On car testing:After the starter motor is torn in and out to check for faults; it is time to check the one on an engine. This practical test is indeed essential in real-life diagnosis and relevant to most regular cases.
What if it is not the battery that fails your car to start, after you have checked there is 12.7V OCV. Turn the car on and it doesn't sound like cranking, but you hear a little click. AHA!!! It is the plunger that still operates.
Those are just saying, but before blaming the starter, check all the wiring first. The circuitry between the battery and the starter terminals and body might contain potential voltage drops that could result in not enough power/torque produced to crank the flywheel. Hence we should put the voltmeter for a test. Parts that need testing are: Batt+ to B terminal(spec is below 0.2V, this is to ensure good condition of conductor); B terminal to M terminal(spec is below 0.1V); and starter body to Batt -(spec is 0.2V). Any higher VD reading shows that the battery will fail to deliver at least 9.5V for cold cranking. These parts are in series, therefore a total of all 3 reading must also be below 0.5V. AND, all the tests must be measured while cranking. Why, because this is the test where the starter is to put to crank the engine, so we only get its readings when it is cranking.
Next, the amperage delivered to the starter to excites the armature must be sufficient in order to produce enough cranking power. With old engine, the reading is expected to be a little bit less than the spec(e.g 110A out of minimum of 125A) this is because moving parts are smoothened(commutator brushes, shaft, overrunning clutch housing etc...) hence power required is a bit less.
the reason the amperage may be lower in an older engine is directly dependant on the condition of the engine i.e compressions.
ReplyDeletenot the wear on the starter commutator