Wheel Came Off!

Super anal OCD mode (complete with wire brush and brake cleaner), courtesy of Popular Mechanics:

To Lubricate or Not
Most times, the specified torque value assumes clean and dry parts. Clean means no dirt, rust, dried-up ­gasket sealer or anything except shiny metal. Wire-brushing the threads will help remove rust or sealant. Engine fasteners, like head bolts or main cap bolts, are often specified to be torqued with 30-weight engine oil wetting the threads and washer. If you're installing a fastener that has a dry torque spec, and the threads and bolt face are oiled, you'll need to reduce the torque by 15 to 25 percent, because the slipperier surfaces will decrease friction.

Teflon-bearing lubes or moly-sulfide engine assembly lubes can reduce friction enough to require a 50 percent reduction in tightening torque. Even casually substituting a zinc- or cad-plated bolt or washer for an unplated one calls for, respectively, a 15 or 25 percent reduction in applied torque, because the plating acts as a lubricant. Fail to heed this advice and the fastener will be seriously overtightened. You'll either snap it or crush a gasket to the point where it leaks. On the other hand, rust or burrs on the threads can increase friction enough that a fastener tightened to the specified value won't provide sufficient clamping force. The shop manual will specify whether the fastener is supposed to be dry or lubed. In either case, prep your bolts. Don't forget that residue from the parts washer or that pie tin full of kerosene you're using to clean parts has oil in it.

Even a quick blast of compressed air to dry off a fastener will leave an oily film behind, affecting ultimate torque. Clean up with aerosol brake cleaner, followed by more air. If you've used grease or anti-seize compound to keep the brake discs from seizing to the hubs, take care not to contaminate the studs or lug nuts.

Bloody good advice. Love it!

We had an issue at my workplace with bolts snapping.
The results were something like 25% decrease from stated torque setting for lubed bolts.
Also effecting torque settings are things like plating and galvanising.
All torque settings are stated for dry conditions (ie, no lube) and usually for black bolts.
Elongation of bolts will only occur if bolts are over tightened beyond there elastic limit.
If elongation (or the exceeding of elastic limit) occurs frequently then you may suffer from the bauschinger effect.
Different grade bolts have different torque levels. Which is why manufacturers recommend torque values.
At least i think i got the (effect) worked out.
I use Norbar torque wrenches and always set them back to zero when you are not actually using it to torque with.
Was that close to correct Pete?
I like the wire retention system, this is used in many applications, from racing cars, bikes etc and even in the aircraft industry. Will look at doing this to mine.

Well I lucked out on this entire episode as Pete was spot on about the tap idea and how hard the flange material is. Very little damage happened to the flange and it cleaned up real easily. The bolts are way softer and took all the beating but were easily found on eBay for $20 a set. The thread pitch is 1.75 so here's the tap the next unfortunate soul will need. Thanks all!

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Sounds like a close call. Glad you and your bike live on for another day.
Trivial information take or leave as you please.
Automotive manufacturers specify that the flange and bolts should be clean and free from grease etc. If you live in a wet country this usually makes it difficult to remove the wheel the first time you get a flat.
The wheels are driven by the clamping force generated by the bolts. The wheels are driven by the friction – they are not peg drive – bolts are not in shear, only tensile loading.
Adding lubricant to flanges or bolts will impact on the bolt torque settings and the transfer of power to and from the wheel, potentially making the assembly ‘peg drive’.
If the torque is correct and the bolts don’t stretch, painting a mark on the bolt and wheel hub would help identify any movement.
For frequent checks on a vital component such as these wheel bolts my preference would be for a high quality deflection type torque gauge.
Just a fianl thought, Guzzi should have used LH threaded bolts with a basic instruction cast in the hub - left tight etc.

Sadly, I sold my GRiSO 12 months ago. To help get over the loss I acquired a LM MKII and a Triumph Speed Triple RS. The triumph is very good but feels like a domestic appliance when compared to the Guzzi. However isolated parts like the rear wheel hub, brakes, suspension are light years ahead of the Italian bike.

I use 80 foot pounds and a quality Norbar Torque Wrench, some bolts are designed as use once. Seen many harley twat bikes with chewed up pulleys because peeps had re used the use once bolts lots of times. From an engineering viewpoint me not being an engineer I find the whole single sided wheel mounting sytem freaky. 4 bolts holding all the torque and weight freaks the shit out of me.
As for wanging them up by hand dont do it unless its joining the two halves of the carc arm and using threadlock

beetle wrote:

It's not common. I think it's been reported here 2 or 3 times. If you correctly torque the screws, they won't come loose. I don't let any non GRiSO person touch mine, and I routinely check mine every few months anyway.

Yup, not common. Only happens when not torqued properly. It's not too high, 80ft lbs if I recall.

110 Nm or 81.132 LBft

Well you can't kill a GRiSO (or the rider apparently) that easy.  I'm happy to report the bike is back in service and the cost of the repairs was extraordinarily low.  $5 for a thread tap, $20 for some eBay wheel bolts, and $35 for a new rear rotor (*insert sound of squealing nickel!).  A 25 mile test ride went great today!

Did anyone else immediately check the rear wheel bolts after reading this topic?

Thanks for sharing in any case, and glad this ended relatively well!