Sidebox mounts and the strength of bolts.

[c_dug]

I have the top box rack fitted to my divvy and have the d rails for mounting the side boxes, however the mounting bolts were lost by a previous owner.

The d rails need to be mounted about 10cm from the rack to clear the bodywork of the bike so i was thinking about knocking something together with some bolts from b&q but I'm unsure if they would be strong enough to support the weight of a full box?

The bolts will have a diameter of around 8cm and as before the space between the rack and the d rails will need to be about 10cm. There will be 2 bolts to each sidebox. The sideboxes are around 40l which I'd guess if packed with heavy stuff would weigh a maximum of 30kg.

Are the bolts likely to snap or bend with that kind of weight plus the force generated by the bike being ridden?

The boxes and rails are made by nonfango, who went bust a few years ago, so buying replacement parts is near impossible.

Thanks
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Nope.]

The bolts will likely be fine, just make sure to either use locking nuts or thread lock as you don't want them vibrating out in the fast lane of the motorway!
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Former: Derbi GP1 50, Sachs XTC 125, Suzuki GSXR 400 GK73A, Kawasaki ZX7R, Suzuki DR250, Yamaha RD350
Current: 2011 Yamaha XT660Z Ténéré, 2003 Yamaha YZR-R1 5PW (In Build), 2009 Kawasaki ZZR1400

[stinkwheel]

The bolt isn't actually supporting the weight. It's just holding the box and the rail together firmly enough so they behave like a solid piece of metal where they touch.

Your footpegs are probably held on with two M8 bolts.

Get a couple of decent ones bolts. I personally would use mild steel ones of grade 8,8 with either spring washers, double nuts or a nylok nut. Although in theory, if you do it up to 19ft/lb with a plain nut, it shouldn't come undone anyway.

You could make a spacer by drilling the middle out of a couple of plain nuts.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[c_dug]

Nope, on mine the weight will be going directly through the bolts and nothing else, there are two styles of racking used on the xj and on mine the top box rack follows under the line of the tail end body work meaning the side box brackets need to be supported away from the main rack to allow room for the boxes to fit.

Mine rack is the same as the one on this bike (but not in red!), you can just about make out the mounts on this bike. https://www.ebay.co.uk/itm/YAMAHA-XJ-900-DIVERSION-/190766845595?pt=UK_Motorcycles&hash=item2c6a970e9b

Hopefully you can see what I mean about there being a distance between the main rack and the sidebox mounts.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[sickpup]

Have you noticed the bracket between the 'u' pieces and the rear of the grab rails?

[woll]

Just a normal pair of 8.8 tensile bolts will do the job. You'd be suprised how much they're used.
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Current Bike- Suzuki DRZ400 SM K6
Previous bikes - Derbi Senda Xtreme50r, Honda CBR 125, Kawasaki ZZR 250, Yamaha DT125R, Suzuki Bandit 600, Gas gas ec 250, Honda CBR600FW
Damaged spleen, damaged kindey, 2 popped lungs, 2 broken ribs, broken face, broken wrist and 5 back fractures... remember kids walls hurt

[c_dug]

Thanks sickpup, hadn't seen that.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[bladerunner]

If your worried about tensile strength...
Buy some 10.2 bolts...a much stronger high tensile grade. B and Q will be cheap spec 8.8 at best but even these with proper mountings should be fine if no gaps between the parts they hold.... B and Q will not be the cheap option if you look up an engineering supply shop or trade centre close to you.
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[reckless_b]

check the advised loading for the panniers, stick to that and you could probably get away with number plate screws, seriously though 8.8 spec bolts will be fine the shear load is way above what you will need.
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40 years on the road on and sometimes off bikes with a very recent OFF

[c_dug]

I eventually got around to making the mounts for my boxes a week or two back. They're solid stainless steel, bolted on either end with M8 bolts.

Should be plenty strong enough!

https://i235.photobucket.com/albums/ee81/paddy2007dug/DSC_0156_zpsxtxu636z.jpg

https://i235.photobucket.com/albums/ee81/paddy2007dug/DSC_0158_zpsk6fs5jep.jpg

I was tempted to drill through and pop a long bolt all the way through but the design of the rails mean they needed a cap head at either end of the mount so I couldn't have kept it neat with a nut.

Anyway, I've noticed with an empty box they twist outwards slightly. I'm guessing this is what the third mount that Sickpup pointed out above is designed to prevent.

It should run from the upper left hole in this picture and end under the back of the pillion handle.

https://i235.photobucket.com/albums/ee81/paddy2007dug/DSC_0158_zpsk6fs5jep.jpg

Sort of like this:

https://i235.photobucket.com/albums/ee81/paddy2007dug/railing_zps59f9ee54.jpg

It's quite difficult to knock on up though as none of the angles really line up, plus one end needs to take a bolt and the other end needs to be thin enough to fit under the grab rail.

I'm guessing it doesn't need to take any weight and is purely for stability of the boxes so this far my plan is to cut a 1mm stainless plate into an L shape, then bend it at the end and bolt through the plate, like this:

https://i235.photobucket.com/albums/ee81/paddy2007dug/Bracketidea_zpsc4556215.png

So I have two questions.

1) Any better ideas for a bracket or any issues with my idea?

2) for the time being do you think a ratchet strap or something similar around the top of the rail and the pillion handle would do the job? I'm not in work for a week and a half now and it would be handy to use the boxes before then.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.