KnifeySpoony Posted February 1, 2022 Share Posted February 1, 2022 (edited) My 420R has the watts linkage. The rear link on both sides of the car where it attaches to the chassis is held on with a bolt and nut (nyloc nut inside, and bolt head outside in the wheel well, each side with a flat washer). These fasteners repeatedly loosen quickly on me. (EDIT: NOTE - the faster is coming loose, but the nut is not turning/coming loose based on paint markings; see blow). I have read that others have had this issue as well on blatchat. What I mean is that after every single drive, the fasteners will need tightening. I will take about 1/16th to 1/8th of a turn to get the torque set properly (34N/m). No other fasteners on my car (not even the forward watts links) have this issue. I am trying to figure out a solution for this, possibly changing to some type of locking washer or loctite or cotter pin or increased torque or??? Any thoughts from anyone with some engineering prowess? Thanks Edited March 25, 2022 by KnifeySpoony Link to comment Share on other sites More sharing options...
fastg Posted February 1, 2022 Share Posted February 1, 2022 (edited) Nylock nuts loose there strength, the more you use them the less there retention strength. There are many options but I would recommend the distorted thread locknut option. But once again this is a single use item, but as you will have to buy a bag of 25 that is not a problem. https://www.mcmaster.com/nuts/locknuts/system-of-measurement~metric/ Graham Edited February 1, 2022 by fastg Link to comment Share on other sites More sharing options...
IamScotticus Posted February 1, 2022 Share Posted February 1, 2022 blue Loctite everything Link to comment Share on other sites More sharing options...
coffee break Posted February 1, 2022 Share Posted February 1, 2022 Two low profile nuts. Install and tighten the first nut. Install the second nut and tighten it against the first while keeping the first nut fixed with a second wrench. aka jamb nuts Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 1, 2022 Author Share Posted February 1, 2022 Ok, I like the suggestions- keep em coming. I'm also considering putting a thin teflon washer underneath the metal washer under the nut so that it rotates more easily on the chassis boss and doesn't apply as much torque to the nut. Link to comment Share on other sites More sharing options...
papak Posted February 2, 2022 Share Posted February 2, 2022 Try Nord-lock lock washers. Available from McMaster, Aircraft Spruce or Pegasus. I haven’t had one loosen yet. Link to comment Share on other sites More sharing options...
sf4018 Posted February 2, 2022 Share Posted February 2, 2022 Suggestions above make sense but I'm curious why the bolt/nut is getting turned instead of the bushing to begin with...is there anything that could be causing the bushings to bind up? Maybe excessive lateral force, not seated against washers properly, etc... Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 2, 2022 Author Share Posted February 2, 2022 14 hours ago, papak said: Try Nord-lock lock washers. Available from McMaster, Aircraft Spruce or Pegasus. I haven’t had one loosen yet. Correct me if I'm wrong, but I don't think this would be an application for a Nord lock or other serrated washer, as they need a flat surface to bind into. 4 hours ago, sf4018 said: Suggestions above make sense but I'm curious why the bolt/nut is getting turned instead of the bushing to begin with...is there anything that could be causing the bushings to bind up? Maybe excessive lateral force, not seated against washers properly, etc... Yeah, I'm not sure tbh. I think I will move the suspension through its range and see what is moving - my assumption is that the bolt head will turn with the link as it rotates but I could be wrong. I guess in theory the bush within the link end should be clamped against the boss on the outer chassis rail, and only the rubber should deflect? ie when I move the axle up and down, the link should rotate but the head on the bolt should stay still. I know there is indeed a lot of lateral force - the whole de dion moves laterally under cornering load - this is easily visible in trackside photos. This means the watts links have to deflect significantly. Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 21, 2022 Author Share Posted February 21, 2022 Ok an update. I moved the suspension through its travel and can confirm the bolt is not moving, so that's good. Before my last trackday, I paint-marked the bolt/nut/chassis, and nothing moved. The nut did not loosen. HOWEVER - when I put a wrench on it, I can tighten it about 1/8th of a turn before achieving proper torque. So I am really confused. How is it that nothing is loosening, and yet I can keep tightening the nut over and over? Link to comment Share on other sites More sharing options...
fastg Posted February 21, 2022 Share Posted February 21, 2022 Because the bolt is getting effectively longer? Is the bolt stretching, or wearing at the head end? Graham Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 21, 2022 Author Share Posted February 21, 2022 It seems either the bolt is getting longer, or the material in between the bolt head and nut is getting smaller. But I don't see how either of those could be occurring. Maybe I'm missing something. Link to comment Share on other sites More sharing options...
Horseless-carriage Posted February 21, 2022 Share Posted February 21, 2022 Perhaps the bolt was yielded at some point, either because of over tightening or some sort of shock load. It might be worth replacing the fasteners with new ones. A yielded bolt will probably just keep stretching, a good bolt will “spring” back to its regular length after the torque is removed. Just make sure you use the correct grade of fastener (8.8 vs 10.9) from a reputable source. Unfortunately I don’t know which grade was used originally. Link to comment Share on other sites More sharing options...
ashyers Posted February 21, 2022 Share Posted February 21, 2022 Any signs of relative movement between the clamped surfaces? Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 22, 2022 Author Share Posted February 22, 2022 Both sides are behaving the same way, and only on the rear watts links. Front links stay tight. It was never overtightened. These are the bolts specified by Caterham that came in my kit. Do you think that lateral loads on the link could be stretching the bolt? Seems like it would take a lot of force to do that. I suppose I could pull the bolt, then run the nut down the threads to make sure it hasn't stretched. ashyers - What do you mean by relative movement? Link to comment Share on other sites More sharing options...
Pokey Posted February 22, 2022 Share Posted February 22, 2022 Any chance that the surfaces aren't perfectly flush and/or orthogonal? I wonder what would happen if you were to torque, then rotate the linkage by hand through the normal range of motion? Would the bolt still be at the same torque value? Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 22, 2022 Author Share Posted February 22, 2022 That's an interesting idea, but I always check the torque (and tighten it), with the suspension at its position with the car settled on its suspension, so it's always consistent. Also, the bolt doesn't turn as the linkage rotates with suspension travel - ie all the movement is within the bushing deflection as designed it seems. Link to comment Share on other sites More sharing options...
Pokey Posted February 22, 2022 Share Posted February 22, 2022 Understood. Just curious, but you mentioned a flat washer on either side - does the rear linkage call for two flat washers on the outside (bolt head side)? Link to comment Share on other sites More sharing options...
ashyers Posted February 22, 2022 Share Posted February 22, 2022 Between the inner shell of the bushing and the bolt/washer/chassis. Link to comment Share on other sites More sharing options...
coffee break Posted February 23, 2022 Share Posted February 23, 2022 Long ago and not so far away I was changing a water pump on a Dodge Colt. I was torquing one of the bolts and it just wasn't getting any snugger. It just didn't feel right. I removed the bolt, and the threaded section was stretched. Lucky for me or I would have been removing a bit of bolt from the block. Another thought is there something the bolt may be compressing or is it all solid metal. Link to comment Share on other sites More sharing options...
KnifeySpoony Posted February 23, 2022 Author Share Posted February 23, 2022 12 hours ago, Pokey said: Understood. Just curious, but you mentioned a flat washer on either side - does the rear linkage call for two flat washers on the outside (bolt head side)? Yes, there's 2 under the head, and 1 under the nut. The front link bolt is different - the head is on the inside (without a washer), with one washer under the nut, which is in the wheel well. 9 hours ago, ashyers said: Between the inner shell of the bushing and the bolt/washer/chassis. I can only assume no movement, but how can I know for sure? How could could the bolt/nut be properly torqued and not clamp it? And if it wasn't locking it to the chassis somehow, I guess movement there could cause wear that would necessitate periodic re-tightening. Link to comment Share on other sites More sharing options...
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