[Healeys] S U fuel pump

[Bob Spidell]

Kees,

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 
thereabouts).

I think one possible problem with points is when they aren't installed 
so as to promote the 'wiping' action to clean them.

Bob

On 10/20/2020 9:16 AM, Kees Oudesluijs via Healeys wrote:
>
> Bob,
>
> 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.
>>
>> Bob
>>
>> 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.....
>>>> Regards
>>>> Ray
>>>>
>>>>
>>>
>>

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