Maverik Posted January 5, 2011 Share Posted January 5, 2011 I'm just about to fit a tow bar plate to my 86 LR90, its a 2nd hand one so missing a few bolts. Whats the standard steel grade of bolts for tow bar applications? can I use standard 8.8 grade bolts or do I need something a little more exotic like 10.9 Its the bolts that fix the diagonal tie bars to the chassis and the bolts that hold the plate to the rear crossmember. Cheers Mav Quote Link to comment Share on other sites More sharing options...
Disco-Ron Posted January 5, 2011 Share Posted January 5, 2011 From this http://cgi.ebay.co.uk/Towbar-Towball-Tow-Bolts-/190060792249?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2c408189b9 I would assume that 8.8's are ok.... as thats what they're being sold for! Quote Link to comment Share on other sites More sharing options...
Maverik Posted January 5, 2011 Author Share Posted January 5, 2011 Hmmm M16's there proper big uns aint they. I was looking at the LR90 parts book at that showed stuff in the realms of M10 & M12, I'll go check out the hole sizes. 240Nm he says... will check that out also. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted January 5, 2011 Share Posted January 5, 2011 Those are the tow ball bolts, and as such 240Nm is designed for an M16, do that to an M10 and you'll likely be removing it in two pieces Yours will need M10/12, unsure of which, as I don't have a Defender Quote Link to comment Share on other sites More sharing options...
Disco-Ron Posted January 5, 2011 Share Posted January 5, 2011 It depends which bolts you need, on my new chassis, the bottom holes in the back of the crossmember are 16mm, the top ones are m12, the ones in the underside of the crossmember are m10 threaded holes..... Quote Link to comment Share on other sites More sharing options...
Mark Posted January 5, 2011 Share Posted January 5, 2011 8.8 grade bolts are more than adequate for standard Towing duties. You only need to think about going above that if you plan to use it as a recovery point for snatch recovery. mark Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted January 5, 2011 Share Posted January 5, 2011 A while ago I asked this question at a certain well-known trailer/towbar fitting specialist in Bristol and their reply was that they’ve always used 8.8 bolts with no reports of ill effects. If you look in BS EN ISO 898-1 (“Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and studs”), it lists the nominal tensile strength of 8.8 as 800 N/mm2 and 10.9 as 1000 N/mm2 (The first 8 in 8.8 and 10 in 10.9, in fact). That’s 116000 PSI, for those who prefer to work in old money, or an absolute sh*tload in rough figures… A more useful figure when doing bolt calculations, 0.2% of elongation, lists 640 and 900 N/mm2 respectively. Bolts will have been sized to a huge factor of safety anyway, so I wouldn’t worry about fitting 8.8s. Just make sure you do the bolts up to the correct torque. Most DIY-priced torque wrenches only go up 200 Nm. Quote Link to comment Share on other sites More sharing options...
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