Mike Bees Posted March 23, 2001 Share Posted March 23, 2001 Torque is specified in the build manual (don't have it here with me). There is a sleeve, the compliance in the bush is what allows the arm to move (just like the other suspension bushes). Mike Link to comment Share on other sites More sharing options...
StewartG Posted March 23, 2001 Share Posted March 23, 2001 Had an interesting talk with Caterham today they agreed that movement of the radius arm is allowed by compliance in the rubber bush. They added the advice that the bolt should only be torqued up with the weight of the car on the suspension. I wonder if those that have had bolts fail tightened them with the suspension at full droop. Link to comment Share on other sites More sharing options...
EFA Posted March 23, 2001 Share Posted March 23, 2001 I've not had the bolt shear or work loose, but I have had the bush work its way out of th forward end of the bar! A bigger washer resolves this problem. Arnie Webb The Fat Bloke blush.gif in a not so Slow Vauxhall wink.gif Link to comment Share on other sites More sharing options...
jonhill Posted March 24, 2001 Share Posted March 24, 2001 The front radius arms should be torqued to 35 lbs ft according to the latest build manual. I was doing mine last night, and the nuts on both sides were totally stripped with this much torque. In the end we did 'em up to 30, as this seemed to be their limit. My torque wrench could be badly calibrated, or the nuts supplied could be made of plastercine. Do nuts, like bolts, come in different specs.? Link to comment Share on other sites More sharing options...
Reg Posted March 25, 2001 Share Posted March 25, 2001 According to my build manual, the front bolts on the radius arms should be torqued up with the radius arms horizontal in order to pre-load the bush so either the manual's wrong again or Caterham's advice is. And 35lbf isn't a lot of torque for that size of bolt so there must be something suspect with your wrench, jonhill. Reg Marjason C7 SEV Link to comment Share on other sites More sharing options...
StewartG Posted March 25, 2001 Share Posted March 25, 2001 I don't understand why you're suggesting Caterham are giving inconsistant advice. I would have thought that with the weight of the car on the springs the radius arms would be horizontal. Link to comment Share on other sites More sharing options...
Dartmoor7 Posted March 25, 2001 Share Posted March 25, 2001 It doesn't really matter if they are horizontal, the important thing is that the suspension must be loaded while tightening. Link to comment Share on other sites More sharing options...
Mike Bees Posted March 26, 2001 Share Posted March 26, 2001 This has B-all to do with bolt failures though, it's just about how the bush should be loaded. Mike Link to comment Share on other sites More sharing options...
R2D2 Posted March 26, 2001 Share Posted March 26, 2001 The real question is why the bolts come loose in the first place. The torque setting will only be valid if the bolt can be correctly loaded in tension. If there is too much stiction in the thread or in the bush all of the torque loading will do is position the bolt it won't cause any stretch and the bolt will work loose. If the bolt is tight in the bush or the thread is crappy or badly lubricated it will not tighten correctly. Perhaps there is more than one problem. 8.8 bolts may not take the share loads and badly fitting bolts may not be tightening up correctly because of friction. Its obviously a serious problem and needs sorting out. If anyone with the problem is in the West Mids I have a torque wrench that was calibrated about a month ago and I would be happy to let anyone who is concerned use it to try to figure out why there is a problem Link to comment Share on other sites More sharing options...
Area Representative Tin Man Posted March 26, 2001 Area Representative Share Posted March 26, 2001 Caterham build manual states the following: These are fitted using a 3/8" x 2 3/4" caphead bolts passed through a plain counterbored bush form the inside of the cockpit. The radius arm is fitted onto the bolt next then a large dia plain washer & nyloc. These should be tightened to 35lbft with the arms parallel to the ground. This pre-loads the bushes in the correct position for when the suspension is poperly loaded. I torqued mine up before loading the suspension & the one on the De Dion ears after. Confusing or what! Edited by - Tin Man on 26 Mar 2001 22:28:39 Link to comment Share on other sites More sharing options...
Dartmoor7 Posted March 26, 2001 Share Posted March 26, 2001 Obviously the build manual must change over the years. Mine (September 1993) states: "...the securing bolts should be tightened with either the wheels on the ground or the car's weight taken by the De Dion tube." Link to comment Share on other sites More sharing options...
StewartG Posted March 26, 2001 Share Posted March 26, 2001 Is the version with the cap head bolt on the inside and the nut on the outside the old version or the new version? What's on the latest chssis? Link to comment Share on other sites More sharing options...
Graham Sewell Posted March 27, 2001 Share Posted March 27, 2001 Returning to ISmall's original post 'My suspected De Dion tube fracture has in fact been confirmed as the radius bolt on the driver's side sheering off in the bush', is this because on the driver's side, the effect of a bump is to act like an impact wrench and tighten the bolt (conversely on the passenger side to loosen the bolt) in a fixed threaded bush in the chassis? If this is the case, surely an appropriately spec'd bolt with teflon washers either side of the radius arm would cure the shearing problem, and using left hand threads on the nearside would prevent the bolt coming undone. Is this feasable, and what would be the costs to Caterham? Cheers, Graham Link to comment Share on other sites More sharing options...
Mike Bees Posted March 27, 2001 Share Posted March 27, 2001 Stewart - the point is that the thing should be tightened up with the bush preloaded, all versions have the bush so all versions should be done the same way (i.e. with the car's weight being taken by the suspension). Mike Link to comment Share on other sites More sharing options...
StewartG Posted March 27, 2001 Share Posted March 27, 2001 I don't understand why the front of the radius arm can't have some sort of pivot surely the weight of the car should be supported by the springs not the radius arm bushes which are torqued up solid with the only compliance in the rubber. Mike, I think the whole point of tightening the bolts with the car's weight on the suspension is to minimise the preload and hence stress on the bushes and in answer to your previous point I can't see how an incorrectly stressed bush can help incorrectly stressing the bolt that secures it and that could cause a failure. Edited by - stewartg on 27 Mar 2001 18:41:44 Link to comment Share on other sites More sharing options...
aideen Posted March 27, 2001 Share Posted March 27, 2001 This is all getting too confusing! As I understand it, it was the "bolt into a threaded bush" setup (e.g. 1997 chassis) that was prone to failure and hence Caterham reverted back to the older method of using a plain bush with a nut and bolt. If I'm wrong here, someone will say. Presumably if an incorrectly specified bolt is used (either setup) then the bolt might shear-off as opposed to "just" working loose. Someone mentioned coating the bolt with grease - the instructions with my torque wrench say: "Don't use grease or molybdenum compounds on screw threads before torque tightening." "Do see that bolt threads are clean and lightly oiled before torque tightening". (presumably where neither Loctite nor Nylocks are being used) Someone else mentioned about their torque wrench stripping the bolt threads. This caught me out too (I flatted the spring washer before I realised the wrench was "lying"). I bought a better wrench (with instructions!) and am now careful about tightening to a lower torque first. The instructions suggest 3/4 of max, then reset to final figure). For the record, here is the 1997 version of the manual: "a) These (the arms) are fitted using a 3/8" x 2" bolt into a threaded bush in the chassis with a large diameter plain washer and spring washer next to the head of the bolt. These should be Loctited and tightened to 35lbft with the arms parallel to the ground. This pre loads the bushes in the correct position for when the suspension is properly loaded." I've added a note (from Tim Ward) that a 12.9 HT bolt was required. : "b) Attach the rear end of the radius arms to the brackets on top of the De Dion tube ... - do not fully tighten yet." We need an online (annotated) Workshop Manual. Aideen Link to comment Share on other sites More sharing options...
Area Representative Tin Man Posted March 27, 2001 Area Representative Share Posted March 27, 2001 Mine was a 1999 K-series. No date on the assembly guide I received with the kit. Link to comment Share on other sites More sharing options...
Mike Bees Posted March 28, 2001 Share Posted March 28, 2001 Stewart - the car's weight *isn't* supported by the preload in the bush if you torque it up with the wheels on the ground. It'd have to be one hell of a bush to take the weight of the car via the leverage of the radius arm anyway, even if you torqued it up at full droop! All of the suspension mounting points (inner ends of front wishbones, outer ends of A-frame, both ends of radius arms, both ends of all dampers) use rubber bushes which become loaded/unloaded as the suspension moves. Yes you could replace them all with rose joints (non-bushed pivots) but the point of the bushes are to add compliance and reduce NVH. Mike Edited by - Mike Bees on 28 Mar 2001 09:39:57 Link to comment Share on other sites More sharing options...
Simos Posted March 28, 2001 Share Posted March 28, 2001 An online annotated manual...? Now there's a thought... what a great idea ! Columns for what the manual says, the reality and one for related tips and tricks. Link to comment Share on other sites More sharing options...
stevefoster Posted April 1, 2001 Share Posted April 1, 2001 While whipping me daily driver cars calipers off to replace the pads the torque thread came to mind. The debait about oiling or greasing threads or leaving them dry is interesting. The idea that greased or oiled threads will do up tighter is interesing too. What happens when you put a bolt under torque to say 35 ftlb is that the threads bind sharing the load and the bolt stretches everso slightly. It is the stretch that keeps the bolt and nut together. This will happen regardless of lubrication when the thread binds. If the threads are rusty and at low very torque settings then the rust binds and could fool the torque wrench. At higher torques this is probably irrelevant. Using Loctite which while liquid must be a very good lubricant all manuals happily say torque up to a given setting. The setting should always seem reasonable to the type of bolt and the level of 'tech' involved. As for the radius arm bolts. I checked mine and they are fine. They were put on with loctite in the first place. I think the bolt shearing or the bush coming off is what to watch for. Maybe some of you guys are loading your cars with so much HP that things are starting to get marginal An R500 should have a much shorter service or check everything interval than say a standard 1600 K. Link to comment Share on other sites More sharing options...
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