Distributor for xk120

I am not getting any spark anywhere around coil/distributor/spark plugs. The distributor used to be on a Mark 9 3.8 engine and I am using same on a 3.4 XK120 engine. Is this possible or do I have to change the condenser/other?? Please help me!

In the early days I ran my 120 with a Mark 1 distributor while I was rebuilding the original. It was not exactly the same, a newer model, but other than the different advance curve and cap, it was compatible, ran anyway, though perhaps not optimal.

So I don’t think your problem is wrong distributor, but an old condenser certainly could be suspect. It is a common size and should be available from your local auto parts store. You can even install it on the outside of the distributor if you want to, or even on the coil, as long as it is in the circuit, pigtail connected to the CB side.

Make sure your points are opening and closing right, and you don’t have a ground short at the connection that passes through the side. That is a common error when changing points and condenser; one reason I like to put the condenser on the coil.

Rob, as usual, you appear as a knight in shining armor. Thanks for your comments. You say to “avoid having a ground short at the connection that passes through the side” I assume you mean the wire from the positive side of the coil to the distributor. In my case, I think this wire is connected to the distributor body which grounds it. Should there be an insulator here so the body of the distributor is not grounded? Thanks again.

I meant inside the distributor.
Either at the red arrow, or at the pivot of the points, sometimes people put them together and there is a ground short even if the points are open, something touching ground that shouldn’t. Maybe a fiber washer missing, yellow arrow.

Ahh. I dont remember a fiber washer indicated by your yellow arrow. I’ll check in the morning. One other thing - the end of the point connected to the pliable portion has a round hole which slips over a supporting pillar in the distributor from my 3.8 engine. I ordered a new set of points from a supplier on Ebay and they came yesterday This same end does not have a wrap around hole but is flat, like the pliable portion with a semicircle cut out. Not sure how this can be fitted. This portion of the distributor is not shown clearly in your pic. Its behind the top left of the rotor arm

This is what Moss sells for 120/140/150 and early saloons.

Right, this is the set I received yesterday. On my distributor, the part on the right has the flat, pliable metal returning on itself to form a hole which fits over a post/pillar in the distributor, with an insulating plastic ring above and below this “hole” to make sure it doesn’t touch the post. So, the post first has two wires slipped over it (one from the condenser, the other from ?) which touch each other and the post, then an insulting ring then the “hole” in the pliable part of the point then another insulating ring then a nut holding it all together. Sorry - no pic as my barn where the 120 is being restored is a few 100 yds away and its late in the evening here.

Sounds like you have E-Type points.

Yes. They look exactly like your pic shows. I’ll take a pic of the top of the distributor internals tomorrow and send it to you. That being the case what would you recommend I do??

This is a pic of the internal dist.

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Obviously having probs uploading pic. Dist for Mark 9 is the same as for Etype. Mine came from Mark 9 engine. I have no insulator where you indicate in yellow in your pic. This might be causing the short. I will add insulator.

Rob was under the impression that you had an XK120 distributor in your XK120, so his advice and picture is incorrect for your MK9 distributor. His picture of the E-Type points is correct for your car. The loop on the end of the spring that is attached to the fiber block loops around that threaded stud on the points plate. The white nylon spacers that are shown on the stud are very important, and their job is to insulate everything from the threaded stud. The assembly sequence is as follows: Insulator with nipple up, spring loop, condenser loop, external coil wire loop, insulator with nipple down, nut. Nothing is supposed to actually contact that stud. If anything contacts it the car won’t run.

Check your condenser before putting it all together. My most recent side-of-the-road stranding occurred because the condenser was dead shorted. It’s a lot easier to replace a condenser on your bench than it is by the side of the road. It’s even easier to change it if it is mounted on the coil, which is why my configuration is now like the one in Rob’s other picture.

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https://discourse-cdn.jag-lovers.com/original/3X/5/b/5b4c5b68f277f20511208b8cecf354a54936e21e.jpeg Add images ![120-Distributor|671x499](upload://d1F2JrhA73Khqsz7AgFEQ9Ok3E2.jpeg)
Thanks Mike for your invaluable info. I was making the mistake of putting the condenser loop and external lcoil wire loop on first and then the first insulator ring. Screwed up royally!! I will do as you say - first change the condenser and then follow your order so all the pieces placed over the stud are insulated and do not touch the stud. Thanks again. Hopefully this will give me the spark I'm looking for and the engine will start.

Rob has been very helpful and solved several problems I’ve had. Unfortunately, I’ve been restoring this 120 over the past 15 or more years and have had several people working on it. I forgot to tell Rob the distributor and coil came off a Mark 9. I had forgotten myself!!

I knew it was a Mark 9 distributor, he said in the first post, but thought maybe Glyn had bought XK120 points. Just showing the difference.
Here is a distributor out of a 3.4 Mark 1, which should be pretty much the same as Mark 9.

The stud with the nut is grounded, so you need to have insulators in there so the black condenser pigtail, the brown wire to the outside terminal, and the points spring loop don’t touch ground.

Thanks Rob. Thinking back, maybe the insulator was at the bottom of the post and the other two wires were located on top of the insulator, then the points, then the insulator, as you pointed out Rob. Even though the connectors on the other two wires are very thin and should fit comfortably over the shoulder of the insulator and leave sufficient room for the points to fit on the shoulder as well. I had trouble assembling them this way and thought that it was too difficult to get both the wires and the points on the shoulder and convinced myself they weren’t supposed to be assembled this way. Big mistake. I guess if the distributor is removed from the car together with the lead from the coil and assembled in front of ones eyes to ensure the two wires AND the points fit on the shoulder and do not touch the stud, it can be done properly. I will do this and hopefully everything will work as advertised. Thanks once again!

Its so frustrating - no spark. There’s something else I’m overlooking! One other thing, when I crank the engine, the book says the reading on the ammeter should rise when points are closed and fall when points are open. The reading on the ammeter in my car fluctuates between a negative reading and zero!

The current will rise when the points are closed and fall when the points are open. A rising current produces a battery discharge, which is a negative reading on the ammeter.

Thanks Mike

Hi Glyn,

My advice is to go back to basics and methodically test everything - I have been there. First test your low tension circuit.

With the distributor cover off crank or turn your engine so the points are closed. With the ignition on, measure the voltage across the two sides of the closed points. It should be 0V, if not then the points are probably dirty or not properly closing (you have checked the gap, right?) and are not conducting.

Next measure the voltage when you manually open the points, it should be full battery voltage - 12V. If not, we can delve deeper. You can open the points using a screwdriver, but remember you only want to pull/touch the outer side - you do not want it to bridge both sides.

Next, change the HT wire that goes from the coils to the distributor with one of your spark plug wires - i.e. connect the spark plug wire in to the coil HT output. Attach a spark plug and rest this somewhere on the engine - anywhere that has a good earth/ground. With the ignition on, you can open the points again to see if you get a spark. If you do not then it could be the coils. Measure the resistances of the low tension and high tension sides of the coil to see if they are in range.

If you are getting a spark, but not when you put the leads and cap back to normal (cap in position on the distributor) and crank the engine over, then the rotor arm may be to blame (replacements were know to be problematical a few years ago). Also check that carbon brush in the distributor lid is not broken.