Civinfo - View Single Post - Suspension URGENT: Defect on Civic Safety Critical Part

Courant · 22nd April 2008, 18:03

TTDegs

1. 0.5mm out of tolerance for this kind of thing could be reasonably significant (if indeed this is the case).
2. The effect of this is:
a) increased clamping force. The fastener is tightened to a certain torque. If the thread is under-sized, the amount of friction between fastener and thread is reduced and the same torque will give a "tighter" fastener. This causes increased stress levels.
b) reduced resistance to coming undone, due to this reduced friction.

Potentially nasty. But potentially not, it all depends on exactly what conditions this is being subjected to, there might acutally be a lot of leeway here. Of course, the consequences of failure are quite severe....

How this was found out. Interesting question because there should be a paper trail! Parts are manufacturered in batches and a number of parts out of each batch are tested. This is then analysed to give a expected range (e.g. a mean and standard deviation in, say, diameter) for that batch, and this should be recorded and checked against the standard as part of the quality control procedure. Either the batch testing failed or was shown later to be inaccurate (you can't test every part, and some may have been missed); or the information didn't make it's way through and/or was ignored.

Basically, wait and see, the onus is on Honda to show that this isn't an issue (which it might not be). Though, if I had an affected car, I'd be getting it checked out, or at least pressuring the dealers for an answer.

Courant

22nd April 2008, 18:03	#45 (permalink)
Courant Locking Wheelnut Join Date: 27th January 2008 Location: Cambridge, UK Posts: 116 Thanks: 0 Thanked 1 Time in 1 Post iTrader: (0)	TTDegs 1. 0.5mm out of tolerance for this kind of thing could be reasonably significant (if indeed this is the case). 2. The effect of this is: a) increased clamping force. The fastener is tightened to a certain torque. If the thread is under-sized, the amount of friction between fastener and thread is reduced and the same torque will give a "tighter" fastener. This causes increased stress levels. b) reduced resistance to coming undone, due to this reduced friction. Potentially nasty. But potentially not, it all depends on exactly what conditions this is being subjected to, there might acutally be a lot of leeway here. Of course, the consequences of failure are quite severe.... How this was found out. Interesting question because there should be a paper trail! Parts are manufacturered in batches and a number of parts out of each batch are tested. This is then analysed to give a expected range (e.g. a mean and standard deviation in, say, diameter) for that batch, and this should be recorded and checked against the standard as part of the quality control procedure. Either the batch testing failed or was shown later to be inaccurate (you can't test every part, and some may have been missed); or the information didn't make it's way through and/or was ignored. Basically, wait and see, the onus is on Honda to show that this isn't an issue (which it might not be). Though, if I had an affected car, I'd be getting it checked out, or at least pressuring the dealers for an answer. Courant Last edited by Courant; 22nd April 2008 at 18:25. Reason: re-read original post again and realised some of my comments didn't make sense in this context!