Adjusting points gap WITHOUT changing timing

[79xs]

I'm familiar with both the points gapping and timing procedure, that's NOT what this thread is about.

I installed new points, set the gaps to 0.016, then set the timing on my bike about 3,000 miles ago. My points gap is now 0.011. The bike runs and starts great, but I'm going to re-gap them to 0.016. Checking with a light, my timing is dead on.

In the past, I have just loosened the screw (screws # 1 and 2 in the below diagram)securing the side of the points that gets adjusted, widened the gap, checked with feeler gauge, and tightened them back down. Then went riding. My timing didn't seem to change. I did NOT loosen the screws for, or move, the large backing plate or the half backing plate that set the timing.

As with pretty much every vehicle with points that I have owned, cars, Harleys, dirt bikes, etc, this is the procedure. The points gap can be set WITHOUT changing the timing.


I borrowed this diagram from a forum member... thanks!

I have recently read on this forum, in several places, that people say you can not adjust xs650 points gap without changing the timing though. Is this true, and I have just gotten lucky in the past?

I usually loosen screws #1 and 2 in the above diagram, set the gap to 0.016, then tighten them down. My timing does not seem to change. Is this just luck or is it how its supposed to work? (I know my timing dead on to begin with, and I check it after to confirm)

EDIT FOR CLARIFICATION: The stationary points (the ones that get adjusted to set gap) should NOT have anything to do with the timing. Timing is set based on when the moving points start to open, and the moving points are attached to the large backing plate. All the stationary points do is sit there, and contact the moving points when they close.... so conceptually I do not understand how adjusting the points gap on a properly timed engine will change the timing... and that is my question. Thanks.

 

[5twins]

You're not understanding how all the components work and relate to one another in a points system. Changing the points gap will change the timing slightly and here's why ..... There is a little points "cam" on the end of the advance rod. It has a high spot or lobe that contacts the rubbing block on each points set and pushes them open. To change the gap, you rotate the points set closer to or farther away from this spinning cam. That makes the lobe on the cam push the points open more or less. OK, now for the timing change - if you move the points closer so the gap increases, the lobe on the cam is also going to contact and start opening the points sooner, so your timing advances slightly. The opposite happens if you move the points away from the cam to make the gap smaller. The cam contacts the rubbing block a bit later and the timing retards slightly.

Now, how can your points have closed up and the timing not have changed? Your points could have pits on their mating surfaces now. The spark jumps between the pits. The actual gap is bigger than what your feeler gauge is telling you. That's why a dwell meter is the most accurate way to set used points, actually the only accurate way. You can't measure between the pits with a feeler gauge.

 

[79xs]

I understand about the points cam, and how the relation of the moving points to this cam changes the timing.

My points backing plates (both the full one and the half one) have a hole in them that the pivot shaft (the small shaft / peg that has a small "E" clip on top that holds on the moving point) for the moving point fits onto. If you make sure that this points pivot shaft stays in its hole in the backing plate, and use it as the pivot point for widening the points gap, then the points feeler shouldnt not move in relation to the points cam.

Maybe the backing plate with the pivot shaft hole and/or points that have the shaft sticking down are not stock items??

I see how if the whole points set was moved up to widen the gap then it would also move the points feller away from the points cam on the end of the advancing rod.

 

[5twins]

It doesn't matter that you're not moving the whole points set. You're still rotating the end of the rubbing block closer to or farther away from the cam. That's still going to cause the lobe on the cam to strike the rubbing block a little sooner or a little later. That will change the timing slightly. Notice I said slightly. It's not a huge change but it does change. The fact that you've never noticed it before may be because it is such a small change.

 

[79xs]

I see what you mean now. Even if the moving point rotates on its pivot shaft, the points follower / 'rubbing block' will move slightly in relation to the points cam.

I probably never noticed a change because I check my points often, and usually only move them 0.001-0.003 and replace them well before they are completely worn / burnt out...

I bet If was to adjust a really out of whack set I might see a change in timing.

Thanks for helping me wrap my head around this... its something I have been thinking about for a while.

 

[TwoManyXS1Bs]

If you check your timing BEFORE and AFTER setting the gaps, you'll see the change.

Many miles later, as the camchain stretches, you'll need to adjust the whole plate to compensate...

What are you using to lube the points cam?

 

[79xs]

Yeah, I know that when the cam chain stretches the timing needs to be re-set.

I usually soak the cotton pieces that rub on the points cam in motor oil, then squeeze most of it out. The cotton pieces usually stay damp with oil for ~3 months after soaking and squeezing out the excess.

My cam seal (behind the whole points case) is starting to leak. I get a few drops out of it on each ride now. Its nothing major, but I'm going to change this seal next time my points need adjusted so I'll be removing and re-setting everything then anyway. I'm thinking it will make it until the end of the riding season.