Setting the points gap - how critical is it?

[Swell]

I'm setting up the ignition on my 1968 6hp Johnson Seahorse and just wondered how critical it is to get the points gap exactly right. It would appear that there are 2 methods:

1. setting the gap at maximum opening to 0.02"
2. using the timing tool to set the opening to occur at the right time

If set using method 2 that won't necessarily result in a gap of 0.02", so what's the best approach? Is it possible to use the second option without having to buy that special tool? Can the tool be home-made? Presumably the position of the key relative to the timing mark would be pretty critical.

I've just set it to 0.02" to coincide with the letter 'O' of the word TOP on the top edge of the driveshaft cam. I've played around with setting the points slightly wide and slightly narrow and it's hard to tell whether it has any significant impact on the performance of the ignition.

 

[F_R]

Re: Setting the points gap - how critical is it?

Well, it does make a difference. Just how much, depends on how far off you have it. And if the two cylinders' timing are not equal, you will get a poor idle.

I'm kind of opinionated, since I make those timing fixture tools. But you are correct, setting the points with the tool often results in them not being .020". In that case, the tool is correct, .020" is only "close".

OK, somebody is bound to come along and tell you that the timing mark on the flywheel will do the same thing as the tool. Yes it will if you want to try to do it that way. Of course you have to have the flywheel off to atach a meter and adjust the points. Not very easy to do without disturbing it as you put the flywheel on and off to check and adjust.

 

[seahorse5]

Re: Setting the points gap - how critical is it?

The rule of thumb is .020" for used points and .022" for brand new ones to let them wear in. Actually on older motors, wear on the upper crankshaft bushing/bearing allows the crank to move back and forth making the points open even farther. Setting them closer - around .018" - sometimes makes a worn motor run better.

For super accurate settings, use a timing light under flywheel at the timer base notches that you use to line up the arms of the "timing tool". You should see a line on the flywheel show up somewhere between the timer base "notched area" for each cylinder.

 

[Silvertip]

Re: Setting the points gap - how critical is it?

Dwell (point gap) affects timing -- but variations in timing do not affect dwell. Fact of life with a points style ignition system. Point gap is adjusted on many motors to achieve proper timing. So yes -- proper point gap (dwell) is critical to optimum performance.

 

[Swell]

Re: Setting the points gap - how critical is it?

To be honest I didn't know you could use a timing light to check timing! The manual only describes using the timing tool. I assume you mean a strobe light as you would use on a car engine? Presumably it should be tested at a certain rpm - what is that and how can I make sure that's correct? Does this method also require adjustment of the cam which pushes the throttle valve open? I'm not totally clear about this method so some more info would be very much appreciated!

I hear what you're saying about the flywheel having to come off to make any necessary adjustment. It should be easy enough to at least check though.

The timing tool option does sound easier - is the timing tool easily available? How much do they cost?

Just to add - mine is an old engine, and there does seem to be an issue with an imbalance in the timing between cylinders which is basically what I'm trying to sort out. It will idle but only just, and it tends to stall. It sounds like it's firing intermittently on the lower cylinder at low revs. I know the carb is ok, the compression is a little low but within 10% between cylinders, and ALL ignition parts are new. So I'm wondering if there is play in the crankshaft. I may try closing up the points as suggested. Is it worth trying a different gap setting for each cylinder?

 

[F_R]

Re: Setting the points gap - how critical is it?

A strobe timing light will show when it is firing. Throttle setting makes no difference. The points are supposed to open when the timing fixture points between the two lines. I know it is hard to believe, but it doesn't matter where the throttle is. Just try it and prove it.

The carburetor cam is a different operation, called sync.

The flywheel magnets pass the first two legs of the coil and generate electricity in the coil primary. As the magnets continue on to pass the second and third leg, the generated voltage polarity reverses. At just the right instant of that reversal, the points break contact. And that is why the gap is important. Has nothing to do with dwell like a car engine.

As I mentioned, I make those timing fixtures. I don't want to get tossed off the forum for selling here, so if you are interested, send me a PM. I don't send out spam.

 

[Silvertip]

Re: Setting the points gap - how critical is it?

Ahhh but it has the same effect as dwell on a car in that it affects timing which is why you are adjusting the point gap on this particular engine in the first place. You just described how "at the right instant" is when the points open. THAT is how correct timing is achieved on these motors. In other words if timing is wrong, you adjust the point gap to compensate since there is no separate timing adjustment. Most folks would not feel one bit of difference in performance if only the feeler gauge was used vs using the timing gauge. In a race situation the timing gauge might prove beneficial or perhaps as a diagnostic tool where some engine wear has occured. This is just my opinion and opinions are like "butts" -- everybody has one.

 

[seahorse5]

Re: Setting the points gap - how critical is it?

Ahhh but it has the same effect as dwell on a car in that it affects timing which is why you are adjusting the point gap on this particular engine in the first place. You just described how "at the right instant" is when the points open. THAT is how correct timing is achieved on these motors. In other words if timing is wrong, you adjust the point gap to compensate since there is no separate timing adjustment. .

You are trying to compare a car igntion system that delivers a constant voltage to the points at all times. The outboards in question have a magneto system (like a lawnmower engine) and the point gap - or timing point - is when the magneto action of the flywheel magnets and ignition coil primary reach their peak voltage change which results in the highest coil output to the plugs. If the points open sooner or later in the cycle, the primary coil voltage will be less so less output is delivered to the plugs which can cause misfiring, fouling, hard starting, etc.

It has nothing to do with overall timing of the piston to the flywheel as that is constantly changing mechanically as you rotate the throttle to change rpm. There is no full advance timing spec or adjustment on many of the smaller motors due to the linkage design that takes care of that. Different years and models have other adjustments.

 

[jmendoza]

Re: Setting the points gap - how critical is it?

It's critical for smooth operation and maximum power, plus prolonged engine life.

It's not critical if you just want to see if the engine runs and test it, but I always use the timing tool followed by a check with the timing light. For the ultimate in low speed trolling, and high speed power, time it close as possible on a twin, or any multicylinder engine.

 

[Swell]

Re: Setting the points gap - how critical is it?

Thanks for all the info - I'm getting the picture now! I need to get my head around the fact that the magneto timing is separate from overall timing. I get the feeling that I need to get this right on my motor. I'm aiming for the 'one pull start' and at the moment it needs at least 3 pulls to get it going and it has a poor idle.

One more question - I have a feeling that the points are not held in place securely enough and tend to drift during use. Is the role of the eccentric screw to just enable fine adjustment or does it also have a role in fixing the points in place? Should it only be rotated in one direction so that it effectively blocks the points from closing up?

 

[F_R]

Re: Setting the points gap - how critical is it?

The breaker assembly is held down by only one screw. There is supposed to be a thin bow washer under the head of the screw. To adjust the points, go ahead and tighten the hold down screw, then use the eccentric to adjust the gap. Yes, in case you are wondering, the eccentric can move it even though it is clamped down.

The eccentric screw is just that---a screw. If you screw it all the way in, it will hit bottom and you can't turn it any more. So, turn it all the way in, then back it off a good half turn or so. Then you can turn it back and forth enough to do its job. Do Not back it off so far that it can rattle out of there. The eccentric screw does Not hold the points in place. They are held entirely by the hold-down screw.

If your points are closing up once adjusted, it generally is because the cam rubbing block is wearing. Unusual wear can be from lack of lubrication, a rough (rusty) cam, or a cracked cam. The cam is lubricated by the wick. Some wicks come pre-saturated with a lubricant, and additional oil should not be added. Other wicks come dry and include a "pill" of special lubricant to apply. In any case do not over-lube!!!!

BTW, three pulls is not unusual for a cold start. Even four or sometimes even five should be considered normal. It takes that many to draw the correct combustable ratio of air/fuel in through the crankcase to the cylinders. Once started, one-pull starting is common for the rest of the day. But don't bet the farm on it.

 

[kfa4303]

Re: Setting the points gap - how critical is it?

you may also want to consider new s'plug wires if you really want to get it to start on the first pull, although 3 really is not bad at all, but I'm OCD too and I like to make my motors start if I so much as look at them. With new copper core s'plug wires, virtually every component of your ignition system, from points to plugs will be fresh and new. you'd be amazed what a difference they can make. no good making good spark under the flywheel, then trying to send it down a crusty old wires. I've even seen folks go so far as to solder the terminals on the end to get even better connections. I believe some folks refer to it as "tinning" (soldering) them in place. Here's a link to some vids of a guy that rebuilt a little 10 hp evinrude from the ground up. He rebuilt the entire ignition system as described above and got his little motor to start in 1/2 a pull. Start around episode 18 of the link below. Episodes 16 and 17 are good too, but they're missing the sound :/ , but still worth a look perhaps. All of the episodes are fun and helpful. Hope it helps.

http://www.youtube.com/user/PistonPumper#p/u/21/QW5wEnUeEew

 

[jay_merrill]

Re: Setting the points gap - how critical is it?

I have several Johnson 6hp motors and a bunch of other 50s - 60s vintage OMC points motors. I don't file points and don't often find myself resetting old points. Generally, if I have pulled the flywheel for ignition related reasons, I will be replacing points and condensors. I generally set all new points at .020.

With the 6hp motors in particular, I find the setting to be pretty critical, but also pretty easy to get right. One trick is that the cam lobe marking on the motor can be misleading. The word "Top" is embossed on the cam, with a small triangle to the left of it. That triangle would have you believe that the peak of the lobe is immediately under it. I often find that this isn't true. I can usually see the highest point of the cam and it is usually to the right (counterclockwise in direction) of the "arrow." I use that position to set the points.

Another common problem with setting points, is the final tightening of the screw that holds the point plate down. First, don't overtighten it - you are screwing a stainless steel screw into an aluminum armature plate, so stripping the plate is easy to do. Second, when you tighten the screw, it tends to rotate the points plate, unless you hold another screwdriver in the offset screw that is used to move the points plate, during adjustment. Even then, its still easy to mess up your adjustment. For this reason, check and recheck your points adjustment, after tightening the plate.

Also, make sure that your feeler gauge blades are clean! This may seem like a "duh" comment, but I have seen quite a few crapped up and rusted feeler gauge sets, in people's tool boxes. Obviously, when you are dealing with differences measured in thousandths of inches, a bit of grime or exfoliated metal (rust), can make a big difference.

 

[An ancient mariner]

Re: Setting the points gap - how critical is it?

Hello Supreme Mariner!
I am interested in one of those timing fixtures.
My PM email is joelively@tds.net

Thanks in advance for your courtesy.
Joe Lively (An Ancient Mariner)

 

[leaguepark]

Re: Setting the points gap - how critical is it?

I would like a timing fixture. My parts manual for 6 hp Evinrude say 383602. Can't find it anywhere>

 

[AlTn]

Re: Setting the points gap - how critical is it?

ya'll need to pm F_R