My friends car's got a loud ticking noise coming from the bottom end of the engine
anyone knows this problem?
timing chain?

ticking...?
is it loud? or just audible? is it a regular, rhythmic noise or is it irregular?
if it's from the bottom, it could be piston slap if it's a regular noise, or you may have one spun big end bearing and it "ticks" every time that piston fires.

could also be a piece of crap in the alternator or the water pump impeller is touching the housing...

could also be a loose rocker or two, or your pushrods are a little worn where they actuate on the rocker but if it's at the bottom then you can rule that out.

there's lots of possibilities there unfortunately, and you have to go thru them one by one until it's solved

its loud i think its similar to knocking
its definitely the bottom of the engine
is it gonna be a big job? expensive?

Is this knocking sound constant, or is is loudest when the engine is in that midpoint between power on,.. & power off? Steam train drivers called it "drifting" That point where the engine is under no load either way.
Is it louder when hot, & quiet when cold?
Have you checked the engine oil pressure when hot? This will also help to diagnose the problem.

I am attempting to determine if we have a crank bearing problem here, although, as long as there is oil in the sump, Datsun bottom ends are VERY hard to kill.

Expensive? Depends on the engine, but compared to some other engines,... no.

At worst, even if you need a replacement crank & rod, along with a balance job, Datsun parts are so abundant that repair costs should be very reasonable.

Its just a constant knocking sound and get louder on load
noise occurs on cold and hot

Did they ever run it out of oil (not low, but out). If so, chances are good it is the main bearings.

first thing i would do would be to remove the water pump and alternator and wash them in warm soapy water and dry them with compressed air. that will remove any grit in the system that may be causing a ticking - for example if you have some scale wedged in your water pump it'll still be there if you rebuild your bottom end! give the radiator a good flush too while the cooling system is apart.

if it's still there after doing that, THEN look towards the bottom end.

edit - actually if it's LOUD loud then maybe the piston / valve clearance is wrong...? is it a new engine?

no its stock engine (old)
we'll take it to the mechanic to get it checked then

With the noise being constant, hot or cold, it tends to steer me away from things that relate to temperature. By that i mean that when the oil is cold, it tends to cushion loose bearings for a while & a bearing noise is quieter untill the oil starts to warm up & thin out.
If it was a piston with more skirt clearance than we want, it would likely be more noticeable when cold, when the piston is at it's smallest diameter, but less noisy, when hot, when it has had time to grow a little.

An oil pressure reading when hot will help to eliminate, or confirm, the bearing theory.

thanks for the advice
will do compression test and let you guys know