Starter Spring Tension

Since putting bearings and brushes through my starter motor a while back it seems to want to 'throw out' quicker than I'd ideally like. Just wondering if there is any science behind the spring tension? Could I potentially have it under to much tension??


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Staff member
The force delivered by a coil spring is a function of the spring constant ( a measure of the spring stiffness ) and the distance through which it moves, i.e., F = kx. If the spring is still moving through the same distance, which I imagine it would, therefore no change in x, and the spring is unchanged, then k remains the same, hence the Force remains unchanged. If you now use Newton's second law, F = ma, the spring-mass is unchanged, and the Force we have just calculated, which we substitute in, then the acceleration of the spring is what it was before.

So unless you somehow compressed it more than it should be, then all remains as it was. If there was a degree of friction between the surface of the spring which worked to reduce the acceleration, and now it is clean and moving with less friction, then that is likely your answer.



Well-Known Member
I understand that the role of this spring is to absorb some energy when the engine kicks the pinion, no matter if the engine eventualy starts or not.
Otherwise the pinon would fail very quickly. The tension of this spring could not be related on when the engine kicks and throws out the pinion.
What you experience is that the engine tries to start, but it doesn't succeed first time. Now, why it happens more now with a refurbished starter, perhaps the starter now spins the engine faster, while before, with a slower spinning starter, the engine turns over for longer, giving it a chance to eventually start without the failed attempts that you experience now.


Active Member
The pinion returns both by the flywheel kicking it back, but also there is a lightweight restraining spring which holds it in the "off" position & stops it vibrating into mesh when the engine is running. The main spring as said is there as a shock absorber and when turning the engine over is only very lightly compressed. I think the change you have experienced is, as others have said, due to the fact it is more free running. The spring tension is designed to take the loads the starter motor will experience. I am not sure if they are designed in collaboration with the application. Regarding your question about tension, as far as I can see from the Lucas Workshop instructions there is no adjustment.
Spent the evening on Youtube looking at Inertia Starter Videos. Can see I was way off the mark with my thinking. I don't recall paying a great deal of attention to the condition of the bendix. May be worth pulling it down for a clean and wear check