Nissan Repair: engine, cylinder head gasket, low oil pressure

Question
Engine is very noizy.Gives good power.Ignition set right.Some specialists say that problem may be oil pump's oil seal,making oil pressure lower.
I really install old one with some addition of sealer after installation of new chain tensioner.
Since that time I have problem with noise, did not have it before installation.I did install new cylinder head gasket because of engine overheat and lack heat inside car;old gasket had three extra holes.Valves clearance okey.Thanks.

Answer
Is the noise on the top or the bottom?  If the headgasket you installed had fewer holes there is a chance that some of those holes were oil galleries that feed oil to the camshaft.

If the noise is on the bottom end the noise could be caused by low oil pressure.  There might be a chance that the oil pump you installed is not putting out enough pressure.  You should not use sealant when installing oil pumps.  I would replace the pump with a new gasket without the use of sealant.

Chcek the oil pressure with a gauge and see if the pressure is correct and you should find the problem.  If there is sufficient oil pressure I would assume the heedgasket is the wrong one.  If the pressure is low replace the oilpump.