I recently had the head in my 250SE rebuilt after it had cracked (thank god for aluminium ). Since the head had been shaved before, there was a chance that there would be ping due to the valves being closer to the pistons.

Well, with the head back on and the car and operational, i've noticed that when I put my foot down on the pedal, I can clearly hear pinging from the engine. My mechanic is on a 2 weeks holiday, but told me that if it needs shimming, he'd do it for free.

I just wanted to know if anyone has had any experisence with rocker arm shims and how effective are they?

I would try retarding the ignition timing a few degrees, before I would look at shims.
If the C/R is actually higher than before, you could also try the very highest octane gasoline that you can find.

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2007 C 230 Sport.

I'm running 98 Octane petrol. Have been for the last 8 months.
There's also some chain slack that the new chain tennsioner didn't take up, which can't really be solved by any other means.

there is no way that u should have slack in the chain. it can and should be fixed.
your whole story sounds wrong.
you need to dial in the cam.
and shim what? the cam bearings? what's this going to
do?
wow!

ahhh, no need to make me feel like a total fool

What is so back about these shims? what damage can they cause? or do people just not like them for some anal reason.

I got another mechanic on the net also telling me off but not accually telling what the longer term effect will be.

sorry, didn't mean to make you feel bad. actually was thinking about the guy working on the car.
ok, first you mentioned rocker arm shims. what is that? what is
trying to be accomplished?
the only shims i know of are for the cam bearing towers for
a warped head. the only other is for the valves. the caps that
the rocker arms rest on. this is for keeping the valve adjustments
near a middle.
if the chain is loose then something is wrong. period. shaving the head will not do this.
when you shave the head you need to check the valve timing and
the safety clearance.
after all this then you can play with the timing. if the dist is worn it can adv timing to fast or give you a hard time timing the engine
at idle and in gear.
you need to start with the chain before all else.
there is a possability that to much was taken off and nothing will help.