EN 16 for brake arm anchor stud

[Andrew Phillips 4Participant @andrewphillips4]

Hi All, I am working on a project to fit a Honda 180mm 2LS brakeplate to my ’54 AJS 500cc bike. The Honda fastening for the torque arm that anchors the brake backplate to the telescopic fork leg is an 8mm bolt, presumably high tensile, screwed direct into the aluminium alloy. AJS used a 3/8 bolt in the original brake, screwed into a steel bush cast into the alloy, and BSA used a 7/16 stud in the same location. I would like to replace the Honda 8mm bolt with an stud and nut of the same size. Would EN16 be a suitable material for the stud, or should I go for EN24 or stick to the Honda bolt? Thanks

[Michael GilliganParticipant @michaelgilligan61133]

That’s a very substantial difference in diameters … but presumably Mr Honda knew his stuff.

I would be inclined to follow his example regards material specifications.

Are there any markings on the original bolt ?

MichaelG.

[Swarf MakerParticipant @swarfmaker85383]

I am not able to give you any advice Andrew Phillips since safety and thus liability, are involved.  However, consider this.  Honda considered that the torque reaction produced by their brake, including a safety margin, was met by an 8mm bolt, to a specification unknown to us, in shear.

EN16T is considered to have very good shear resistant properties (look it up) and is used in many similar situations.  You could calculate the shear loading since you know the moment arm and the mass of the bike & rider.  Whatever you choose for the anchor bolt/stud, do remember to let your insurance company know that your bike has been modified.

[DiogenesParticipant @diogenes]

How does the mass of your AJ compare with the mass of the Honda the brake came off?

[Michael GilliganParticipant @michaelgilligan61133]

For context … I presume this previous topic concerns the same project:

https://www.model-engineer.co.uk/forums/topic/motorcycle-brake-arm/#latest

… is everything going nicely to plan ?

MichaelG.

[Andrew Phillips 4Participant @andrewphillips4]

They weigh about the same, 350 – 360 lbs.

[Andrew Phillips 4Participant @andrewphillips4]

Hi Michael, thanks for your interest.  I have a New Old Stock original Honda bolt, which has no markings and appears to be bright zinc plated.  A stud would be more convenient than a bolt, and the protruding length threaded 5/16 BSC to match the rest of the nuts/bolts on the bike, but I can live with the bolt with its metric head especially as I know it will the the job – I may well choose to stick with it.  I sent you a reply about my other project but as the powers that be have changed the website since I last used it, I am not certain it was actually sent – as a Roman general is alleged to have said in around 100 AD, “Change! Change? Aren’t things bad enough already?”.

[SillyOldDufferModerator @sillyoldduffer]

For safety related applications, I always recommend buying a manufactured bolt or stud.   Apart from Honda doing the sums, choosing the right grade of steel, and testing, their threads are made by rolling, not by cutting.   Rolled threads are considerably stronger than cut ones because rolling strengthens the metal by compression and leaves fewer stress-raisers.   Stress raisers cause rapid cracking when a highly loaded thread is vibrated, making cut threads a poor choice for brakes and aircraft wings!

The advantage of a lathe cut thread is it can be made to almost any size, and they’re plenty good enough most of the time.  But they’re not suitable when the strength and reliability of a stressed component is important.   More to making a strong thread than getting the right steel – rolling is a much better process, sadly beyond most workshops.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Andrew … ‘no markings’ is a bit disappointing … I was hoping for something exotic !

MichaelG.

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P.S. __ No message received as-yet

[Gary YeadonParticipant @garyyeadon51936]

Metric Bolt Grades to consider.

The most common metric bolt grades include:4.6: Basic low-strength bolts.
8.8: Medium-strength bolts suitable for general applications.
10.9: High-strength bolts used in critical structural connections.
12.9: Extremely high-strength bolts for demanding applications.

[Michael GilliganParticipant @michaelgilligan61133]

Useful listing Gary

Given the small diameter, and its duty, I had presumed Mr Honda would have used either 10.9 or 12.9 … but it appears not.

In my personal opinion, this one qualifies as a “Jesus Bolt”

… single point-of-failure ^^^

MichaelG.

[duncan webster 1Participant @duncanwebster1]

More strength often means less ductilty. If something is strong enough in mild steel, no point making it from anything more exotic, not that I’m suggesting it’s mild steel. Before deciding what material, work out the stress.

[Michael GilliganParticipant @michaelgilligan61133]

Fancy having a go, Duncan ?

MichaelG.

[RobinParticipant @robin]

I was thinking about fitting inscrutable Honda 500 180mm brake shoes to my Warco round column mill as a spindle brake.

Truly universal 😀

best

Robin

[Michael Gilligan]

On Michael Gilligan Said:

Fancy having a go, Duncan ?

MichaelG.

You’d need to know the mass and position of the bike plus rider in relation to the front wheel,and there would be a fair bit of weight transfer under braking. However if you take a worst case of the back wheel being on the point of lifting, just take all the mass on the front wheel, then assume a coef of friction of 0.9 (figure off learned paper on interweb) and it will give the torque on the front wheel, which can then give the load in the link stopping the backplate rotating, but I don’t have any info on the geometry.

My point was not intended to be just about this. We once got a query about bolts to secure counterweights to a crankshaft and lots of people jumped in with EN24 and similar. Working out the stress showed it was very low, and what an old boss of mine referred to as ‘dried snot’ would have been adequate

[Michael GilliganParticipant @michaelgilligan61133]

Fair response, Duncan

my thinking was that we could [either figuratively or physically] suspend a mass representing bike plus rider … from a linkage equivalent to the rolling radius of the front wheel jointed to the torque arm … and then give it a jolt or two.

I’m guessing that the low-grade M8 bolt might take the static load, but fail after a few cycles.

MichaelG.

[bernard towersParticipant @bernardtowers37738]

My understanding of motorcycle front brake anti torque are that the b olt that is used is done up tight, this means that some of the strength required is taken by the clamping force as well as the fixing bolt. perhaps this makes it uneccesary for an exotic bolt?. Rear brake torque reaction is a different ball game(chain adjustment).

[Gary YeadonParticipant @garyyeadon51936]

Looks as the use a Free Body Diagram would be useful to consider how the Forces are applied.

Maybe look at EN16 T & EN24 T which I seem to remember  being an ideal choice for this sort of application.

[duncan webster 1Participant @duncanwebster1]

Having re read the original post I’m getting confused. If the original AJS fork are being retained, is the 3/8″ (BSF? BSW? Cycle?) thread a given? How can the original Honda bolt be used? If the original thread is a given then can the original AJS bolt be reused?

[Neil AParticipant @neila]

Just an observation on this post. We have been concentrating on the material of the fastener, but perhaps we should also be considering the material that the fastener pulls into. The Honda set up is into an aluminium alloy of unknown specification. The AJS is into a steel bush cast into the aluminium alloy again of unknown specification. Going straight into aluminium will reduce the torque loading that can be applied to the fastener.

Are there any torque loads given for these fasteners? That might give you a starting for the selection of materials. I assume that the M8 is ISO coarse, but you have not given the thread form for the British bikes.

If I were designing this fastener I would most certainly choose a rolled thread for the reasons already given, and I would not be using a 12.9 as it is too hard to cold roll and you do not want to heat treat after rolling. Remember, this is a “Safety Critical” item.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

[ Red Herring input ]

This may only be generally  representative of Honda’s engineering style … but at least it’s a decent image of the right-sort-of thing:

 

Borrowed from ebay: https://www.ebay.co.uk/itm/166368629508

 

I note that the head of the bolt is marked … but is it original ?

More questions than answers !

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Maybe a good place to start:

https://youtu.be/VHd_eSXwbIc?feature=shared

MichaelG.

[Nick WheelerParticipant @nickwheeler]

Surely the fastener in question is well down the list of what is likely to fail first? The sheet metal backing plate, thin torque arm and well-seasoned(if it isn’t actually knackered) are much more questionable

[Michael GilliganParticipant @michaelgilligan61133]

You may well think that, Nick

… but we were asked about the fastener.

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

You may well think that, Nick

… but we were asked about the fastener.

MichaelG.

I do think that. The implication is that other things are likely to fail or wear out well before any fastener made of at least 8mm diameter steel.

[Author]

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