Shortening a Silca Frame Pump

Despite the popularity of mini pumps, which now are often small enough to fit into a seat pack or even a back pocket - sometimes a classic frame-fit pump is a great way to go. And when it comes to frame-fit pumps, the most common choices have long been either the Zefal or the Silca. I've used both, and honestly the Zefal works a little better - but the Silca is my sentimental favorite.

The classic plastic-bodied Silca Impero has long been discontinued, but lightly used or even NOS examples are still easy to find. Getting them in the right length, however, can sometimes be the trick. Not all that long ago, there was a discussion on the Classic Rendezvous group about shortening a Silca frame pump. The timing was pretty fortunate, since I had recently picked up a nice old pump on eBay that turned out to be just about an inch too long for any of my bikes (always make sure about whether the seller's measurement includes the pump head or not!). Since I didn't really want to bother with the hassle of trying to return the pump for a refund, I decided to look into shortening it instead.

There are a couple of methods for shortening a pump. The method that the CR friends seemed to agree was the most reliable is pretty clever, and seemed easy enough to follow, but unfortunately, also requires a drill press for the best results, which I don't happen to own or have access to. However, I did find someone in the group who was kind enough to shorten the pump for me, which was great. Still, even though I didn't end up doing it myself, I thought that revealing the method might prove useful to some Retrogrouch readers who might want to give it a try.

So here, with some pretty simple diagrams, is the method for shortening a Silca frame pump:

First, you'll need to disassemble the pump. Easy enough to do. Remove the plunger, and take off the head, rubber gaskets, and metal sleeve.

Remove the plunger by unscrewing the knurled ring at the top of the barrel.

Unscrew the pump head and remove the gasket and the metal sleeve. Cutting operation will begin by removing material at this end of the pump, and then re-gluing the nipple end back into the shortened plastic barrel.

From here on, you'll have to refer to my home-made diagrams:

Carefully cut the pump to the desired length from the nipple end of the shaft as shown. Make sure that the cut is straight, and clean up any burrs on the barrel with fine sandpaper.

To make it easier to work with for the next step, you may want to make another cut to remove some more of the excess material. Get it down to roughly one inch or a little less.

Here's where the drill press comes in. Carefully chuck the nipple end into the drill press. Take precautions not to damage the threads. The drill press will essentially work like a lathe.

With the end of the pump spinning in the drill press, and using a file, remove the remaining bit of the barrel tube from the "plug" that is glued into the end. Work slowly, and remove just enough material to reveal the plug. You can always take off a little more, but you can't put it back on once it's gone. When it's finished, it should just slip into the newly cut barrel tube.

Use 2-part epoxy to re-glue the plug into the newly shortened pump barrel. Make sure everything is clean and grease-free before gluing.

Next, you need to shorten the plunger tube by the same amount.

Again, cut straight, and make sure the cut is clean on the piece you're saving.

The plunger itself is simply pressed into the shaft and held in place by a couple little punched-in "dimples." Carefully put the plunger shaft into a vise and file through the aluminum shaft to free the plug.

Press the plunger piece into the newly shortened shaft.

Tap with a center punch tool to make new dimples to hold the plunger piece in place. Really - that's how they did it a the factory. If you want to add some epoxy in there just to be safe, it probably won't hurt, but it will make any future changes more difficult.

As you can see, the process seems pretty straightforward. The only thing that prevented me from trying it is the lack of a drill press. If you have a Silca Impero that is too long, and you have the tools, it might be worth a try.