What would cause the car make a knocking sound when starting?

Answer 1

oil pump may be clogged or bad or timing is off

*improvement*

Yes the Oil pump may be broken or the timing is out

The timing is easily adjusted but i would still only recommend having this fixed by a qualified mechanic.

more details on the timing:

Every engine is carefully timed.

the knocking may be created by the piston hitting the closing or opening inlet/outlet valves on the way back up.

this can cause severe damage to the engine as the valves could potentially bore through the piston resulting in possible damage to the piston walls as it slowly starts grinding its way through them.

you may want to have this seen to.

*further improvement*

If the Oil pump is damaged the I would have this fixed immediately as no oil would be lubricating the crank case or any other parts of the engine.

this can result with a broken crank case, piston wall, piston or other moving parts inside the engine and can shred the whole thing to bits.

this would also have to be seen to as soon as possible unless theres a grinding noise by now in which case it might already be too late.

i would check the timing belt tensioner. the other answers are really far fetched