Setting starter drive to flywheel clearance ??

Hello Folks. I have a 1981 Pontiac Parisienne 305 Auto. Suddenly wouldn't start. Nose of starter was broken off. What would cause this ? Not enough clearance between flywheel
(Flexplate ) teeth + starter drive teeth ??
I'm installing rebuilt starter. How to manually engage starter drive with flywheel ring gear to measure clearance + determine need for shims ?? Book says to put 0.020 in. dia. rod between root of ringgear + crown of starter drive ... but how to engage the two gears manually with starter not energized ?? Book says to use screwdriver in small hole in underside of starter nose to pry drive gear into position. I haven't been able to do it.
Any advice gratefully rec'd. Please reply to NG.
Thanks. -JP
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question snipped-for-privacy@home.org (john) wrote:

Mount the starter but do not connect the wires. Connect your remote starter switch or run a jumper to the solenoid terminal, energize the circuit, this will pull the starter drive into the flywheel allowing you to measure the clearance between the starter pinion and the flywheel ring gear.
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If the starter had been in service for a long time before the casting broke, clearance is probably not the cause of failure (although you have a good idea checking it with the new one). Possibly the timing is off...this can break starters. I've broken nose castings on the 'small' starters on stock, in-tune motors a couple times. I've kinda decided that some of them are just junk--porous castings, fatigue, who knows...
mark
On Sat, 03 Apr 2004 14:21:58 -0700, Neil Nelson wrote:

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