my old 1/10 scaled nitro crusher by Tamiya has been having problems, it stalls often and since Tamiya dont mark parts its becoming hard to find them.

so i had an idea to get a new engine as its cheaper were i live than to do an engine rebuild, does anyone know a good engine brand which would fit into my RC?

I believe the engine looks to be made by Toki, the brand is owned by Mecoa now, so it's a place to start looking.
Shuwa Industry - TOKI engines

If the engine mounts in the standard configuration - on the side engine lugs, I’d change the engine for a better replacement than the Toki/Shuwa version. Some of these engines mounted from the bottom of the crankcase - of which I’ve only seen from these Toki/Shuwa Engines. If that’s how the engine is mounted, stick with that style unless you want to change the engine mount to fit a modern engine. Some pictures of the engine and mount would be helpful IMO.

thanks for replying guys, i will measure the engine mount when i get home.

any ideas on a decent brand and engine size to go for?

I googled the Nitro Crusher. Looks like it came with a .15 sized engine. The mounting tabs on the engine look standard. The engine has a side exhaust port. It also looks like you could mount an engine with a rear exhaust port. You would just need a different exhaust but it looks like it would fit.

so is there much difference in size between a .18 and a .15 engine?