View single post by Mark Rosenbaum
 Posted: 07-25-2005 12:44 am
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Mark Rosenbaum



Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
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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