I think it's depending on the vehicle, there may be a spacer between the starter and the motor. There may be a shield between the starter and the transmission housing if your starter is bolted to the transmission.
Wrong starter, wrong fly-wheel, Bad starter drive, worn fly-wheel. Starter may need to be shimed.
FInd the transmission, find the fly wheel, find the fly wheel then the starter motor wheel be right next to it.
It has to line up with the fly wheel between rear of engine and front of transmission.
depends what type of car you have and how many amps yor battery puts out along with the starter. all the fly wheel does is when the starter engages the fly wheel turns from the starter. once the car is started the fly wheel goes along with the motors rpms the faster or more rpms the car is putting out the faster it will spinn.
Sounds as if the starter bendix is staying engaged in the fly wheel. Possible wrong starter or starter needs shimmed down out of the fly wheel .
maybe a bad starter gear,or a loose starter,or loose fly wheel bolts,or maybe your having starter problems but there is no way to know until you give more information
worn fly wheel or ring gear.
take it out before you bust the fly wheel
broken tooth on the fly wheel if your starter is turning over and not just spining what's wrong if the starter's just spinning?
I'm not sure what you mean by "slips". Is the starter making a grinding noise or does the starter sound like it is missing the flywheel completely? My first thought was a bad starter drive (part of the starter) but if you replaced the starter with a new one it shouldn't be that.
it conects the crankshaft to the trans- as well as the starter uses it to crank the motor
This can happen if there is a broken tooth on the starter. It can be a broken tooth on the fly wheel but more than likely it is the starter tooth that is broken. Or the starter sylenoid is bad in the starter.