Classic cars forum & vehicle restoration.

[ka]

I realise there have been quite a few topics on this, having commented on a few using the Maplins ignition assist kit.
I also once owned a Crypton analyser, (really cheap now as very few are wanted in the trade), and after reading an article on distributor wear, it was eye opening to see this on the screen, with timing to each cylinder varying considerably due to the wear in the shaft. I fitted an optical pick up, which I replaced with the magnetic impulse type when it failed, to iron out any wear, as this system depends less on the points gap. But I have returned to the points/Maplins kit for reliability and the ability to be able to repair it at the 'side of the road'. I have spent some time rebushing the distributor to reduce the slop, and the crypto showed the net result. Any views anyone?
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KA

Better three than four.

[ukdave2002]

Hi Ka

The distributor wear you describe affects the dwell and timing, as you say is very visible when the engine is hooked up to a scope.

Unless the problem is resolved, it may be a bent distributor shaft and or wear in the shaft and bearing, the trigger be it conventional points, optical or hall will have some error.

Nearly all the add on electronic ignitions are based on the transistor assist design As introduced by most mainstream manufacturers in the 70's, personally I don't like the optical trigger because it is susceptible to dirt, Hall effect is us full for high speeds where contact bounce may have been a problem, but for the bulk of classics retaining the points is IMHO the preferred solution and as you point out makes a roadside fix in the event of electronics failing a simple affair.

By the way I saw the Vellaman kit in our local Maplin sale a couple of weeks ago priced at £5! So I bougt the 4 that they had in stock.

Cheers

Dave

[Old Wrench]

Just to add top Dave's comments:

Timing problems caused by a classic mechanical distributor can be:

1. Wear in the distributor shaft/bearing, causing is to effectively "oscillate" at different frequencies at differing rotational speeds:

2. Wear and slop in the mechanical advance weights/springs:

3. Uneven wear on the distributor cam profiles and lobes which causes different timing periods across the cylinders:

The shape of the cam "ramps" both opening and closing sides, effects the opening period and as Dave already stated, can create points "bounce", at high RPM.

For racing in the late 1960s early 1970s, we always used a special distributor, without vacuum advance, special cam profiles, and a much higher spring loading than standard points spring. Some tuners made special sets of points using two modified standard points springs.

These worked very effectively on (e.g.) A Series BMC (Cooper S, MG Midget) > 10,000 RPM: and same unit for Lotus Cortina Twin Cam engines and all derivatives.

What is always critical is the Dwell Angle: this is essential to allow sufficient time for the coil to charge, properly, remembering it is the collapse of the flux which creates the High Tension EMF and thus spark.
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Well, apart from that, did you enjoy the play, Mrs Lincoln?

[peter scott]

I prefer originality in old cars. I hate seeing modern coils, alternators instead of dynamos, sealed for life batteries etc, etc.

I don't cover a high mileage in my old car and can only think of one occasion when old electrical technology let me down in 25,000 miles of my ownership.
http://www.jaguardriverforums.co.uk/showthread.php?t=357

I will confess to one small reliability upgrade and that is to replace my single contact set in my SU pump with a twin set (no pearls) and that is nicely hidden.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[kevin2306]

As you may know but earlier this year i was having running issues with the Singer.
Turned out to be a combination of a poor carb (bought a new old stock one) and the aftermarket (1970s?) Lucas electronic ignition system failing slowly.
Due to needing it up and running I bought an accuaspark unit for £58 delivered..I was quite skeptical as to its suitability but it totally transformed the starting and general running of the car, superb infact. so +1 for going electronic.
However, whilst waiting for the accuspark to land, I managed to source and buy a new old stock original distributor, complete with the correct and original points, condenser, cap and rotor..Its on the parts shelf and it is my aim to fit it before next season, just to keep things original.
To be fair, apart from the accuspark distributor being a little bright, to the untrained eye it appears stock.

kev

[Old Wrench]

[goneps]

[peter scott]

The twin set I transferred from an original pump has been trouble free with me for years whereas the single needed periodic attention (was probably dating from 1939).

A diode is a good idea but I haven't added one.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon