I have a 1996 XJ6..
I replaced the tack generator..
This one was geared..
The car now turns over, but will not start..
Chilton Manual has no reference to this..
Is there a timing issue with this?

 

Are you referring to the half engine speed sensor, driven by a worn gear off the auxiliary shaft which also drives the power steering pump. If so, this sensor produces a signal once per every 2 engines revs and allows the engine ECU to distinguish Top Dead Centre (TDC) firing stroke from Top Dead centre non-firing stroke. This sensor must be correctly "timed" when it is installed. There is a circular perspex window in the top of the sensor. Through this window can be seen an upturned metal "cup". There is a hole in the cup, which when the engine is rotated will at one position line up perfectly with a hole marked in the centre of the perspex window. Rotate the engine until cylinder 1 is at TDC on the compression stroke. There is a TDC marking on the crank trigger wheel which should line up with a pointer bolted onto the front cover. However, on its own this won't help you determine TDC compression/firing from TDC exhaust/intake. When cyl. No.1 is at TDC compression/firing then cylinder 3 is 240deg before TDC firing and so the inlet valve are fully open. If you remove the oil filler cap, then you can check that cyl. 3 inlet valves are open and so cylinder 1 is on the correct stroke. Then set the half engine speed sensor.

 

The Camshaft sensor can fail and the engine will start with the Crankshaft sensor although it would take more rotations .

Codes ? Can you hear the fuel pump turn on for 3 - 5 seconds then turn off ? Is your tachometer showing any RPM's as you crank it . Go you have a fully charged battery as it runs low it will effect the engine ECU ?

To time the Camshaft sensor place the Crankshaft front toothed gear on the missing tooth at the Crankshaft sensor face , look at the opening in the oil cap as Andy mentioned . Once you know you are truly at TDC of the # 1 cylinder you can line the dot in the window of the Camshaft sensor as you bolt it down . Takes a couple of tries to bolt it down and get the dot in the window .

The Crankshaft turns 2 revolutions for every Camshaft revolution in a 4 cycle engine

Any questions , just ask and someone will help

 

There is a TDC marking on the crank trigger wheel which should line up with a pointer bolted onto the front cover.

After going back and reading this I learned something new and would suggest following Andy's advice . He really designed this as a Jaguar Engineer on this engine .