What’s the difference between the CX500 or GL500 and CX650 or GL650 tappet screws? Can you use one in the other? In a nutshell, no – here’s some comparison photos – 650 valve adjustment screws on the left, 500 on the right:
Removed:
500 – ~6mm:
650 – ~7mm:
The locking screws differ in thread diameter and height; 650 on the left:
Different lengths too, at least between these two engines – though one could just be more worn… here is the 500:
…and 650:
In terms of part numbers, the 650 screw is 90012-414-000 (eBay) and the 500 screw is 90012-415-000 (eBay). The parts manuals show that the GL500s theoretically used the same screw as the CX500.