Renault Master tappet noise?

I have a 1994 Renault Master T35D LWB which is converted to a campervan. When I bought it what appeaered to be a very noisy Tappet sound was evident. I didi ask a couple of mechanics but they said it was an exhaust noise. After about three months a velve stem broke and wrecked the engine. I was able to buy a second hand bottom engine and a second hand head which was built up by a mechanic but when taken out for a road test was found to be even noisier than the first engine.
How does one check the tappets and is it possible to shim this engine and if so advice would be appreciated.
As I am just an enthusiastic DIY advice in the simplest form would be appreciated.