Any (small) Lego Technic parts not in whole units? This is aimed at building a GBC module, not to reproduce an actual engine.

I need a piston type construction with stroke length of 3 units, which means a crankshaft radius of 1 1/2 units. Are there any existing LEGO Technic parts that will support this?

Edit:
TechnicTechnician provided the answer - the technic cam (6575) proved to be exactly what I needed. In case my original question wasn't totally clear I've added a picture of the solution below.



The distance between the two crank axles is 1½L, which means that the other end of the connecting rod (point X) will move a total of 3L as the crank rotates.
I assume you mean L when you say units?

Well anyhow, unless I'm misunderstanding, I would try these: https://www.bricklink.com/v2/catalog/catalogitem.page?P=6575

You can stack 3 of them up to get 1 and a half L

If you mean 3L long instead of 3L wide, this should still work because it has axle holes which is 1.5L apart, it also has axle holes that are 3L apart.

Search youtube/eurobricks for 'technic mini engine' / 'technic micro engine' for some ideas.