My 1986 GMC Sierra Classic K1500 4x4 350 engine has problems starting . The starter hits the flywheel or it meshes but can't turn the flywheel over. The starter is new. Would the battery size have anything to do with it . Thank You

a mechanic knows the difference between cranking/turning over and starting
you say that the flywheel is not turning so obviously it will not start
now you have to tell us if the starter pinion is engaging in the flywheel teeth but the starter is not cranking the engine --indicates that the engine is seized up
now it it is an automatic , there is a possibility that the flex plate ( automatics do not have flywheels )) is broken and the teeth are no longer in a position to mesh with the pinion gear

I'm not familiar with your vehicle, but I've never encountered a vehicle needing shims on a starter motor.

What may happen is the teeth on the ring gear - the teeth on the outside of the flywheel - become worn. The starter meshes with these teeth and spins the engine to start it. If the teeth are worn the starter cannot mesh with them and consequently, can't turn the engine over.

Because of compression the engine usually stops in the same position - the worn teeth are at the starter.

Try turning the engine by hand/with a wrench through 180 degrees so that any worn teeth are away from the starter, and then try starting it. If the engine spins - the fault is worn teeth on the flywheel.

On some models of general motors starter shims are required to maintain
the recommended clearance between the starter and flywheel.
If not, then the starter will hang on the flywheel after motor is started and
damage it (The teeth are bottoming out when this occurs). They sell starter shims at
the auto parts store.
Hope this helps.

It's not a flywheel, it's a flex plate that bolts to back of engine. Why do you need one? If your starter is grinding it needs a starter drive (bendix)

it sounds like you have the wrong starter or flywheel on the truck. aif the transmission has ever been changed, it may have been changed with the wrong size. the bolts line up fine to fit the engine, but the flywheel is too small or the tooth size is off

Could be a starter sticking but that would cause more of a grinding noise, my best guess is that your flex-plate(flywheel) is broken if the noise is coming from between the engine and transmission. Remove the access cover for the bell housing and take a look at the flex-plate.

Need more info -- but I will try to help you as much as i can. If the starter is not turning -- you will have to ck your cables from the battery to the engine. So you need to ck the positive or red cable to the starter, this one is the large wire on the starter soleniod. Ck it all the way to the starter, from the battery and any conections in between. It must have a good conection and be hot same as the battery voltage (+12.+dc). You will have to ck the ground or black cable conection to the frame and also the engine block. The battery grounds to both locations. You have to have a solid conection to turn the starter on both of thses wires. Ck these wires and the conections to the starter and the engine. Next problem could be a bad flywheel.  The flywhee has teeth on it like a gear- and the starter has teeth that mesh into these teeth to turn the engine over. The flywheel could be damaged in the area that it is in now at rest, so the quickest way to find out is to turn the engine over by hand. Using a ratchet with the right socket fitted (to the crankshaft end-- the largest pully center bolt) turn the enging 1/4 turn and get the ratchet out of the pully and try to start the engine, if it turns over and trys to start you have a bad flywheel my friend. 

Yes your problem because you have changed the starter then you have 6 bad 1/2 worn teeth on the FLYwheel and the only way to fix your problem is to either remove the engine OR gear box and remove the flywheel and have a new starter ring fitted to flywheel and refit what was removed and away you go finished ...
THEother way to start every time till you do it is to HAND brake off put in 1st gear and turn engine over 1/2 a turn ,and then it will start every time, as the engine will stop the same place every time so thats were the 6 worn teeth are. Have a goodday
Let me know hoe you get on Ron
ARE you on Skype

Change the starter. The starter has a gear that moves forward, meshes with the flywheel, and cranks the engine over. From what you describe, the gear is spinning, but not advancing on it's shaft to mesh with the flywheel.

did you put the shims back in the starter?