On a shim-under-bucket engine you do indeed have to remove the camshaft to change the shims. This is because the bucket must be completely removed to access the shim - it's _under_ the bucket. I rather doubt there are any automotive engines left using this design. I do know the "classic" Jaguar straight six used shim under bucket, hence labor for a valve adjustment was very high. This design is still common on high performance motorcycles. I owned a recent Kawasaki which used shim-under-bucket, and it was mucho work to adjust the valves and resync the cams. Accurate valve timing is rather important on an engine with a 14K redline.

I also owned a Ford sedan powered by a Yamaha designed and built DOHC 24 valve V6. It used the shim-over-bucket design as described earlier in this thread. The shim could be changed by using a special set of tools to slightly compress and hold the bucket. The camshaft did not need to be removed. But the valves never needed adjustment in the ~100K miles I kept that car.

- JimY