Originally Posted by ChrisH

On an ST170 the shim is the follower unless someones done away with that like we did. So if the clearances are too big you need to buy a thicker follower.
Take the cam cover off, check the clearances using feeler gauges (To check a clearance make sure the lobe of the cam is pointing upwards on the clearance you're checking) Compare them with what they're supposed to be. If some of them are out, take the timing belt off and cams out, take the follower out using a magnet (a clean one) and measure it with a micrometer, record your result and then say the clearance is 0.15 and it's supposed to be 0.20 you take 0.05 off the follower size and you have got a rough size.