Olde-Worlde Ignition Help

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Two-strokes usually have a set of points for each cylinder. This is because a spark per cylinder is needed each revolution. A single set of points would not be able to operate quickly enough to cope with that number of operations.

It would be impossible with a mechanical system to guarantee accurate timing of each cylinder with separate points, so it is common to have some means of setting the timing for each cylinder independently.

Chris

Reply to
Chris Whelan
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Early Rover V8 engines had a single set of points and revved to about 6000 rpm. Equating to 12000 rpm on a twin two stroke. Twin points and coils is probably cheaper (and more reliable) than a single set and distributor.

Reply to
Dave Plowman (News)

electronic ignition in a similar distributor, it was the first component that failed when I raced one, the bizarre bit was that I went out looking for a points distributor at a breakers, I walked into the portakabin and asked, the guy rummaged on the desk heaped with bits and produced the exact item, 20 quid later I was racing again.

Reply to
MrCheerful

What about the speed of rotation of the distributor?

What did the later V8's use?

Chris

Reply to
Chris Whelan

Same as all distributors - half engine speed. But it's the number of lobes on the cam that matters.

Depends how far you go. ;-)

Electronic ignition via a VR etc sensor arrived with the SD1. Several varieties - the original Lucas Opus wasn't too reliable. Last versions had mapped wasted spark - so no dizzy.

Reply to
Dave Plowman (News)

Because the cranks aren't exactly precision made, so there are some relatively large 'twists' in many of them, meaning you need to set the timing on the 2 points independently.

Reply to
SteveH

So, to update...

I have everything set up-ish. But I lost my new feeler gauges, and I still cannot work out the best way to set the timing.

I reckon with a new set of gauges, and working out how to do the timing, within half an hour it'll be running very nicely.

It's fine pottering around the local industrial estate, but started to stutter under load on the local bypass.

Reply to
SteveH

I have had a bit of experience with two-stroke twins (Ariel Arrow and Norman B4 Sports Twin motorcycles in the Sixties), and found accurate ignition timing was desirable for optimum performance.

If you were really pottering, you might find it needs a brief period of high revs before it will run smoothly again.

Chris

Reply to
Chris Whelan

It was definitely missing - so I think the points gap is probably out.

Hopefully the electronic ignition kit will arrive before the weekend.

Reply to
SteveH

Points gap is important. The coils need long enough to build up the maximum flux. So set that accurately first, then check/adjust the timing. The points also need to have the correct shape on their contacts - domed. If they are pitted, you can't set the gap accurately.

You can use a DVM set to continuity to tell when the points open - that is the firing point.

Reply to
Dave Plowman (News)

The points gap sets dwell. If you close the gap down the points open earlier and close later, increasing dwell. Wider gap less dwell.

Nice graphic at bottom of this page.

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Every time you adjust the gap the timing will move and will need resetting. Reduced gap advances the timing, increased gap retards but gap is not used to set timing. Set the points gap for dwell, then the timing has to be reset.

Finding single cylinder dwell meters was always impossible, veritable rocking horse poo even back in the 70/80's. They were plenty around in Halfords for 4/6/8 cyl but nothing for singles. Amazon is listing a Draper one, does 3/4/5/6/8 but not singles or modern wasted spark system with 2 coil/4 cyl.

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6 and 8.
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*Version*=1&*entries*=0 Says "for 4 cyl double 8 cyl scale" Problem is you could use one set on a different number of cylinders and multiply the reading up but it lost accuracy. With a 4 cyl on that setting you could set to about +/- 1/2 degree. On a single you get 1/4 the reading 4 x 12 = 48 degrees or is it reading 4 x 12.5 = 50 degrees, now the accuracy is +/- 2 degrees. 8 cylinder one you will be down to around 7.5 degrees and +/- 4 degrees accuracy.

Dwell meter is constant current source and a resistor capacitor. Changing the number of cylinders is just a switch for different resistor. This is a 6 cyl dwell circuit and switch is change of function to voltmeter.

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Reply to
Peter Hill

Cheapy neon timing light. This was the first tool I ever bought when I had my 1st car - B-reg 998cc Nova I inherited along with a set of imperial spanners. It was a bit of a whim but the Haynes manual banged on about timing and it seemed within my realms of understanding at the time.

It reqired almost pitch darkness to see anything by the neon-y glow (the strobe version was at least twice as much in 1995!) but revealed that the timing was *miles* out (used to start without any choke.) Loosened the dizzy with an ill fitting 1/2" or 9/16", give it a huge twist and Bingo! the marks lined up. Ran loads better, needed choke to start and, although I checked it a few times, never needed adjusting ever again.

After that I never had a car with carbs or points and binned it eventually :-(

Reply to
Scott M

The dwell is just a posh name for the ratio between them being open and closed. Assuming the cam isn't worn and you know how to use feeler gauges, setting the gap correctly will result in the correct dwell. A dwell meter is only really needed for checking they are correctly set quickly. Or with the very rare types where the gap can be adjusted with the engine running.

Reply to
Dave Plowman (News)

But dwell can compensate for uneven points which may throw your gap measurement off.

Tim

Reply to
Tim+

A friend has a 1938 McCloughlin Buick straight 8 He waited ages to find one and loves it, often going to the states to source parts, RHD having come from Canada (IIRC) Knee action suspension too, the first year it was available, nice to drive too, the engine is very smooth.

Reply to
MrCheerful

Fit new points, then. They're cheap enough. Trying to adjust points using a dwell gauge is a pointless exercise - unless they can be set with the engine running.

Reply to
Dave Plowman (News)

Well yes, worn points should be replaced but my point was that setting a points gap is all about getting the correct dwell. Dwell is the end goal, not points gap.

Tim

Reply to
Tim+

When I was a lad my grandfather had a straight eight Buick. I am told that these suffered all sorts of timing problems due to the length of the main shaft bending with revs due to its length. One claim was that in an extreme case the shaft would bend so much that it would hit the engine block smashing it.

Reply to
Norman Rowling

Assuming the mechanical condition is good, one will achieve the other.

I do have a dwell gauge and used it to tell when the points needed replacement. But setting them with feelers accurately always resulted in the correct dwell.

Reply to
Dave Plowman (News)

That led to:

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which comes under the heading "You learn something every day".

Reply to
Davey

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