1600 dwell angle?

Discussion in 'Mech Tech' started by orangefeeling, May 8, 2017.

  1. A quick one, what is the suggested dwell angle for 1600 engine? Haynes doesn't seem to say! Cheers
     
  2. 45 - 50 degrees
     
  3. Cracking - thank you.

    Slightly different question, what happens if it's 57 degrees. Would I get an occasional misfire under load?

    Or rephrasing, I have cocked up, just checked and it's 57 degrees now is my own numptiness the reason I have the misfire I was trying to find?
     
  4. I don't know, I've long since given up on points because the timing and dwell "wanders"

    Electronic ignition is the way forward, once set, the timing stays put. :thumbsup:
     
    Last edited: May 8, 2017
  5. If you've got contact breakers, just set the right gap and forget about the dwell angle.
     
  6. mikedjames

    mikedjames Supporter

    The points need to be closed for long enough for the current in the coil to reach a maximum value so the energy stored reaches 100%. Beyond that point the coil just heats up and reduces the energy stored by increasing resistance with temperature.
    Dwell settings and coil design is really for good spark at high RPM.
    At low RPM the dwell angle represents too much time so modern systems feed current into the primary for a more or less fixed time before firing each plug. Which means you need adjust dwell angle with rpm. Hard to do with a crude distributor, easier with Accuspark or later Pertronix.

    The main problem with setting dwell too high is that the points are only just opening on the rounded nose of the cam when the current collapses and fires the plug. If you reduce the dwell the points will open on the steeper slope of the cam at a better defined time. This will be less affected by any side to side slop in the distributor shaft.
    I would suggest reducing the dwell as the timing will become more precise and drift much slower.
    But a misfire at speed is more likely some other electrical problem - coil flashover due to dirt or damage, distributor cap too far round relative to rotor arm so it is cross firing at high advance and rpm.. (oh that is dwell angle related as it fires at the end of a too long dwell time)
     
  7. But I have a shiny meter I want to use - makes me feel all big and important!!

    I set the gap with a feeler, but note that it can give a range of dwell angles for what seems to be the same gap, which makes me think dwell is better measure than gap.

    Might be over thinking it.

    I had one, but due to a moment of madness with red and black leads it is no longer with us. Having a huff that it's not polarity protected as standard so using points again for now!!

    Thanks for the reply. Speed is fine, it's load that causes the misfire. It's like a little cough, then off it goes again. Not during acceleration particularly. Big hills or too high a gear cause it.

    Was checking timing and points first, next is valve gaps and fuel.

    Thanks all for replies, appreciated as always.
     
  8. Just set it to the right gap and forget about it. A lot of the time (at low revs) the dwell is far greater than it needs to be. It's a completely agricultural system, and unless the points have closed right up, will make absolutely beggar-all difference to how your engine runs.
     
    Bhubesi likes this.
  9. But my shiny meter?!?

    Cheers, will set gap and leave well alone!!
     
  10. Stick it on eBay ;). As Mike says above, brainier ignitions vary the dwell angle according to RPM, so the coil doesn't get hot. Long dwell is mostly wasted energy. The coil probably saturates anyway.
     
  11. Set the dwell to 50 deg. Setting the dwell averages out any wear in the cam lobes.
    Point ignition because it is not variable has to use a compromise dwell setting that is relevant to the rpm that the engine will mostly work at. Electronic ignitions can have a variable dwell best suited to the engine speed 10 deg at idle rising to 50-60 deg at mid rpm and above.

    [​IMG]
     
  12. mikedjames

    mikedjames Supporter

    A little cough can be a symptom of a loose wire brought on by engine twisting and vibrating.

    The other day I felt a slight wobble in the engine then engine braked for a roundabout on the A43. Coming out of the roundabout the engine misfired every time I took my foot off and changed up a gear. Still went at 65mph once it settled.
    Two or three roundabouts later it cleared up. When I got to Techenders I tightened up all the female spade connectors by disconnecting them and giving a squeeze with pliers.
    No further sign of a problem and even on the same roundabouts on the A43 driving foot hard down last weekend the problem has gone.
     
    orangefeeling and Valveandy like this.
  13. Good point, I bought a bag of spade connectors off eBay and they are poor - been slowly replacing them, will check none are lingering on key wires.

    Cheers.
     
  14. Well the misfire got worse, now popping and crackling all over the shop.

    Checking timing and dwell with meter (yes I know, just use a feeler gauge, but it's a gadget!) it was hopping and skipping wildly. Problem traced back to the new points, which having done around 200 miles no longer meet each time they close. Old points back on seems better, but neighbours have asked if I really need to be setting the timing at 3,000+ rpm as they can't hear the telly, so that's it for tonight!

    Why oh why oh why do I spend more time replacing the new bits than the old bits? We can produce driverless cars and space probes, but not it appears a set of points. Grrrrrr!
     
  15. Points are so rarely used these days, there's little incentive for folk to make them properly. Same with condensers.
     
    orangefeeling and 77 Westy like this.
  16. I know, I had abandoned as well until I couldn't tell the difference between black and red and fried the Electronic ignition.

    Will save the pennies and get another one I think, will be cheaper in the long run than switching points every 200 miles....
     
  17. Going from what folk say, you'll be switching Accusparks every 200 miles ;)...
     
  18. Oh, and dissy rotors and caps. Who has 'em?
     
  19. I used to use a dwell meter to set my points, and found it much more accurate, and that the van ran much better. Maybe it's just me and my jittery hands- but I'm not that old just yet. Another plus point is that you can plug your gauge in and write down what your dwell angle is. Sounds stupid- but if you set it with a feeler gauge, what's it set to? I always found the points would close up a bit when you tighten up the lockscrew, and are you holding the points slightly open? the spring isn't exactly strong. It's the same reason I use a CO meter for my carb- you can set it to a figure, and you're measuring the direct result rather than your input.

    Though to be fair, last few years I found every set of points I bought closed up after a few months. Went to Accuspark in the end- £40 well spent.
     

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