TDC Query

[DavidAH]

Hi. I am trying to check TDC on my 1967 1098 Morris.
Car currently starts OK and runs fine, with no evidence of pinking.
All the info I have read says that to position the engine at TDC the timing marks should be aligned, No.1 piston fully up, and the rotor arm should then be pointing at No. 1 plug.
When I set my timing marks up and No. 1 piston is fully up, my rotor arm is pointing towards No. 4 plug.
I have tried turning the engine again to see if I can get it to be any different, but the rotor arm always ends up pointing at No. 4 plug.
Reason I am asking is I want to fit an electronic ignition distributor and the instructions say rotor should be pointing at No. 1 plug when engine is at TDC.
Has anyone come across this before?

[svenedin]

There are two strokes when piston 1 is fully up. One is the compression stroke and the other is the exhaust stroke. You need number 1 at TDC compression. Take number 1 spark plug out and put your finger over the spark plug hole. Turn the engine over on the starting handle and when you feel compression trying to push your finger off the spark plug hole that is the compression stroke. Then line up the timing marks underneath the timing chain cover which should not be far off. The rotor arm should now be pointing at the HT lead for number 1 cylinder.

Number 1 is the cylinder nearest the radiator.

Piston 1 and piston 4 are both fully up at the same time (and 2 and 3 are both BDC, bottom dead centre) but they are on different strokes of the 4-stroke cycle (one compression, one exhaust).

Stephen

[DavidAH]

Thanks Stephen.
I will give it another go

[oliver90owner]

I’m guessing here that you do know which pot is number one.

It is the one at the front of the car, not the one at the left while standing at the sideof the car. The plug leads can be 180 degrees out on the distributor cap….

[DavidAH]

Hi Oliver.
Thanks….yes I do know which is number 1 piston…..(the one at the front)
The rotor arm should be pointing towards that plug (at roughly the 2 o’clock position) when at TDC, but it is at the 10 o’clock position

[philthehill]

If the car is running well using the existing timing set up then just fit the electronic ignition using the existing settings.
I suspect that the shaft between the camshaft and distributer has been fitted incorrectly which is a common fault.
Fitting the shaft correctly is set out in the BMC workshop manual.
Be careful not to drop the shaft into the sump when altering the shaft.

[Bill_qaz]

Sounds like the common discussion.
The engine is valve timed on number 4 (timing gear marks aligned) and ignition timed on number one. So as Phil points out if distributer drive is fitted 180 out the number one position is 180 out. It makes no difference if timing is correct unless it bothers you that number one on the distributor cap is in a different position.
"If it ain't broke why fix it"

[svenedin]

I didn't want to overcomplicate this but it does happen that the distributor drive spindle is fitted incorrectly and if this happens then the distributor rotor does not point in the expected direction when cylinder 1 is at TDC compression.

The important thing is that cylinder 1 is at TDC compression (not exhaust) AND the distributor rotor is pointing to the HT lead in the distributor cap for number 1 cylinder. What actual direction the distributor rotor is pointing is not really important but it is nice if it does follow the workshop manual.

As it happens, my engine came back from rebuild with the distributor drive spindle incorrectly fitted and it annoyed me so I refitted correctly. As Phil says, if you do need or want to remove and reinsert the distributor drive spindle, take great care not to loose the spindle into the depths of the engine. The workshop manual says to use a cylinder head stud as a tool. These are too short really and a longer bolt would be safer. Take care to follow the workshop manual instructions for the 1098 and not the 948 as they are different in this regard.

Stephen

[DavidAH]

Thanks guys for the advice.
I think I will leave it as it is….its working fine.

[myoldjalopy]

Good decision. If its 'working fine' then leave well alone. Scattered throughout this forum are posts of the 'it was working fine but now I've fitted this new-fangled gizmo-gadget the car won't start/runs rough/can't get a good brake pedal etc. type