Re: Engine Problem

Mon Jun 30, 2014 7:38 pm

Rick Spivey wrote:Let me take a stab at some of this, not being there in person, it is not easy to fully comprehend.

Okay, the magneto is set to a standard of 13 degrees advance. When the impulse coupling is engaged, it is RETARDING the magneto for hand cranking, and to cause the magneto to spin faster when producing the spark (hotter spark). Once the engine is running, the impulse coupling drops out, so you are back to 13 degrees advance. What I didn't understand in your earlier post is that you advanced the timing light to 13 degrees, but you didn't say that aligned the spark with the pointer. In fact, being below the pointer indicates retarded timing.

First I really appreciate you taking the time to explain the operation of the magneto in such great detail. Hopefully I am beginning to understand.

When using the timing light nothing that I have done gets me to the point where the light shows the notch on the pulley at or above the pointer. When I rotate the mag top away from the engine all that it will go the notch still is below the pointer when the light flashes. When I static time and then hand crank, I hear the click when the notch lines up right with the pointer and this is the part that I don't understand. If it lines up when hand cranking what happens to cause it to be below the pointer when the engine is running? If the governor is off by a tooth why doesn't this show up when static timing? The place that I probably got in trouble was thinking that if it I was able to static time it and get to the point where I heard the click at the moment the pointer and the notch lined up, the governor was installed correctly.

I think your governor is off a tooth, but I also think your distributor cap may be allowing the spark to arc across all the wires. I don't believe your "norther lights" description to be normal. If you haven;t replaced the cap, give it a try. Or at leaf clean the inside and look for possible arcing. Also, retime your magneto to the governor, or governor to the engine. Lastly, make sure the rotor and pinion inside the magneto are timed correctly to one another, using the marks.]

I have a new distributor cap and I looked inside and see no evidence of arcing. When you say "Retime your magneto to the governor, or governor to the engine" I assume that you mean that I need to remove the governor and try to get it aligned in the correct tooth? I'll have a new gasket for this on Wed. and can try that then. I put a sealer on the existing one and probably won't be able to reuse it. Lesson learned. I have checked that the rotor and pinion marks are lined up but it can't hurt to check again. It wouldn't be unusual for me to make this kind of mistake. One additional piece of info-- the Pinion has a small amount of play when you turn it. By small I mean about 1/3 of a tooth. Don't know what impact this might have.

Again thanks for analyzing my problem in such detail and I am sure this will help lead me to a solution and when I resolve the problem maybe I'll understand what I fixed?


Re: Engine Problem

Mon Jun 30, 2014 9:34 pm

Maybe I don't have my head completely around this and will just muddy the water but I keep thinking; are you sure you don't have a two notch pulley? With the first one filled in with dirt, grease, paint, or what have you?

Or asked another way; Are you sure #1 cylinder is at TDC when the mark you are looking at is by the pointer?

I would scrape around on the pulley and be taking out #1 plug and shining a light down the hole to see where the piston is. (Then again I'm from Missouri and you have to Show Me!)

Re: Engine Problem

Mon Jun 30, 2014 11:12 pm

The pulley was cleaned along with the rest of the engine by the machine shop. I remember it being very clean when I painted it but I was not looking for the notch at that time. Maybe it got filled with paint and I don't see it now. I'll check again first thing tomorrow morning. That would explain a lot of what I am seeing.


Re: Engine Problem

Mon Jun 30, 2014 11:41 pm

I couldn't wait until morning so I just went out to the barn and checked. I did not see a second notch. The pulley seems smooth except for the one notch. I did not scrape off the paint but there is no sign of another notch. Tomorrow morning I'll scrape all of the way around the pulley just to be sure.


Re: Engine Problem

Tue Jul 01, 2014 5:18 am

To be a little more clear, with the seal out, you should be able to find small punch marks on the governor drive gear that line up with a similar mark on the idler gear that it mates to. I believe it is one mark on a tooth, and one mark each on the two teeth it goes between. Those gears are helical, so to end up at the right place, you have to start (on the opposite side) a bit further away. That is what makes it difficult to get timed correctly (engine timing). I found it easiest to try to paint or chalk the top of the teeth on the idler, so that I could start the governor in the right place. When you take the magneto out, you should be able to tell if your governor is off by the potion of the drive lugs. There is a photo on this forum that will help with that, but they are normally at 2:00 and 8:00 as viewed from the driver seat.

If I can find that picture in the time I have, I will post it; if not, maybe someone with more time this morning will do that.

If the rotor and pinion are off, that will not actually "retard" the timing, it will simply send a spark to the wrong tower, or send it nowhere, which will burn up a coil. So please double-check that so we can eliminate causes, but I don't think that is the root of your problem.However, to fully explore that issue, make sure that your plugs (numbered 1,2,3,4 from radiator to back) are connected correctly (1,3,4,2 in clockwise order on the distributor cap, and that number 1 is somewhere close to 12:00 or 1:00 in position.

Criswell wrote:Here is a picture showing the timing mark that is on the drive gear on the governor shaft. It is nothing more than a simple dot.


John *.?-!.* cub owner wrote:Note, if the governor is timed right, the drive slots will be in this position when any piston is at TDC.


Re: Engine Problem

Tue Jul 01, 2014 6:35 am

When I installed the governor I found the dots and used white chalk to mark the single tooth and I also "chalked" the top of each tooth on the gear that this tooth fits into. My problem was that I had the oil seal already installed and couldn't see the teeth at the actual point when they mated up. I am attaching a picture that shows the governor with No. 1 at TDC (notch aligned with pointer). Note in the picture that there is a line filed into the edge of the engine and it aligns with the grove that the magneto fits into. I assume that the previous owner (my dad) had put this mark in to show when it was installed properly. I'll recheck everything again and see if I have made a dumb mistake.

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Re: Engine Problem

Tue Jul 01, 2014 7:07 am

Water in the fuel will cause rough and weak engine performance too. The period from March through the end of June this year brought a good bit of temperature cycling beyond 25 degrees Fahrenheit in a day and a great amount of moisture and humidity, where I live. Even though I was pro-active to keeping my tractor fuel tanks full, some water condensed in the tanks and I had moisture condense inside the distributor caps too.

Water is heavier than fuel and, therefore, sinks to bottom of the tank where it quickly makes its way to the carburetor. Simptoms of water in the fuel is inconsistent engine will struggle then smooth-out repeatedly. If you a getting some smooth combustion with periods of roughness, water in the fuel may be a factor.

Moisture inside the distributor cap will corrode the contacts there. Corroded contacts will rob the spark plugs of voltage and current causing weak and/or inconsistent sparking. I use an electrical contact cleaner, along with a small wire brush on a Dremmel tool to remove corrosion then apply an electrical shield grease. Even with these measures, I get contact corrosion that has been a regular maintenance issue the past few months. I would recommend using a distributor cap that has brass contacts instead of the one with aluminum contacts...the aluminum goes to pot faster.

Re: Engine Problem

Tue Jul 01, 2014 8:39 am

Clownfish wrote:........ Tomorrow morning I'll scrape all of the way around the pulley just to be sure.
No need to scrape all the way around, if there's a second one it'll be less than an inch from the one you see.

Re: Engine Problem

Tue Jul 01, 2014 9:26 am

I don't find a second notch.

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Re: Engine Problem

Tue Jul 01, 2014 11:52 am

IIRC, the notch on a single-notch pulley is at TDC, and the impulse coupler retards timing by 13 degrees at cranking speed. That means that at idle and above, the tractor is firing at 13 degrees BTDC, and the pointer should not line up with the pointer when the tractor is running. Not sure if the notch should be "above" or "below" the pointer, but the simple fact of it not lining up when running is normal.

Re: Engine Problem

Tue Jul 01, 2014 1:56 pm


The problem is resolved. Raymond was kind enough to come over and look at my Cub. He said that it was running too well to be out of time as much as it was showing with my timing light. He believed that my digital timing light was not giving a correct reading. He he went back to the carb. In the end he replaced the main jet in the new Carb that I got from McDonald Carb with a jet that had a larger orifice and the Cub now runs great.

Bottom line is that the timing was good and it was a carb problem which is what almost everyone thought originally. The bad timing light side tracked me but by seeing the tractor first hand, Raymond was able identify the problem. Thanks to Raymond for giving up a day of his time and to everyone that provided input. This certainly was a positive learning experience for me and I am sure that I'll be back with more questions as I continue the restoration.


Re: Engine Problem

Tue Jul 01, 2014 2:59 pm

No problem Glenn, glad I was able to help! :D

For a synopsis of was happening, the Cub ran great at idle (around 500 RPMs) but would start to stumble when you increased the throttle unless you manipulated the choke lever (starving for fuel). We re-timed the Mag to TDC. The timing light flash would jump around a bit, found that the pinion gear in the Mag was worn, so that will be changed shortly.
After confirming that the timing had to be right on (other than the slight jumping from the worn pinion gear), and the valves were adjusted to specs, we turned to the Carb. We changed out the Viton needle and seat for a good metal one, readjusted the float, and changed the jet to one that had a larger opening.
After some fine tuning with the idle adjustment and the idle air/fuel mixture screw, she's running like a sewing machine. The Carb/idle settings will need additional tuning as the breather hose is added and the engine gets some hours on it, but all in all, things are good to go.

Re: Engine Problem

Tue Jul 01, 2014 4:06 pm

Nothing like being there to diagnose the issue. Thanks for your help Raymond! And Glenn learned some other valuable information in the meantime.

Re: Engine Problem

Wed Jul 02, 2014 12:19 am

Did you happen to notice the venturi size? I have a 1977 IH with a larger venturi and can't seem to find the correct collection of jets, nozzles etc to get this thing right--for now, it's a "bench warmer".

Re: Engine Problem

Wed Jul 02, 2014 8:19 am

The jet was made by a machinist, not IH, and it was different than any that I'd seen before. The main body of the jet was the same, but the orifice end had a rather large drilled opening, then closing down to a very, very tiny metering opening. I did not have any gauges with me to measure it, but I'd say just from looking at it was close to half the diameter of a normal metering jet orifice.
Luckily Glenn had two other jets on hand, a stock one and a stock one that had been drilled out a bit. We chose to go with the stock one first and that was left in after things run so well.