Bigport & Smallport distributor parts interchangeability

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Rogue-AE95
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Bigport & Smallport distributor parts interchangeability

Postby Rogue-AE95 » Thu Apr 09, 2020 11:20 am

For USDM parts. I have what I am pretty sure is a stock SP distributor, came from a 1990 Geo Prizm GSi. And an MR2 dizzy which I know is OEM because it still has the Toyota part number decal.

I set both to what I was pretty sure was TDC, but looking at the reluctors(?) inside, they aren't quite in the same place. Are they supposed to be slightly different? I know the cap & spark plug wires are different, since BP wires sit higher on the valley compared to the SP ones.

Speaking of, can you use BP or SP cap/wires set on BP or SP dizzy? Depending on what valve cover & valley cover setup you have. Like, BP valley cover on a SP head, and BP cap/wires on a SP dizzy?

I'm asking because I wanted to disassemble both, but put the SP guts into the BP dizzy and use the BP shaft & gear (and of course replace the old internal seal). The BP shaft & gear seem like a better setup, since the gear is set in place with a pin. I don't like the idea of pressing the SP gear back in place but getting it slightly off.
'88 Corolla All-Trac

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Rogue-AE95
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Re: Bigport & Smallport distributor parts interchangeability

Postby Rogue-AE95 » Sun Jun 14, 2020 4:39 pm

Anyone? Lots of views...
'88 Corolla All-Trac

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jondee86
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Re: Bigport & Smallport distributor parts interchangeability

Postby jondee86 » Mon Jun 15, 2020 1:53 am

Can't speak for USDM but the JDM/Euro spec AE92 smallport and AE86 bigport distributors
were different. Both engines were MAP sensored and the bigport had 4 + 24 trigger wheels.
The smallport had 1 + 24 trigger wheels. The bigport had 8mm wires and the cap was held on
with springs clips. The smallport had 5mm wires and the cap was held on with screws. And
from memory I think that the smallport had two pickups on the cam position wheel whereas
the bigport only had one.

So apart from the obvious differences in cap geometry, wires and valley covers, I wouldn't
want to bet on the innards swapping over from one to the other. However, if they do and
you can handle any difference sensors/wiring with an aftermarket ECU, it should not be a
problem to sort the timing. Most aftermarket ECU's have provision for setting the actual
spark timing by adjusting the offset from the pickup signals.

I never heard of the gear on a smallport distributor coming loose. Being a fraction out on
the placing would only mean a bit of fiddling with the distributor adjustment to set the
timing if you were using an OEM ECU.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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Rogue-AE95
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Re: Bigport & Smallport distributor parts interchangeability

Postby Rogue-AE95 » Thu Jul 02, 2020 4:26 am

Thanks Jon. I didn't know an aftermarket ECU would be able to compensate for the distributor being slightly different.

USDM distributors are definitely different than the ones you described. They both seem to have 4 and 1 pickups inside.

I guess this will turn into a weekend project (on some weekend, who knows when). Biggest problem is I don't have a running 4A-GE to test out the distributor on after messing around with them.

One additional question, something I thought of recently. Should the internal brass(?) bushing be pressed & swapped out as well? Like the shaft has bedded / worn itself to that bushing? Or is it like a valve guide, as long as it's in spec it doesn't matter?
'88 Corolla All-Trac

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jondee86
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Re: Bigport & Smallport distributor parts interchangeability

Postby jondee86 » Thu Jul 02, 2020 2:30 pm

Rogue-AE95 wrote:One additional question, something I thought of recently. Should the internal brass(?)
bushing be pressed & swapped out as well? Like the shaft has bedded / worn itself to
that bushing? Or is it like a valve guide, as long as it's in spec it doesn't matter?

There is distributor DIY posted here... http://www.matrixgarage.com/content/16- ... or-rebuild
... and it does not make any mention of the bushing. Nor have I seen it mentioned
anywhere else, so I'd say it is not designed for replacement. Even if it has a bit of wear
on it, the new bearing higher on the shaft should keep radial movement of the trigger
wheels in spec.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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