Difference Between Dwell Meter and Feeler Gauge For Point Gap

If I use my dwell meter set on 8 cylinders and set my dwell at 23.5 degrees should the physical point gap be what is called for in the FSM at .3mm to .4mm? If it is then I have something amiss because after setting my dwell at 23.5 to 24.0 degrees I end up with an actual point gap of .51mm to .53mm, or just slightly over .020". Just to verify what I was getting I have used two different dwell meters and rechecked my measurements three times. I would have thought that setting my dwell at the proper angle should have resulted in an actual point gap much closer to what is called for in the book, but the gap is much larger. Or should I just disregard the actual point gap and go by the dwell meter reading? Any thoughts or ideas would be appreciated and yes, I know I should go pointless, but I am old fashioned.
Rick H.

Analogue is good Rick, it'll always get you home. Faulty electronic pickups and your stuck in the middle of nowhere.
Regarding dwell gap, I never bother with feeler guages and always go with dwell. Too small dwell and your coils wont charge sufficiently, too large dwell and the surplus charge has to go someplace so arcs back through the points causing pitting.
Open points are open points regardless of gap. It makes no difference if they are open 0.3 or 3.0 as long as the dwell is correct and the points do open.
Slight differences in points manufacturers products such as heel height or hinge point will mean each manufacturers points will need a different gap to acheive the correct dwell.

If you put a wrench on the crank and turn it, you can estimate the actual degrees of dwell. That lets you know if you are in the correct ballpark. Based on your "23.5 degrees", I assume you are shooting for 188 degrees of crank dwell. So the wrench should basically make about 1/2 turn of the crank.

Like Warren said, as long as you have near the correct dwell, I wouldn't worry too much about the actual gap.

Are you using the Sun meter from this post:
www.kzrider.com/forum/forum-index/9-chit...-with-sun-test-meter

If so, I thought you would be using the 4-cyl mode and multiplying by 4.

Thanks for the replies gents! Here is what I did this morning to fill my desire for knowledge. I set each set of points to mechanical gap of .012" to .014" which should be right at the book specified .3mm to .4mm. This allowed me to dial back my timing plates so I wasn't at full right lock on the plates and gave me some adjustment room. When I checked my mechanical gap the dwell is 30 and 31 degrees, not the 23.5 to 24.0 recommended. Set the correct timing for both sets of points and went for a ride. Surprisingly the bike ran pretty good. Seems a bit snappier in all but low rpm situations. Could be my imagination but it doesn't seem as smooth as it was before when taking off. Since I have had this bike back together it has always had a rather noticeable vibration kick in at about 3,000 rpm which subsides a 3500 rpm. Today although the vibration is still noticeable, it is much less prevalent. I used to be able to feel it in my feet as well as the handlebars, but the vibration in my feet was gone. When I got back home I checked everything once again and it is all where I set it. Dwell on the points is 30 degrees on left side and 31 degrees on right. There was no popping, spitting, missing or hesitations on my test ride, just the low speed item I mentioned.

So I will leave things as they are for now and see how the bike runs over the course of a few days. I can always go back to the recommended dwell I had before, but time will bear this out. I should mention there are far fewer spark flashes noticed on the points with the gap set where it is now. And loudhvx to your question, no I was using my Mac Tools dwell meter and an Innova Pro timing light that I bought. The Innova timing light is the cats hinder for this work. Unfortunately, I just couldn't find anyone that would repair the Sun Tach and Dwell meter that I bought. I even had the retired president of Snap On Tools trying to locate someone that could repair it as they bought out Sun Equipment some years back, but he drew a blank too. I eventually sold the Sun meter to a guy that wanted it for parts for a Sun distributor machine. Another bright idea gone astray, but I really liked that Sun meter darn it!

Rick H.

Thanks Rick. Yeah that old equipment is very cool to look at.

We generally set new points to the .012 - .014 range with a feeler gauge, then set static timing with an analogue multimeter just to get the engine started. Once running, we fine-tune dwell to 23.5 ~ 24 deg., then set spark timing. Once set, dwell will gradually change as the rubbing block wears, affecting both dwell and timing concurrently. The next time we have ignition instruments connected to look at those specs, we only set dwell back to the original value; spark timing follows dwell and will return to the original value at the same time.

OP doesn't indicate if the points are new. When point contacts open countless times, the spark that condensers are meant to (mostly) mitigate will always cause material transfer from one contact to another. The spark is always present even if it's not large enough to be visible. Try watching points in a dark space & it can be observed. The material transfer causes a pit below the plane of the contact on one side, and a corresponding raised deformity above the plane of the other contact. The raised deformity can be many thousandths high, which will throw off a gap measurement when using a feeler gauge by the same amount as the height of the raised deformity. That's why points files were so ubiquitous in the day. The raised material can be filed off, and/or a dwell meter, unaffected by material transfer can be used to re-set dwell if the rubbing block has worn.

Have to agree with warren3200; points will most always get you home. Field lore from the day - points closed up? Sit down on the side of the road with a business card folded over as a gap gauge, set points, you're on your way.

Good Ridin'
slmjim & Z1BEBE

Thanks Slimjim+Z1BEBE, just for grins have you ever checked the actual gap on a set of points after you set them with a dwell meter just to see what the gap is in thousandths of an inch? Here's the odd thing I found, the gap after I set the points with a dwell meter is not what is spec'd in the book. It's much larger. Plus the gap is different from one set of points to another. The left side has a smaller physical gap. These were brand new OEM points and have about 1400 miles on them and are lubed on the cam. My simplistic brain tells me the gap should be close(er) to what is called for in the FSM when I set it with a dwell meter, but perhaps not and it is what it is. In other words should a reading on the dwell meter of 23.5 degrees equal a gap of .012" to .016"? Thanks for any comments.
Rick H.

Rick H. wrote: ... have you ever checked the actual gap on a set of points after you set them with a dwell meter just to see what the gap is in thousandths of an inch?
We have, and it's within or very, very close to spec. This is with OEM Kawasaki points on stock street motors. We've seen enough weird points behavior with aftermarket point sets that we just don't attempt to use them anymore.

Plus the gap is different from one set of points to another. The left side has a smaller physical gap. ...
Dunno about that one. Could be inaccurate manufacturing of aftermarket points? As a thought experiment, could the reason be if the points mount(s) are somehow offset closer/farther from the crank axis if it's an aftermarket points plate? Perhaps using a caliper or micrometer to measure from crank axis to the pivot of both points would be informative, and/or from crank axis to each stationary contact. Thinking through it a little more, it might be easier to measure from the same location of the point cam, either on the base circle or at the top of the lobe. Either way, both should be the same,

Rick H.

Dwell is the number of degrees of crank rotation the points are closed, feeding current to the coil primary windings. This current builds a magnetic field within the coil assembly itself.

When the points open, current flow to the primary windings is interrupted, causing the magnetic field to collapse through the secondary windings, which have many more turns of much finer wire than the primaries. The secondary winding is attached to the spark plug. The collapse of the field causes a very rapid rise of high voltage potential in the secondary winding, which results in the spark at the plug gap. Then the points close again, starting the process over. All this happens in a very tiny of a fraction of a second.

The current flow in the primary winding builds the magnetic field until magnetic field saturation is reached, after which continued current fl;ow from the points has no effect on field strength, and only serves to heat the primary needlessly. Once saturation is achieved, we really only care about when primary current flow stops, creating the spark.

Let's say as an example with mechanical points, dwell in crank degrees is 25 deg. In clock time at idle, 25 crank deg. is far longer that what's necessary to achieve primary saturation. Now lets look at dwell at 8,000 RPM. Crank degrees is still 25, but clock time is only a tiny fraction of what it was at idle. Is this long enough in time to achieve primary saturation? It would require a scope to answer that question. Hopefully the design engineers did their homework.

Dwell time as elapsed clock time usually isn't as critical on stock street motors as it is on highly-tuned, high compression motors that achieve much higher RPM. Electronic ignition modules can be programmed to extend current flow time to the primaries as crank speed increases, while still breaking current flow to the primary at the right time to make a spark.

On a points system, if point gap is too small, excessive arcing can occur resulting in rapid pitting of the contacts regardless if dwell in crank degrees is correct or not.

If we haven't lost you yet, all this is to say that if the gap isn't too small when dwell in crank degrees is correct, the gap being larger than spec on the other set is unlikely to be a problem, as long as dwell in degrees is also correct.

Good Ridin'
slmjim & Z1BEBE