[Healeys] S U fuel pump
bspidell at comcast.net
Tue Oct 20 19:57:36 MDT 2020
I fit diodes per the 'standard:' https://en.wikipedia.org/wiki/Flyback_diode
I don't remember how I fit the transil; I'm pretty sure I did it
correctly because they came with instructions. AFAIK, transils are a
pair of zener/avalanche diodes in both polarity, so they 'breakdown' and
allow current flow at the nominal rating (IIRC, they were 20V or
I think one possible problem with points is when they aren't installed
so as to promote the 'wiping' action to clean them.
On 10/20/2020 9:16 AM, Kees Oudesluijs via Healeys wrote:
> Did you fit the transil in the same way the diode was fitted? If so
> this is not correct. It should be fitted as the capacitor is fitted,
> between the small screw that holds the points blade and one of the
> bigger screws that fix the Bakelite bridge to the coil body. You can
> fit the transil instead of the capacitor or parallel to the capacitor.
> A diode is fitted in series with the points, a transil or capacitor is
> fitted over the points.
> Kees Oudesluijs
> Op 20-10-2020 om 17:18 schreef Bob Spidell:
>> The late Dave DuBois, who designed the transistor-switch fix, quit
>> doing the conversions when he found the reduced voltage cross the
>> points allowed them to oxidize. I tried the transil fix, but didn't
>> get much more longevity than a stock points setup with a diode; I do
>> know some have had better luck with them.
>> I have a points/diode pump in my BN2 that works well, but I only have
>> a few hundred miles in the car. I've lost track of what I've got in
>> my BJ8.
>> On 10/19/2020 11:31 PM, Kees Oudesluijs via Healeys wrote:
>>> When rebuilding SU electrical fuel pumps I ad a transil (e.g.. 1.5
>>> KE18CA) over the points, parallel or in stead of the capacitor if
>>> fitted. This reduces the max voltage across the points to 18V
>>> instead of several hundreds when the contact is broken and the
>>> points spark.
>>> It is also important to clean and polish the points using flower
>>> paper (2-3000 grid), also when new!!
>>> A transil is more or less a bi-directional Zener diode. They cost
>>> next to nothing. I buy them in bulk and pay about $0,15 but when
>>> buying only one expect to pay between $1 and $5. Ebay is an
>>> excellent way to source transils (mainly from China).
>>> A transistor circuit similar to those used in early transistorised
>>> ignition systems does a similar job by limiting the current through
>>> the points
>>> Kees Oudesluijs
>>> Op 20-10-2020 om 07:50 schreef Ray Juncal via Healeys:
>>>> I'm rebuilding a couple of early S. U. fuel pumps for my 100. In
>>>> checking my reference files I came across an article from the MG
>>>> club about adding a transistor circuit to reduce the amps across
>>>> the points. That would keep the points from burning and extend the
>>>> life of the points. Has anyone on the list tried this? The author
>>>> of the article claims he has 20,000 miles on the conversion and new
>>>> looking contact points. Thoughts, comments, suggestions.....
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