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Very poorly designed chain tensioner for the timing belt in L20-L28 engines at least on early models. It was discovered a couple of years ago when the cylinder head needed repair due to leaking valves.

The cylinder head was removed, and the chain loosened causing the tensioner's spring-loaded rod to fall out of its housing. This was signaled by an unusually high noise from the chain during the first start-up after replacing the cylinder head.

In summary, unplanned work was performed: removal of radiators, crankshaft pulley, front engine cover and installation of a new tensioner. Additionally, worn shoes and the front crankshaft seal were replaced.

Later on, some interesting tips were found online:
1) The tensioner has an improved clone version that features a latch which prevents it from falling out of its housing.

2) Nissan designed a special tool – a wedge for securing the tensioner. This tool can be easily made at home.

It is best to make the wedge from hard wood since you need to hammer it in with some force. Attach a piece of wire to it so that it can be removed after completion of work.

Here's how to use it:
Loosen the bolt on the camshaft sprocket, then set top dead center (TDC). Hammer the wooden wedge into the chain housing within the block. This is convenient to do with an extension from a socket wrench set. Then remove the sprocket (the chain can be held in place by electrical clamps) and loosen the cylinder head bolts. Remove the cylinder head.
Make sure to put back the sprocket with the chain before removing the wedge! If there are issues removing the wedge, slip a wrench onto it and gently rock it back and forth.