Bolts vibrating loose?

[johnpbransfield]

At Curborough sprint on Sunday when I shot onto the infield when the back end went weird. On inspection the RARB passenger side had come undone where the cap head bolt goes through the bracket. Refitted it and all OK now. Got back home and took the bonnet off to check the oil and two of the three bolts that hold the rocker cover on we're hanging on by a thread....literally. This has never happened before........just coincidence or could it be something more sinister....anything worth checking? Any suggestions much appreciated. Thanks in advance.

[aerobod - near CYYC]

Higher revs, more vibration, higher forces on the components compared with road use will all contribute to nut and bolt loosening. I always spanner checks on critical fasteners before events.

The bolts I have had the most issues coming loose on my R400D are the lower cap bolts for the diff to diff carrier (lost a couple on track in the past until I increased the torque above the recommended value), engine mount to block (blue loctite and frequent checks now) and the coil cover bolts (blue loctite now).
 

[Tom_Arundel]

Just adding lightness as Colin would want!!

[Shaun_E]

I used to lose K-series engine mount bolts with alarming regularity plus alternator mounts and I went though 3 block mounted coils before changing to a remote coil pack. It's just the stresses and vibrations. Loctite helps and regular checks. I recently lost the nut from the nearside upper wishbone balljoint :-o 

[7 wonders of the world]

Schnorr washers under the engine mounting bolts sorts those - not had an issue since fitted them, likewise on the caliper bolts, for belt and braces you can get metal lock tabs or drill the bolts and lockwire them in place.

Basically go around the car and replace any spring washers as their locking properties are akin to a chunk of lard.

Collect all the spring washers up and make a door chime with them or weigh them in for scrap. 

[Bricol]

Spring washers are basically a flat washer when done up - so do nothing.

I'll see your Schnorr washer and raise you a Nordlock washer :) - they don't come undone easily when you want them too, never mind when you don't.   As long as you do the bolt up correctly first - use a torque wrench until you have some "feel".

[7 wonders of the world]

 

[Geoff Brown]

Helical coil washers as they are known were always ideal for general applications to compensate for looseness between components & like ordinary washers spread load. 

The first law is never re use. The second never use where there is the likely hood of sympathetic vibration or a harmonic - like a Seven?

The attitude to 'spring washers' in aviation has always been one of suspicion & generally not used in a lot of applications but substituted by stiff nuts, lock wire & split pins. But you will still find them some where on an airframe but in a tertiary application.

NASA has outlawed them as in their opinion when flat they are no better than an ordinary washer- post #6.

With the advent of Schnorr & the like I think spring washers may have had their day for a lot of machinery or chassis applications. But one will still find them so replace with the modern equivalent or do not re use, replace.

Of course not withstanding all of this thread lock & a regular nut & bolt torque check goes a long way to bits not falling off  !!

[elie boone]

Volvo Cars only use Nordlock washers where no loctite is used.