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A distribution of distributor problems  Rating:  Rating
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 Posted: 07-24-2005 04:51 pm
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George
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I too am installing a Pertonix ignition in my car, and like everyone else it seems, I am having my share of problems. I have read most of the other helpful posts and sites, but now have a particular problem or misunderstanding of how one is supposed to set the timing.

My distributor was attached to the oil pump by one 10mm bolt going thru a metal plate that is welded to the bottom of the distributor. Where the bolt goes thru this plate it has a slot that allows for some play. I read all the warnings about loosening the metric nut to take out the distributor and not touching the clamp. I am not sure I removed the correct thing, but there seems to be no other. Is my distributor missing some sort of clamp that I am supposed to use to adjust the timing? The little knurled knob on the side will not move at all, but it may just need more force, but I can’t see as the knob has anything to shift. Any ideas?

Does someone have a photo or two they could post of what the base of the distributor is supposed to look like? I would post a pic of mine, but my camera broke yesterday. Thanks for any help.

George

JH5 19062

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 Posted: 07-24-2005 06:45 pm
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Mark Rosenbaum
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Attached is an annotated photo showing a stock JH distributor and its clamping plate.  This plate is held in place solely by friction when the clamping bolt is tightened.  There may be some dissimilar-metal corrosion sticking things together.  If any actual welding, brazing, or even silver soldering were involved, I'd presume that the distributor housing was distorted by the heat, and plan on a replacement.

Reportedly, installation of a Pertronix gadget often results in a radical change in the static timing, so most likely you will need to loosen the clamping bolt and rotate the dist. body to get the correct static timing.  Frequently the vacuum capsule will contact the engine and prevent this.  If so, you may need to rotate the distributor 90 degrees, which in turn will require relocating the four spark plug wires in the distributor cap.  And even if none of this occurs with your car, you'll still have to re-set the timing once the engine is running again.

The hole in the clamping plate for the oil pump stud should indeed be slightly oval, but the oil pump stud itself is supposed to be 6mm in diameter, and its nut 10mm across the flats.  If not, you may want to examine the oil pump in detail with an eye toward discovering whatever other peculiar things a PO might have done.

The knurled knob attaches to a threaded shaft (standard  right-hand threads) whose other end is affixed to the body of the vacuum capsule.  A spring surrounds the shaft, and a sheet metal curlybracket-shaped detent spring prevents undesired rotation of the knob.  The vacuum capsule's diaphragm, in turn, is connected to the distributor's moving (points) plate by a long spring.

While the knob is often a little stiff to turn by hand, it should not be frozen.  Possibly it's just screwed all the way to the end of the threads on the shaft, or there's some corrosion somewhere, either associated with the vacuum capsule, or with the moving (points) plate, or both.  This needs to be looked at, as otherwise you may have unexpected timing changes that in turn cause peculiar performance problems or, worst-case, engine damage.

If desired, you can remove the vacuum capsule by (a) applying a bit of penetrating oil to the various moving parts, (b) using a pair of needle-nose pliers to carefully move the end of the long spring free of the points plate, then (c) unscrewing the knob (anti-clockwise) until the vacuum capsule falls free of the distributor body.  When you reinstall the capsule, turn the knob until it's about half-way down the threads of the shaft.  Once the ignition is static-timed, the knob can then be used to mke fine adjustments to your ignition timing.

Finally, any discussion of a JH distributor should touch upon the oil leak issue.  The o-ring on the distributor shaft spigot must be replaced periodically.  All available replacements are in the original standard inch-based size.  Due to owner complaints about oil leaks, the factory later changed this to a slightly larger o-ring in some odd metric size that AFAIK is not currently manufactured anywhere in the world.  There is also a shaft oil seal at the top of the distributor spigot, and this also can wear out and permit oil leaks.  A better-than-factory replacement for this seal is commonly available for US $2-$3, but its installation requires disassembly of the distributor.

 

Attachment: 25d4 annotated 2.jpg (Downloaded 91 times)

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 Posted: 07-24-2005 07:52 pm
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George
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Many, many thanks Mark. For the info, pic and quick response.

As I was afraid, it appears my distributor has been welded to the clamping plate, there is no clamping bolt. I assume that a new distributor is in order as there appears to be no way to adjust the timing once I put in the Pertronix. On more careful study it appears part of the lip of the dist which sits down into the clamping plate is broken, which might account for the welding. Is the clamping bolt part of the distributor or the clamping plate? Just curious.

I have a bad feeling that a new distributor is going to be rather pricy. Am I correct in assuming that although other cars use the 25D, to get one with the proper drive dog, I’ll need to contact Delta? Or does anyone know a good rebuild resource?

Thanks again.

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 Posted: 07-25-2005 12:44 am
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Mark Rosenbaum
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It's fairly common to install a JH distributor incorrectly, either because the clamping plate was installed upside down, or because the distributor body isn't pressed tightly against the oil pump casting.  Eventually the distributor body will slip, particularly if there's any oil present.  The natural but incorrect response is simply to tighten the clamp bolt.  If that is done repeatedly, it eventually will crush the distributor body where you describe.  Surprisingly, this has no effect on distributor operation unless the crack gets really bad.

AFAIK, the required clamping plate is unique to 907-series engines.  Possibly you can clean up yours and re-use it; if not, you'll have to get one from Delta, a Lotus dealer, or from some JH owner with a spare.  If you need the clamping bolt, too, I believe it's Whitworth but there's nothing special about it other than that it uses a square nut -- something in Grade 5 from the hardware store should work, Delta may have them, or you can order one from Moss by pretending you have a Spitfire, Spridget, or MG.

You may be able to find a good used JH distributor from Delta, the wrecking yard in Vista CA, or from some of the other Brit car parts sources, but they won't be inexpensive.  OTOH, 25D distributors show up on eBay all the time, and often sell for $10-30 plus shipping.  Although only a very few of these are actual JH distributors, you can use just about any 25D having an o-ring groove on its spigot, provided you're willing to dismantle things and install the necessary parts from your current one.

The distributor comes apart quite easily.  Remove the vacuum capsule, and the screws holding the fixed plate to the body.  Support the drive dog, then use a hammer and pin punch to force out the precision pin or roll pin that secures the drive dog to the shaft.  Next, gently tap on the end of the distributor shaft until everything falls out.  (Do this in a plastic bag so you don't lose any small parts.)  Clean everything, and look for signs of wear or damage.

The critical parts from the old distributor, which must transfer to the new, are (a) the vacuum capsule; (b) the points cam (which must be marked 11 degrees; be 100% certain to check this, as a PO who welds distributors doubtless does other truly horrible things!), (c) the springs for the centrifugal advance weights, and (d) the weights themselves.  For all the rest, including the drive dog, use whichever parts look best and have minimum wear.

You will probably want to install a new shaft seal.  The counter guy at your local bearing supply shop will call this a lip seal.  The correct type is a Chicago Rawhide (CR) part number CR4912, a Transcom (TCM) part number 13X19X3VG, or any reasonable equivalent.  If you need to find something online, you're looking for an oil resistant lip seal for an 0.500" dia shaft, that fits into a recess that's 0.75" dia. x 0.125" deep.  When installing the seal in the distributor body, it is vital that its groove (hollow side) faces toward the drive dog end of the distributor spigot, as any oil under pressure leaking into the distributor will act to tighten the seal's lip against the shaft, preventing leaks.

Putting the distributor back together is no more difficult than taking it apart.  The online Moss catalog has a beautiful line drawing of an exploded 25D distributor, which is worthy of use as a reference.

 

Last edited on 07-25-2005 12:46 am by Mark Rosenbaum

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 Posted: 07-25-2005 03:56 pm
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Brett Gibson JH5 20497
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George, just a idle thought, the dizzy is alumiun and the clamping bracket steel is it possible just to file away the weld and release the bracket from the Dist. there by regaining the full movement for adjustment, or is the thing so cobbled up your better off starting over.

Bruce Madden in Atlanta has been know to rebuild Dist. It might be worth giving him a call.

Good Luck             Brett 

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 Posted: 07-26-2005 05:54 am
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Jensen Healey
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Give me your address and I will send you a distributor from a low mileage engine. I have no idea how well it works but it has to be better than yours. You can email me at klhoush@comcast.net 

Kurt Housh  

JH 13148

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 Posted: 07-27-2005 03:18 pm
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George
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I'm taking Kurt up on his kind offer and will let people know how I get on.  I have learned that my problem is not that uncommon.  People overtighten the clamp and break the base of the distributor.  I have attached a photo as a warning to others!  Thanks for all the help

Attachment: 2005_0828Image00201.JPG (Downloaded 65 times)

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 Posted: 07-27-2005 04:01 pm
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Mark Rosenbaum
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George,
Just so you'll know, there were two different 25D4 distributors used in JH's with Strombergs. These are identical save that the specs for the vacuum capsule are slightly different.  The 'x' in both cases is the revision code for the part, and will be either a blank or a letter from A to Z.
* Lucas 41497x, up to engine number 4802
* Lucas 41584x, from engine number 4803 until the changeover to the 45D4.


I'm trying to fill a few holes in the JH knowledge base, and would appreciate it if you could let me know what markings are stamped into the vacuum capsule of your current (welded) distributor.  There should be an 8-digit Lucas part number, such as 5441xxxx, and a set of numbers describing the vacuum characteristics of the capsule, such as 5-12-6 (meaning no action at 5" Hg, full action at 12" Hg, and 6^ total action).  Sometimes these marks aren't clear until 30 years of dirt is cleaned off....  Thanks in advance.

 

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 Posted: 07-27-2005 05:43 pm
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George
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My distributor is numbered 41584  A, 43 74, but I cannot find any numbers on the vacum capsule.  I cleaned it up, but no luck.  Did they all have numbers on the outside?

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 Posted: 07-27-2005 11:36 pm
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Mark Rosenbaum
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It's my understanding that the numbers should be on the turrets, as indicated in the attached photo.  But we're talking British parts from the 1970s here, so quite possibly the person who made any particular item might have 'neglected' the numbering process for one reason or another.

Since it is rarely possible to order new distributor components for a JH, the only way to assess the utility of a potential replacement part is to compare its specs to the desired ones.  And while the shop manual lists the basic specs for the several distributors used, the way these specs are written does not entirely coincide with the descriptions that Lucas would have used.  And apparently no one ever bothered to provide sufficient information about the vacuum capsules.

Finding answers thus becomes a matter of asking owners for information, and hoping they'll respond.

Attachment: Vac capsule numbers.jpg (Downloaded 52 times)

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 Posted: 08-02-2005 12:59 pm
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George
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Thanks to all for the great help. I put the Pertronix into my old distributor and tried it out - and surprisingly, the timing was close enough to adjust it with the slot in the welded on clamp. So that’s what I did for now. As I am still not happy with set up, I will go ahead and replace it with the one Kurt is sending after I rebuild it. A good small winter project.

Mark - it wasn’t til after I put the old one back in that I remembered to look for the vacuum capsule numbers and now I can’t read them. I’ll send them to you when I take it off to swap it out. Sorry about that. You must have quite a library of JH part pictures!

Now on to the Flamethrower coil.

Thanks again - George

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 Posted: 08-05-2005 04:29 pm
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George
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Kurt - Thanks. Very nice of you to send the distributor. Although my old one is working, it ain’t right and I will use your shell to build a new one. What was that old line from the Six Million Dollar Man, "We can rebuild him better than before . . ." Something like that, anyway thanks again.

Mark - I got the numbers off of Kurt’s first thing so I wouldn’t forget. He sent me distributor number 41584A dated 11 74. And the vacuum capsule is stamped 84427140. The 8 may be a 3, these numbers are hard to read. Unfortunately, I cannot find the other set of numbers you are referring to. I have the cleanest vacuum capsule around but no numbers. Sorry about that. I’ll get you the numbers off the other when I remove it. Hope this helps.  Thanks again.

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 Posted: 08-30-2005 04:29 am
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Joel
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So - now I'm the idiot. I just busted my distributor by tightening the clamp too far. The dang clamp is out of round and misshapen a bit and I wasn't paying any attention - until I heard the snap.

Guess I'll deal w/ this crap later.

Then I'll worry about why it appears I have more wires than the diagram going to my coil. . .

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 Posted: 08-30-2005 02:49 pm
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George
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Sorry to hear of your misfourtune.  I suppose you could always weld it on.  : ] 

Actually if its just the clamp, I found they were pretty inexpensive($9) from Dave Bean in California.  They were very helpful too.

FYI - I had too many wires on my coil as well.  I just reconnected them and figured I may sort them out at some later date.

good luck

George

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 Posted: 08-31-2005 12:16 am
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Joel
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Okey dokey. Here's my dilemma. The break is definately in the distributor itself. As I noted before, I was putting the clamp back on the distributor and broke the lip of the distributor by cranking down too hard. The clamp was a little out of shape and I wasn't paying attention.

My question is - does the lip of the distributor lie flush to the oil pump and form a seal? (It wouldn't be a very good seal as it is metal to metal) If it does not, I should be able to use the dist as is. Just a 1/4 or so of the lip broke and I think I can still get it to stay tight in the clamp. If it works, I can at least get the old girl running while I'm trying to find another dist.

Just a thought. Or, I could weld it ;-) .

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 Posted: 08-31-2005 05:09 am
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Mark Rosenbaum
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Joel,
The part where the clamp goes doesn't seal or hold pressure, it's just a mechanical stop, so you can try to re-use the distributor at least for a little while.  I suggest using emery cloth or something similar to slightly roughen the remaining lip on the distributor body, and the inner surface of the clamp, so that you'll get sufficient friction to hold things together until you can arrange for a replacement.

 

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 Posted: 08-31-2005 05:52 am
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Joel
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Thanks for the comment Mark. I'm glad my thoughts were not so far out of line.

Unfortunately, I'm busy as heck right now and won't have time to screw around for a bit. Too many 'hobbies'. . .

Thanks again,

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 Posted: 08-31-2005 02:23 pm
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Brett Gibson JH5 20497
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Joel, dont sweat it, I broke probably the same thing you did on my distributor and I have been using it for the last 2 years, I only recently got a replacement, as long as the Dist. is clamped flush in it's housing and youve set the timing it should stay put with no trouble or leak's, if it does leak then thats an O-ring issue.

Brett.  

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