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The Little A-Cs - Chapter 9

This book was written exclusively for Yesterday's Tractors Magazine. It is not published in any physical form but only available on this site. No part of this text may be used in any form other than as provided electronically from www.yesterdaystractors.com without express written consent of Yesterday's Tractors. Copyright 1996-1998.

View the table of contents.

9. Tips, Tricks and Maintenance

I wont bother to duplicate the wealth of information that is needed for basic internal combustion engine, transmission and drive train of tractors. Instead, this section is limited to the specifics problems and requirements that I have encountered on these particular models and the items that for some reason are not covered in the manuals.


Most information pertaining to maintenance and repair procedures is covered in the manuals available for the individual models though unfortunately you must locate at least two manuals to get the whole story.  There are other texts that zero in on specifics of components that are extremely valuable and these should be included also. The other category of reference material includes those books and manual that while not necessary are important to those who have become tractor fanatics like myself.  While others are curled up in front of the fire with a good novels, we fanatics are curled up in front of the shop stove with the parts breakout manual and serial number reference books.

The basics are the AC Dealers Service Manual and the AC Operators Manual. If you have an IB, this will mean settling for a B Operators manual. Fortunately everything applies. The operators manual covers items not covered in the service manual and is necessary. The AC Dealer Service manual is sold as a 3 section manual covering the G, B and C, and CA in individual sections. Reprint dealers frequently reprint these sections as individual manuals which is convenient if the other 2 are irrelevent to you. The B anc C Service manual adequately covers the IB. An additional manual that is required is the Intertec Shop Service Collection that covers all ACs of that time period. AC was somewhat brief in describing certain procedures and the Intertec (also called I&T) Manual fills in the gaps quite nicely. A third must-have book is a general reference that will provide even more background. Though I cannot recommend a specific book, the Motors and Chiltons references of the time period are extremely valuable in helping to understand theory and procedures for engines built in the 40s and 50s. This type of book can be skipped if you have a background in engines and don't need the basics.

A book that people frequently leave out of their library is the parts manual. To a degree this can help in identifying parts for purchase but more importantly it provides breakout of assemblies that can really aid in reassembly or just knowing how to get something apart.

The books that zero in on specifics such as "How to restore your Magneto" by Niel Yerigan (Published by Motorbooks) and "How to restore your Farm Tractor" by Robert Pripps (Published by Motorbooks) can go a long way to building your confidence prior to starting a project.

Maintenance Problems

When working on these and other tractors, many procedures have hidden pitfalls. I cannot pretend to cover all the factors related to general tractor maintenance but can provide a few items I have found that pertain only to this series. In some cases, performing your work can lead to a damaged part while other cases could present a hazard to you. Before working on your machine, thoughly review the AC Operator's manual, Service manual, and the Intertec (I&T) manual for tips on proper maintenance. Here are a few items that are not covered or are not evident.

Rear Wheel Removal - The pivot point for the front axle allows the front of the tractor to radically tilt. If the rear wheels are removed without thorough shoring of the final drives and wedging the front axle (to block pivoting action), you may drop the entire tractor on the floor. Obviously if you are underneath this can be a deadly problem. The problem becomes more severe when you are also removing the final drives. In this case you must carefully block then entire frame and even then when the first final comes off, the instability due to unbalanced weight can bring the tractor down.

Final Drives - Don't presume that you can remove a final drive casing with out a hoist of some sort. The are deceptively heavy. Once you begin removal, it must be pulled out as straight as possible to avoid damage to the axle, seals, bearings, and retainer.

Brakes - When you remove the finals or just pull out the brake linings for replacement don't forget that there is likely 50 years of asbestos dust lurking in the case. Appropriate precautions for the handling of asbestos should be taken.

Splitting the Tractor - Splitting your tractor at either end of the torque tube presents the same pivot problems discussed above for the front end and has another pitfall in that the entire rear of the machine can pivot forward and backward on the tires. If the wheels and tires are removed, this problem becomes more pronounced. It is possible to box the rear with timbers or employ a seperate hoist to overcome this.

Flywheel Removal - When removing the flywheel bolts you will find that there is insufficient surface area to hold it up without the bolts in place (i.e. be ready for this heavy piece of metal to fall on your foot when you pull the bolts).

Starting Problems

Many people have a tendency to purchase new starters and batteries for their old tractor to try to make up for the fact that they turn over so slowly and can be difficult to start. Before spending the big money on these items, check over the battery connections. With the age of these machines usually comes rust and corrosion at the ground hookup and and starter. While not obvious, this can have a major impact on reducing amperage to the starter. Even worse is the practice of putting smaller 12 volt cables on the battery, this is common since premade cables are only available in the lighter gage wire. When these conditions are put together and combined with corrosion at the terminal, it is a wonder that it would work at all. If you excessive resistance at the ground, it will show up as excessive heat. Correcting this will help correct starting. The place to check this is at the steering column ground bolt where the battery box and wire attach.

The starter switch can be a source of problems. After completely removing the Negative cable (remember this is the hot one on a positive ground system)  from the tractor, this switch can be remove with 2 screws allowing you to examine the contact surfaces of both the switch and the starter. To work correctly the center rod must be completely insulated from the casing throughout its full in-and-out range. I have rebuilt these but I would not recommend it as it is too difficult to locate suitable parts.

It dies when it gets hot?

There are many reasons for this problem to occur but if it is not severely overheating and you are getting sufficient fuel to the engine, it is likely that you have a faulty condensor. Whether battery ignition or magneto, the condensor shows that it is failing by getting warm and ceasing to function (or total failure which comes under the heading of "no spark").

Erratic Running

I have had a C and B both run start easily and run for a few minutes only to begin faltering at any speed above fast idle. The first reaction for most people is to rebuild the carburator because this suggests insufficient fuel and a clogged float valve.  A far simpler problem may exist on this tank. The connection point for the sediment bowl on these machines is the lowest point in the tank and there is no screen and tube extending up into the tank on the original equipment valve. It is easy for the rust of the years to clog the opening under such conditions. Many other machines have at least a lip to prevent this problem and many aftermarket sediment bowls have an extended screen and tube that rises up an inch. Removal of the sediment bowl can quickly determine this and the fix is obvious.  Of course stopping the rust in the tank may be a bit more work (such as coating the tank) but at least you will be running for the time.

Carburator Float Valve Leaking?

You might wonder at something this basic appearing here. The only real issue with this tractor series is that the majority of carb float valve replacements that are contained in the common kits listed for Zenith carburators may not fit. This has been a common problem due the the later replacements using a different depth seat and valve to match. Don't throw the old one away until you try it. Also not to get your hopes up and leave you high and dry, it is likely the float or valve that is the problem if this problem exists.  The manuals cover the necessary adjustments on this carburator.

Timing your Magneto

The magneto is timed by locating top dead center, turning the cogs on the side that mates to the drive gear until the rotor lines up to the number 1 plug wire and then mounting to the engine. Dial this in by rotating the magneto counterclockwise to till the case touches the block. Now locate TDC again by taking the engine through its strokes. When #1 TDC compression stroke is reached again, slowly rotate the magneto until it clicks and tighten. This should be very close to perfectly timed. 

When you are crank starting your tractor to test your timing job, be especially careful and follow instructions provided in the AC Operators manual on the correct way to hold the crank. If the timing is off, it will backfire and do its best to break your arm, thumb or whatever else is in the way as the crank violently takes a counterclockwise swing.

Switching Back to Positive Ground

Returning the tractor to its original 6-volt positive ground is something that is required with nearly every original restoration.  The procedure is:

  • Remove Battery cables from the battery

  • Turn the battery around (if it is backwards in the battery box) such that the positive post is at the rear.

  • Open the instrument and wiring box and reverse the connections on the ammeter.

  • Connect the ground cable from the positive post to the rear battery box mounting bolt. This will bolt throught the steering post and should be clean of rust and paint.

  • Remove the fan belt from the generator pulley.

  • Using a jumper cable from the negative battery post, momentarily "motor" the generator by touching the outer post extending from the casing. Be careful not to touch ground in the process. Motoring repolarizes the generator, failure to do so may damage it.

  • Re-tension the fan belt and connect the main starter lead to the negative post of the battery.

Switching to 12 volt

The pros and cons of this switch are simple. The 6 volt should be kept intact if you are restoring for show. The system will function adequately. If you are using the tractor for work, the 12 volt system will make sure your machine is ready to work everytime you are (like during that heavy winter snowfall).  Besides, the conversion is reversable if you take care to retain the original wiring.

Switching the system to 12 volt requires the following components.

  • Alternator and regulator (preferrably internal regulator)

  • Light bulbs for original head and tail lights or complete replacement lights.

  • Generator or alternator mounting bracket for top mount.

  • A tube stock shim and long bolt to hold the shorter alternator bottom mount in place.

  • Battery

  • Ballast resistor for battery ignition model's 6 volt coil or 12 volt replacement coil.

Existing components that can be reused are:

  • Ammeter (leads will require reversal for the switch to negative ground)

  • Starter and Starter switch (should not be cranked excessively under 12 volt without giving cooling period)

  • Wiring (Wiring that is designed for 6 volt should be more than sufficient as the amperage at 12 volts is reduced by half).

Components that will not be reused are the Generator, Cut-out relay and light bulbs or lights. Additionally the light switch should be connected such that it only activates the lights meaning the 3rd position high-charge will be unused. Any new standard regulator will automatically control charging levels on an as-needed basis

If the alternator you select will not tension correctly with the existing top mount (that bolts to the frontmost manifold stud), you may find that slotting some bar stock on one end and drilling a single hole on the other end will produce a reasonable mount when attached to the leftmost water pump mounting bolt. If this method is used, a replacement bolt should be used that allows for the extra length.  If this bolt is removed to install a new mount, remember that the coolant can flow out from the water jacket as if this were a drain hole. You may want to drain the radiator prior to doing this. Also there is the possibility of inducing leaks from the water pump-to-block gasket.

When connecting your 12 volt system, you will no long use the third position of the light switch. This is the connection that uses the resistor. This position is for raising the charging rate with the lights off which will be superflous with the new regulator. As mentioned above, to allow reversal of the conversion, the wiring should not be altered. Retain the "3rd Brush" lead by simply insulating and tie wrapping it up by the alternator. Also use a small pigtail to convert from the old style connection to the new Alternator/Regulator lead connection.

Do not throw away your unused components.
Remember that while you may use this tractor as a working machine and have no interest in showing, there may come a time when it may become a "collector" machine either to you or a future owner.  The Generator, Cutout, unused wiring, lights or bulbs and belt tensioning bracket may be needed in the future for this purpose. Store them in a dry location and remember to include them with the tractor if you sell.

Governor Troubles

The governor controls the speed of the engine by monitoring the your preset throttle position (on the throttle quadrant) and adjusting the RPM up or down depending on conditions. A spring keeps the carburator set to the minimum RPM you select. Any engine load is sensed by the weights falling back toward their resting position which pushes the rod to increase RPM.  It is located on the upper right front of the engine block and is turned by the same gear that controls the magneto or distributor drive.

The governor consists of simple hinged weights that pressure the protruding carburator control rod based on centrifugal force. The rod should move freely to allow rapid RPM adjustment by the governor.  The system is oiled by a oil line that connects to a fitting on the head. The line must be kept clean to insure that the governor is well oiled. Additionally the bushing that allows the movement of the rod must be smooth and non-scored. Lastly the hinge points of the weights must not be sticky so as to alter the characteristics of the design. If you have difficulty moving the rod by hand or with the throttle arm, it is likely that the governor needs to be opened up, cleaned and possibly the bushing replaced. If you have trouble moving the rod, the weights won't be able to move it either.

Jerky  Hydraulics

The piston style hydraulic pump is reliable and will probably give sufficient service for as long as the tractor will exist if it has not been abused. If the pump seems to be jerky in raising the lift, it is likely that one of the pistons in unable to provide flow due to a bad valve. A bad valve simply means it is allowing 2 way flow when it should be allowing only one way flow. The supply side valves consist of a spring, ball, and seat. The I&T manual provides a good description of removal. What to look for is foreign objects, gunk, a broken spring or spring that has lost its tension, or a ball and seat that is out-of round. A simple method of determining which valve is disfunctional is to remove the pump, set the intake pipe in a small can of fluid and vigorously pump the piston by hand. You will get flow from a good valve while one that is  not closing properly will fail to pump any oil and would be the one you would want to remove.

If the implement raises correctly but tends to fall back on its own, check the return valves as the balls are likely not returning to their seat due to identical problems as described above. On the B and C, this can also be caused by overadjustment of the screw on the actuator rod. On the CA, there are several adjustments that can cause incorrect operation of the fall rate and hold. The AC Owners manual has information concerning this.

Another possible problem causing jerky operation would be bad surfaces and seals in the ram. In this case you  should see excessive quantities of oil escaping from the chevrons (expensive little seals at the end of the ram tube).

Hydraulic Oil

A common problem arises when you get ready to fill the hydraulic oil and transmission case. The manuals provide outdated specifications and nomenclature for the oil used in this casing. Since the oil is shared for both the hydraulics and the transmission and differential it will have special properties of being designed to lubricate gears and bearings while being non-foaming and lighter than gear oil.  All Farm Cooperatives and Feed stores (that carry oil) will have a hydraulic oil that is designed for shared sumps. Go to this type of store and ask for it. I have found that most auto parts stores can get this type of oil but will be of little help when you ask for it.

Gaskets and Seals

Engine gaskets and seals are still off-the-shelf items for these machines and are readily available. Drive train gaskets are not. You will have to make many of the gaskets that are used throughout the system such as PTO cover, final drives, pinion castings, and hydraulic pump. The gasket material sold in bulk by auto parts stores is sufficient for these purposes but care must be taken when selecting the thicknesses for certain components. These are:

  • Outer Pinion axle Bearing Cover

  • Radiator support to Lower steering gear support

  • Differential to pinion casting

These are singled out because they are shimmed surfaces to adjust the play in these components. The differential and steering shims are important because they determine the contact patch of bevel gears. If you select thick gasket material, you alter the shimmed depth. During removal, retain a section of the OEM gasket and try to match this. You will likely find that these are very thin. Re-shimming involves considerable trial and error (and no one likes to tear something apart more than once).

Oil pump gaskets are also require critical tolerances. These gaskets should be paper thin. I have used thin manilla envelope stock successfully. High quality gasket sets such as those currently provided by Yesterday's Tractors provide these, but other sets we have sold from the most common distributors do not and they will have to be fabricated.

The final drive cover gaskets should be made from cork stock as these covers are frequently beat up from their low position and may not mate perfectly. 

All seals are still available from multiple manufacturers. Agco Allis can supply these as can any good bearing house as long as you have the AC part number or a replacement part number off the seal itself. The replacements will be of the neoprene variety rather than the original leather or felt style.

Prev Page  Table of Contents   Next Page
1. Introduction
2. What are they?
3. History in Brief
4. Competing Tractors
5. Appearance
6. Identifying Numbers
7. Similarities and Differences
8. Cosmetics: What did they really look like?
9. Tips, Tricks and Maintenance
10. Using the Little Allis'
11. Tune-up Data, Quantities, and Specifications

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