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Ignition dwell angle

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Can anyone tell me if a camshaft from a Dominator distributor with a cam dwell angle for a twin, can be used successfully in an ES2? Of course there will be a wasted spark, but does the different dwell angle make any difference to the performance, or does it affect the life of the coil?

Comments will be appreciated.

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Hi Richard,

No one else seams to want to reply and I’m certainly no expert but as I understand it the dwell angle is the angle through which the cam rotates while the points are open giving sufficient time for the capacitor to fully energise ready for the next spark. (I may not be using the correct terminology so expect to be corrected).

This being so the dwell angle can be adjusted to whatever you prefer just by altering the points gap. I have never seen inside the distributor as my 99 is magneto so presume the twin cams are similar to a conventional Lucas car type. If so and you don’t want the wasted spark just carefully grind away the unwanted cam. To check the dwell angle with the distributor off make a small timing disk to fit on the bottom of the drive shaft and mark the ‘points open’ and ‘points closed’ positions using a battery and bulb on the contacts. Then simply measure the angle between the marks on the timing disk. Adjust the points gap and recheck until you achieve the required setting.

If you are unsure of the angle required use the same method on your existing cam and points gap.

Hope this helps and is not too confusing.

Regards

Dick

 

Hi again Richard,

I have just sat and had a rethink about my comments. The dwell angle isn’t the time the points are open it is the time they are closed to reenergise the capacitor so removing the second cam would in effect give longer dwell between firing.

Never alter the points gap after the engine has been timed as it will also alter the timing.

I’m sure there will be other corrections/suggestions to follow by others.

Regards

Dick

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I'd hazard a guess that most of will never have bothered to measure dwell angle (not having the kit to do so). Surely it's simply a good way to get the correct contact breaker gap and quicker than feeler gauges which makes sense in a commercial setting.  If that's OK and if the points open at the correct time there's no reason why the origin of the cam matters.  As long as the wasted sparks don't appear at the wrong point in the cycle.

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...for your comments.

Maybe I should have explained the situation more clearly. The ES2 I bought was fitted with the cam from a twin. After rebuilding starting the bike was a dangerous job due to kick backs and flames out of the carb. Nearly set my trousers alight!

I discussed this with a knowledgeable friend and we decided to remove one cam lobe.

Since then starting is fine, no kickbacks, no flames. Bike runs ok, but could be livelier. 

It has now been suggested by someone else that due to the vastly increased dwell angle (angle when the points are closed, as you say) that the coil will soon fail. Hence my questions about the life of the coil and the bike's performance.

To change the angle by changing the points gap makes sense but will changing the gap affect anything else?  Does this mean that for all the years I've been setting points gaps accurately, it's only to set the dwell angle? If this is correct, it follows that the dwell angle is very important and removing one cam load will have a tremendous effect.

 

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.... what is more important, points gap or dwell angle?

Surely changing the points gap has no effect other than to change the dwell angle? Yet if the dwell angle must be so accurately set, why is my ES2 unaffected by removing one cam lobe? 

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I think the dwell angle setting was really just a convienient way  for garages to check  the points were  OK  without getting hands dirty . I have had cars that have had distributors that were so difficult to get to that  no one bothered  to adjust points all the time the dwell was fair.I can imagine that too long a dwell may overheat the coil . Points were designed to operate  with a  set gap and springs were designed to  contain the action but not wear out the heel too fast. You may  have to wait and see if the extra dwell is detrimental to the coil. A small change in points gap can make a significant  alteration to the timing .

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The Dwell angle is in effect the 'charge' time for the coil. (nothing to do with capacitors, they are there to reduce points sparking and increase the efficiency of the spark). The springs are also there to control the advance time ie the the advance range. If you have an old fashioned automotive multimeter they will measure Dwell angle. But I have never done it. As you say above, if the Dwell is too long it is possible that the coil can be 'cooked'.

By the way I can fit Boyer ignition into the 18D1/2, you do need 12V. The Dwell angle is taken care of by the Boyer Bransden amplifier.

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.... for your comments.

As the dwell angle on my modified twin cam (one lobe removed) is almost certainly different to that on an original single cylinder cam, I have no option but to use the bike and see what happens.

If it does cook the coil I'll have to change to something else.

 

 


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