F150 has a noise when at 20rpm only

[orlando]

hi i have a problem with a f 150. yamaha i would like to know if shims on lifter are changeable or build up of carbon or salt would cause the noise on the head part it does not sound like primary fuel pump they are ok camshaft is tietened thank in advans

[boats.net]

Yes if the valve clearance is of then would need to change shims in shim buckets, if you are going to do it yourself get a service manual first.