Is the battery connected with the correct polarity

 

Should be. But I will check! How could that effect the starter!

 

Welcome......Usually, the centrifugal force of the spinning starter makes the gear jump out to the end of the shaft to engage the ring gear. The fact that it happens on 2 starters, makes me believe that the starter is not spinning fast enough. Maybe low voltage to the starter?

 

I will put on charger for a bit!

 

Had an elderly gentleman bought a new battery put it in then starter would just spin. He called me to come look see and i noticed the starter was spinning backwards he had the battery cables on the opposite battery post reversed polarity. I agree with Poncho battery may be weak and not turning starter enough rmp to spin the starter gear up into the flywheel

 

Good possibilities above. Also, could be flywheel is missing teeth at that spot. Turn flywheel 1/4 turn by hand and re-try.

 

I just dealt with this today....Zero Turn Starter would spin....no engagement. Battery read 13.3 Volts.
Checked all connections. Put the trickle charger on it for a few hours and it started right up. Ordered a new battery...pick it up tomorrow.

 

Another possibility : The starter pinion uses its inertia to climb the starter shaft to engage the flywheel when the motor starts spinning. One cause could be if the starter shaft is dirty or gummy. That would inhibit the pinion's ability to move up the shaft. A free and easy thing to check while you're at it.

 

except OP says he tried a new starter.

 

If you have ever 'tested' a starter motor on the garage floor, using jumper cables, you will know how much starter motor armatures kick when power is applied.
The armature spins from zero to full rpm almost instantaneously. The Bendix drive uses the inertia of the Bendix to keep the drive still while the armature spins up. The drive staying still causes it to climb a ramp internally, and force the gear against the flywheel teeth. When it spins, and doesn't engage, it can be a failing Bendix(one way clutch built internally) or lowered voltage/amperage that fails to accelerate the armature quickly enough, OR there is grease/dirt/etc on the Bendix assembly/ramp making it stick to the armature instead of spinning and moving up the ramp.
If the Bendix gear can be spun in both directions without causing the armature to turn, the internal one-way(sprag) clutch has failed, and the Bendix needs to be replaced.

tom

 

but he tried a new starter and it doesn't engage.