Springs: the machine's opinions

A spring is the machine's opinion about where a part should be when nobody's pushing on it. Every "default" in the logic is a spring: the lock should be locked, the hammer should be up, the slide should be home, the door should be shut. When a spring gets tired, the machine doesn't stop having the opinion — it just holds it weakly, and things start drifting into wrong states between cycles. That's why spring problems look like intermittent problems.

Metaphor (Dan). Valve springs. A weak one doesn't fail outright; the valve floats at speed and you get a misfire you can't pin down until you check spring pressure.

Never swap a spring by length. Wire diameter and coil count set the rate. Two springs the same length with different wire are different parts.

Washers and spacers are logic too. They set the side-to-side position of levers, which decides whether a hammer meets its hole, a slide meets its lever, and the jackpot tab meets the cabinet. Never throw out an "extra" washer. Log every stack (Appendix A.2).

4.1 How to tell a bad spring without removing it

You've got a huge advantage: this machine has three of almost everything. Three stop levers, three stop-lever springs, three sets of hammers, three brakes. The two healthy siblings are a known-good reference sitting right next to the suspect.

flowchart TD
    A[Suspect on reel N] --> B[Find the same part on the other two reels]
    B --> C[Work all three by hand, same stroke, same speed]
    C --> D{All three snap home the same?}
    D -->|Yes| E[Not the spring. Look for gum, a bent lever, a bad pivot]
    D -->|One is slow, weak, or dead| F[That one's the suspect]
    F --> G[Photograph all three in one frame — IMG-]
    G --> H[Measure the suspect and one sibling in place — §4.2]
    H --> I{Wire dia / coil OD / coil count match?}
    I -->|No| J[Wrong or replaced spring — order to match the sibling]
    I -->|Match, but weak| K[Fatigued — replace with the sibling's spec]
    I -->|Match and strong| L[Pivot or dirt, not the spring]

Other tells, all at Level 2 (chassis out, nothing unbolted — see Chapter 6):

• Listen. A healthy spring gives springy resistance and a snap. A broken one gives a dead clack and free play.
• Look with a flashlight and a dental mirror or a cheap USB borescope: kinked coils, an opened hook, a stretched section, a missing spring, rust.
• Slow-motion video at 120 fps: parts that don't fully re-seat before the next stage engages.

4.2 Measuring in place

Wire diameter:    calipers across one coil
Coil OD:          calipers across the body
Coil ID:          OD minus two wire diameters
Active coils:     count them, ruler behind, photograph
Body length:      coiled section only
Installed length: hook to hook as mounted
Hooks:            photograph both ends straight-on

Compare to the sibling. The sibling's numbers are what you order.

FILL IN (way down the road): the spring survey — every spring, wide shot then close-up with a ruler, and the register in the Appendix. Not urgent while everything's snapping home. Urgent the day one doesn't.