Marty's DOHC tappet overhaul.
It's quite easy to fix noisy DOHC tappets. More often that not they gum up due to incorrect oil grade etc so just a strip down and clean will sort them out.
1. Here's a DOHC tappet.
2. This is the hydraulic part of the tappet (circled in green)
3. To remove grasp the tappet firmly and bang it down on a VERY FIRM surface.
4. This is the hyd adjuster, don't drop it.
5. Here you see the empty tappet bucket.
6. Give the bucket a GOOD clean inside and out with some sort of solvent. If possible blow the oil hole with some compressed air (A can of PC compressed air will do).
7. Open the hyd adjuster by pulling/twisting. Give that a good clean too. Once clean lightly oil ALL the parts and re-assemble.
8. That's it. Remember they will rattle like hell for the 1st few seconds after the engine starts until they are primed.