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Big G

Timing and points gap

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Hey RollaGurus

So the Princess decided to take her 55 hardtop for a visit into Brisbane the other day to do whatever it is that teens do. Didnt miss a beat on the way in. Thats were the fun stops. She was following me home, as usual stop start traffic down the freeway. She pulls up beside me and says it is idling roughly.  So She stalls a couple of times at traffic lights when in suburbia.Her rage growing with every hiccup and cough. At this stage I'm thinking maybe I wont go home. So she gets home and it stalls dead. I tried to start it but it just wouldnt fire. So straight to the dizzy I go to find the points gap has shrunk considerably. So reset them and turn her over and she fires straight away. All good or so I think. Took her for a run around the block and she was pinging her head off under load. So checked the timing upon my return and it was about 25DBTDC. adjusted it back and she is back to her amicable self. The car... not the Princess. My question is why would the timing suddenly change just by adjusting the points gap to where they started from in the first place, I fail to see the relationship. The points , dizzy cap, rotor and leads are only a monthish old. Any ideas guys??? 

 

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Points gap has a huge effect on ignitiin timing. If you ever touch the points the ignition timung should be checked.

Big question is why did the points gap "shrink considerably"?

Long term i think you should convert to electronic distributor. By long term i mean right now.

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I understand that if the gap changes the timing will go to. But if I restored the points gap to what it was to start with shouldn't the timing go back to the same position it was in before the gap closed and she started to run roughly.

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I had a similar issue. I don't know if it was old age of the points or what. But when the car got warm the metal of the points expanded and the points gap closed (this is a guess). I managed to get it to a mates and recapped them and it was fine. 

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The points are not that old and really havent travelled that far the princess only travels 20 minutes each way to work each day. The adjustment screw was well hard in position so i don't think it closed coz of that. Maybe the rubbing block has worn down coz they don't make anything like they used to. But i am still baffled about the timing going haywire after i reset the points.

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I can't explain why it changed, but the best way to set points is with a dwell meter.

That way it doesn't matter what the surface of the points is like, because once they are used the surfaces are not paralell or flat anymore.

Grease on the rubbing block? I'm sure you did..

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Modern points don't come with the little sachet of grease like in the good old days. But i found some from the 80s in the bottom of my toolbox. It was a vintage year. I used to have a dwell meter but it seems to have vanished over the years of me being out of the car scene. She is running fine now. I was just trying to get my head around the whole incedent.

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this is my terrible attempt to illustrate how points wear causes a change in timing.
IN my diagram, u see the distance from lobe to the pivot point of the points, (and therfore the distance away from perpendicular to the actual rubbing block) changes as the points are allowed to wear away.
U stick new points on after removing old points, without setting the timing, its likely to not start.

points wear.png

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Nice-  i've amended it slightly to show how a big points gap (new points) opens the points earlier from their closed position in the middle of the flat part of the shaft 'cam'.

The worn points have to wait longer before the lobe pushes them open, the rotor has turned further, so the spark occurs a few degrees later. They also don't open as far and close sooner, and that upsets the coil charging time.

points.jpg

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Also remember correctly adjusted points are supposed to last for ages, as long as spark plugs, if not longer. 20,000kms etc. They are not supposed to be temperamental or constantly need fiddling with. In the 4years i had my 4kc I think i replaced the points once, I checked the adjustment a few times but they were never very far out of spec. I was even too poor back then so I cleaned up the contacts on a set of points i had and put them back in.....

 

 

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OK so now I can see the relationship between the points gap and the timing now that you have added a worn rubbing block into the equation. So if I had replaced the existing points with no wear on the rubbing block then the timing should have been OK as it was originally set with a full rubbing block. The only unanswered question is why would the rubbing block suddenly wear down on a single trip. I know that the adjusting/fixing screw was well hard to undo so I know that it didnt slip. The Princess may have to consider an electronic dizzy set up in the future as suggested by Dave. I will see how it goes for now. 

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Grrr!  This new Rollaclub is pissing me off! I can't post links in my old Firefox!

OK, you're right, if the timing hasn't been touched you can replace old points with new ones and it all runs like new. The timing goes back to 10deg.

Now, if you buy an electronic dizzy you will have to change the springs on the advance weights under the plate that holds the modules on.

They are designed for a forkhoist, so they have a really slow advance curve with a low total advance, and the car runs but has no acceleration.

All about it is here-

 

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if u touch the points, (undo the screw even), the points themselves can move away from that perpendicular linear line i mentioned earlier, so by replacing the points u can cause the same thing.
they're all ever so slightly different. timing must be set every time.

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