CwazyWabbit Posted June 18, 2011 Share Posted June 18, 2011 Just a small point, the M10s are being stressed in a different way to the M12s .... the force applied to the M10s is trying to shear the bolt whereas on the M12s it's trying to strip the thread. Would you be happy mounting the tow ball itself with M12s ? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 18, 2011 Share Posted June 18, 2011 Maybe you could get a 16 hole saw? Other than that it's looking good Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted June 18, 2011 Author Share Posted June 18, 2011 I believe the M12s will be stronger in tension than the M10s will be in shear. If something lets go I would bet it will be the M10s first. Two 8.8 class M12s give a combined ultimate strength of about 14,000kgf (see below), which I think is a large enough safety factor for a 3,500kg tow coupling. If I find a way of taking them out to 16mm then I shall do for the sake of completeness, but I don't think it will affect the safety of the system as I believe the M10s to be the weak link (Source: http://www.tech.plymouth.ac.uk/sme/desnotes/boltb.htm) Quote Link to comment Share on other sites More sharing options...
PaulMc Posted June 18, 2011 Share Posted June 18, 2011 ...but I don't have a 16mm drill bit (let alone a drill that it would fit!) You need a Reduced Shank Drill Bit, like this - http://uk.rs-online.com/web/4087988.html . Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 18, 2011 Share Posted June 18, 2011 I believe the M12s will be stronger in tension than the M10s will be in shear. If something lets go I would bet it will be the M10s first. Two 8.8 class M12s give a combined ultimate strength of about 14,000kgf (see below), which I think is a large enough safety factor for a 3,500kg tow coupling. If I find a way of taking them out to 16mm then I shall do for the sake of completeness, but I don't think it will affect the safety of the system as I believe the M10s to be the weak link (Source: http://www.tech.plymouth.ac.uk/sme/desnotes/boltb.htm) I was quite surprised by how much stronger in tension the M12s were than the M10s in direct shear, makes you wonder why they have used M16's anywhere on the hitch. Quote Link to comment Share on other sites More sharing options...
mickeyw Posted June 19, 2011 Share Posted June 19, 2011 The earlier drop plates only had holes for 12mm anyway. I think what you have will be plenty strong enough, as long as you have sufficient washers to stop the M12 head trying to pull through the Ø16 hole. Quote Link to comment Share on other sites More sharing options...
rovernut Posted June 19, 2011 Share Posted June 19, 2011 If its designed to have 16mm bolts then you should use 16mm bolts and I do not care how many washers you use to stop the 12mm pulling through. The heads on the 12's are only 19mm whereas the 16's are 24mm You would not have a leg to stand on if a trailer broke away. A NATO hitch is only mounted with 12mm bolts but there are 4 of them. I have been fitting Towbars commercially for 10 years and would not even consider this. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted June 19, 2011 Author Share Posted June 19, 2011 I'll let you know if my <100kg trailer causes it to break away I can't tow more than about a ton due to lack of license, when I can hang 3.5 tons off the back of it legally I'll change the bolts. But I still think the M10s holding the angle to the 2mm chassis brackets will give first... Quote Link to comment Share on other sites More sharing options...
mickeyw Posted June 19, 2011 Share Posted June 19, 2011 If its designed to have 16mm bolts then you should use 16mm bolts and I do not care how many washers you use to stop the 12mm pulling through. The heads on the 12's are only 19mm whereas the 16's are 24mm You would not have a leg to stand on if a trailer broke away. A NATO hitch is only mounted with 12mm bolts but there are 4 of them. I have been fitting Towbars commercially for 10 years and would not even consider this. Don't forget there are another 4 off M16s teamed up with these two M12s holding it on to the truck! Quote Link to comment Share on other sites More sharing options...
rovernut Posted June 19, 2011 Share Posted June 19, 2011 I'll let you know if my <100kg trailer causes it to break away I can't tow more than about a ton due to lack of license, when I can hang 3.5 tons off the back of it legally I'll change the bolts. But I still think the M10s holding the angle to the 2mm chassis brackets will give first... I have no doubt that your 100kg trailer will not cause any failure. However I know of a guy who just bolted a ball onto the crash tube on his Mitsubishi Delica because he was only occasionally towing a little trailer for garden rubbish. He later sold the vehicle on and unfortunately the new owner decided to tow a twin axle tipping trailer until 1250kg of trailer and 1000kg of sand parted company. The crash bar was only bolted on with 4 8mm bolts. These didn't shear, they pulled out of the body. Fortunately no one was killed although quite a lot of property damage occured. Now, and not before time, the tow bar is inspected as part of the MOT. Just playing Devils advocate. Poor towing equipment and dangerous trailers are my pet hates Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted June 19, 2011 Share Posted June 19, 2011 I think, James, that it would be rather foolish not to use the correct bolts for the sake of a couple of quid. No doubt the M12s would hold but always better safe than sorry. The consequences of something going wrong could be with you for the rest of your life ! Mo Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 20, 2011 Share Posted June 20, 2011 Mo, I see where your coming from in the fact it was designed with M16s so in the event of an accident they could blame James for using the wrong parts. Using that argument you could also argue the use of 5mm plate instead of the original 10mm plate for the part it's bolted to is also a no - no. I imagine they would have to show it as a contributory cause in an accident as the vehicle is old enough not to require a type approved tow bar. Caveat to that is I'm not a lawyer and the above is personal opinion .... I would have used like for like if I was doing it. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted June 20, 2011 Author Share Posted June 20, 2011 I am confident that it is safe and that I would have no problems pulling 2,000kg let alone 100kg. Bear in mind that Series vehicles had no stays at all, just the slider frame and the angle bracket under the crossmember, and I'm sure a few of those have pulled some weight! Dixon Bate Series Drop Plate Kit - Paddocks However, I see the points that you chaps are making and I will re-make my bracket so as to use 16mm bolts (which I already have). Not because I doubt the strength of the M12s but because of the fact that I'm using a 12mm bolt in a 16mm hole. However, given that I'm only lugging this small trailer around at the moment the current setup is fit for this purpose. I need to scavenge a slightly larger bit of steel from work and then drill some 16mm holes in it. Then bolt it up and repeat the process of last time, hammer action until it lines up with the angle...then drill some 10mm holes Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted June 20, 2011 Share Posted June 20, 2011 Mo, I see where your coming from in the fact it was designed with M16s so in the event of an accident they could blame James for using the wrong parts. Using that argument you could also argue the use of 5mm plate instead of the original 10mm plate for the part it's bolted to is also a no - no. Indeed it is CW, you're quite right and in fact James has committed himself to rectifying these now... which was nice. Mo Quote Link to comment Share on other sites More sharing options...
Smego Posted June 21, 2011 Share Posted June 21, 2011 I have a whole tow bar with single electrics in the front garden if you want it just collect, only missing the c plate as I needed that bit. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 22, 2011 Share Posted June 22, 2011 Mo, I see where your coming from in the fact it was designed with M16s so in the event of an accident they could blame James for using the wrong parts. Using that argument you could also argue the use of 5mm plate instead of the original 10mm plate for the part it's bolted to is also a no - no. I imagine they would have to show it as a contributory cause in an accident as the vehicle is old enough not to require a type approved tow bar. Caveat to that is I'm not a lawyer and the above is personal opinion .... I would have used like for like if I was doing it. Looks like I need to have some humble pie I think ..... I met up with James today and he rather politely pointed out that the four bolts holding my tow bar to the rear cross member are M12's and not the M16's that they are supposed to be! In my defence I didn't fit it, however I will be sorting it out before I tow anything again, I'm also going to consider adding the piece of angle iron to drop the hitch to it's correct height as James also pointed out there is a good chance there are no crush tubes on two of the bolt holes. previous owners, grrrrr Quote Link to comment Share on other sites More sharing options...
lrfarmer Posted June 22, 2011 Share Posted June 22, 2011 This has been an interesting thread for me as thanks to this I have noticed the previous owner has installed my adjustable hitch with 4 bolts into the rear cross member. This of course means the whole thing is a couple of inches higher than it should be but has also got me wondering if this configuration is weaker than the standard one as the long piece of angle iron that is normally bolted to the bottom of the cross member would surely spread the load over a greater area..... Looks like I need to have some humble pie I think ..... I met up with James today and he rather politely pointed out that the four bolts holding my tow bar to the rear cross member are M12's and not the M16's that they are supposed to be! In my defence I didn't fit it, however I will be sorting it out before I tow anything again, I'm also going to consider adding the piece of angle iron to drop the hitch to it's correct height as James also pointed out there is a good chance there are no crush tubes on two of the bolt holes. previous owners, grrrrr i have movered my tow bar to the same place, there was crush tubes on all three sets of holes i moved mine up as when RTVing it was hitting every stone and bump i have had to fit a drop plate to the sliding bit as it was to high for towing my caravan Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 22, 2011 Share Posted June 22, 2011 I'll have a look this weekend and check there are crush tubes in all the holes then I'll be off shopping for some M16's at the least, thanks for your reply lrfarmer Quote Link to comment Share on other sites More sharing options...
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