I've got the blessing from the FAA to take the general and powerplant exams, I was wondering since I know next to nothing about piston engines are there any study guides I can buy to help prep myself so I don't bomb that section?

I'll edit to add that I've found one from King Schools that's on sale for $149....curious if I should pull the trigger or look elsewhere.

I want my powerplant rating in the next year that way when I'm done with the Navy I can go to school for airframes and get on with my life. Any inputs would be awesome.

Get some hands-on.

Just walk around the maintenance area of the base / ship you are on.
Chances are there is one in pieces, or one you can dis-asemble.

Piston engines are all basically the same, difference is 2-stroke or 4-stroke.

Or, rebuild the one in your car - when it runs again, you will know about piston engines.
Better yet, find a 1960's flat-4 volkswagon engine.

Airplane piston engines are real simple, compared to autos.
They are basically 1930's technology, with a few twists thrown in.
Most auto mechanics / engine builders look at a airplane piston engine and go
Things like carburetors, magnetos, pushrods, air cooling will make you scratch your head.

You probably have an advantage, not knowing anything about modern piston engines,
because with airplane piston engines, you will have to forget most of it anyway.

I'd probably pull the trigger on that King deal.

When I was in A&P school, we had a version of the exams on the computers at school. I think it was ASA. I have no idea how many times I did the simulated exams, but it was a lot. By the time I did the exams for real, it was a piece of cake.

https://www.faa.gov/training_testing/testing/test_questions/
Test questions for free ^^^

And the ASA study guide is pretty cheap, like only 10% of that king book. There is an airframe, powerplant, and general study guides available. These are written test questions only though, you will still have to pass your oral and practical exams with a DME.

ETA
The O's & P's exam rules changed this year. It is no longer at the DME discretion, he hits a computer button and the required tasks are randomly generated from the FAA and given to him to test you with. So actual recip knowledge and skills may be required to make it through like set valves on a radial or time a magneto.

I got those ASA guides on Amazon, they'll be here Friday.

How receptive would local maintenance facilities be to some OJT if I asked? I get the whole liability thing but I love learning hands on.

I have all of my A&P books from when I went through school 20 someodd years ago. If you want them, they're yours. Just say the word.

SBD

Let me punch out an IM to you, thank you!