Series 1.5 4.2L backfiring under load with new 123 distributor

[Gfhug]

Lloyd, using a gauge to accurately judge TDC can be difficult as there is so little movement of the gauge around TDC. Another way is to use a drilled out spark plug with a 8 or 10mm threaded rod to check for roughly 90 degrees when the vertical movement is maximum. The threaded rod is held in place with nuts top and bottom to hold it solid.

You move the cylinder to one direction 90 degrees out, mark that on the pulley, then rotate the engine down through BDC to the other 90 degrees point and mark that. Then you measure and mark half way between those points and you’ll have a far more accurate TDC point.

There’s a much clearer explanation somewhere on here with photos. It doesn’t need to be exactly 90 degrees, just roughly there and at the same vertical distance each time.

Found it: viewtopic.php?f=3&t=5856&hilit=Alternative

Worth considering.

Geoff

[politeperson]

The timing mark on the crank pulley cannot be relied on as the crank wheel has a bonded centre which I have seen slip with age.

As Steve says you need to Tipex on the crank pulley TDC to the pointer, or better still 10 degrees TDC with pistons no.1 or no. 6 at the top of their strokes.

Compare your tipex mark to the stamped mark on the crank pulley and if you have a difference of 20 degrees, that that is your answer.

It doesn't matter about the distributor drive being wrong, as said you can rearrange the plug leads with the arm in the correct location for number 1. Check the front cam lobe on the exhaust manifold is pointing directly horizontally by peeking through the oil filler for the firing stroke. You just need to remember that 15 is too young, 36 is too old but 24 is just right.