Dave's 1650 Project

[ClickClickBoom]

Originally Posted by cdlong

I had the same hard start after I rebuilt the 1450. was the timing. I finally used a timing light. Using the test light to set the timing was off. Now I have spit & spudder run on after the key is turned off. I'm getting the chevy points bracket and stock chevy points so I can adjust the gap while the engine is running.

the chevy points bracket was the best $25 I ever spent. Just takes a lot of frustration out of a tedious process.

Whomever designed the pry apart kohler points should be shot.

[CC1650Dave]

hmm, I don't recall reading about using a Chevy points bracket and all anywhere...looks like something I'll definitely be interested in trying.

[JayJay]

I've read sixty-four (64) pages of postings, many at their limit of space, and the tractor still isn't together? Talk about a tease!

You've certainly eliminated the possibility of faulty cam timing.

Seriously, if and when you do get back to it, I would decide on an ignition timing method and stick with it. It sounds like the there may be a problem with the partial throttle operation, but there are so many variables its hard to know where to start.

Of the two methods mentioned to set the initial (static) timing, I prefer Matt Gonitzke's method. I would be curious if a test lamp yielded a different "mark" than the Ohm meter. The other way to go is to set the points gap at 0.020" and use the timing light to dial it in. Of course, you could check behind Matt's method with a timing light too.

Perhaps a new points push rod will help the situation.

In any case, if you are able to get the motor running in a tractor at half to wide open throttle as before, I would run it the mandatory 30 minutes or so, retorque the head bolts, change the oil, and fire it up again and put it under load to "break it in" good for an hour or so, change the oil again and repeat for at least another good hour or three before changing the oil again. Then and only then would I attempt to access the engine's performance.

In a word, everyone may have been obsessing about the timing issue, i.e., "it's back firing, it is a timing issue, must fix it." I can certainly relate to your trepidation, with all your fine work and documentation, you deserved to have the engine fire right up and work fine & dandy from day one.

As a precaution, I would also recommend by-passing or replacing the key switch, because failures at the switch and at the grounds are the most mysterious and frustrating failures on any 12 VDC system.

Basically, I'm recommending letting the engine run, if it will, to eliminate mechanical causes of failure, leaving only electrical or fuel issues as the culprits.

Jeremiah

[cubfixer]

I agree with Jayjay - let it run for a couple of hours.

Also I think that we may need to discuss dwell angle in these engines. The dwell angle is adjusted by setting the points gap to a specific gap at maximum opening. A narrower gap gives more dwell and a wider gap gives less. Excessive dwell (points gap too small) means that the points close too soon after opening, cutting off the magnetic field collapse from the coil before it delivers all its energy to the plug. Too little dwell (points too wide) gives the magnetic flux insufficient time to build up to the maximum and delivers a weak spark to the plug.

Both conditions give a weak spark which gets even weaker as the engine RPM rises and produces misfiring at normal operating speeds. The dwell, as well as spark plug gap, do have an effect on ignition timing. The later the points open, the later the spark comes (timing is retarded). The earlier the points open the sooner the spark comes (timing is advanced). That is why timing is the last thing to be set in a tune-up.

I am thinking that we should set the points gap at the maximum opening to 0.020” as the manual calls for. Set the plug gap at 0.025” as the manual calls for. Your manual may be different, since I have a manual for a 125 and a 100.

I suspect that if you are getting a gap of 0.040”, then your dwell is way too short, and your coil is not putting out as hot spark as possible. To increase your dwell angle (and give you the hottest possible spark), set your points gap to 0.020” at maximum opening.

I know that a lot has been written about setting the timing on a Kohler engine, but please remember about dwell angle.

[JayJay]

Cubfixer: I had the same thoughts about the dwell angle, but as I was writing it up, it occurred to me that with a single cylinder engine, with a maximum 3,600 RPM, surely the coil has enough time to recover, compared to the same ignition system working effectively to 6,000 RPM on an eight cylinder automobile engine. I know that when the RPMs get too high on an eight cylinder, the points became a problem, so they went to dual-point distributors, but always with a single coil. I also remember from electronics that the change in voltage polarity for an inductor occurred instantaneously, but I agree, I think it takes some time to "build the field" but I can't remember the formula. I do remember that one of a capacitor's signal characteristics is the time it takes to charge, something like 1/5 the time remaining or something involving complex exponents (the formula was kind of tricky), but it discharges immediately, yielding a spark, unless a resistor of some kind is wired in parallel with the capacitor to allow it to discharge "quietly."

All of that being said, I'm still not really sure what the condenser (capacitor) adds to the ignition circuit except ensuring that there will be a good amount of voltage available across the points at a certain set period AFTER they open (the period being determined by the value of the capacitor/condenser). If the capacitor were not in the circuit, when the points open, the DC current path would be blocked until the points closed again --period, there would be no buildup of voltage if the plates of the capacitor weren't there to receive it. With the capacitor in the circuit, the voltage available in the coil builds up until it becomes great enough to clear the air gap at the points. The quick discharge of the coil's primary winding is replicated in the coil's secondary winding which discharges across the air gap at the plug, if I understand the circuit correctly. (I'm a little confused as to if the discharge [spark] at the points "triggers" the spark [discharge] at the plug; or if the action of the secondary circuit simply mimics or "echos" the action of the primary circuit; if the action of the secondary circuit mimics the primary, then the buildup of voltage in the primary while the capacitor [condenser] is replicated in the secondary and the discharge at the plug occurs for the same reason [voltage builds up enough to bridge the air gap] but is not necessarily caused by the spark at the points. The more I think about it, the more I think they are parallel systems, and the key component is the condenser/capacitor, because without it, the voltage/spark is not possible.) Consequently, if the air gap at the points is too large, the voltage in the capacitor is not enough to overcome it; if the air gap at the points is too small, the voltage does not build up enough to generate a spark at the plug.

And to support your point about the magnetic flux discharge, the spark must be the trigger somehow, because if the spark at the points does not take place, then there is no spark at the plug. Even though the spark at the plug can be affected independently of the points; the air gap at the plug can be too small, rendering a weak spark at the plug; or it can be too large, preventing a spark at the plug from occurring at all, or there can be deposits on the plug, cracked insulators, manufacturing defects, etc. preventing a spark at the plug in the secondary, while the primary is working fine. So, the voltage discharge (spark) at the points must be as important to the circuit as the voltage buildup in the condenser/capacitor. In other words, although the primary and secondary circuits function in parallel, they function somewhat independently, yet they are linked by the interaction of the fields in the primary and secondary coil windings.

Note to self: I need to go back and study this very simple circuit some more.

Considering all the analysis above, on the motors in question, the Kohler K Series, setting the points gap wider or narrower has a dual effect. Not only does it determine the relative size of the spark (within the limits of the capacitor/coil/plug setup), it also determines when it occurs in the cylinder's stroke cycle, within the limits of the cam/pushrod arrangement. If the coil, condenser, ignition voltage and grounds are all working effectively, the spark at the points is going to occur at a certain time after the points open (determined by the value of the capacitor), if the points have not opened up too far during the "charge period" of the condenser/capacitor.

Since CC1650Dave reports that he has to set the points' gap at 0.040" in order to break the points at the proper time in the cylinder's cycle, it may very well indicate that the push rod has worn considerably. That is, since the points' plate has to be pushed so far in to engage the push rod (because it is too short), it means that the push rod is much further down the cam lobe when the points open. However, given the electrical characteristics of the circuit, just because the points are gapped at 0.040", it doesn't mean that the spark will occur when the points are fully opened, in fact, it probably ensures that the spark will NOT occur when the points are fully opened. The spark is going to occur when the voltage in the capacitor builds up enough to bridge the air gap. If the system is functioning as designed, then spark will occur when the gap is widest; I doubt the spark could bridge the gap at 0.040", so the spark is probably occurring at some point (or points) BEFORE its widest gap; worse, the spark's timing may not be consistent from cycle-to-cycle --it is bridging the gap whenever it gets ready. The cam lobe's profile is probably not the same either, so the points are probably opening a little (or a lot) later than they would if they were being actuated by the upper portion of the lobe, since the push rod is probably much further down the "ramp" when the gap is at 0.040".

In other words, there is a mechanical component to the ignition system in a Kohler not found in an automobile ignition system. In an automotive system, the distributor is driven by a gear, and wear in the gear is usually not considered as a factor. The mechanical part of the system is the square (4 cylinder), hexagon (6 cylinder), or octagon (8 cylinder) cross-section of the distributor and the plastic portion of the movable point that rides on it. The dwell angle is that portion of the distributor's rotation in which the points are riding on the flat; while they open on the "points" of the square/hexagon/octagon. Mechanical wear occurs on the plastic portion of the movable points "rider" causing the dwell angle to increase and the points opening to decrease. The quality of the spark is affected, and so is it's timing, to a certain degree by the size of the point's gap. But the REAL timing is set by turning the distributor clockwise or counter-clockwise. (The distributor can also be set a tooth one way or the other on the cam's gear, but that's a story for another day.) The Kohler K series has no provision to move the actuating lobe of the cam; it is as if the distributor were locked down; the only means of changing the time when the spark occurs in the cylinder's cycle (i.e., the ignition timing) on a Kohler K series is to open or close the air gap of the points, which, in turn, may have an adverse and unintended effect on the quality of the spark itself (and I contend, its actual "running" timing is affected too, to a certain degree).

I'm going to agree with Roland Bedell who posted on this or another thread, that the air gap should be within a range of 0.015" to 0.025". If you check when the points open with Matt's method, and the air gap of the points is beyond this range, you need to replace the points push rod in order for the system to operate as designed --mechanically and electrically-- at least that is the conclusion I draw from all the discussion and my analysis given above.

In a word, the timing gets all screwed-up when the points push rod becomes excessively worn. I would bet money that if an engine were statically timed with Matt Gonitzke's method using a new push rod, it would be confirmed as within the range given by Roland Bedell with timing light; but if a worn push rod is used, the timing light would likely reveal a significant discrepancy when the air gap is out of range. In such cases, the discrepancy using Matt's method would be less than it would be if the manual's standard 0.020" gap were used. His own tutorial confirms this in a way, because his gap winds up at exactly 0.020" --it would be interesting to hear from others if there is a great deal of variance between point gaps on Kohlers when a new push rod is used.

Could it be that the value of Matt's method is to allow for variations in push rod lengths?

Well, I've got to stop posting on this topic, my head is beginning to hurt.

Edit: On second thought, Cubfixer, although I agree with you in the larger sense that dwell angle should be considered, I don't think that it is as much an issue for a Kohler K series, as it is for an automotive engine. In an automotive application, the dwell angle is important because it gives the coil time to recover and conversely ensures that the condenser has enough time to charge, as well as confirming the proper air gap at the points; with a Kohler K series, the dwell, I think, could vary considerably by most accounts, what is important is the spark's timing. The points opening / timing point could be converted to a dwell angle to confirm the air gap range given by Roland Bedell, and would be yet another data point to confirm that the system is operating properly. If you knew the condition of the push rod, then you could be fairly confident of the timing without having to worry about pointing a timing light through the peep hole.

[cubfixer]

Thinking about what you have said about worn pushrod, I am trying too visualize what would happen to the points. I think that a worn pushrod might not allow the points to open enough.

But would a worn cam lobe be a problem? I think that a worn cam lobe would not have as much dwell as a "normal" lobe, nor as much travel to open the points as wide.

The capacitor (condenser) is picked for the amount of charge that is allowed to build up in a given time. A Kohler cap should be different from an automobile condenser, due to the amount of discharges and charges per revolution of the crankshaft.

When the points are open, the capacitor is charged up by the battery circuit. When the points close, the capacitor is grounded through the coil, discharging the capacitor through the coil, exciting a magnetic field in the secondary windings which are stepped up (just like a transformer). When it hits a large enough voltage in the secondary windings, then it is able to leap across the spark plug gap to ground. Voila! Spark!

This is giving me a headache...

[JayJay]

Cubfixer: OK. I get what you're saying about the discharge at the points --in the primary circuit-- triggering a discharge in the secondary circuit at the plug. We're very close in our understanding of this circuit.

I think we agree that the secondary circuit IS triggered by the primary. But I think the discharge happens at the point the spark flies across the gap: think about it, the current has found a path to ground. The voltage in the primary, stored behind the capacitor, is discharged across air gap at the points; the field collapses, and the voltage in the secondary is discharged across the air gap at the plug. After the points close again, the steady current flow is re-established and the field in the primary can build again, inducing a voltage in the secondary. If the points don't close, the current doesn't flow and the inductor (primary winding) is unable to either build a field itself, or induce a field in the secondary. In other words, the "dwell" (points closed) is as important as the points opening (spark/ field discharge).

I know that the current has to flow to build the field, and I know that voltage needs to be present in order for the spark to take place; beyond these two facts, I'm still confused about the action of the primary winding and its interaction with secondary winding and the means by which the spark is triggered.

Concerning Dave's 1650, I think that a worn cam lobe would only exacerbate the timing problem. I still think that the static timing of the points' opening depends for its accuracy on the mechanical components of the system. The components include the cam-to-crank timing (the drive and driven gears must be aligned at the dot), the timing lobe of the cam must be in good shape (which sets the duration of the points' opening), and the points push rod must be of the proper length (again, affecting the duration of the points' opening). Certainly, there are some "tolerances" involved, and adjustment of the point gap can overcome some mis-alignment and wear of the components listed, but there are limits to the variances which the point gap adjustment can overcome, that's all I'm saying.

Based on the discussion so far, I don't think the engine is properly timed if the points gap is at 0.040" even if (perhaps especially if) the points begin to open when you see the "S" through the peep hole.

All I can figure is that Kohler is "promising" you that if the points open at the "S" then the spark will occur at the proper time in the piston's cycle. That "promise" can only be kept if points are opening at the proper rate. If the cam's profile is altered, by being too low on the lobe, either because the cam's lobe is worn or because the push rod is too short, then the opening will not "progress" as expected and the "promise" of a spark at the right time will be broken. It may not vary enough to have any appreciable effect, but I don't know that; I would expect that performance would be affected. I know that on an automobile, a couple of thousandths difference in point gap can mean the difference between a smooth running and a rough running engine, and I would expect the same would be true in a Kohler; again, I'm just not sure to what degree the performance would be affected. I suppose what saves us most of the time is that ignition timing probably isn't all that critical to the typical Kohler application, as long as the engine runs and pulls strong we're OK.

I think there are some pertinent documents on how the ignition system works in the Technical Section that I need to review . . .

Edit: OK, I'm back. Cubfixer, you're right, the points opening is the key event, not the spark --I'm wrong. However, the capacitor is also important. Without the points opening, there is no voltage induced in the secondary, and the points opening alone will not induce enough voltage in the secondary to "jump the gap" at the plug. The condenser function in the system is to sustain the inductive process in the secondary long enough to build up the voltage required to bridge the plug gap. Further, the voltage required at the plug varies with conditions in the combustion chamber. The capacitor (condenser) is actually charged by the primary coil and discharges through the primary coil until all the energy in the primary is dissipated. In short, the capacitor tries to KEEP a spark from occurring at the ignition points. If the points don't open up fast enough, there is a sputtering spark across the ignition points which interrupts and/or defeats the induced charging process in the secondary. The IH Electrical Manual, starting at p. 30 makes for very interesting reading: http://ccmanuals.info/pdf/IH_electrical.pdf

[CC1650Dave]

wow - great discussion guys. I gained a lot of insight reading this. I'll need to re-read before I get back into it, of course.

I may be able to find the time to try once again on the timing issue before the tractor goes into the storage unit.

[JayJay]

CC1650Dave: Good to hear from you. For me, the practical take-aways from the discussion are that for a properly functioning ignition system, you need:

Mechanically:
1. Cam and crank need to be properly aligned so that the "S" & "T" marks are valid and the spark is triggered at the proper point in the stroke cycle (usually not an issue, unless engine has been reassembled) .

2. Cam Lobe for the points needs to be free of wear and not grooved by the push rod so that the points open properly and don't "sputter-spark" delaying or preventing the buildup of voltage required in the secondary in order to deliver a spark at the plug (not usually an issue because the material of the push rod is softer than the material of the cam).

3. Push rod needs to be the proper length for the same reason.

Electrically:

1. Known good spark plug of proper heat range, properly gapped, if in doubt replace with new part properly gapped. I don't know what gap to recommend, some say that the manual calls for 0.025" and some say 0.035" I suspect there are differences between magneto fired systems and systems that use an external coil.

2. Good set of points, not pitted or corroded. If new, run some paper through them to remove any oil, or sand them lightly.

3. Known good Condenser (capacitor), if in doubt replace with "known good" or new, quality, part.

4. Proper "Ballasted" Coil with internal resistor to knock voltage down to 6 Volts for the primary. (The concern here is not burning out the points and/or overheating the coil and damaging it too.)

5. Full Battery voltage at the coil, which means that the ignition switch and wires to the coil, and to ground, need to be solid. If in doubt, run a wire directly from battery to positive side of the coil, and check the connection to ground at the condenser and points (and the battery).

Initial Timing Methods:
1. If all of the above are true, then before starting the engine, the points need to open when the "S" is visible through the peep hole so that the spark at the plugs is properly timed in relation to the piston's upward movement in the cylinder (BTDC).

2. As an alternate method to Step 1. above and in conjunction to Step 3. below, the points gap can be set to 0.020" with a feeler gauge (if the points are in excellent condition) or set with a dial indicator gauge if there is any doubt about their condition; and the engine should start.

6. As an optional final step, the running timing could be checked with a timing light.

If the required components are in good repair, and if a valid timing procedure is followed, I believe that the result will be a smooth-running, powerful engine.

For myself, I would want to check the timing for steady, clear pulses at Top No Load speed. Although I can't cite an authority, I suspect the engines are tuned to run best at Wide Open Throttle, since that is the recommended speed when any sort of load is placed on the engine. The fuel used will also affect when the spark is needed in the cylinder; so too, I suspect, will atmospheric conditions like barometric pressure and humidity, overall engine condition and the health of components like rings and valves.

From what I read, the secondary will deliver the spark when the conditions are "right" within the combustion chamber, if the required voltage is present in the secondary winding of the ignition. Which is to say, the plug doesn't always fire when the voltage reaches a certain point, say 20,000 Volts; 5,000 Volts may be sufficient. So the spark may be delivered to the cylinder when the push rod is riding at different points on the lobe and when the points are open to a different gap. Bottom Line: the timing of any particular spark in the cylinder is not entirely dependent upon the physical settings of the mechanical components in the primary circuit, nor should it be. Higher RPMs require higher voltages and a spark that arrives somewhat earlier in the combustion cycle. There are features of the various components (the resistor in the coil, the coil windings, and capacitor) as well as conditions in the combustion chamber (like higher pressure) that promote this. I discovered that ambient temperature is a huge factor: the cooler temperatures in the coil available at higher RPMs (the coil has less time to saturate between discharges) cause the internal resistor to lose its efficiency, which promotes higher current flow, and results in higher voltages within the primary and secondary windings, creating a stronger spark at the plug which arrives sooner. All of this mechanical and electrical interaction allows the coil to "keep up" with the increased RPMs; but the fact remains that there is neither an initial advance mechanism (like rotating a distributor), nor an "automatic" advance mechanism in the Kohler's ignition system (like centrifugal weights or vacuum diaphragms). I want to be sure the system can deliver its maximum power when I need it most, and ignition timing is a big part of that. The only components available for adjusting the ignition timing on a Kohler are the ignition point gap, and the air gap at the plug.

The best thing an average owner can do is to make sure that all the components are "up-to-snuff" and that the proper adjustments have been made.

As an aside: I'm not sure how one would dyno-test a tractor (--maybe hook it to a plow and drop it 6" into the soil?), but there should be some way to tell when you really have it dialed in. I remember when mechanics would set the timing "by the ping" --advance the spark to the point that you could hear the engine "ping" ("pink" if you're English) when under full throttle and decent RPMs, and then back it off a bit. This procedure assured that you had the spark "right on" despite manual instructions, EPA regulations, etc. (although it can't address such valve timing issues as harmonic balancer rotation throwing off the timing marks, wear in timing gears or timing chain stretch).

Anyway, I hope you get your 1650 together, from everything I've heard, the end result will be worth it --they're a beast of a machine with the largest single cylinder ever put in a Cub Cadet!

Good luck, and happy Cubbing.

Jeremiah

[cubfixer]

JayJay,

You've said it!! There is nothing I can add!

John