch
U = 0.20 (unlubricated coefficient of friction)
K = 1.33 (constant)


As an example, a Grade 8 fastener has an ultimate strength of 150 ksi and a yield strength of 130 ksi (130,000 lb per square inch). The thread area (minimum diameter of the fastener) of a ½ diameter bolt is 0.1599 square inches according to MIL-S-8879C. Therefore, the full yield strength is 130,000 lb per square inch X 0.1599 square inches which equals 20,787 lb. 67% of the full yield strength is 13,927 lb.

Inputting this gives you T = (1.33) x (0.20) x (0.500 inch) x (13,927 lb) = 1852 INCH LBS or 154 FT LBS

Remember that this assumes you know what grade fastener you are using and whether or not it is lubricated. If we had chosen the lubricated case, the result is much different.

Here is the same example, but this time using a lubricated fastener.

T = (1.33) x (0.09) x (0.500 inch) x (13,927 lb) = 834 INCH LBS or 70 FT LBS

Notice that the torque required for a lubricated fastener is LESS THAN HALF that of an unlubricated fastener. I hope you note how important the coefficient of friction is and how it affects the required torque setting to achieve the same preload.

:excuseme:




:applause:

  • grayracer513

Posted April 27, 2007 - 09:36 PM

#17

The thread pitch is missing from these calculations. Please explain.

  • gbalias

Posted April 27, 2007 - 09:51 PM

#18

if im not mistaken, the account of the pitch is incorporated in the function of thread area. the finer the pitch the more thread area. it plays into the calculations when determining the preload.

or am i totally just in outer space here?

  • grayracer513

Posted April 27, 2007 - 10:07 PM

#19

Within any particular bolt diameter, a coarser thread will differ from a finer one in three ways.
> There will be fewer of them per inch

> They will be deeper

> The thread angle from the bolt axis will be lower

The first would reduce the thread area, but the second would increase it, so they would offset to some extent. I don't know how much.

The third, however, reduces the mechanical advantage of the thread. It takes more torque to achieve a given level of tension on the bolt with a coarse thread than with a fine thread, even though it takes less rotation to accomplish it.

I'm sure it needs to be considered.

Other than that, good stuff.

  • gbalias

Posted April 27, 2007 - 11:37 PM

#20

ya...youre right....

so i dunno about the whole 'MIL...' specs but i assume they are accounted for in that listing. plus, that info is from the rock-crawling community....their bolts are a lil bigger than ours. hahaha.





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