Thought I'd copy this over on here as I've learnt that the tappets in my ZS are identical to those in my Citroen BX! I was taught this by the guys on the 205GTi drivers forum (who rape the BX 16v for it's Mi16 engine to use in their trackcars, but luckily aren't afraid to get stuck in and share their knowledge!)
This might help cure the noisy tappet syndrome alot of people seem to suffer with on here, and I've not seen this technique mentioned anywhere else on here after quick search. New items are priced at £60+ for a set apparently, so it's a nice little way to save money in between other jobs (H/G change no doubt!)
The tappets need to be removed to do this, so it's cams out and cambelt off if you wish to attempt it (thankfully you can remove the cams without disturbing the headbolts/head gasket). You also need to allow days for this, due to the need to soak certain parts in desgreasers etc. If you have a parts cleaner to hand, you could probably speed the whole process up.
Remove the rocker cover to expose cams (ignore missing exhaust etc....was in the middle of H/G change):
Remove the timing belt, and then remove the cam carrier ladder from the top of the head so the cams can be removed. This is all detailed in the Haynes manual
The tappets have been removed in this pic (I forgot to take one with them in!). Easiest way to remove them is a magnetic retreval tool.
Heres the underside of your grubby tappet. The outer part is the bucket, the inner part is the piston assembly.
I then pop them in cups of Gunk for 24hrs to aid the next step. It's best practice to keep all the tappets marked to the valve from which they came, although on my K-series they all got mixed up and have since gone back together completely fine so I wouldn't panic if you can't keep them together. Much more important is to keep the internal contents of the tappet with it's bucket....don't mix these up with other tappets.
The next step is to cup the tappet in your hand and whack it repeatedly against a plank of wood until the piston assy drops out. It's been recommended to wear tough gloves doing this, as it kills your hand after about 5 mins! You're left with this:
If you put the bucket to one side for a minute, the piston that's just dropped out comprises of three parts....the piston body, the spring and the relieft valve. They might resist coming apart due to the vacuum of the oil but they will come apart. If they're anything like mine in the ZS, they'll look like this:
The valve that oil passes through is under that thick crap, so little wonder it was tappy!
Place all three parts of the piston, plus the bucket in degreaser and allow to soak. Then use a suitable brush (the teet end of a babys bottle brush works well!) to scrub out the components:
Remember to ensure they're clean throughout and check the feed hole in the side of the bucket is clear, as they won't fill with oil once in the engine unless it is! Place back in degreaser for a while before washing with warm water, at which point they'll look something like this:
If you're not going to reassemble immediately, spray them with WD40 or GT85 etc to stop them rusting up, which they will....quickly!
Next step is to redress the top of the bucket. I'm not completely sure why this is recommended, I assume it quietens down valve gear noise when the cam presses down on the bucket. To do this, place the bucket upside down on a piece of 60 grit (yes, 60 grit!) sandpaper and proceed to do figure of 8 patterns.
Every few figures, rotate the bucket 90 degrees and perform again until you've eventually rotated it the full 360 degress. You'll end up with this:
Redressed on right, old glazed unit on left
Now to reassemble. Take the piston/relief valve and piston body, fill with water and squeeze together. They'll resist until you depress the relief valve like so:
....at which point water will spray out under pressure, depending on how hard you're squeezing it! This makes sure you've fully cleaned the valve out....if it it dribbles, time to degrease again.
If all is well (it usually is), next stage is to dry off and refill the piston body with fresh oil and do the same again. However, this time press lightly before pressing the valve. You aren't trying to expell the oil, only the air trapped around it. Once all the air is gone, it's done.
Then, fill the bucket with oil until it reaches the lip of the hole the piston sits in, and re-insert the piston assy back into the bucket:
You'll spray some oil out of the filler hole and probably end up with some preload (about 1mm is fine, its nearly impossible to get all the air out) but once they're all clicked back together, you're done:
Refit to head and reassemble cams/timing belt etc as instructed. When you restart the engine, the amount of noise from the tappets will depend on how well you got removed the air from the tapets, but it's not abnormal to need to leave them 2mins or so to shut up fully. One of mine took 10mins in the ZS (they do if you forget to fill the bucket with oil :O ) but it now runs sily smooth and silent.
Hopefully this'll help someone out just as it helped me out!