Are they interchangeable? I opened up my TII engine and found the teeth on the rear stationary gear are eaten and jagged. I have a spare S4 NA engine and the rear stationary gear is in great shape. I haven't looked at them closely but are they identical? And if not, what about an S5 NA stationary gear?

Thanks!

They should be identical but the easiest way to find out is to look. s4 and s5 engine parts like that are usually always identical.

Awesome, thanks, you just saved me from having to find another one.

I thought the TII gears were heat treated or was that s5 TII only

I'm not sure. I think the FD ones were hardened but don't quote me on that.

it was the FD gears that are hardened. That's why engine builders use them in S4 and S5 high power buildups. They are cheaper then buying some from somewhere like Racing beat.