V70 start engine cranks but fails to start engine

[Anubisxc70]

2004 V70
Hello
My uncle V70 has an issue.
Some times we crank but looks like the starter doesn't start the engine looks like its doesn't engage to start the engine. After some times , maybe after 10 times it engages and the car starts and runs with no problem....
Is this starter or ground wires or a combination of both.
I will try to post a video

Many Thanks

[wynnj]

Could be;
1)the solenoid doesn't operate or is too slow engaging the pinion onto the starter ring, or

2)the pinion and/or the starter ring teeth are very worn so the starter won't turn the engine over.

As engines usually always stop at the same part of the cycle, the starter always engages with the same teeth before turning. You can check case 2 fairly easily by turning the engine over through one compression cycle by using a 30mm socket or large adjustable spanner on the crank nut and then try the starter from there. If the engine turns over it's worn teeth. A sluggish starter can wear the teeth very quickly as the starter will start to turn before the solenoid fully engages the pinion.

Case 1 - the starter should still spin.

If you change the starter, check all the starter ring teeth by inspecting them through the aperture once the starter is removed, and turning the engine over a few degrees at a time.

If the starter ring teeth are worn it's gearbox out job to replace the 'flywheel' flexplate