Starter Motors and Solenoids: Click, No Crank and Slow Cranking

Turn the key, and the engine cranks and starts. Turn the key and get a single click, a chatter of clicks, a slow groaning crank, or nothing, and you are into the one fault on a boat that is almost always diagnosed wrong first time. The starter motor gets replaced for faults that live in the battery, the cables or a connection the size of a fingernail. This guide gives you the five minute test with a multimeter that tells you which it is, and explains what is different about a marine starter when it does turn out to be the motor.

What happens when you turn the key

The key switch sends a small current to a solenoid. On an inboard or sterndrive that solenoid is usually on the starter itself; on most outboards there is also a separate slave solenoid, a small can on the engine bracket, between the key and the starter. The solenoid does two things: it closes a heavy contact that connects the battery directly to the starter motor, and on a pre-engaged starter it pushes the drive pinion out into the flywheel ring gear. The motor spins, the engine turns, and when it fires the pinion is thrown back out of mesh. Every symptom maps to one of those steps.

Click, no crank

One solid click and nothing else means the solenoid pulled in but the motor did not turn. Either the motor is not getting enough current through the solenoid's main contacts, which burn and pit with age, or the motor itself is seized or has dead brushes. A rapid chatter of clicks is the solenoid pulling in, dropping the system voltage so far that it releases, and pulling in again: that is a flat battery or a bad connection, not a starter. Nothing at all, not even a click, is upstream of the solenoid: the battery isolator, the neutral safety switch that stops the engine starting in gear, the kill switch lanyard on an outboard, a fuse, or the key switch itself. Check the gear lever is properly in neutral before anything else, because a shift cable that is slightly out of adjustment will hold the neutral switch open.

The voltage drop test

Set a multimeter to DC volts and read the battery at its posts with everything off. Our battery guide has the figures, but in short a rested battery under about 12.4 volts is not full and under 12 volts is suspect. Now have someone crank the engine while you read the battery again: a healthy battery will hold above about 10 volts while cranking, and one that drops into the eights or nines is finished regardless of what it read at rest. If the battery holds up, measure across each cable while cranking: put one probe on the battery positive post and the other on the starter's main terminal, then one probe on the battery negative post and the other on the engine block. Each reading is the voltage being lost in that cable and its connections, and anything over about half a volt means a corroded terminal, a frayed cable or a green crimp is eating the current the starter needs. That single test finds more slow-cranking faults than any other.

Slow crank and grinding

A slow, laboured crank with a good battery and clean cables is a tired starter, usually worn brushes or dry bushes, or an engine that is hard to turn for a mechanical reason. On a diesel, slow cranking is also the commonest reason for a hard start, because a diesel needs cranking speed to make compression heat. A grinding or screeching noise as the starter engages, or a starter that spins without turning the engine, is the drive pinion not meshing with the ring gear: a worn pinion, a sticking bendix or missing teeth on the flywheel. Look at the ring gear teeth through the starter opening with the starter off; three or four chewed teeth in one spot is a flywheel that has been stopping in the same place for years, and the fix is the flywheel, not another starter. Our used flywheels and ring gears cover many of the older outboards for which new ones are no longer made.

Marine starters are not car starters

On a petrol inboard or sterndrive the starter sits in an engine bay that can hold fuel vapour, and it has to be ignition protected: sealed so a spark inside cannot ignite vapour outside. An automotive starter that happens to bolt up is not, and it is a genuine explosion risk as well as a survey failure. Marine starters are also built with corrosion protection on the housing and the terminals that a car starter does not have, which is why they cost more and last in the environment. Volvo engines take the genuine units in the Volvo Penta starters and starting range, and for outboards and other inboards we carry the aftermarket marine starter range, built to the original specification. For a motor out of production, our used marine starter motors are bench tested before they go on the shelf.

Fixing it properly

Whatever you replace, clean every connection from battery to starter and back: posts, terminals, the solenoid studs and the earth strap to the block, which on an outboard is often a single bolt hidden under the cowl and is the most neglected connection on the engine. Replace a frayed or stiff battery cable with tinned marine cable of the correct size from the electrical cable range, and protect the terminals afterwards. A starter that is slow after all of that is a starter. If you want the right one for your engine, ring 0412 532 984 with the make, model and serial, and tell us what the clicking sounded like.