Distributor driving gear, off by one tooth?

As was stated earlier, the gear position doesn’t matter a damn except to ensure the vac capsule doesn’t hit the block when following the book procedure. The book is written so people can follow the pretty pictures in the knowledge that their car will still fire, even if they do not understand why.

You can set it anywhere you like if you understand what is necessary versus what is described (which is arranged so beginners can do the job by imitation rather than inherent knowledge).

If your rotor ends up half way between posts simply undo the clamp and twist until it isn’t. Remember to check both static retarded and full advance by twisting the rotor. Obviously, if setting up at TDC the rotor centerline will have passed the firing position slightly.

Technically you could use any cylinder you please, but the timing marks are positioned to be read when 1&6 are used. Having positioned the engine at TDC you then check which one is firing by seeing which way the exhaust cam is pointing under the oil cap and wire up the leads in sequence from 1 or 6 as preferred. Since it only takes one added turn at most, I always time off #6 up front.

I don’t mean to confuse you with the above, and it IS best to rebuild by the book. My reason for going back to first principles is to save you from unnecessary work if you find you’ve screwed up slightly. That’s when a minor adjustment to the instructions is all it takes to work around the mechanical setup you’ve now got and end up in exactly the same running condition as planned without dismantling stuff.

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Here’s the rotor arm position for the firing stroke for what it’s worth.

Yes the book position Wardell, but this will confuse Eric. !

Thank you all for this, I think I am finally getting what may be going in here… Will try tomorrow.

Also, does anyone here use one of those 123 Ignition distributors? The advance curve selector us on 0 and i am not sure this is ok, since I cannot find the original advance curves in the worship manual…

Thanks.

You need to search the forums for a bit for the best setting.
It’s a little confusing but really not that complicated as soon as you understand how it all works. I struggle too. Don’t let yourself be confused by the book position now!

Hi Eric…use switch setting 2…i had this running on an xj6 S1…and should get you going…from there you can try other settings…Steve

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Eric
As you do not have the Bluetooth version, it is impossible to remove the plug and change the settings with the 123 still in the car. I have to remove mine every time I feel I need to change the setting.
So be prepared to remove and re-install several times to get the correct curve.
I started with #2 and then went to #5 for my 4.2. I may go back to #0 later.

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My dist. Drive is the same as wardell

But do you point the vac capsule down like that? I turn mine to be pointing about 60 degrees clockwise (i.e. tucked towards the block) and fit the plug leads accordingly.

My distributor vacuum unit tucks in towards block facing aft. The picture shows it firing #6 cylinder.

Which would still be true if the vac unit and dizzy were turned clockwise 60 degrees and the leads moved and clockwise by one post each.

Which in turn shows there’s no such thing (functionally at least) as being ‘one tooth out’ or stressing about the drive and plug numbers matching the pictures, provided you understand the system and there’s enough slack in the leads to cope with mild repositioning.

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Ok.
I still have to figure out why the rotor does not align with any contact in the dist cap when the light is green… In other words, electricity is available to the HT leads only when the rotor is in between HT leads…

Is your rotor pushed into the drive correctly? Pull the rotor off - note the notch - put back together?
Green means spark and the rotor will have to be aligned to the cap. If not, the rotor is not aligned to the drive dog (which means it’s somewhere in the distributor and either the 123 is faulty or the rotor is not installed right).

If the distributor is correct you will be able to turn it to a green light position, connect the wires in accordance to where the rotor points to, and it will work. Tooth off or not, what creates the green light or spark is keyed to the rotor which is ‚keyed‘ to the cap.

This is a long shot but are the points installed correctly? They are what fire the coil.
Pat H

It’s an electronic distributor. But the principle is exactly the same. Imagine the rotor was not stuck on correctly.

Hi Eric it is the leading edge of the rotor that fires to the contact in the cap…so the rotor dosnt exactly need to line up with the contact when the green light comes on…Steve

Last few engines I built i used the dot on distributor gear and lined it up with edge of casting on block. Seems to be perfect…

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Interesting. Will look for it. Since I only work on those parts when the bare block is being built on a rotating engine stand, it’s not too hard to look down the hole and see it it’s lining up with the crank at TDC.

I know I mentioned this before, and acknowledge you probably have forgotten more than I know, and also I am not familiar with that dizzy, but it sounds like you may have a old points dizzy laying about, so I would go back to basics with the Service Manual, and set everything up from the start exactly as per the book. If that cannot be done, there must be a reason why

If that means taking things apart, so be it, but I cant see why you could not still get the engine started by moving plug wires

On past occasions, I have failed to see the tree due to the woods

…and the time our Jag Club did an entire technical day on a fellows V12 XJS engine “problem”…wont even tell you about that one…

have other causes of non-start been eliminated ?

I was just going to reseal my engine, so marked my distributor. It was set correctly with the vacuum module tucked in towards the block.
Upon disassembly I checked the dot. It all lines up on reassembly. One of those things not in shop manuals, but possibly was a trick for the assembly line???

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