Steering Stem Torque

RossKean · Mar 15, 2011

The final torque setting using the Yamaha tool is designated as 13 ft-lb. This is based upon a mechanical advantage afforded by the "official" spanner. I don't have one to measure but my estimate from pictures of the tool suggest that from the center of the steering stem to the center of the hole where the wrench is inserted is something around 2.3". If using a castellated socket, the effective mechanical advantage is going to be the radius of the nut itself - perhaps 0.7" or so. This suggests (to me) that there is around a 3X mechanical advantage using the spanner vs using a castellated socket.

Am I missing something here? (Maybe I need geometry lessons?) I have not seen a discussion on this before and was wondering if anyone is using a different torque specification (i.e. 39 ft-lb.) when using a castellated socket? Maybe its not all that critical but I am just starting to do some needed maintenance on my bike and want to make sure I am doing it right.

I was thinking about making a tool to tighten this nut but have to consider the critical dimensions or correctly compensate for torque value. By the way, does anyone have measurements for the official tool I could copy or a good photo of the spanner placed on a gridded paper? I found one in my search but it was hard to do precise measurements from it.

Thanks

Ross

dannymax · Mar 15, 2011

I drilled a 3/8" square hole in the handle of a small spanner wrench(3/4" - 2" I think it is) to receive a 3/8" drive torque wrench. If you place the torque wrench at right angles to the spanner there is no need to calculate for mechanical advantage.

RossKean · Mar 15, 2011

dannymax said:
I drilled a 3/8" square hole in the handle of a small spanner wrench(3/4" - 2" I think it is) to receive a 3/8" drive torque wrench. If you place the torque wrench at right angles to the spanner there is no need to calculate for mechanical advantage.

Perhaps I am not visualizing things correctly (or maybe I really do need geometry lessons) but I would think that a longer effective arm on the spanner would put more torque on the nut than a shorter arm. I get your point on the necessity of having the torque wrench at right angles to the spanner but in my mind (quite possibly flawed), the distance between the center of the nut and the center of the torque driver will have a bearing on the torque applied to the nut. Might be one of those things I would have to actually try in order to convince myself.

I'll think about it some more...

dannymax · Mar 15, 2011

Wish I had the mental horsepower to explain the geometrics behind it but unfortunately, it's just one of those things that I read, or was taught, long ago and accepted as fact.

Now you got me thinking....

RossKean · Mar 15, 2011

dannymax said:
Now you got me thinking....

Careful, that might be dangerous! Thinking is what got me started on this and I am not sure that I am right - just a little confused.

dannymax · Mar 15, 2011

Roger that confusion!! But it certainly seems logical that lengthening the spanner would yield more advantage....

Agh! I'm hurting my brain!! :dribble:

Fred W · Mar 15, 2011

RossKean said:
The final torque setting using the Yamaha tool is designated as 13 ft-lb. This is based upon a mechanical advantage afforded by the "official" spanner. I don't have one to measure but my estimate from pictures of the tool suggest that from the center of the steering stem to the center of the hole where the wrench is inserted is something around 2.3". If using a castellated socket, the effective mechanical advantage is going to be the radius of the nut itself - perhaps 0.7" or so. This suggests (to me) that there is around a 3X mechanical advantage using the spanner vs using a castellated socket.

Am I missing something here? (Maybe I need geometry lessons?) I have not seen a discussion on this before and was wondering if anyone is using a different torque specification (i.e. 39 ft-lb.) when using a castellated socket? Maybe its not all that critical but I am just starting to do some needed maintenance on my bike and want to make sure I am doing it right.

I was thinking about making a tool to tighten this nut but have to consider the critical dimensions or correctly compensate for torque value. By the way, does anyone have measurements for the official tool I could copy or a good photo of the spanner placed on a gridded paper? I found one in my search but it was hard to do precise measurements from it.

Thanks

Ross

Ross,

When using the Yamaha spanner wrench it is required for you to place the torque wrench at a 90 degree angle to the spanner. This makes the mechanical advantage of the spanner length = zero since there is no effective lengthening of the lever arm.

If you were to arrange the torque wrench handle in-line with the spanner's arm then you would have to account for the added length.

When using the castellated socket type of wrench there is no chance of applying anything but what the wrench is reading. It's one reason I like mine so much.

RossKean · Mar 15, 2011

Fred W said:
Ross,

When using the Yamaha spanner wrench it is required for you to place the torque wrench at a 90 degree angle to the spanner. This makes the mechanical advantage of the spanner length = zero since there is no effective lengthening of the lever arm.

If you were to arrange the torque wrench handle in-line with the spanner's arm then you would have to account for the added length.

When using the castellated socket type of wrench there is no chance of applying anything but what the wrench is reading. It's one reason I like mine so much.

Fred

It's clear to me that if the torque wrench is "in-line" with the spanner, the spanner length would be critical in terms of torque applied. It is less clear to me, as I indicated above, how the force is applied when the wrench is at 90° to the spanner. Even with the 90°, intuition (often wrong) says that more torque would apply with a longer spanner - I am visualizing what would happen with a spanner a foot long. Posting before morning coffee is generally a bad idea but even now, with a less fuzzy brain, it is still not entirely obvious. I am not disputing what you are saying; just need convincing.

Fred W · Mar 15, 2011

Here's a reference web site for ya:

Clicky

ionbeam · Mar 15, 2011

Pre Edit: Didn't see Fred's link before I posted this, will leave my post anyway.

Goodness, we had such great fun with this the last time it was discussed. As the dearly departed TWN observed, the past discussion turned into another "Airplane on a Conveyor" thread.

So, lemme try. The OEM wrench specifies that the torque wrench remains90º to the center of the steering stem. Draw a rectangular box so that one end passes through the center of the steering stem and over to the center of the pivot of the torque wrench drive, one side runs up the length of the torque wrench, the opposite end line makes a 90º corner and is ~2.5 inches long and the final side makes a 90º turn and goes directly down to the center of the steering stem. We now have a classic rectangle where the end lengths are equal, the side lengths are equal and all the angles are 90º. As long as we retain this relationship all lengths remain the same so there is no change in mechanical advantage. As soon as the rectangle's angles are distorted past 90º the length of the path for the applied force changes when compared to a true rectangle. The length change offers a change in mechanical advantage, be it loss or gain determined by which side of the former rectangle gains length

RossKean · Mar 15, 2011

Fred W said:
Here's a reference web site for ya:

Clicky

Fred

Great reference site. Some thought definately went into it. It certainly points to the importance of the angle being EXACTLY 90° when using the factory spec'd spanner. I like the idea of the castellated socket a lot better for this.

Alan

As always, you have made muddy water into something that is merely murky

. All humor aside, it makes sense to me. I think I'll see about taking a Dremel to an old socket and see if I can create a tool for this job.

(I always liked the "airplane on a conveyer" discussions)

Ross

lnewlf · Mar 15, 2011

I use a drift and a hammer..

RossKean · Mar 15, 2011

lnewlf said:
I use a drift and a hammer..

So where do you buy a calibrated Torque Hammer?

Denver_FJR · Mar 15, 2011

RossKean said:
lnewlf said:

I use a drift and a hammer..

Click to expand...

So where do you buy a calibrated Torque Hammer?

Same place that carries castellated drifts of course!

dannymax · Mar 15, 2011

The imagined 'rectangle' kind of makes sense, I will have to set up a 'proof station'...that'll be a large nut & bolt and bench vise! :blink:

Or castellate a nut....or use v max technology, if it wobbles tighten it till it stops wobbling, if it wanders loosen it till it stops wandering!

lnewlf · Mar 16, 2011

Drift & hammer technique has worked for me for 35 years on many bikes..Jack the front end off the ground, tighten the castellated nut until the front end slowly rotates from center to full lock either side with just a nudge. It should not fall over quickly or stop at any point. I have found that factory torque setting sometimes are not sufficient [is it 13 ft/lbs on the FJR] to damp out headshake when off throttle. If you overtighten you will know right away as there will be a weave . And yes, I have an ugly looking nut- oh wait..

Fred W · Mar 16, 2011

One of the reasons to actually use a torque wrench is that you want to preliminarily tighten the bearing stack up to a higher torque value (37 ft-lbs) to seat the bearings and squish the grease out for the next step. You then loosen the nut and re-tighten it to only the desired preload of 13 ft-lbs.

I suppose that if you weren't using a torque wrench, one could forgo the preliminary tightening step, but that may allow the bearings to shift later on. If you attempt the first step without a torque wrench there is a risk of dimpling the bearing race if/when you over-tighten the bearing.

Also, running the bearing at too high of a preload will cause uneven race wear that will result in notchy steering. It is certainly possible to dampen out any steering oscillation, generating dampening in the bearing by tightening it past 13 ft-lbs, but that may result in needing to replace your steering bearing sooner. If you are getting oscillation (head shake) with the bearings preloaded correctly to 13 ft lbs then you have something else wrong.

It really isn't that hard to do it right.

Bogus · Aug 4, 2014

Twigg · Aug 4, 2014

Fred W said:
One of the reasons to actually use a torque wrench is that you want to preliminarily tighten the bearing stack up to a higher torque value (37 ft-lbs) to seat the bearings and squish the grease out for the next step. You then loosen the nut and re-tighten it to only the desired preload of 13 ft-lbs.
I suppose that if you weren't using a torque wrench, one could forgo the preliminary tightening step, but that may allow the bearings to shift later on. If you attempt the first step without a torque wrench there is a risk of dimpling the bearing race if/when you over-tighten the bearing.

Also, running the bearing at too high of a preload will cause uneven race wear that will result in notchy steering. It is certainly possible to dampen out any steering oscillation, generating dampening in the bearing by tightening it past 13 ft-lbs, but that may result in needing to replace your steering bearing sooner. If you are getting oscillation (head shake) with the bearings preloaded correctly to 13 ft lbs then you have something else wrong.

It really isn't that hard to do it right.

This ^^^

It isn't hard, especially if you understand what it is you are trying to achieve.

You want the bearings fully seated, hence the first setting of 30 ftlb. Then you want a final tightening that puts the bearing under very slight tension, and no more. 13 ftlb isn't actually much more than "hand tight" .... It is only 13 pounds with one foot lever!!

Once you grasp the reasoning, you can get closer with a basic wrench than you ever will with a so-so torque wrench.

Steering Stem Torque

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