Replaced worn starter cog, which worked but worn, on 18hp oppose twin with a new cog and upon engagement cog broke in two. Installed another , same problem. Frustrated

1. Check that armature is not loose in starter housing.

2. Check that gear is the correct one for the type of starter ring on the flywheel.

3. Check the starter gear when installing bevel on gear should face up to the starter ring on the flywheel.

Thats all I can think of....

Best of Luck.....

Thanks Ken, it turned out to be inferior after market parts. Bought the Briggs replacement and all is well. Tom

Curious, what brand of aftermarket gears were you using?