I recently had to remove both trip springs from my SP-15. I approached each one differently, so I’ll explain both methods.
The discovery that not just one but both springs were broken came a couple months ago, but it took some time to procure the right tools for removing the old springs, namely a cold chisel and the 3 lb. hammer appropriate to the task (following the instructions for Flat Leaf Spring Replacement in the maintenance book). I also tried in vain to locate anyone who had purportedly performed this same operation on an SP.
The longest cold chisel I found was just shy of eight inches, with a blade about 7/8″ wide — very nearly as wide as the gap it needs to operate within. Chisels of a more suitable width were too short to reach the target while also protruding enough to get any grip on. I enlisted the help of a friend who is well versed at hammering on metal, and before coming over, he fashioned a cold chisel with a 3/8-inch blade and a 12-inch stock — something that may not exist in the wild. The added length meant it can be gripped around its midpoint—ideal for holding it steady while readying a hammer blow—while the blade rests against the target, a full five inches inside the carriage.
We followed the instructions for the fracturing of the spring, but ultimately the spring didn’t fracture: the repeated hammering on the spring loop caused it slowly to open (See Fig. 2). After about an hour of careful blows (not by me, but by the seasoned metalworker) the loop had widened enough that we could wrench the spring off its post.
It was only after we’d removed the spring that we could see its anatomy clearly (see Fig. 4). I hadn’t understood that the old spring is in fact an open loop. Knowing this, I approached the second one differently. With the second spring, instead of aiming to fracture it, I flipped it upward to expose the cleft (see Fig. 3), and, inserting a shim to brace the spring in place, pointed the chisel directly into the cleft. It took only a few substantial blows to distend the spring enough to wrest it loose with pliers. (and this time it was my own, inexpert hammering) I highly recommend this second approach if you can maneuver the spring into the appropriate position. It was both faster and felt far less risky.
