You need to supply ACF with the post ID, in this case that is the product ID.
https://stackoverflow.com/questions/27385920/woocommerce-get-current-product-id
add_action('woocommerce_shop_loop_item_title', 'custom_pre_title');
function custom_pre_title(){
global $product;
$id = $product->get_id();
$field_value = get_field('field_name', $id);
}