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Distributor questions

Distributor Caps

Making progress on the hard starting problem (and unfortunately replacing parts one by one as I check them!) I need a replacement distributor cap, rotor, and points. All I have seen in the catalogs and have been quoted pricing on are for the kind where the HT lead fits into what looks like a knurled nut that goes into a nipple on the top of the cap. That is similar to what the service manual discusses but totally unlike (of course) what is in the car. The parts manual has no diagram of the distributor, nor do the other books I have. The distributor cap currently on the car has the HT leads entering through holes on the side of the cap near the top. They appear to have a screw on the inside that fastens down on the leads. Was there a different cap for cars with C-type heads, is mine the original equipment or was it taken from some other model? If the side connection cap is correct, are replacements still made? - Regards, Jim Voorhies

Dear Jim, Watch out ! Many moons ago I had one of those side entry caps on my first 120. It was NOT original and though it seemed simple enough, the wires coming out may NOT, NOT be in the same order as the standard, top insertion ones. This could surely account for starting problems. I was up for 42 hours straight before I finally realized that the cap was changing the firing order. True, I was a kid then and somewhat inexperienced but not totally so stupid that I'd change the firing order. Regards, Barry P.S. Re: the wiring done in my 140...the information is buried and I am leaving for a few days, will try to find it (on the wiper motor) upon my return.

Jim, I believe I have a NOS distributor cap. What is the LUCAS # on yours? - George Badger

A neighbor of mine recently noted and expression of "MIO" that he sometimes uses to indicate "Misbehaving Inanimate Object" - which is, of course, almost an oxymoron and merely meant to put things in perspective as an inanimate object is not capable of "misbehaving". I am reminded of this when it is suggested that a distributor cap was "changing the firing order". What changes the firing order is making a false assumption and connecting the wires to the wrong plugs in relation to the sequence in which they are "pointed to" by the rotor inside the distributor cap. With the wire connections coming out the side of the cap, the sequential order may not be obvious but it is still simple. When they come straight out the top, it is both obvious and simple because the circular arrangement as viewed from the top is identical to the circular arrangement inside the cap. When the electrical paths are bent 90 degrees, it is possible for them to connect with a contact on the side they enter or with a contact on the other side of the cap. Usually, one can determine the external sequence by visual inspection of the inside of the cap. If there is any doubt at all, a simple continuity check with an ohm meter or a test light will clarify the relationship and the firing order of the connections coming out the side. - Bruce Cunningham, '53 XK120 OTS

Jim, the side entry cap is associated with the early XK120, where the plug wires ran around under the carbs and came up behind the head and into the valley. I believe they went to the top entry cap and wires going over the cam cover beginning with engine no. W6697, so your 140 should most likely have the top entry cap. Be aware that the top entry cap for 120/140 is different from and may not be interchangeable with the cap for 150. - Rob Reilly

Jim, On both of the 140s that I have had the HT wires came through the top of the distributor cap. - Sam Bell

Hi Jim Voorheis & all -- in 34 years with Jaguar (including '55 XK140MC OTS with C-Type head), I've NEVER seen or heard of any distributor cap other than with 6 plug terminals + center (coil) straight up, screwed into cap. My latest, original Mk IX (792817 BW) is the same as all the others. A side-connection cap was NOT an original Jaguar fitment for your XK140MC. Also -- C-Type head made NO difference re: distributor cap -- they were ALL the same. Someone has changed yours; it's NOT the original cap. I hope this helps -- Larry Martz

Bruce, I believe I read earlier that you were going to the XK50 event. Are you taking your car? Have you made reservations at any hotels yet.? Have you ever seen a source for the early distributor caps with the side connections? - Larry J, 660636

Rob, Was the change in the distributor caps made when they installed the heaters in the cars? - Larry J, 660636

Not related to XK's but predating them, my '51 Mk V 3.5L arrived with a side-entry distributor cap. I purchased a NOS cap from Jagparts and the replacement is TOP entry with all the connections of the screw down variety (i.e. you bare the central wire core, splay out over a small washer and that is pressed into contact with a bit of metal embedded in the cap that caught the connection from the rotor arm inside). - Dick Clements, '51 Mk V 3.5L Saloon

Side entry caps: it is certainly true that these existed for models other than 120s, therefore those picked up at say a swap meet may look like but not be original. I have seen side caps advertised recently at huge prices. Regards, John Elmgreen

Larry, The change from side entry to top entry cap does not seem to be associated with any other change that I can find other than the updating of the distributor from 40199D to 40199E, which I suspect was some sort of very minor internal change, and of course the spark plug wires and clips. Why the change? Nothing to do with the heater, as I see it, because early FHC's had heaters and also had the side entry caps. Some problem with it as installed in a Mark VII? Don't know. I'd be more inclined to suspect that they were getting arcing between plug leads with the oblong spacer clips (borrowed from the Mark V incidentally) so they wanted to go with the six hole spreader/spacers most of you are familiar with, but maybe they would then be too close between the head and firewall (scuttle)? Just guessing of course, and if anybody has a better guess I'd like to hear it. The side entry cap is correct for Mark V (I have two of them). For those who are not familiar with it, the pushrod engine has the distributor on the left hand side near the rear, and the plug wires go around the back to the plugs on the right hand side. The distributor is turned at a different angle from what it is on an XK engine. Coincidentally I was just cleaning the cap off my MkV the other night, and I was going to mention how to remove the coil lead. There's no screw in the bottom like the other six leads as Jim mentioned, the coil lead is simply stripped back, folded over, and pushed in, nothing holding it but friction. I didn't know that, was afraid if I just yanked on it I might break something, so I cut off my old lead, then with a 1/4" drill bit in an archaic hand crank drill that must be two decades older than the car, carefully drilled out the rest. John mentioned caps at flea markets. Question might be was this same Lucas cap used on Rolls, Bentley, Alvis, Austin Healey 100-6, Armstrong-Siddeley? Can't think of any more 6 cylinder cars of that era offhand. Any trucks? High priced? I just paid $94 US for a Bosch cap & rotor for a 6 cylinder BMW (grumble, grumble). - Rob Reilly

Hi Dick & all -- Dick, you've just described the distributor caps on ALL of my cars -- all XK engined, earliest was '52 XK120 OTS -- top mounted, etc. - Larry Martz

Rob: I have a note that these other cars used the same horizontal lead caps. Not a lot of practical help I suspect, except for the other Jag models: Rover 75 48, Commer, Humber models, Jaguar 3 1/2 litre 48-50, Rover 75 49, Jaguar 2 1/2 litre 48-51, Alvis TA21, TB 21 Alvis TC21 - Regards, John Elmgreen

Interesting comment about the Mk V Distributor cap, Rob. The Mk V fired up yesterday (after much cranking!) and then proceeded to warm a very cold garage up remarkably quickly despite the up-and-over door being wide open........ I was looking at the beast as she ticked over and got to considering the cap issue I was on the point of thinking that maybe mine had a side entry cap as the fuel line runs clear across the mid line of the distibutor about and inch off the top of the cap so without major mods to the copper pipework a top-entry cap is a no-no. As far as my own investigations go, I am convinced that I still have an original fuel rail (albeit with a non-standard modern plastic in-line filter) so I am prepared to accept that the side entry version is correct. It certainly makes the plug wiring easier! Not obvious from any of the service manuals, is it? - Dick Clements, '51 Mk V 3.5L Saloon

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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