nikewai,
i drive a mazda and know how how you feel. i've jsut recently completed my problem of noisy adjusters ( Hydraulic Lash adjusters ) and maybe i can be of help.
First of all, it is not the brand of oil that is the concern. some say that thin oil lke synthetic helps. the truth is, thin oil would only help to pressurized the adjuster by taking / washing away some of the grime or air that's trapped inside the adjuster, hence making it quiet. the reason for adjsuters making tapping noise is JUST that the valve inside is not pressurized and hence is tapping against either the rocker arm ( if mitsu engines have one, or not it would be the cams ) or hitting against the valves. so, the issue hence is why are the adjusters not being pressurized ?
it needs to be pressuzied so that the lash clearance between valve and adjsuter is ZERO, hence producing exceptional engine performance and no noise.
there are a couple of reasons. one is that dirt has been caught inside the adjusters and is not allowing the valve trap ( in mazda's case it would be a ball ) to seal in oil. the other would be that air is trapped inside the valve.
both are the main reasons for tapping adjusters, but are not big problems.
Bearing in mind, in either case scenarios, THE ADJUSTERS ARE DESIGNED BY DEFAULT TO NEVER FAIL IN ITS OPERATIONS. this is the beauty of hydraulic adjusters.
so, what you got to do is this. open your engine up, ( i think mitsu engines don't need to remove cams to take out the adjusters ), check each adjusters for sponginess. a good adjuster would NOT allow you to depress it. if it does, then its not working right. remove the adjuster, fully disassemble it ( there would be no rubber seals in an adjuster, therefor you can safely disassemble ) clean throughly with diesel or degreasing liquid. assemble back, soak adjuster in oil and depress to let air out untill adjuster becomes hard, you can see air bubbles coming out. let adjuster soak in oil for another day and repeat steps to let air out. this is so that you make 100 % sure that adjuster is working properly. then install back.
all this are ASSUMING that as soon as you inspect adjusters, the springs ( there would be one big and one realy small ) are intact and not broken. if its broken, adjuster has failed and you would have to change to new.
with this method of checking, you can service / replace only spongy / failed adjusters. that would cut your repair cost down substantially.
Remember, adjusters are designed to NEVER fail under normal operations (unless springs are broken ), so don;t let a mechanic bully you into changing a set of new ones. if adjsuter completely fails, ie springs break, your engine timing would go hay-wire, which is very obvious.
to take precautions so that future grime do not rest in the adjusters, switch oil to semi or full synthetic so that engine would be cleaner. or should the tapping noise come back after some time, service them again. chances are that inside an engine, only a couple are spongy.
hope this helps as it did mine...
