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tips, technology, tools and techniques related to vehicle driveline components

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murray forbes-arnold
(16 posts)

09/13/2018 01:25AM

Main British Car:
1973 MGB GT ROVER 3.5 V8

how to swap a dizzy.
Posted by: murray.arnold
Date: September 27, 2018 02:01AM

Good day.
I have 2 issues. First when I remove the old dizzy, how do I ensure that the new dizzy is set up properly regarding timing. Secondly, I understand my new one has 3 wires and the old one has 2. Any one have any ideas.


Ivor Duarte
Gloucestershire UK
(979 posts)

02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: how to swap a dizzy.
Posted by: 88v8
Date: September 28, 2018 05:58PM

Mmm, more wires.
Does it not come with instructions? Or you can look it up online if you have the make, do a search with the adjunct +forum and someone will have discussed it.
What are the new/old dizzies?
Are you sure the new one has the correct drive dog for the oil pump? You know there are two types, one on the P5/P6 engine and one on the SD1. If the dog is wrong, you can punch out the roll pin and swap in the existing dog.

Turn the engine to the correct static timing mark on the crank pulley.
Remove the cap from the dizzie and see which spark plug is firing. Remove that plug from the engine, reconnect it to its cap and lay it on top of the engine so the plug body is making electrical contact with the engine.
Loosen the dizzie clamp bolt.
Rotate the dizzie body a few degrees in the direction of rotation.
Switch on the ignition.
Now slowly rotate the dizzie body back again, that is to say opposite to the direction of rotation. As you do so, watch the plug, it should fire. As soon as it fires, stop turning.
Switch off the ignition.
Make a sketch of the orientation of the rotor arm, and the way the cap is oriented. This is so you can get the plug wires back on the new dizzie. If the new dizzie is pointing in a different direction, some of the plug wires will be too short and you'd have to shuffle them all around.
Now remove the dizzie, removing the cap and leaving it connected to the plug wires.

If the new dizzie has points, set them to the correct gap and lightly smear the cam with Vaseline.
Fit the new dizzie to the engine.. First, look down the hole, and align the rotor arm with the oil pump drive so that the rotor arm will be pointing the same direction as before. As you fit the dizzie, you'll see that the rotor arm will move around a few degrees as the gears slide into mesh, so you may need to start sliding it in with the rotor arm a bit further round than you expect.
Connect the three wires.
Swap in the new cap, don't connect the plug wires yet.
Rotate the dizzie body until you can orient the cap the way the old one was, and reconnect the plug wire for the plug you took out.
Now make sure the spark plug you took out is still in contact with the engine, and repeat the process of rotating the body a few degrees in the direction of rotation, switch on the ignition and slowly rotate the body back until the plug fires.
As soon as it fires, stop turning.
Now the timing is as it was.

Switch off the ignition and gently tighten the clamp bolt.
Swap the plug leads into the new dizzie cap one by one, don't muddle the firing order.
Preferably check the timing with a timing light.


Edited 1 time(s). Last edit at 09/29/2018 05:17AM by 88v8.

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