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Author Topic: Hollow Motor mount bolts - Why?  (Read 2267 times)
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donpearsall
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« on: March 05, 2018, 11:50:15 AM »

My Suzuki Hayabusa has motor mount bolts that are hollow. They are 12mm OD and made of some type of steel material. But they all are hollow all the way through. Why? Is there an engineering reason for this? I can't see that it is for weight savings as that would be only an ounce or less total for all of them. I have always wondered about this. Any thoughts?

Don
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stay`tee
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« Reply #1 on: March 05, 2018, 04:27:09 PM »

I will be interested to also know the answer to this,, as my Kawasaki ZX12 has similar mounting bolts  smiley
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Stan Back
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« Reply #2 on: March 05, 2018, 05:50:24 PM »

Tariffs.
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mtiberio
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« Reply #3 on: March 05, 2018, 07:32:10 PM »

Tariffs.

Almost choked laughing.

And yes, it is weight.
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manta22
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« Reply #4 on: March 05, 2018, 08:45:33 PM »

I suppose a hollow steel bolt is cheaper than a solid titanium bolt.

Regards, Neil  Tucson, AZ
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wobblywalrus
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« Reply #5 on: March 05, 2018, 09:10:12 PM »

The Triumph has hollow axles.  An expert explained to me why this was done years ago.  It is to prevent the formation of fatigue cracks.  The surface needs to be in cyclic loading between tension and relaxation or compression cycles to form fatigue cracks.  It is easier to keep the surface in constant tension with a hollow fastener under some load conditions. This is more critical with larger diameter fasteners where not enough bolt tension can be applied to keep them constantly stretched if they have a full non-hollow cross-section.

The axle is a good example.  It cannot be stretched too far 'cause the wheel bearings would be trashed.  So, it needs its cross-section to be reduced so it is always under tension with the torque that can be applied to the nut.

Hopefully my memory is right on this.  It was told to me about 40 years ago. 
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edinlr
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« Reply #6 on: March 05, 2018, 11:30:18 PM »

Weight isn't the issue on a nearly 600# bike.  It has to be some engineering theory, or just an exercise for trick looking fasteners.  I don't think my H2 Ninja has any hollow bolts, but the fasteners on the bike are much nicer looking than on the cheaper bikes.  My Ducati is sprinkled with titanium, which is a shame given my plus sized figure.
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salt27
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« Reply #7 on: March 06, 2018, 01:44:46 AM »

Suzuki's Hayabusa advertisement talks of hollow bolts reducing the weight of the braking components.

So maybe it is weight, a little here a little there all adds up.

Who knows?

  Don
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« Reply #8 on: March 06, 2018, 06:17:12 AM »

The KawasakiZX12 has hollow axel bolts, and the bolts holding the brake calipers together also, imho weight has f#@&all to do with it, weight saved would add up to less than half that of a Mcdonalds cheese burger  grin
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Koncretekid
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« Reply #9 on: March 06, 2018, 07:00:43 AM »

A larger diameter hollow component is definitely stiffer in bending resistance than a solid smaller diameter component of the same weight.  This explains the reason for hollow larger diameter axles which have been used for years.  But hollow motor mount bolts are more of a puzzle, as they appear to be in shear where strength is related to area and tensile strength. It might have something to due with the larger bearing area of the larger diameter bolt head and nut against the weaker parent frame material, especially aluminum frames which are more susceptible to fatigue failure.

But Canadians (thanks for the reminder, Stan) are thinking about making all our steel components hollow to make equivalent items 25% lighter - - take that Trump! (And we'll probably invite all the DACA immigrants up here, as well.)

Tom
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« Reply #10 on: March 06, 2018, 03:44:12 PM »

A larger diameter hollow component is definitely stiffer in bending resistance than a solid smaller diameter component of the same weight.  This explains the reason for hollow larger diameter axles which have been used for years.  But hollow motor mount bolts are more of a puzzle, as they appear to be in shear where strength is related to area and tensile strength. It might have something to due with the larger bearing area of the larger diameter bolt head and nut against the weaker parent frame material, especially aluminum frames which are more susceptible to fatigue failure.

But Canadians (thanks for the reminder, Stan) are thinking about making all our steel components hollow to make equivalent items 25% lighter - - take that Trump! (And we'll probably invite all the DACA immigrants up here, as well.)

Tom




     Tom I like your ideas  cheers
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« Reply #11 on: March 06, 2018, 03:47:54 PM »

OOOOH hollow bolts! they must make it a lot faster! Advertising gimmick?
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« Reply #12 on: March 06, 2018, 07:16:24 PM »

While I tend to be in the weight reduction camp, another consideration may be as follows.
Typically the motor mount bolts are rather long and are mounted athwartships in the chassis, spanning across a considerable length of aluminum.  In the same way that fatigue resistant bolts often have the OD sculpted and reduced to produce a more springy bolt, the same may apply to the M/C bolts which would be subject to load variation when the aluminum goes through the thermal cycles induced by the alternate heating and cooling of the engine case.
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« Reply #13 on: March 12, 2018, 08:17:40 AM »

I believe it was the late Pete Robinson that said the easiest way to take #100 off a racecar is to find 1600 things you can take an ounce off.
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« Reply #14 on: March 12, 2018, 10:19:27 AM »

I believe it was the late Pete Robinson that said the easiest way to take #100 off a racecar is to find 1600 things you can take an ounce off.

To save pounds start with saving ounces (even grams).

Circle track racers drill lightening holes in weight boxes. Then add weight to make the required weight break. 

Joe
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