2.8 engine noise

[Harry]

I was asked to have a listen to a 2.8 Bighorn which was making a knocking sound.It was ok when started from cold but as it warmed up and with an increase in revs it made an intermittant tapping sound, too light for a bearing but too heavy for a tappet and quite irregular.The owner had been told by a mechanic that the motor was stuffed and he wanted another opinion.the motor doesn't smoke any more than most Bighorns on startup.It does have a slight misfire that seemed to improve when I took out the very dirty K & N air filter.I suggested that he have a look at the tappets, possibly for a very loose one or a broken valve spring but if it's one of those I'd expect the noise to be more regular.Does anybody have any other thoughts?I don't have time to do it myself so I'll just be passing on suggestions.
Regards,Harry.

[James W]

What frequency is the noise? is it in time with each combustion? or one in 4 or 8? It will help loacte the problem.... a tappet etc will be once every two revolutions or one in four combustions. Are all pulleys tight? particulary the crank pulley. Time to get a stethascope or screwdiver out.

[geeves]

Power steer pump will make a noise like that but will be acompamied by foamy power steer fluid. Otherwise try piston slap or bad gudgons which fits with the mechanic or the one I had which was a loose cranckshaft pully which is far more common than it should be. Its caused by mechanics undoing the wrong bolts when replacing cam belts. On mine this made most noise at 1500 rpm. You need to replace the spacer behind the cambelt pulley and look at the keyway if this is the cause