For Forks Sake
So far, our T5 project has fought Stan all the way. Will a fork rebuild finally turn frustration into co-operation?
When we decided to celebrate Vespa’s 75th birthday by breathing life back into an unmolested, but somewhat neglected, Mk1 Vespa T5, all the signs were that it would be a quick and easy rebuild. Unfortunately, things haven’t turned out that way. My plans to save every inch of original paint were frustrated and while I waited for the frame to come back from the paint shop, I turned my attention to the forks.
Lord of the Rings?
Although around 36,000 Mk1s were produced, they have the feel of a hand-built special. Having tackled just about every nut, bolt and washer on our project scooter, I’m surprised at just how many minor variations there are from a standard PX. Among the more unusual of these features is the arrangement for securing its headset to the steering column. On the PX, and on pretty much every other Vespa model I can think of, the steering column is held in place with a series of nuts and locking washers. These ‘stack up’ at the top of the column with the headset being dropped into place above them. A pinch bolt runs through the headset and when tightened this holds the headset in place. Simple, but for some reason it wasn’t good enough for the Mk1.
Excluding the speedo, a Mk1 headset comes in three parts, with the upper and lower shrouds being moulded in plastic. These conceal an unsightly metal plate to which the throttle and gear tube carriers are welded. The plate also houses a trio of special sockets which accept the control cable outers. Unlike the PX there is no pinch bolt; an adaptor collar sits at the top of the bearing stack. This has two prongs on its inside face that hold the collar to the steering column. On its top face are two metal ‘blocks’ which fit into a machined section under the headset plate. A locking nut sits on top of the plate and, once this is tightened, the steering lines up automatically. If this sounds messy, it is, and it feels like the designers were trying out ideas for the impending GTS family. Needless to say, this particular arrangement didn’t stand the test of time. It took three attempts before Piaggio’s designers managed to properly secure the Mk1’s headset. That the headset may work its way loose isn’t a particularly reassuring thought as I plan my end-of-build adventure!
Cutting Crew
A check on our Mk1’s MoT history showed advisories for excessive play in the steering, a fact confirmed during a very wobbly test ride. When the headset was stripped down, I discovered the cause wasn’t the loose locking nut I’d assumed it to be, but instead the special adapter collar had cracked. Over time the collar had spread, allowing it to move and cut into the steering column’s threads. Already frustrated by revealing some unexpected frame rot,
I’d dealt with this additional setback by standing the forks in a corner of the garage. With the frame away for painting I could ignore them no more. At first glance things looked bad. The adapter collar works by being a close fit to the steering column and the threads appeared to have been badly chewed. I was reluctant to scrap the forks, but it took some time before I could pluck up courage to file away the burr. To my surprise this revealed that only a fraction of a millimetre had been worn away from the very top threads. I found a replacement adapter collar online and when slid on to the steering column it fitted perfectly. Finally, the Mk1 was co-operating.
Die Hard
The next challenge was reinstating the damaged threads. I don’t know about you, but I haven’t got an M36 die knocking about the workshop. Fortunately, I’m not alone and, as engineers in the audience will already know, it’s possible to buy a serrated file that’s designed especially for jobs such as this. The good news is that they’re inexpensive, the bad news is that they need to be handled carefully. Select the incorrect spacing or file at the wrong angle and irreversible damage can be caused. All I can say is that I managed it, and I’m very short on engineering finesse. Once the threads were viable, I used an old locking nut to finesse the cut.
In the world of unobtainable Mk1 parts, among the scarcest is the first generation of top locking nut. A common workaround is to use Piaggio’s final solution of two standard locking nuts but I wanted to see if mine was salvageable. The main problem is that it’s made of fairly soft metal. This enables the torqued-down nut to be held in place by punching its top edge into the steering column grooves. Having roughly filed the damaged nut into a circular shape, I then recut the damaged threads with a small Dremel blade. Fortunately, the metal’s soft enough to use the fork stem as a tap and after a few turns the nut was once again ready to hold the headset straight and true.
With the thread drama resolved, everything else was fairly straightforward. The alloy casting at the top of the forks had started to oxidise so that was treated to a proper respray. In keeping with my aim of conserving rather than restoring, the fork leg was sealed with a coat of clear shot. Thankfully neither the axle nor any of the bearings showed any signs of wear so I was only left with the job of fitting a set of replacement seals and O-rings. Because the black front shock is such an integral part of the Mk1’s appearance I’ve decided to keep things standard in that department. For now anyway…
Surprisingly, the fork rebuild was much less of a drama than I’d anticipated. However, should I ever be crowned Master of the Universe I’ll reserve a special place in hell for the headset’s designer. Cabling this multi-layered arrangement was no fun whatsoever. Hopefully the T5’s now stopped fighting back and I’ve got my fingers crossed that there’ll be no surprises when the engine cases are split. That will certainly be a first on this build….