What retracts a " modern" starter drive?

[oldbike99]

I am installing a modern starter drive, already having had to fish broken parts of an original style drive out of the bellhousing. I am confused as to what retracts the drive after the starter stops turning.
Thank you in advance.

 

[Mikeinnj]

The original Bendix system places the starter drive pinion on a helical drive spring. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to wind the spring forcing the length of the spring to change and engage with the ring gear. When the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of the starter, at which point the drive pinion is forced back and out of mesh with the ring gear.

The main drawback to the Bendix drive is that it relies on a certain amount of "clash" between the teeth of the pinion and the ring gears before they slip into place and mate completely; the teeth of the pinion are already spinning when they come into contact with the static ring gear, and unless they happen to align perfectly at the moment they engage, the pinion teeth will strike the teeth of the ring gear side-to-side rather than face-to-face, and continue to rotate until both align. This increases wear on both sets of teeth. For this reason the Bendix drive has been largely superseded in starter motor design by the pre-engagement system using a solenoid.

For a detailed explanation of the modern type epicyclic reduction gear mechanism sold by vendors
follow this link :
http://www.google.com/patents/US4528470

 

[MikeK]

Nothing. There is a helical coupling, like on a Bendix, but internal and much finer and weaker. Unless the engine starts and spins the body against a slower moving, decelerating, or stopped starter motor shaft the drive will remain engaged. I've worked on several 'modern' drives that have failed. The same abuse that destroys the original Bendix, kickback from too much advance, quickly breaks the brittle internal helix and jams the 'modern' barrel drives.

 

[Joe K]

Nothing. There is a helical coupling, like on a Bendix, but internal and much finer and weaker. Unless the engine starts and spins the body against a slower moving, decelerating, or stopped starter motor shaft the drive will remain engaged. I've worked on several 'modern' drives that have failed. The same abuse that destroys the original Bendix, kickback from too much advance, quickly breaks the brittle internal helix and jams the 'modern' barrel drives.

Probably the big advantage of the modern "drum" bendix is that they're enclosed (dirt is the enemy of the Model A Bendix) and they have rubber "cushions" to soak up the slam at either end of bendix travel.

This aspect the farm was counting on when they converted the Ford 9N to a 12V ignition - and that 6V starter engaged with "authority" under the new voltage regime.

It was still working no issues last I knew...

Joe K

 

[oldbike99]

Nothing. There is a helical coupling, like on a Bendix, but internal and much finer and weaker. Unless the engine starts and spins the body against a slower moving, decelerating, or stopped starter motor shaft the drive will remain engaged. I've worked on several 'modern' drives that have failed. The same abuse that destroys the original Bendix, kickback from too much advance, quickly breaks the brittle internal helix and jams the 'modern' barrel drives.

Thank you. That makes sense

 

[hardtimes]

I am installing a modern starter drive, already having had to fish broken parts of an original style drive out of the bellhousing. I am confused as to what retracts the drive after the starter stops turning.
Thank you in advance.

'what'....centrifugal force !

 

[Tom Wesenberg]

No centrifugal force is involved. A body at rest tends to stay at rest (aka my lazy brother), so when the starter armature starts spinning, the heavy weight on the pinion helps to keep it at rest while the armature drive spring turns the helix and the pinion moves forward to mesh with the ring gear. When the engine starts then the ring gear speed is greater than the pinion speed, so it spins the pinion back on the helix until it comes to rest as you stop the starter by taking your foot off the switch.

If someone forgets to retard the spark, then the engine can suddenly kick back and bend the Bendix drive spring and/or the armature shaft.