Modern Vespa

So I had an exciting few moments on my scoot Saturday evening...

Coming around a corner and I hear several pings followed by some sicking cthunks while feeling the rear end start to wobble...

It turns out 4 out of 5 bolts sheared off -- I know I've never over-torqued these bolts, so the only thing I can figure is I've smacked a few too many speed bumps are too high of speed, and they finally gave up the ghost.

Quick call to a friend, and I've picked up some bolts from the hardware store, followed by some vocal musing about how badly named 'easy-out' tools are, and I've cleared 2 of the sheared bolts, enough to basically walk the bike the last 1/2 mile home.


I have a few questions for you guys:
The bolts seemed to be pretty soft compared to some VW bug lug bolts I had to drill and extract quite a few years back -- would replacing the bolts with hardened ones be a good or bad idea?

assuming I should just use oem bolts -- any idea who would have them?(i'd call AF1, but they are closed on Mondays.

I pulled and inspected (cheap microscope) the bolts for the front tires but
I'm not confident in my ability to spot metal fatigue-- think I should just replace all the front tire bolts as a precaution?

You over tightened them at some point, bolts just don't break

Order the bolts from a local dealer to get the correct bolts.

I'd like to think that, rather than the alternative of either I've been bouncing off speed bumps that hard or the lug bolts being that shitty

-- got any ideas on how to check the calibration of a torque wrench? I don't want to buy a new one

*edit looks like I'm using this:
calibration

if your questioning your torque wrench for cal there are a lot of places that can recalibrate them. just google.

Personally I wonder if they were UNDER torqued. I'd think to over-torque to the point of failure like this it would have to be WAY overdone. How long is your extension when you tighten the bolts? (Did you have the wheel installed by someone else that may have over tightened them?). When I put wheels on, I just make the bolts "tight" with a ~6" long 6mm allen wrench. Never used a torque wrench here.

Doesn't the lip on the hub assembly mated with the ID of the wheel keep the wheel from moving radially from bumps?

Too loose, even a little, could allow the wheel to rotate slightly fore and aft with application of brakes and throttle, and also allow a little free play (once they got actually loose) to be put in tension/neutral axial stress cycles around turns. I mention these cyclic loads due to fatigue. In your picture, the bolts at ~10 o'clock and 2 o'clock appear to have failed by fatigue, and the screw at 12 o'clock by brittle fracture.

Make sure there is no grease on the mating surface between the wheel and the hub. It should be clean and dry.

I have a bunch of these bolts if you need the stock ones.
I replaced all of mine with Chrome Ones on all of my Bikes.
PM me your address, I will send.
Just ask you paypal me about $5 for the shipping.

Keith,
Marietta, GA

I'd imagine that It should be fairly easy to check the calibration of a torque wrench by placing the socket end in a vice and hanging a known weight at the end and seeing if the torque wrench clicks with that torque setting..

Anybody tried that?

I'll take you up on that. Thank you much!

not even close. I did a detail when I was in the military for a week, I did nothing but calibrate torque wrench's.

we had to set the wrenches to a specific number and then it had to test on the instrument 3 times and be within 3% of the set number. Oh the calibration on the torque instrument was done monthly by our PMEL lab to ensure the values were accurate.
if a torque wrench was ever dropped while in use you had to get another one and the dropped one was red tagged and sent in for testing. If anyone ever tired using one for a hammer they would get wrote up and again the wrench was sent in. The torque wrenches were always set to zero when not in use or to the lowest setting so as to not but long term tension on the springs inside. They were also always stored in their proper cases.

Interesting about dropping them also requires calibration. I knew that you should release the tension.
Do the new digital versions also require recalibration?

We used to re-calibrate the once a year in the Air Force. I use two of them now to check the torque

yes, just because they read digitally they still have a spring inside and that is what needs checking to ensure they are still within spec. at a specific setting.

also did you know your suppose to exercise the torque prior to using it.

you do this by cycling it at the lowest setting, then about half way to your intended setting and once more at your setting before actually using it on the intended fastener. this will ensure all the internal parts are moving and not sticking which can cause a false reading.

In the military, we were required to always set our wrenches back to ZERO before we stored them. That is a good procedure I still follow.

Far as I'm concerned the factory bolts are POSs with their tapered heads that strip out in no time. Just replace them with allen head bolts w/washer and that's the end of your problems. I don't use a torque wrench to tighten these. I've done so many things like this I instinctivly know what's tight and what's not.

If you're stripping them, your over tightening them, maybe you should get a torque wrench

I hear ya, but I never use "Instinct" on that Dam Header Pipe...
Then your Screwed...

"Hand Tight, then Torque..."

Keith,
Marietta, GA

Know it all, look at the bolts closely........they're designed to fail. It's as if you are only supposed to remove your rear tire/rim rarely. Do what I do and your problems are over assuming you don't strip the recessed hex head bolts.

In this particular case, take that 1 good bolt out and spray WD40 on the busted bolts. Use a puller to remove the rim.

I use a torque wrench and have no problem with the lug bolts. If you broke a bolt, there are no IF, ANDS or BUTs, you over tightened the fastener, or it would not have broken.
If you're stripping the bolt heads too, get better allen head wrenches.

btw, Rear tire lug bolts on the 500 aren't hex cap bolts, they're regular M8x40 that take a 10mm socket

There's a few scenarios that will shear lug bolts without requiring over-torquing.

In this case, though -- definitely over-torqued. My wrench was off by over 50%

The problem with the OEM bolts is the edges of the heads are tapered, so it doesn't take much of a standard socket to round the edges off and then you can't get the bolt out w/o cutting a slot in the head or using vise grips. Maybe special sockets are made to match the bolt heads, I don't know, but hex head bolts are the way to go, IMHO. And no I don't shear off head bolts this size ever.

wow thats a lot to be off. How did you determine it was off that much?

What brand was your Torque Wrench?
Digital?
That's a lot to be off, never seen one that bad.

Keith,
Marietta, GA

wonder if it was set on the newton meter side versus the ft pound side.

whatever brand you get from harbor freight

I set it to 15 ft-pounds, then pulled the handle with a fish scale (scale was tested with a barbell plate) It didn't click until 30.
On the plus side, I don't need to figure out how to adjust it -- it's off by 15 throughout it's range so, set it to 50 it clicks at 65, set it to 80, clicks at 95.

I came across this on ebay this morning.
Could you not use this?
Your getting more then just Bolts?

http://www.ebay.com/itm/2010-09-10-11-12-PIAGGIO-MP3500-MP3-500-BV-SCOOTER-OEM-HUB-DRIVE-ROTOR-/331849872903?

Keith,
Marietta, GA

that would have cost just a bit more than I already shelled out -I replaced brake pads at the same time I was working on the hub/replacing lugs.

good find, thanks

too bad it's scarred and looks to be worn out. You can get a new rotor for not much more.