Anyone brave enough to tryMy casual mention of modifying a Toyota distributor for use on a Type I VW
engine produced enough responses to justify a general post on the subject.
So here it is
First off, it's not a bolt-up. You have to do quite a bit of machining on the
Toyota distributor. That means you need access to a lathe and know how to use
it.
So why did I call it a fairly simple modification? Because it is, if you
happen to be a machinist and understand a few basic principles of both machine
work and engines, one of which is the fact that, at least in theory, the
distributor from ANY four-cylinder Otto cycle engine can be used on any other
four-cylinder Otto cycle engine. In theory. That's because the cam, reluctor,
electronic switch or whatever has four poles. Trying to use a distributor from
a six or eight cylinder engine would increase the complexity of the task by
several orders of magnitude, making it so difficult you'd probably be better
off to start from scratch. But if you have a distributor from a four cylinder
engine you're already about 90% of the way to your goal.
The other aspect has to do with machine work. You don't have to be a rocket
scientist to understand that it's pretty simple to SHORTEN a shaft that's a bit
too long... you just cut the thing off, whereas trying to LENGTHEN a shaft can
be blindingly difficult. By the same token, if you have a bar of metal 2" in
diameter it's a simple chore to turn it down to some SMALLER size... but
virtually impossible, within practical limits, to turn it into a size LARGER
than 2". This also applies to holes. If you already have a hole, making the
hole LARGER is a trivial task whereas making it SMALLER is extremely
difficult... you would have to weld it up and remachine, being careful to
preserve your center.
So how does all of that apply to the modification of a Nippondenso distributor?
First off, the spigot shaft of the Toyota distributor is EXACTLY the same
diameter as the spigot shaft of a Bosch distributor - the thing will plug into
the hole in the Type I crankcase without any machining. It won't FIT but only
because the Toyota distributor's spigot shaft is TOO LONG. But as I pointed
out above, shortening things is pretty easy. Finally, the Nippondenso
distributor has a LOT of extra metal in its base. You can machine away nearly
a quarter of an inch off the Toyota distributor without weaken it, plus you can
saw off the clamping lug and a couple of casting bosses, allowing you to use
the standard VW distributor clamp. (Which is a rather shoddy piece of goods
but it saves you having to figure out a better method of clamping.)
The distributor's shaft is too long but it's almost exactly the same diameter
as the Bosch distributor shaft -- you simply cut the thing to the proper length
and drill it to accept the dog gear from the VW distributor. Along the way,
you will have to move the lower bearing in the Nippondenso distriubutor but
here again, the machine work is relatively easy - you simply deepen the
existing bore.
So why would you want to do all that? Because a new (or nearly so) Nippondenso
composite distributor is about a hundred times better than what you're probably
running in your VW right now.
Like all modern vehicles the Toyota used a composite distributor, having vacuum
sensing to provide the necessary sensitivity, combined with a centrifugal
advance mechanism to provide a wide dynamic range. This is a completely sealed
distributor, with an O-ring between the body and the distributor cap, which is
installed with screws rather than spring-type clips. Best of all, it comes
complete with a modern electronic ignition system.
Inside the Nippondenso distributor is a magnetic pick-up coil. Instead of a
cam on the distributor shaft operating a set of ignition points, it has a
four-lobed reluctor. Each time a lobe of the reluctor sweeps past the magnetic
pick-up it induces a voltage in the pick-up unit. That voltage goes to a solid
state 'ignitor' - a tiny amplifier and a husky transistorized switch --
attached to the ignition coil. The 'ignitor' is connected to 12v and ground
and controls the discharge of the coil, just like on a modern car
So why isn't everyone using Toyota distributors? Well... quite a few guys are.
But the distributor is physically larger than the Bosch and can't be used with
some mechanical fuel pumps. On the other hand, the later model Toyota's use an
HEI system -- the coil, pick-up and ignitor is all built into the cap of the
distributor. Once you get it set up it's a virtually bullet proof system that
can win you the race. For your daily driver, it's a zero-maintenance ignition
system, other than checking the air-gap every 50,000 or so... about the same
time you need to replace the plugs, if you're running platinums.
If your stock Bosch unit is still within spec there's no reason to replace it.
But if your shaft is showing some wobble you might want to look into the mod.
As for Toyota (or Nippondenso) part numbers, there's a bunch of them, just as
there are for the different Bosch distributors. The one I've modified came off
a 22R carburetted engine and the data plate reads '19100-35130,' which I think
is the Nippondenso part number, followed by '29100-8801,' which I think is the
Toyota p/n. But I don't really know (or care). In the process of fooling
around with this mod I've accumulated several Nippondenso distributor (at about
$20 each). The castings are identical but the numbers are different. That
also applies to the ignitor & ignition coil, of which I've used two. Both
worked exactly the same (same connections, etc) and while physically identical,
they had different part numbers.
Finally, I've no idea how well the thing will hold up. In the Toyota the
driven-end of the distributor shaft is supported by a bushing. When modified,
the driven end is free (ie, as with the Bosch unit). I suspect the lack of
support will lead to accelerated wear of the shaft bearings but I've no idea
how long it will take for the thing to fall out of spec. One thing I do know,
it's a hell of a lot easier (and less expensive) to find a good-condition
Nippondenso distributor than it is to find a VW distributor that's still within
spec.
-Bob Hoover
Seems to have potential;wonder if this mod will work with EFI...
