1991 907 I.E. Rear motor mounts

[Tamburinifan]

+1 on jcslocum, I experienced exactly this:
http://www.duc.bz/DUCTests_nichols_engine_mou.htm
Indeed too expensive but worth it on my M900 -97.

[samandkimberly]

*The bolts, nuts, and washers/spacers are designed such that the threads are well outside of the area exposed to shear forces. The stock bolts place the threads (the weakest part of the bolts) right in the shear zone.

*The bolt diameter is ~10.3mm vs. ~9.9mm. This makes the difference between a slightly sloppy fit in the frame lugs and the cases vs. a nice snug fit that should help elimate movement between the engine and the frame.

*There is much more thread mating area between the nuts and bolts.

In theory, the bolts should be squeezing the frame to the motor so tightly that shear force should not be a factor. Neither the Nichols or Ducati bolts are specifically designed for shear load - if they were they should use shouldered bolts/nuts. The standard torque for this bolt is 40 N*m - with a 1.25mm thread pitch this equates to 27,000N or ~6,000 lbs force per bolt. For reference, this is like parking a rather large car on top of the bolt to keep it from moving! Shear should not be an issue, unless the bolts aren't properly torqued.

Sam

[jcslocum]

In theory, the bolts should be squeezing the frame to the motor so tightly that shear force should not be a factor. Neither the Nichols or Ducati bolts are specifically designed for shear load - if they were they should use shouldered bolts/nuts. The standard torque for this bolt is 40 N*m - with a 1.25mm thread pitch this equates to 27,000N or ~6,000 lbs force per bolt. For reference, this is like parking a rather large car on top of the bolt to keep it from moving! Shear should not be an issue, unless the bolts aren't properly torqued.

Sam

The Nichols bolts get torques to 50 Ft. Lb. which is 67Nm. A MUCH higher clamping force is induced by these bolts.

What friction (K) factor did you use to calculate the load??

[samandkimberly]

What friction (K) factor did you use to calculate the load??

0.15.
0.10 is typical of lubricated metal to metal, but I'm not sure whether that means "lightly oiled" or "slathered with grease". I have no idea what CF loctite has, but I'd bet it's similar to "lubricated".

To be clear, though: I'm not saying that the Nichols isn't stronger than the stock solution - it absolutely, positively is. I'm just not convinced that the standard bolt, installed and torqued properly, isn't good enough, and I don't think the shear argument holds water in this particular application.

And...just because I'm skeptical doesn't mean it doesn't work - as I've pointed out twice before - a few people I trust swear by the Nichols bolts. It's worth pointing out that newer Ducs have larger motor bolts too. But some of them also have 120 HP, and they all have to show year on year technical improvements in order to sell.

Sam

[jcslocum]

Warning Warning Pocket Protector Science Content!!!

Sam,

We (you and I) could go on about this forever and enjoy every engineering moment to the max. I'm not sure how much our fellow Paso owners would like it tho :-)

I would like to correct some basic facts tho from your post.

***.15.
0.10 is typical of lubricated metal to metal, but I'm not sure whether that means "lightly oiled" or "slathered with grease". I have no idea what CF loctite has, but I'd bet it's similar to "lubricated".***

Both oil and grease are bad thread lubricants in my opinion.

.10 is the K factor for a good copper based anti sieze. .15 would be for "machine" oil on the threads. An unlubricated dry steel on steel has a friction factor of .40!! In my experience, this is the condition of most bolting done in the aftermarket. Very few mechanics use antisieze and I never see it done by a DIY'er.

I know we are talking about "thread" lubricants but there is MORE friction UNDER the HEAD of the bolt/nut than there is in the threads!! I never see anyone putting antisieze under the head of the bolt or on the face of the nut. In general, 40% of the friction in the bolted joint is in the threads and 50% under the bolt head or the mating surface of the nut. This means that only 10% of the applied force goes to tensioning the bolt!

I don't know if Loctite gives an extact K facor but .15 should be in the ball park.

The shear component is there, I just don't know how much of a factor it plays in the initial install, but over time as things work on each other the frame may flex to the point of using the bolt in shear. The way that the frame is pulled to one side by the chain forces, makes me think that this bolt is placed in shear, even if this wasn't a consideration in the design.

I agree that they are better bolts, much better. I have them in my 900ss and the make a marked difference.

[Kurt]

I for one think that I benefit from this discussion, at least I have some grasp of as opposed to the electronic threads haha.

Anyway, I thought that most tork specs are for dry threads, is that right? So, are we over torking if we apply loctite?

And, are you suggesting applying anti-seize to nut faces and bolt underheads?

Thanks,

Kurt

[jcslocum]

I for one think that I benefit from this discussion, at least I have some grasp of as opposed to the electronic threads haha.
Anyway, I thought that most tork specs are for dry threads, is that right? So, are we over torking if we apply loctite?
And, are you suggesting applying anti-seize to nut faces and bolt underheads?

Kurt

If it's been engineered properly then it is always a lubricated fastener. There is so much loss due to friction that the threads must be lubed. If you look in a modern factory manual, they list out the types of lube to use depending on the location/application. Using the wrong lubricant can also over tighten a stud/bolt too. If you go from using a copper based thread lube that has a .10 to .11 K factor to a Moly lube with a .065 K factor then you just might break the fastener.

Yes, the proper lubrication procedure is to lubricate the bolt/stud threads and under the head of whatever fastener you are turning. When a bolt is elongated (stretched) it is put under very high bearing loads on the mating/sliding surface. Evey little bit of friction makes a huge difference in the actual load "retained" buy the stud.

BTW, most galling of threads is done during assembly. They show up at the time when you take the device apart but this is 99% of the time the "reveal" of the galling. I have analyzed many many failed bolts from 1/4" up to 7" and they always show the galling/shearing/tearing of the metal in the tightening direction.

I'm happy to hear you enjoy this subject. I could go on forever! My dog is named Archemedes after the inventor of the screw thread.

[Kurt]

Thanks, Jon, I have the anti-seize handy in the shop and usually apply it to threads, will go for underhead now, too.

Kurt

[samandkimberly]

I could go on forever! My dog is named Archemedes after the inventor of the screw thread.

I could too. FWIW, my dog's name is Sprocket:



BTW - an interesting test for how well the mounting bolts work would be to put a thin layer of hard paint on the joint between the frame and motor, and check for cracks after spirited riding. I just may have to do this....

Sam

[Tamburinifan]

BTW - an interesting test for how well the mounting bolts work would be to put a thin layer of hard paint on the joint between the frame and motor, and check for cracks after spirited riding. I just may have to do this....

Been done, Nichols show significantnly less wear.

A trouble is finding material like that quailty in Nichols bolts and machining them to those specs f less money,
not so easy task. They are rare, durable & special f a reson.
And f sure, not a magicians stick that will transforn your bike but a nice & noticeable improvement.
My 2c.

[jcslocum]

I could go on forever! My dog is named Archemedes after the inventor of the screw thread.

I could too. FWIW, my dog's name is Sprocket:



BTW - an interesting test for how well the mounting bolts work would be to put a thin layer of hard paint on the joint between the frame and motor, and check for cracks after spirited riding. I just may have to do this....

That pic is so wrong on many levels!! :-)

Paint is actually a really bad thing in the bolting world. Good for a test but bad in application. A few years back I did some trouble-shooting for caterpillar on why the track bolts were falling out after being tightened to the proper spec. These were short bolts taken to a very high load (unlike the engine bolt which is quite long) and they would start falling out after a few hours in the field. This had never happened before and they were really scratching thier heads. The only difference between the earlier tracks was that they were painted after being assembled vs. painted before assemly. It was the thickness of the paint under the head of the bolt that was cracking away during use that made the bolts come loose. Short bolts have very little elongation and these were only .002" longer when tight. That was the thickness of the paint in certain places. Once that paint failed the bolt was loose! Remove paint before installing bolts and problem was fixed.