Systematic Breakdown Troubleshooting

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Systematic Breakdown Troubleshooting

Postby lazyuniondriver » Wed Sep 26, 2012 1:08 pm


It is ironic just last night I added to a thread about systematic troubleshooting and this morning I had a breakdown of my own requiring troubleshooting skills that turned a bad morning into a better morning in less than 10 minutes.

Being a firm believer in preventative maintenance, it really annoys me to have a breakdown as I spend a lot of time and money, (when I have both), to make sure breakdowns are avoided on everything I own to the best of my ability.

I'd rather work on the tractor when its warm and there is no snow on the ground or after the grass has been cut vs. standing outside in a blizzard wondering why it died or looking at 12 inches of grass wondering why it won't start.

Today I was bringing my plow cub up front for winter service. Its used for towing things around during the summer so it has been run recently.

I have noticed in the past a very occasional brief ignition cut out or complete miss every once in a while, nothing long enough to stall it, just a very brief skip every now and then... Stuff that a tune up and other basic maintenance procedures could never seem to rid the cub of, but it has been doing it for a while, maybe every third or forth use.

This morning it cut out, stalled and wouldn't re start. I thankfully was able to coast it down hill into my front garage for shelter from the rain that started just after it died.

I have a system I follow to systematic trouble shoot breakdowns. Fuel, Air, Compression, Spark or F. A. C. S. is what I teach people to remember to get them on the right track when trouble shooting a breakdown... Just like human life, Airway, Breathing, and Circulation. The A. B. C.'s of life, picked up years ago and never forgotten.

Fuel... I had about half a tank and the shut off was open, should have gas to the carb at least. At this point I was pretty satisfied the carb was not the issue as it shut off like it was turned off and not starved for fuel.

I moved on to the air. Choke was open, the lever wasn't slipped on the shaft, nothing should be prohibiting it from breathing and it was breathing well before it stopped.

Onto compression. The engine was running well and as I cranked it, it sounded the way you would expect a normal engine with compression to sound when cranked. Again, it was running well so for now I will move along to spark.

Spark. This has to be it. All my other systems at this point seem to be a go.

Removed a plug wire, no spark. Check for spark from the coil wire no spark. Checked to make sure the ignition switch was on, it was, wiggled it, still cranks with no spark. This is where a lot of people get off track (and I'm sure glad I didn't this morning) and take off the distributor cap and start messing with the points and rotor.

I next grabbed a test light to check both low voltage connections on the coil.

The terminal with the short wire to the distributor should blink the test light when the engine is cranked with the ignition on as the points open and close and the other terminal should light the test light with constant voltage from the ignition switch.

Since the distributor wire to the coil is easiest to reach I checked that first. Nothing, no light. Could be the points not operating properly? Checked the other terminal. Nothing here either. No power from the ignition switch. This is why the other coil terminal is dead, there has to be power from the ignition switch which there seems to be none.

Slipped some vacuum hose over all but the very tip of my ice pick style test light to prevent shorting things out behind the dash and found power to the ignition switch and power to the wire that runs to the coil when the switch is pulled out.

About have it solved now but why isn't the power getting to the coil?

I started un-taping the original wiring harness with the ignition, voltage regulator, and headlight wires. This cub has the original wiring harness which had been wrapped with electrical tape by the prev owner.

I proceeded to find something I had missed during my maintenance inspections.

Behind the rockshaft which also has a boomerang bolted to it, was a very short section of harness that had been rubbing the back of the rockshaft right at the edge of a metal harness retainer clip.

The ignition wire was the outer wire in the bundle so it took the beating and this morning took its last rub before being rubbed through.

Since the PO had wrapped the harness with electrical tape it made the chafed area dark and the rockshaft with larger boomerang hid it from plain sight. Had it been the headlight wire, not as much of a problem. But had it been a voltage regulator/headlight switch wire, this would have made for some interesting charging system problems.

Experienced mechanics probably won't have read down this far but I am targeting the guys who are still learning or want to improve their troubleshooting skills so if you're still with me good.

Please take 3 educational things away from this post.

First, signs of trouble seldom cure themselves. Something was making that tractor cut out all along and I knew it. I just didn't spend enough time looking for the culprit because the cub ran like a watch 99% of the time.

Second and most important. Be very systematic when you trouble shoot. In the case of a poor running engine, yes there can be several issues keeping it from running like a watch. But when it comes to a tractor stopping dead in its tracks, 99.9999% of the time there is only 1 thing that caused the break down.

As you can see, too many times a breakdown like I experienced this morning turns into a real bad experience because a troubleshooting system wasn't followed through. Getting ahead of things such as ripping into the distributor wouldn't have solved a thing but added a potential starting issue once the actual problem was detected.

It took less than 10 min to locate the open wire, crimp and heat shrink and wrap the repair and get back to what I was doing so I had time to type this!

The third thing to remember is always go back to the last thing you messed with in case of failure!

If you just treated the distributor to new points, codenser, cap and a rotor, it runs briefly and stops, even though you are 100% sure it sounded like it ran out of gas or the carb clogged up, it is almost 100% guaranteed the last thing you messed with caused the problem you have now, like the points slipped or the condenser wire grounded out.

If you start tampering with more than one system at a time or fail to completely follow through trouble shooting in a systematic manner, you are asking for a headache and will have a tractor on your hands that you will likely never get started without help.

Comments, suggestions?

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Re: Systematic Breakdown Troubleshooting

Postby brichter » Wed Sep 26, 2012 7:49 pm

I really appreciate posts like this. I think I tripled my IQ. Thanks, Driver.
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Re: Systematic Breakdown Troubleshooting

Postby Bill Hudson » Wed Sep 26, 2012 8:14 pm


Very well done. Thanks for upping my diagnostic knowledge.

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Re: Systematic Breakdown Troubleshooting

Postby Rudi » Wed Sep 26, 2012 8:21 pm

lazyuniondriver wrote:If you start tampering with more than one system at a time or fail to completely follow through trouble shooting in a systematic manner, you are asking for a headache and will have a tractor on your hands that you will likely never get started without help.

Excellent piece of advice. Sometimes we forget that and it can lead to a very long process of getting back to a running state. I learned a lot in this thread and I don't even have a Cub with a distributor system, mine are all magneto based.
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Re: Systematic Breakdown Troubleshooting

Postby beaconlight » Thu Sep 27, 2012 8:49 am

You give a very nice detailed explanation of how to trouble shoot. My 34 years of trouble shooting telephone equipment led to ways similar to yours. Just wish I could explain it as nice and clear as you did.

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Re: Systematic Breakdown Troubleshooting

Postby Buzzard Wing » Thu Sep 27, 2012 11:15 pm

Well said!

I had a long talk with an old friend (trains auto mechanics) on a drive a while back and for some reason a few of the 'problems' we discussed were all 'free' fixes. A couple cost $$ to 'fix' and were both 'wiring' or ground problems. Oxygen sensor (corroded connector) and a Ford tractor charging system (two generator rebuilds and a VR, turned out to be a crimped terminal on the VR). The check engine light on my car was a 'knock sensor' but I switched gas stations instead of buying one. Never saw the light again!

We are 'trained' to throw parts at a problem, when often it is something simple. Part of the problem is the way the world is today, things are not designed to be 'maintained' and people are just too distant from 'making it work'. Probably why I like Cubs so much!
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Re: Systematic Breakdown Troubleshooting

Postby lazyuniondriver » Fri Sep 28, 2012 12:32 am

Excellent piece of advice. Sometimes we forget that and it can lead to a very long process of getting back to a running state. and I don't even have a Cub with a distributor system, mine are all magneto based.

Thank you for the kind remarks and compliments gentlemen.

As I skim over the Farmall Cub postings, it is evident the vast majority of frequent posters posess a tremendous knowledge base of cub tractors and have a multitude of mechanical and fabrication skills.

For the benefit of the many people still continuing their education, let it be known, many mistakes were made and many tasks were accomplished by trail and error by everyone on the forum, even the most seasoned vet.

Be thankful for the internet and this forum... Lord knows how many cub front engine cases have been saved because word travels fast when someone breaks off the ears and is able to warn someone new to the forum about the danger of twisting on the wrong nut before they make the same mistake.

I learned about the second grease plug on the IH distributor base housing here on the forum. I found the one on the distributor myself and was shocked I missed the second one, I had to run outside and see if it was actually there! It was... Covered with grease and farm dust like Bondo but it was there!

The most frustrating thing about mechanical work I have encountered my entire life is a simple breakdown that went real bad, real fast when the owner jumped from here to there without using any method of troubleshooting, then brought the unit in along with a basket of parts.

The practice of swapping out parts, turning screws and knobs actually make things incredibly hard for service techs to troubleshoot once the owner gives up.

For me it was a challenge... for the owner, nothing but pure frustration, and a repair bill along with the list of unnecessary parts the owner previously purchased.

Some forum readers posess skills when used in the proper sequence will be more than adequate to solve and fix their problem.

I'm positive the telephone guy would have gotten to the bottom of my electrical feed problem just as fast as I did by being systematic at troubleshooting. He needn't be a carb guy, engine or transmission specialist to skillfully track down an open circuit due to his years of electrical and circuitry experience gained on the job.

But the same guy going in blind with no method to his madness could easily be tempted to first mess with the carb because he perceived a fuel starvation problem and never will find the electrical problem.

Systematic troubleshooting is mandatory and second nature to skilled technicians so it is double mandatory to people who may not be well versed in any one section of the repair manual.

As I previously mentioned, go back to the last thing you messed with if you have a problem. Limit that last thing to the ONLY thing you messed with prior to a function check.

Practice this: When doing a tune up, exchange only one component at a time before you start the unit to determine if in fact it does start and does run at least the same if not better than before you removed and replaced that part.

Change your plugs, start it. Change the plug wires, start it. Change the cap, start it. Move to the points... Check your work every step of the way to insure plugs are gapped properly, plug wires on the right plugs etc, etc, etc.

Avoid at all costs rebuilding a carburator and a complete tune up at the same time without starting the unit up between steps to verify the carb was done right or the tune was spot on.

Make a habit out of making things easier for yourself by limiting what can go wrong to just one thing... And go right back to that one thing if you experience failure.

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