While working on my new 383, I had a grinding noise with my starter (starter is a new high-torque model, flexplate is new, too). I put two shims in it and it sounded better but still not 100%.

I then added two more shims, the noise seemed to get worse so I took one back out. It sounds about the same as it did with two shims.

Anyway, nothing is broke (yet) and I'd like to keep it that way. I'm trying to figure out how to determine what's causing the noise, wondering if there are any tricks? When I installed the starter, I followed the instructions and even went as far as verifying the gaps between the gears with a feeler gauge.

 

Do you have the right number of teeth? There are two flex plate sizes (153 and 168 teeth I believe) You have to have the matching starter setup for the flex plate.

 

First off make sure you have the battery disconnected. It's very easy to bump the solenoid or remove the bolts and drop the starter. It won't be fun to see smoke and have a bad solenoid on your new starter.

IMO it's a pain to set the gap with anything but a paper clip. I know most directions say use a feeler but that's just awkward. If you uncurl the paper clip you can use it to check the gap between the flexplate and the starter with the gear pulled out with a screwdriver. Make sure you don't mar up your starter gear.

Make sure you have the right bolt alignment as afremont has mentioned, but if you're already checking gap I wouldn't think it's an issue.

Easiest way of doing a starter swap is keep track of the shims and replace them in the same order and placement as the previous starter you removed. This will give you an exact or very very close starting point (depending on if it's a different starter).

Usually shims are cut out so you can leave your inner most bolt to the oil pan in the starter and slide shims in and out. The outside bolt goes directly through a hole in the shim. This will let you change out shims and adjust it without having to worry about the starter flipping all around.

IMO if you're more than a few shims short you will usually just hear a ping as the gear smacks off the flexplate.

Also make sure you have the bolts snugged when you check the gap. There is no need to torque them down super tight but you don't want them to have any slop between the starter and the block or shims.

Make sure you bolt holes in the block are clean. If there is fluid in the holes say from penetrating oil that can make you think the bolts are tight when it is not.

If you hear grinding or anything unusual after the starter was properly gapped and working fine the bolts for the starter probably backed out. Check those and re tighten them if necessary.