I’ve been contemplating the 1973 XJ12 distributor that Robert
Warnicke was good enough to send me for perusal, and I think I may
have come up with a minor improvement. For reviewing the parts I’m
discussing, you can refer to
http://www.jag-lovers.org/xj-s/book/DistributorOPUS.html
One of the things that bugs me is that the upper bearing on the
distributor shaft (the ball bearing) is separated from the crankcase
by the shaft seal below it and is open to the inside of the
distributor. There isn’t even a dust shield on the bearing itself.
Anything floating around inside the distributor can fall down into
the rollers themselves, and that includes oil as well as dust, dirt,
dropped screws, whatever.
Without the oil falling into it, it would go unlubricated. I’m
familiar with “permanently lubricated” ball bearings, but I think
those always have dust shields to help keep the lubricant inside.
With this bearing being fully open, it seems to me any lubricant
applied at assembly is going to either get blown out during operation
or it will get washed out by oil and solvents being used on the
distributor above.
On this 1973 distributor, there is a cupped washer just above the
bearing that spaces it on the distributor shaft. My proposal is to
install an O-ring, 1/8" thick, 15/16" ID, just above the bearing and
surrounding this cupped washer. I have the parts in my hand, and
they fit together as follows:
One side of the O-ring rests on the flat side of the outer race of
the bearing.
The OD of the cupped washer is a hair larger than 15/16" and it has a
45� bevel facing the bearing. This 45� bevel contacts the ID of the
O-ring.
The sealing effect I hope for is between those two contacts. Both
are smooth machined surfaces. In this application, the outer race of
the bearing will be stationary while the cupped washer rotates with
the distributor shaft, so this O-ring becomes a shaft seal.
Using an O-ring as a shaft seal is kinda hokey, but it does work. I
spent many years bicycling, and as soon as you quit racing and start
touring you find that you need to start devising your own sealing
methods. Bicycle component manufacturers generally don’t seal
anything because bike nuts find the added friction unacceptable, and
when they do apply a seal it’s usually an unreliable seal; as soon as
a load is applied and everything flexes, it no longer seals. So, you
take a crank arm off the axle, stack some O-rings on the axle, and
reinstall the crank arm so that it compresses the O-rings lightly
against the bottom bracket bearing shell. A then you don’t have to
rebuild the bottom bracket every time it rains any more.
In addition to those contact points, the O-ring may contact the flat
bottom side of the centrifugal advance base plate. It won’t seal
anything on this OPUS distributor because there are two holes through
the plate right where the O-ring makes contact. I don’t think the
contact will hurt anything, though.
The O-ring may also contact the aluminum distributor base at the
corner of the opening the bearing presses into. I suspect this
contact won’t hurt anything either, but if it’s convenient to chuck
the base into a lathe one might consider applying a 45� bevel right
there just to minimize this contact.
I fully expect that the O-ring will rotate with the distributor shaft
and slide on the surface of the bearing outer race. This will make
turning the distributor shaft a little stiff at first, but it’ll wear
a bit of the rubber away (or the rubber will take a “set”) so the
contact isn’t so forceful and the shaft will turn more easily.
Since the O-ring is unsupported at the OD, one might get concerned
about centrifugal effect distorting the O-ring or pulling it out of
position. This shaft only turns at 1/2 crank speed and the O-ring is
only 1" diameter, so I really don’t expect a problem – until the O-
ring dries out and gets hard and cracks, when it’ll probably get
broken open and tossed out into the bottom of the distributor where
it will sit and do nothing, while your bearing returns to the level
of exposure to contamination it originally had. Obviously, a Viton O-
ring might be a good idea here.
I personally like this idea so much that, if this were MY distributor
and I was reassembling it for use, I’d be putting that O-ring in.
My original intention in thinking about this was to provide a mere
dust seal, keeping the big chunks outta the bearing and keeping
grease in. However, considering how well I expect it might seal, the
probable condition of the shaft seal beneath the ball bearing, and
the fact that that shaft seal is NA, there is another plausible
purpose for this mod: to REPLACE the shaft seal. If some Loctite 518
is applied to the OD of the bearing prior to installation in the
distributor base and some more is applied to the ID of the cupped
washer where it contacts the inner race of the bearing, this O-ring
should provide a very secure seal indeed. Leave the shaft seal out!
This would have a side effect: the seal would now effectively be
ABOVE the ball bearing rather than below. Hence, the ball bearing
might get some lubrication from the crankcase below.
I dunno how any of this idea might apply to the later CEI
distributor. For one thing, the later distributor has a different
rotating base plate for the centrifugal advance mechanism. Also, the
ball bearing in the CEI is installed in a loose-fit hole with a wavy
shim around it to hold it centered, while this OPUS distributor has
the bearing pressed into the aluminum distributor base. I don’t even
know if the CEI distributor uses the same cupped washer. All of
these factors may affect how an O-ring would work in the assembly.
BTW: the bearing in this 1973 distributor seems to be in good
condition except that it was seized. Seizure isn’t really a problem
here, you’ve got 260 hp to turn it, it’s GONNA turn. The only reason
this one was seized was apparently that it hasn’t turned in a long
while. It does appear to be exactly the same thing that happens to
the centrifugal advance: the lubricant dried out and gummed it up.
With this bearing in my hand, a little Liquid Wrench loosened it
right up so it spins nicely.
– Kirbert
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