MOTOR STARTER

550 651 83B MOTOR STARTER is what actually kicks the main diesel engine over on your rig. You hit the key, and this thing engages the flywheel, spinning the engine fast enough for it to fire up. Without it, you’re not drilling, plain and simple. It's a heavy-duty electric motor, designed to handle that initial surge of power needed to get tons of iron moving from a dead stop. It's got a solenoid that pushes the pinion gear out to mesh with the ring gear on the flywheel, then it cranks.

When this part starts to go, you'll usually notice it first thing in the morning. The engine might crank slow, sound sluggish, or sometimes you just get a 'click' and nothing else. That's often the solenoid not engaging properly, or the motor itself drawing too much current because the brushes are worn out. Sometimes it'll crank fine when it's cold, but once the engine's hot, it struggles or won't turn over at all. That's a classic sign of internal resistance building up when things heat up.

Replacing one of these isn't usually too complex, but make sure you disconnect the batteries first – you don't want any sparks flying around that high-amp circuit. When you're putting the new one in, double-check all your cable connections, especially the main battery leads and the smaller trigger wire. A lot of times, a 'bad' starter is actually just corroded or loose battery terminals, so give those a good clean and tighten before you condemn the whole unit. Also, check the ground strap from the engine block to the chassis; sometimes that's the real culprit.