What is the oil pump bolt size for a 455 Oldsmobile block?

There isn't a single "oil pump bolt size" for a 455 Oldsmobile block. The oil pump has multiple bolts, and their size can vary slightly depending on the year and specific configuration of the engine. Some are likely to be 7/16" and others may be 1/2".

To know for sure, you need to:

* Consult a shop manual: A factory service manual specific to the year and model of your 455 Oldsmobile will have the precise bolt sizes and torque specifications. This is the most reliable source.

* Check the existing bolts: Remove one of the bolts and take it to a hardware store or auto parts store to have it matched.

* Use a bolt size gauge: If you have access to a bolt size gauge, you can measure the bolts directly on the oil pump.

Don't rely on generic information online – always verify with your specific engine's documentation for accurate measurements and torque specifications. Incorrect bolt sizes or torque could lead to serious engine damage.