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Discussion Starter · #1 · (Edited)
After the fuel system was sorted out I had poured some E0 (Ethanol free) gasoline into the tank and attempted to start the engine for the first time. Predictably it did not start, it didn't even sneeze once. I bought the tractor in the no-run condition, so I didn't really expect it to start. The newer aftermarket CDI unit dangling on its harness and the old, weathered CDI unit in the dirty box with old parts were hinting of some kind of ignition problem. Pulled one of the high tension wires off its spark plug and connected it to my ignition tester. No spark, just as expected.
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At that point it had become obvious that the CDI was the likely culprit. The newer aftermarket unit installed by the previous owner's repair shop had no p/n on it and it was both wider and longer than the original unit. I swapped the new aftermarket unit for the old original one just for the peace of mind, and predictably the tractor had failed to start either. I would hazard a guess that when the tractor originally died, the repair shop had correctly identified the CDI as the likely culprit but incorrectly ordered the replacement CDI with AC excitation instead of the DC one. The engine with the wrong type CDI in it once again had failed to start. At which point the owner decided to pull the plug. The tractor had sat like this for a few years before finally making it to FB Marketplace just 40 minutes away from me. I had been on the lookout for a H4518 for over a year both on FB and CL so I hopped into my minivan and snagged it for a song.

The rest was easy. I cut a groove on the perimeter of the plastic case a couple of mm deep and carefully pried the box open with a 1"wide hard putty knife that I keep around for such occasions. Wire wheeled the rubberised conformal coating compound off the PCB, and lo and behold ... the problem that had turned this tractor into a lawn ornament stared me in the eye. Here it is, in all its glory, circled in blue.
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Since I was not in the least impressed by the sloppy quality of the original solder job of this PCB, I had gone through each and every solder joint with my digital pencil, fresh AgSn solder with a dab of quality industrial water soluble flux that I use in the lab.
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Coated the PCB with hot glue, reattached the previously cut off lid and let the CDI sit in the vise overnight.
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The next morning I attached the newly repaired original CDI box to its harness and cranked the engine. This time around bright and solid sparks were cheerfully zapping inside the spark tester. Pulled the spark tester out, reattached the high tension wires to the plugs and reattempted to start the tractor. The engine took some cranking, but eventually started and rewarded me with kitten purr. Such a stark contrast with the loud air-cooled Kohlers and the Onan in my previous tractors.

... to be continued.
 

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Discussion Starter · #4 · (Edited)
Thanks, folks.
The reason I decided to retouch every solder joint was their poor initial quality. IMO this board should have not passed the QA control at the factory.

The vias on this board are of the same size. This is probably because the manufacturer had decided to save some money on tooling by not drilling different vias for different through-hole components. The unfortunate consequence of this is that all vias need to be as large as the largest pin found in all of the components in this circuit. This in turn leads to some pins sitting in their vias as a pencil in a cup. In order for this board to make it through the production floor w/o components falling out in the process (this looks to be a hand soldered board, not machine re-flown) the pins needed to be bent. That's OK if the pins are either cut short (~1mm above the foil) or they are bent alongside the tracks, not across them. From the looks of it, the person who was manually populating this board with components either did not understand this or did not care, so some of the pins were bent across the tracks, and in a few instances were almost bridging the gap between the adjacent tracks, potentially creating a short. Here's one example thereof: the original portion of the PCB and the same portion after I had trimmed the offending pin with an Exacto knife and re-flown the joint.
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The second issue with this board is the scarcity of solder on the joints. Granted, I am used to adhering to stringent MIL spec requirements in my day job, but this tractor also sees some harsh vibrations and temperature swings, especially if it sits all year long outside in a 4 season climatic zone. Even here, in the Mid-Atlantic, we often see +100°F in the summer and a few years ago we had a fortnight of -14°C in February if I recall it correctly. Vibration and thermal expansion/contraction cycles inevitably lead to solder joint fatigue and subsequent cracking. IMO there is simply not enough solder. Also, the original coating was rubber like substance which is OK for moisture insulation, but adding some hard clear varnish conformal coating for harsh environments IMO would've dramatically increased reliability of this board.
 

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'81 Gravely tractor, 50's 60's 70's 80's 90's Gravely tractors Various Honda Power equipment
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I think I need to send you the circuit board for the instrument panel in my truck...
It sounds like you have a GM truck, which have a failure rate of almost 100% with the circuit boards in the dash. Join the club. They are a little bit expensive and have to be reprogrammed at a dealership before they can be installed depending on what year you have.
Good luck with it, I had mine replaced for the same problem.
 

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It sounds like you have a GM truck, which have a failure rate of almost 100% with the circuit boards in the dash. Join the club. They are a little bit expensive and have to be reprogrammed at a dealership before they can be installed depending on what year you have.
Good luck with it, I had mine replaced for the same problem.
No, mine doesn't have a bad circuit board, just needs the pins to the LED display resoldered, as one or more of them has an iffy connection (sometimes it works, sometimes it doesn't, when it doesn't, I can usually make it work by pressing on the IP). I just haven't made time to do it myself, but I'm not nearly as good at soldering as the O.P...
 

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'81 Gravely tractor, 50's 60's 70's 80's 90's Gravely tractors Various Honda Power equipment
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No, mine doesn't have a bad circuit board, just needs the pins to the LED display resoldered, as one or more of them has an iffy connection (sometimes it works, sometimes it doesn't, when it doesn't, I can usually make it work by pressing on the IP). I just haven't made time to do it myself, but I'm not nearly as good at soldering as the O.P...
That's what happened to mine, the LED went out for the gear indicator because of bad pin connectors plus a few other gauges started having problems.
We had it apart and found the bad pins and felt it was better to get a rebuilt dash assembly from GM.
They improved all of the pin connectors because of that problem.
 

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Discussion Starter · #9 · (Edited)
Next I decided to test the compression, so I let the engine warm up to the working temperature before shutting it off. Pulled the plugs out and discovered that they were only finger tight. This explained the long cranking time: the compression must have been low because of the loose plugs.

The other thing that surprised me was the plugs' brand and model. They were Champion RN9YC whereas the specs were calling for NGK BPR5ES-11. I don't care much for Champion plugs and feel that NGK are vastly superior. I like NGK so much that I install them in my Audis instead of the OE Bosch. The other thing that disturbed me was the one step colder heat range of those Champions. This explained lots of soot on their skirts. Why would anyone install colder plugs in a low revving, low compression, low power atmospheric tractor engine is beyond me. The only engine where I had ever installed colder plugs was in the car that I tracked at club events. That engine ran on a 3bar Motoren Technik Mayer brain and on a cold day was able to reach 25psi of boost and would ping on anything less than Sunoco 94 so colder plugs were justified. In this little Honda OTOH the colder plugs had only led to excessive Carbon deposits since they never reached the temperatures needed to burn them off.
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Screwed in my compression tester into the 1st cylinder, opened up the throttle wide and cranked the starter. The compression in that cylinder had climbed to 170psi which was the maximum for a new engine. Wow! Not bad for a 29 y/o tractor.

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However, the 2nd cylinder had only reached 90psi which was below the acceptable minimum.

Since there were no leaks of coolant or oil on the outside, both plugs had equal amount of Carbon deposits, there was no foam on the dipstick and the coolant had no traces of oil in it I had ruled out the blown gasket. This left only two plausible explanations: a hanging valve or a stuck ring. Since I knew that the tractor had been sitting motionless for a few years I decided to test the stuck ring hypothesis first. I pulled the plug out of the 2nd cylinder, squirted some Kroil into the combustion chamber and let it sit overnight. Came back the next day, reinstalled the plug, ran the engine up to the operating temperature and retested the compression. This time around the 2nd cylinder had reached 170psi as well.

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It was a lucky guess indeed. It appears that this tractor has had very few hours on the clock despite it being only #53 of the first year of production.

Installed a pair of new NGK BPR5ES-11 specified by the manual and torqued them to 25Nm. From that point forward, with the proper plugs and the compression at the maximum for a new engine, the tractor has been consistently starting from a quarter turn.
 

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Actually back when I had the 4514 it had the same NGK plugs but one had gone totally bad and it ran on only one cylinder. Did much the same for troubleshooting because the machine gave me no indication at all the previous run (purring like a kitten). So I too feared the worst. I am sure BTW the plugs I pulled were the ones it was born with. I tried to find the proper NGK ones everywhere. No dice. I looked up a Xreference chart and it Xed to the same Champions you saw. I too did a compoosh test (though I have an aversion to pulling plugs out of a warmed up aluminum head) so I did mine cold. 220 PSI in both jugs. Threw in the Champs and it was back to purring away
 

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Nice catch on that cold solder joint. Takes me back to the older days of home PCs..... I had a crappy gold star (should have been called brown star) monitor that would begin to fade after about 30 mins..... I told my brother who was a USAF simulator tech at the time - he said "well, you could hit every solder joint in the hope you find the cold one". A friend that worked in computer lab discharged the CRT, and I spent half a saturday touching every joint. Only added solder to a few, and lo and behold, it worked!

I had a 1983 yamaha xt 550 motorcycle with a bad CDI - same thing. I'd be driving it to work and it would just quit. Wait 10 minutes and it would start right up, and run for about 10 minutes.

Have not tried this trick on a CDI, I will next time.

C Monk
 

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Discussion Starter · #13 · (Edited)
I guess I'll just keep adding electrical stuff to this thread as it comes along.

The original battery terminals were old, badly oxidised and were intended for automotive style round battery terminals.
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Since nowadays tractor batteries with flat terminals with square holes are more prevalent and cheaper I decided to cut off the original terminals and replace them with the newer style.

Bought a set of pure Cu terminals (Dorman 85638, 6 AWG, for 3/8" stud) at a local autoparts store.

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The easiest way to connect them to wires would've been to fill them with solder bits and heat up with a MAP torch. Quickly discarded this idea because open flame would've inevitably covered the Cu terminals with black CuO that would've needed to be sanded off later, which seemed rather silly. The second reason was the likelihood of melting and burning the wire insulation. As much as I generally dislike crimping, the latter seemed to be a better option.

Since my crimper could handle only up to 10AWG, and since smashing terminals in a vise, or with a cold chisel or with a steel ball produced rather ugly results in the relevant DIY videos I decided to look for alternatives. Fortunately I already had a tool suitable for this job if used with some creative approach. It's a high end hydraulic flaring Mastercool tool that I had to buy in a pinch for a one-off job when I got stuck trying to free up a hard brake line frozen to the right rear caliper in my wife's car.

Anyway, I opened up this awesome tool, found a couple of suitable mandrel dies (methinks they were for GM fuel lines but don't quote me on this) flipped them 180° so that they were butting up against each other back to back and crimped the terminals. The result has exceeded all expectations.


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Discussion Starter · #14 · (Edited)
Shrunk some heat shrink tubing over the crimps, BLK - on the negative cable
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RED - on the positive cable
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inserted some 5/16"-18 carriage bolts whose shanks perfectly matched the square holes in the battery terminals and tightened them up.
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Discussion Starter · #15 ·
There was one more non-working electrical component in this tractor that I have fixed. It is not too important but perhaps it is also worth mentioning.

In the box with the old parts given to me I had found a broken buzzer whose housing was cracked open and only one wire was soldered to the board. The other wire was broken off at the solder joint. My guess, the wire broke, the buzzer stopped working, the owner tried to take the PCB out, broke the housing in the process and gave up.

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No problem, that's an easy fix. First of all I reverse-engineered the circuit just in case I would need to fix it later: the transistor might needed replacement if the previous owner had accidentally shorted it under power while trying to pry open the housing with a screwdriver.
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Desoldered the other wire, cut, stripped, pretinned and soldered both wires back to the PCB. Discarded the old stiff black OE protective tubing and fed the wires through a piece of TechFlex protector stocking that I use in the lab.
Cut a piece of plastic tube with the ID matching the OD of the broken buzzer housing, pressed one into another and filled the back of the PCB with hot glue to make it watertight.
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Plugged the buzzer in and got the parking brake ON warning working again.
 

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Discussion Starter · #17 ·
Thank you for the kind words, tracktortag and the other folks who gave me the thumbs up.

I hope I didn't bore you guys to death by my pedantic obsession with technical details. I have learnt lots of useful information from this forum over the years and would like to give something back in return.
 

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'81 Gravely tractor, 50's 60's 70's 80's 90's Gravely tractors Various Honda Power equipment
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People like the technical details, that is what helps many of them when they can actually see what the problems are with the pictures.
 

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Thank you for the kind words, tracktortag and the other folks who gave me the thumbs up.

I hope I didn't bore you guys to death by my pedantic obsession with technical details. I have learnt lots of useful information from this forum over the years and would like to give something back in return.
Are you in the electronics, or engineering field?
 
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