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And the wheel goes ’round

January 22, 2008

When I was changing the tire the other day, I noticed the rear hub was loose. Not flopping-around loose, but loose enough to notice if you grabbed the mounted wheel and shook it.

The back end of the bike felt a tiny bit loose going around corners, so I decided to minimize trips until the ride Fuzz organized on Saturday. At that time I’d be able to get Doc’s opinion. Doc is a great guy to have on rides—he knows how to fix scooters and people!

Doc said it felt like the nut holding the hub to the stub axle was a tiny bit loose. The nut is held in place with a castellated cover (it looks like a castle turret, hence the name) which is in turn held in place with a cotter pin. Any cotter pin might work in a pinch, but I got one from Big People; that way I know it’s the right one.

Again, apologies for the lack of pix, but the Haynes Vespa P-Series manual or will illustrate things better than I can. The black plastic dust cover will come off with your fingers, so pop it off. To get the cotter pin off, bend the twisted parts straight and pull it out by the rounded end. Once the cotter pin is out, remove the castellated cover. It should come off easily, the operative word being should.

Lo and behold, there is the nut. Yes, it was loose. I could turn it with my fingers. Yikes!

Of course, that’s why the castellated cover and cotter pin are there. Somewhere along the line, someone forgot to torque the nut. And it wasn’t me.

Obviously, letting something like this go unchecked for too long could’ve had dire consequences, but nothing was otherwise amiss. Tighten the nut, torque it, put the cover back and install a new cotter pin, we should be good.

Tightening it requires the proper size socket. The nut is bigger than 17mm, but my 19 and 21 are still too small. No big, there’s a Schuck’s in Ballard.

Decision time: do I get the 23mm socket, or the 24? I go for the 24, go home, try it. It’s just too big enough to be loose. Not good—you’ll round off the edges of the nut. Ho-kay, back to Schuck’s for the 23. Back home. It’s too small. Arrghh!!

I do what I should’ve done to begin with; remove the nut and take it with me. No harm here, there’s a thick washer behind it holding everything in place.

This time I’m going to Sears. I know with Craftsman® tools, when the socket says 24mm, you know for sure it’s 24mm.

I try several sockets, and waddaya know… the nut is 15/16″. Yes, the PX is European, so one would think everything’s metric, right? Whatever. At least the socket is 6-sided, therefore no chance of rounding off the edges of whatever nut it might be driving. Avoid 12-sided sockets at all costs!

Back home, the nut goes back on the stub axle, with your fingers! Strip the threads on the stub axle and you’ll need a new one, which requires splitting the case! Difficult if you do it, really expensive if you pay someone.

Before you torque the nut, put the transmission in gear (I’ve found I can slip it into 1st without running the engine) to secure the rear wheel. It was thoroughly drummed into my head during my racecar crewing days that you can’t get an accurate torque reading on a wheel nut if the wheel can turn.

Neither the Haynes nor the Piaggio manuals had a torque spec for the rear-wheel nut that I could find, so I consulted Doc. He pulled up his handy spreadsheet and told me I needed to set the torque wrench to 62-65 ft/lbs.

Getting a nut or bolt too tight can be just as unpleasant as having it be not tight enough. These days a good torque wrench is quite inexpensive, so there’s no reason not to have one. Or two. If you wrench on a lot of different kinds of vehicles, an inch/pound torque wrench could come in just as handy as the standard foot/pound kind.

Another thing drummed into my head about torquing nuts and bolts: you cannot get an accurate reading unless the wrench is moving when it clicks. (Yes, get one that clicks. They’re easier to work with.) So, get the bolt snug with a ratchet, then take the torque wrench to it.

Oh, and make sure the bike is stable while you’re torquing. You don’t want it falling over on you. In case you were wondering, it didn’t. Quite.

Keep in mind, the stub axle has a hole for the cotter pin to pass through. You want two of the four notches in the castellated cover aligned so they completely expose each end of the hole. If you need to back the nut off a skosh to accomplish this, go ahead, but the cover seems to have enough ribs in the wide part to make it possible to simply adjust it by taking it off, turning it and putting it back.

The nut’s bang-on 65 ft./lbs. and the castellated cover goes right on, the holes visible for the whole world to see. There’s no more wobble, and the wheel spins freely (yes, I took it out of gear). All that’s left is to install the cotter pin.

Turn the wheel so the hole’s vertical, and drop the cotter pin in from above. This way you make certain it goes in as far as possible. Then take needlenose pliers and bend the protruding halves up so they look the way they did on the old cotter pin. The idea is for the cotter pin to be tight in its mount, so make sure you do this right.

Once the cotter pin is secure, pop the dust cover back on. You’re done. It’s going to be sunny tomorrow, so I can road-test my work then. Favicon


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