Digsy Posted August 4, 2004 Share Posted August 4, 2004 I know a few of you on here have stripped down and re-assembled split rim alloy wheels before. I am about to put my BBS 2-pieceers back together and I have a quandry over the torque of the rim screws. Each wheel has 16, 7mm dia by 1mm pitch (20mm long in total) screws. The screws are titanium (grade unknown but I'm assuming about 1100N/mm^2 UTS / 960N/mm^2 yield - roughly similar to a 10.9 steel screw). The rim is diecast aluminium. I'm assuming a UTS of 225N/mm^2 (about the same as LM25TF). If I fed all this into a programme here at work, it tells me that I can torque the screws up to 24Nm if I have 16.5mm of thread engaged in the assembled condition. As Sod's law would have it, I have 17mm engaged, so if I did them up to 24Nm I would be running a very high risk of thread stripping. My instict tells me that 24Nm is way too high for a 7mm fastener (more like 8mm). However, I don't want to back off too far in case I "underdo it". Of course I will be using threadlock, but I want to get the torque right. Just wondered if anyone had any experience in this area? TIA Quote Link to comment Share on other sites More sharing options...
Ian C Posted August 4, 2004 Share Posted August 4, 2004 I just did mine up tight and the wheel hasn't fallen apart yet Engineer freak -Ian Quote Link to comment Share on other sites More sharing options...
Digsy Posted August 4, 2004 Author Share Posted August 4, 2004 Originally posted by Ian C Engineer freak The chicks love it. Quote Link to comment Share on other sites More sharing options...
jagman Posted August 4, 2004 Share Posted August 4, 2004 tight is the answer, text book torque values can only be used as a guide, the actual torque will vary due 1 the bolts are not new ,2 threadlock applied will vary the torque,3 the grade/quality of the thread/bolt , the accuracy of the wrench, just do em tight and try to keep them even, using a clock torque method a la cylinder head- then re-tighten after running the wheels for a short time Quote Link to comment Share on other sites More sharing options...
eldudereno Posted August 4, 2004 Share Posted August 4, 2004 I wouldn't go over 20Nm myself. Why not contact BBS and ask their advice? Quote Link to comment Share on other sites More sharing options...
jagman Posted August 4, 2004 Share Posted August 4, 2004 a standard aircraft stainless bolt of about that size would have a torque of 50-80 lb/inch ( 9 ish Nm) reduce the torque by 10-20% for a lubricated installation( dry or wet lube) also titanium fasteners should not be tightened using chrome plated spanners or sockets -like we all got industrial finish sockets-not Quote Link to comment Share on other sites More sharing options...
jagman Posted August 4, 2004 Share Posted August 4, 2004 before anyone asks the plated sockets usually on nickel cadmium ,the cadmium can be deposited on the titanium bolt this can cause embrittlement / intergranular weakness in titanium esp in heated enviroment causing early failure of bolts hth Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 4, 2004 Share Posted August 4, 2004 Jeez Darren, what are you smoking.... ??? Just do them by hand, to what "feels" right, I'd guess at 12 to 15 lbs ft (I don't "do" metric, sorry. It's a wheel rim, not some piece of aerospace hardware You've proabably spent more time computing all this than it should take to assemble 4 rims. I have done *HUNDREDS* of piece race rims and none have seen a torque wrench, none have come undone, and very few leaked. Just get on with it.... Quote Link to comment Share on other sites More sharing options...
Digsy Posted August 4, 2004 Author Share Posted August 4, 2004 Cheers for the replies guys. Well, I guess I just want to get it right The wheels are two-piece, and the screw goes right into the cast ali rim. Unfortunately I have a bad habit of stripping threads in ali and having spoken to BBS in the past I know they are naff all help in getting spares. Basically if I mess up a rim or a screw then I can't get any more and that will be a whole wheel knackered. Anyway: Jagman: The 24Nm figure wasn't from a tect book - it was calculated using some standard software we have here. It takes into account the material properties, thread type, diameter and pitch. Class of external and internal thread, coefficient of friction between the two, etc, etc. It works out the tightening spec for elastic and plastic region tightening. The bolts themselves have been cleaned and I'll clear out the female threads with a tap. I can't re-tightned them after running because if there is any movement it will break the anaerobic threadlock. 9Nm on a 7mm screw with over 2xD engagement into a good grade ali sounds low to me. I would have thought that 10Nm was possible even on an M6? More like 28Nm for an M8 so I was expecting about 19Nm for an M7, which kind of ties in with Chris Wilson's 12 to 15 ft lbs (16.8 to 21 Nm). eldudereno: I was thinking about knocking it doen to 20Nm. I will call BBS, but as I said above, they have been NO help at all during this refurb. I rang every BBS Direct distributer in the UK and none of them could help me with spares. The head office in Germany did not answer my e-mails. Basically I was told that they were only interested in doing a full refurb back at the factory - kerrr-ching! Chris: Baaa! I just wanted to do it as good as I could and not damage anything The calcs took about 1 minute on one of those new-fangled computer things. Good input, anyway. Cheers all! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 4, 2004 Share Posted August 4, 2004 Well, if you bugger a thread up I have an M7 helicoil kit, which is probably a VERY rare one indeed! Renault Alpine used that thread for the clutch bolts on the 2 plate clutches on the R5 Turbo 1 and Turbo 2 (mid engined homologation special) that I used to own and I still do work on them. REALLY odd size, trust Alpine.... The TVR Tuscan race rims (BBS I think) used a bizarre fastener with something between a Torx and Allen head, for which they refused to sell the tool. In the end someone made a form tool to make a copy of the socket and sold loads to the race people. Awkward buggers these rim makers! Quote Link to comment Share on other sites More sharing options...
Digsy Posted August 5, 2004 Author Share Posted August 5, 2004 Originally posted by Chris Wilson Well, if you bugger a thread up I have an M7 helicoil kit, which is probably a VERY rare one indeed! Renault Alpine used that thread for the clutch bolts on the 2 plate clutches on the R5 Turbo 1 and Turbo 2 (mid engined homologation special) that I used to own and I still do work on them. REALLY odd size, trust Alpine.... The TVR Tuscan race rims (BBS I think) used a bizarre fastener with something between a Torx and Allen head, for which they refused to sell the tool. In the end someone made a form tool to make a copy of the socket and sold loads to the race people. Awkward buggers these rim makers! Triffic! It's M7x1. I'll let you know if I need the kit. Good to have a backup... The screws are BBS special jobs, but thankfully use a standard 12 point spline drive. I nearly knackered one trying to take it out with a 6 sided sllen key style drive. Right tool for the right job and all that Quote Link to comment Share on other sites More sharing options...
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