I have two ways I have repaired engines with this problem. The first is just get a longer screw, you can measure the depth of the hole to see what you need , just be care full & don't over tighten . The other I have used is to find a much longer bolt with a nut on it , screw the bolt in until it bottoms out then tighten the nut down on your back cover, cut off the excess bolt. The manufactures have more threads in hole than they have bolt length, these have worked every time for me . Good luck MAX H.