split rim bolt torque value??
Turbo Mini Forums

i'm replacing all the bolts in my MB split rims for obvious reasons inherent with these MB wheels

anyway i was wondering what else people have torqued split rim bolts upto (M6 size)??

i was thinking of just torqueing them upto just under their fatigue limit stress, which by my calcs works out at about 17Nm for a 12.9 bolt (unbrako), which doesn't seem unreasonable for an M6 after looking round

any thoughts much appreciated...

Carl is your man to answer this one.....

Dan - I wouldn't think you'd want to take any M6 nut and bolt combo this high - remember the nut you are using is made of platercine not high grade steel! - same goes if you are planning on putting washers under the heads of the bolts, these are plastercine as well, if you torqued to 17Nm the very small surface area of the bolt would bite into the low grade washer - causing yield then the bolt would come loose, not a good idea! - I would have thought 6-8Nm would be more than sufficient spread over 12/16 bolts..........

If Carling made Mini engines
it would probably be like this one!

my info came from image years ago, there recomedation was 10lbs,

but recently i have spoken to afew miglia drivers looking for an alternative wheels and they tell me they do theres up to 20lbs, [ HOW MUCH!!,yes thats what i thought] so i tried it with the usual 1/2 nut and i stripped every one , a full nut will take it but it feels like the bolt is goint to break,,
so i go for 8lbs and never had any probs, baring in mind the rims are sat on a lip so the bolts are not in sheer.
but if you google bolt torques there are some high torque setting on some of these sites also, they just seem high to me, as john said its the nut thats the weak link when torquing up but it seems the bolts break with time,

carl

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

look in FAQ , torqe settings..

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

thanks for the info guys, must admit i'd had a re-think after i posted regarding the different materials of the bolt and the alloy rim/centre and the effects of expansion, although i'd not considered the nut/washer as a factor

8lb works out at about 11Nm which seems reasonable

i'll take a look in the faq carl

many thanks

Edited by dan on 26th Sep, 2006.

Another thing - the annoying part with cap heads is they are all 12.9 grade, which in itself makes the part fairly brittle - though strong, the worst part is the coating on these bolts - my advice (I'm a qualified/ time served chassis design engineer) is not to use 12.9 bolts with a zinc coating, a zinc based coating will cause hydrogen embrittlement on 12.9 grade material - look it up on google, the result of this embrittlement is fatigue failures early in the parts life through crack propogations along the surface. Always use fasteners which have a coating on them and that have been de-embrittled, quality fasteners will state this fact. If you can't get hold of these type of bolts and are stuck with zinc coated parts - lower the torque on them and keep an eye on them in stressed working conditions! For holding your wing mirrors on or something the zinc coated ones would probably be fine.

John

If Carling made Mini engines
it would probably be like this one!

i'm using the black coloured unbrako ones so should be okay on the zinc plating side of things

thanks for the info johnK

With the historic f1 cars we run a mb racing wheel, admittedly a little wider than the ones thast are used on minis. With a washer under the bolt head of a 12.9 grade M6 cap head bolt we torque them up to 9 lb ft and have no probs, but these wheels are only used for 8 weekends a year so fatigue cycles aren't really to be worried about!!

But o/t but I have a set of oz splitrims on my golf.I need 2 new outer rims and the other 2 could do with a good polish around where all the bolts are.

Thing is they use oz special bolts,in m7 size,most of them are rusty,undoable, you need a special sockets and cost £1.20 eachx120 thats quite a bit.
Can I redrill them and use 12.9 rated m8 allen bolts instead(free from work),maybe even cheesehead ones as they will have a larger surface area under the head.
When I asked about bolts at southwest fasteners they refused to sell me anything once I mentioned they were to hold wheels together.

Metro turbo weekend driver,Mini turbo in the making again!