Engine speaking, a journal is what the main bearing inserts sit in. It can also apply to an engine with an overhead cam where the cam has a bearing cap that's removable.
Guides generally refer to the valve stem guides. The hole in the cylinder head where the valve stem runs. The guide is the sleeve that's pressed into the head.
Also, a journal can be a log of expenses or the build process of a car. Guide was the company that formerly made all GM automotive lighting fixtures.
