water pump housing bolts

I think I know why some bolts have washers and some don't.

the bolt holes end up having different depths from the casting variances .....I have standardized the bolt length and location on all my big blocks and today I found a block the has a more shallow bolt hole than my other blocks. the same bolt that tightened up on one 440 block bottomed out on this block and the same bolt tightened up with 3 less turns than the first block I tried on even another block.

so I think when engines are assembled at the factory, they have a way of determining bolt hole from the fresh cast block and use a washer to compensate for tolerance where as if the bolt hole is cast and has enough room to not bottom out within the last 3 turns, then no washer is used. Like with anything that is mass produced there has to be a tolerance.

it has been a long time mystery to me as to why some bolts have a washer and some do not.