Gravely Form No. 16188P1 (11-74), a photocopy of which was given to me by the late Arnold Belkins, proprietor of Belkins Tractor in Georgetown, MA, and an enthusiastic and knowlegable Gravely fan. Written for just about the last production of Gravely-engined units, this document is largely applicable to earlier Model Ls. In a few places I have hyper-linked in notes regarding my own experience working on Gravelys. In general, the spelling and punctuation are unchanged from the original. The text is complete, but because my copy is not original, I haven't given priority to trying to scan the half-tone illustrations. At some point I may get around to adding scans of the line drawings, though.
Another page of mine offers more general information on Gravely 2-wheel walking tractors .
This manual is designed to give servicemen an indepth service procedure for the Convertible 7.6 tractor, and as an aid in diagnosis and repair.
This manual cannot take the place of proper routine maintenance, care and adjustments.
Gravely reserves the right to change specifications, or design at any time without notice or incurring obligation.
LH means Left Hand, RH means Right Hand. Directions are given from the operator's position; that is, as you would stand behind the tractor.
The importance of maintaining an air cleaner in proper condition cannot be over-emphasized! Dirt induced through improperly installed, improperly serviced or inadequate dry type elements, wears out more engines than does long hours of operation. Furthermore, operating with a clogged element causes a richer fuel mixture which can lead to formation of harmful sludge deposits. Always cover carburetor or air horn when air cleaner is removed for servicing.
Dry type air cleaner elements should be serviced only when required. Need for air cleaner service is evident by a sudden loss of power for no apparent reason.
To clean, remove element and tap lightly on a flat surface to remove loose dirt. Replace element if dirt does not drop off easily or if the element is damaged in any way. Also, replace element if there is any evidence of dirt on the inside surface of the element.
DO NOT wash dry elements in any liquid or attempt to blow dirt off with air hose as this will puncture the filter element.
Handle new element carefully - do not use if the gasket surfaces are bent, twisted or damaged in any way. Use only genuine Gravely elements. Use of other elements will void warranty. Not only must the proper element be used but it must be properly installed to prevent unfiltered air from entering the engine.
Install air cleaner assembly in this sequence on the air cleaner mounting bracket:
Be sure the element gasket surfaces fit tightly on the base and cover. The wing nut should be finger tight.
Note: The above describes the late side-mounted ring-type filter. Earlier Model Ls used a wet filter mounted ahead of the cylinder. I've found the latter a little less vulnerable to icing when blowing dry snow, but the intake air certainly is hotter in the summer.
Oil capacity is 5 U. S. pints. Use API classification SC or SD oils.
Summer - SAE 30 or SAE 10W-30
Winter - (32F or below) SAE 10W or SAE 10W-30
Maintain at oil level at full mark on dipstick. Be sure tractor is level when checking oil.
Change the oil after the initial eight hours of operation. Then change the oil every 40 hours under normal conditions, oftener under dusty conditons and/or periods of extended operation.
Drain oil by removing the oil drain plug, the bottom bolt on the L. H. axle housing.
Be sure oil drain washer is in place when replacing the bolt.
Under normal conditions, change the oil filter every 80 hours, however, under extremely dusty conditions and/or extended operation under heavy load, change the oil filter every 40 hours.
The oil filter must be installed by hand. Install the filter following the instructions printed on the filter.
Periodic oiling of all linkage pivot points aids operation.
The fuel supply system is made up of the threaded fuel inlet, the fuel valve seat, fuel valve needle, float and fuel bowl.
The fuel supply line is connected to the threaded inlet. The fuel travels through the fuel valve seat and passes around the fuel valve and into the fuel bowl. The level of fuel in the fuel chamber is regulated by the fload through its control of the fuel valve. The fuel valve does not open and close alternately, but assumes an opening, regulated by the float, sufficient to maintain a proper level in the fuel chamber equal to the demand of the engine according to its speed and load.
The inside bowl vent as illustrated by the passage originating in the air intake and continuaing through to the fuel bowl, is a method of venting the fuel bowl to maintain proper air fuel mixtures even though the air cleaner may become restricted. The balancing passage is frequently referred to as an "inside bowl vent".
The idle system consists of two idle discharge holes, idle air passage, idle adjusting needle, idle jet and fuel pick-up passage.
The fuel for idle is supplied through the main jet to a well directly below the main discharge jet. The pick-up passage is connected to the well by a restricted drilling at the bottom of this passage. The fuel travels through this channel to the idle jet calibration. The air for the idle mixture originates back of (or from behind) the main venturi. The position of the idle adjusting needle (normally one turn from its seat) in this passage controls the suction of the idle jet and thereby idle mixture. Turning the needle in closer to its seat results in a greater suction with a smaller amount of air and therefore a richer mixture. Turning the needle out away from its seat increases the amount of air and reduces the suction, and a leaner mixture is delivered. The fuel is atomised and mixed with the air in the passage leading to the discharge holes and enters the air stream at this point.
The high speed system controls the fuel mixture at part throttle speeds and a wide open throttle. This systems consists of a venturi, controlling the maximum volume of air admitted into the engine; the main jet, which regulates the flow of fuel from the float chamber to the main discharge jet; the well vent, which maintains uniform mixture ratio under changing suction and engine speeds; and a main discharge jet, which delivers the fuel into the air stream.
The main jet controls the fuel delivery during the part throttle range from about one-quarter to full throttle opening. A main jet adjustment permits a limited control of the main jet fuel. Ordinarily an adjustment of 1 1/2 turns from its seat will give proper mixture. To maintain a proper mixture ratio a small amount of air is admitted through the well vent into the discharge jet through the air bleed holes in the discharge jet at a point below the level of fuel in the metering well.
At high speeds the fuel flows from the fuel chamber through the main jet and into the main discharge jet where it is mixed with air admitted by the well vent, and the air-fuel mixture is then discharged into the air stream of the carburetor.
The choke system consists of a valve mounted on a shaft located in the air entrance and operated externally by a lever mounted on the shaft. The choke valve is used to restrict the air entering the carburetor. This increases the suction on the jets when starting the engine. The choke valve is of a "Semi_Automatic" type, having a poppet valve incorporated in its design, which is controlled by a spring.
The poppet valve opens automatically when the engine starts and admits air to avoid over-choking or flooding of the engine. The mixture required at starting is considerably richer than that needed to develop power at normal temperatures. As the engine fires and speed and suction are increased, the mixture ratio must be rapidly reduced. This change is accomplished through adjustment of the choke valve and the automatic opening of the poppet valve to admit more air when the engine fires.
In the Gravely Operator's Manual , it gives a different main jet adjustment for the carburetor, as follows:
My experience has been that the 2 3/4 turn adjustment works, and the 1 1/2 turn adjustment recommended in the Service Manual I'm transcribing here doesn't. I was recently told by an experienced Gravely mechanic that the Service Manual is wrong on this point, but I'm enough of a stickler that I've left the original text intact.
Spark Plug - Champion H-8 Gap - .025 inch
The only lubricating point in the magneto is the cam wiper felt. This felt, which lubricates the breaker arm at point of contact with the cam, should be lubricated with 2 - 3 drops of oil whenever it is necessary to replace the breaker contacts.
Incorrectly adjusted spark plug gaps cause magneto failure more frequently than any other condition.
Spark plugs should be inspected at frequent intervals, the size of the gap should be carefully checked and adjusted, and the plugs thoroughly cleaned.
All oil, grease and dirt should frequently be wiped off the magneto, lead wires and spark plug insulators. Keeping these parts clean and the spark plugs properly adjusted will improve the engine performance and at the same time will prolong the life of the magneto.
The magneto cover can be removed by loosening the four screws which hold it in place. When replacing the cover be sure that the cover gasket is in its proper place.
The breaker contacts should be adjusted to .015" when fully opened. To adjust the contacts, loosen the two clamp screws enough so that the contact plate can be moved.
Insert the end of a small screw driver in the adjusting slot and open or close the contacts by moving the plate until the opening is .015", measuring with a feeler gauge of that thickness, tighten the two clamp screws.
To replace the contacts remove the breaker, the spring clamp screw, the breaker arm lock and washter, and then lift the breaker arm from its pivot. Remove the spacing washer and the two breaker plate clamp screws. The breaker plate can then be removed.
If the contacts need replacing it is recommended that both the fixed contact and the breaker arm be replaced at the same time, using replacement breaker set.
After assembly the contacts should be adjusted as described above. Lacquer thinner is an ideal cleaner for this purpose.
To remove the condenser, first disconnect the condenser lead by removing the breaker arm spring screw, then remove the two condenser clamp screws, and the condenser clamp. When replacing the condenser make sure it is properly placed and that the clamp screws are securely tightened.
The coil and coil core must be removed from the magneto housing as a unit. Disconnect the primary wire from the breaker arm spring terminal by removing screw, take out the two coil core clamp screws, and remove the clamps. The coil and core can then be pulled from the housing. When replacing this group make sure that the bare primary wire is connected under the core clamp screw and that the insulated wire is connected to the breaker arm spring terminal.
The coil is held tight on the core by two wedges. It will be necessary to press against the coil core with considerable force to remove it from the coil. The coil should be supported in such a way that there is no danger of the primary of the coil being pushed out of the secondary.
When replacing the coil on the coil core, slide it on then press in the two coil wedges, one on each end, until they are flush with the primary of the coil.
My Gravely Operators Manual gives the spark plug as an Autolite TT-10, which a mail-order parts catalog identifies as the right one for a 6.6 HP engine (plug at a slant). The 7.6 HP engine (smaller plug, vertical) is listed in the catalog as needing a Champion H-10 - I haven't checked to see if this is a successor to the H-8.
Governor service is indicated when the governor is not functioning properly under load.
Two governor repair kits are available. If the components of these kits cannot repair the governor, it will be necessary to replace the governor.
Remove the governor from the tractor and proceed as follows:
Pack the internal component parts, especially the bearings, pins, shafts and all rotating and sliding parts, with lubricant. A total of 3 ounces of this lubricant is to be packet within the governor housing, in order to supply maintenance-free operation of the governor.
NOTE: The above apparently describes a permanently-lubed governor. I fear it is not identical to the Pierce unit used on earlier Gravelys, which had oil fill and level plugs, and periodic checks by the operator.
A clean tractor is much easier to work on than a dirty one. Also, dirt will be prevented from entering the tractor. After being repaired it will look better and operate cooler.
On extremely dirty tractors, it may be necessary to raise the fuel tank and fan housing assembly to clean the tractor thoroughly.
Before steam cleaning a tractor, remove the magneto. Use care in cleaning around the carburetor, do not direct the steam or water into the air cleaner. After cleaning, replace the air cleaner element.
Oil Pressure: At full throttle (2600 - 2800 RPM), the hand on the oil pressure gauge should be approximately 3/4 of the way over the normal range.
Low oil pressure is a possible indication of a serious problem. However, before teardown, check the following:
PROBLEM| REMEDY | |
| Low oil level | Check level, add oil as required |
| Low rpm | Adjust to 2600-2800 rpm at full throttle |
| Low relief valve setting | Adjust relief valve setting, with adequate pressure a heavy stream should still be visible through the oil filler neck. |
| Loss of pump suction due to air leak - usually evident by oil leak, | Check fittings for tightness. Torque pump cap bolts to 80 in. lbs. |
Compression: The results of a compression test can be used to check the condition of an engine. High compression readings, 70-80 psi, indicates the engine is in good operating condition.
POSSIBLE CAUSE | REMEDY | |
| A. Cylinder head gasket blown due to cylinder head warped or loose. | A. Remove head, check for flatness. Reinstall with new gasket and secure in proper sequence to specified torque value. |
| B. Piston rings worn - blowby occurring. | B. Recondition cylinder, see page 12. |
| C. Valves leaking. | C. Recondition cylinder, see page 12. |
Higher than normal compression can indicate that excessive carbon deposits have built up in the combustion chamber.
If tractor is getting hot, check for blockage of the cooling system. Air is blown around the cylinder and across the cylinder head by the fan. The fan housing and the cooling fins on the cylinder and cylinder head must be kept clean and unobstructed at all times.
NEVER OPERATE WITHOUT FAN OR FANBELT OR WITH ANY AIR DEFLECTOR OFF. The air deflector directs air flow around the cooling fins. Removal results in improper air circulation.
Improper timing can cause the tractor to run hot.
External surfaces (tractor as well as engine) must be maintained in a clean condition, free of any dirt or oil accumulation, which reduces cooling efficiency.
The fan shaft is supported by two bearings with a spacer between them. The bearing housing is packed with general purpose grease upon assembly.
Whenever a tractor is overhauled the bearing housing shoudl be repacked with grease. Be sure the spacer is in place between the bearings.
Check all surfaces to be sure that they are free of all gasket fragments and sealer materials. Surfaces must be free of all scratches and nicks.
Diameter of standard cylinder is 3.2545 - 3.2535. Measure the cylinder bore at two points 90 degrees apart at the top and bottom of the wear pattern to determine wear.
| Bore Diameter | Piston Size | Ring Size |
|---|---|---|
| 3.2545/3.2535 | Std. | Std. |
| 3.2585/3.2595 | .005 oversize | .005 oversize |
| 3.2635/3.2645 | .010 oversize | .010 oversize |
| 3.2685/3.2695 | .015 oversize | .015 oversize |
| 3.2735/3.2745 | .020 oversize | .020 oversize |
| 3.2785/3.2795 | .025 oversize | .025 oversize |
| 3.2835/3.2845 | .030 oversize | .030 oversize |
Cold - intake .015
exhaust .015
Remove cylinder from engine. See Cylinder Reconditioning steps 1-5.
Pistons and rings are available in standard, .005, .010, .015, .020, .025 and .030 oversize. Be sure to use the correct rings with the correct pistons. Also, be sure the pistons and rings are correct for the rebored cylinder.
Never reuse old rings
A new piston pin should be used with a new piston or rod. Always use new retainers even though you may be using the same piston and pin.
Piston is equipped with three rings.
The three-piece oil ring should have from .015 to .055 end gap for the two flat segments. The top chrome compression ring should have .012 to .020 end gap. Measure the end gap with a feeler gauge, with the ring removed from the piston and held in the cylinder bore.
Piston skirt clearance is .0039.005. Measure with a feeler gauge at right angles to the piston pin.
Carefully examine all parts for abnormal wear or damage. Check for damage also on the timing pinion shaft and the drive pinion shaft in the flywheels.
If a new rod is used, and crankpin must be used. If a new crankpin is used, a new rod must be used.
a. Crankpin diameter is 1.497 - 1.498"
b. Oil Pump
Oil pump bushing - .4373 - .4388
Master gear shaft - .4363 - .4368
Oil pump cap (18073P1) has no gaskets. Use of Loctite No. 68 plastic gasket is recommended. After application, the Loctite must cure for 12 hours. Do not run engine until after curing.
To insure proper engine operation, accurate timing of the camshafts is necessary.
Each camshaft gear will have one timing mark on it and the idle gear has three ring marks on it.
Line up the mark on each camshaft gear with a timing mark on the idle gear. The other mark should be centered between the camshafts.
| Trouble | Determination | Cause | Solution |
|---|---|---|---|
| Clutches engaged; drive wheels won't turn | Bound linkage, missing clevis pins. Bent clutch rods, bent or broken actuating shaft levers. | Repair linkage | |
| Engage PTO and Hi-Lo planetary, PTO does not turn | Broken drive pinion shaft | Replace parts as required | |
| Engage PTO and Hi-Lo planetary, PTO does not turn, pinion shaft could be tight indicating broken parts in planetary | Hi-Lo planetary - gears broken, broken or worn clutch | Replace parts as required | |
| Engage PTO and Hi-Lo planetary, PTO turns. Check differential action by raising wheels off ground, turning one wheel by hand and other wheel should turn freely in opposite direction | Forward-Reverse planetary - worn or broken clutches, broken gears | Replace parts as required | |
| Tight or no differential action. Free wheeling tractor or tractor wheels won't turn | Differential problems | Replace parts as required | |
| Transmission seems to be loading engine, even to stall point with Hi-Lo engaged. Ground speed about 3 times as fast as normal speed when Forward-Reverse is engaged | Frozen Hi-Lo planetary | Replace parts as required | |
| PTO will not shift in or out of gear or will not stay in gear | Binding of external linkage | Repair external linkage | |
| Broken or worn internal PTO shifting mechanism | Replace parts as required |
To gain access to the Forward-Reverse planetary, remove the attachment or attachment cover plate, PTO mechanism and the advance casting.
Rotate the actuating lever and release the planetary system. Carefully examine all parts for wear, excessive play or damage.
Before disassembling the planetary, check the fit of the gears on the pins. If gears appear too tight or too loose, disassemble the planetary and check the gears and pins for wear. (NOTE: Bolts have left hand threads). Assemble and time the planetary as follows:
When replacing this unit in the transmission, mesh the teeth of the actuating rod and clutch slide rods and slide the unit in position.
When internal high-low planetary problems are suspected it is necessary to remove the engine as described on page 11 .
Rotate the actuating lever to release the planetary system.
Carefully examine parts for damage, abnormal or excessive wear.
Before disassembling the planetary, check the fit of the gears on the pins. If gears appear too loose or too tight, disassemble the planetary and check the gears and pins for scoring or abnormal wear.
It is necessary to time the planetary upon reassembly. Align the gears so the punch mark on the gears form an equal-sided triangle around the sun gear in the rear pin plate. Install the orbit pins, pin spacer and bolts. Check assembly by placing inside internal gear. The assembly should spin freely.
Place the clutch cup on the pin plate orbit gear assembly. Install internal gear rear spacer and clutch rods.
Before assuming internal differential problems, carefully check the external linkage. Check for binding, interference and be sure all parts are intact.
Check adjustment of shifting springs. The upper spring length when in low range should be 2 1/2 inches. The lower spring length when in high range should be 2 1/2 inches.
Check the adjustment of the toggle spring. It should be compressed to 15/16 inch.
Check the stationary clutch bolt for sharing and tightness. Torque to 45 ft. lbs.
The shifting yoke, shifting clutch, stationary clutch and clutch housing can now be inspected without further teardown. Carefully check that the stationary clutch is in the proper position. Make sure that the sliding clitch slides freely on the shifting gear. If no discrepancies have been found at this point or if the failure is obviously a part of the differential assembly, disassemble further as follows:
Using a screwdriver or similar tool, check the differential assembly for play. Running clearance should be .008 - .012. Adjust by adding or removing an equal number of shims from each axle housing.
Adjust axles for .008 - .012 end play. Add or remove shims from behind bearing cap.
Carefully check the bearings and gears for wear or damage. Replace excessively worn or damaged parts. Reassemble differential back in tractor using an equal number of shims on each axle housing.
Torque axle bolts to 45 ft. lbs.
Refill the differential with 5 pints of oil of proper viscosity. Replace oil filter if damage was found in the transmission.
| Cylinder head bolts | 20 ft. lbs | Valves - intake | .015 |
| Spark Plug Gap | .025 | Valves - exhaust | .015 |
| Breaker point gap | .015 | Spreader bolt | 45 ft lb |
| Compression | 70 - 80 psi | Stationary Clutch Bolt | 45 ft lb |
| Engine RPM (Max) | 2600 - 2800 | Swiftamatic Bolts | 20 ft. lb |
| Oil Pump Cap Bolts | 80 in lb | Axle Housing Bolts | 45 ft lb |
| Cylinder Dia. (Std) | 3.2545 - 3.2535 | Point Resistance | 0 Ohm |
| Timing Pinion Shaft | 90 ft lb | Primary Coil Winding | .5 - 1 Ohm |
| Drive Pinion Shaft | 90 ft lb | Secondary Coil Winding | 5000 - 8000 Ohm |
| Forward-Reverse Planetary Spacer Bolt | 30 ft lb | Connecting Rod to Crank Pin Running Clearance | .002 to .003 |
| Pen Plate Quill Bolt | 80 in lb | Flywheel to Crank Pin interference fit | .001 to .003 |
| Axle Bearing Cap Bolt | 12 ft lb |
When internal PTO problems are suspected, remove the attachment or attachment cover plate and check the shifting mechanism
If difficulties are noted, remove the shipper shaft and shipper shaft guide assembly. Carefully check all parts for excessive wear and/or damage.
If nothing abnormal is found, remove the attachment dog and pinion shaft. Check for wear or damage and check pinion shaft for twisting.
Check the thrust bearing assembly in the advance casting for wear or damage.
Carefully reassemble parts in the following sequence. Be sure a gasket is used under the shipper shaft guide.
Shifting from OUT to IN
Shifting from IN to OUT
NOTE: Similar tightness can be reached with an 8" length handle wrench when used by an average man. This adjustment should realign the shifter arm to the correct position.
NOTE: On both of my Gravely L-8s, the bolts which secure the shipper assembly to the advance casting are run in from the top, into threaded holes in the advance casting. The left side bolt , on which the control arm pivots, has a habit of working loose in service. This can be helped by using a longer than normal bolt and a Nylock nut on the threads protruding on the inside of the advance casting. Lots of extra thread length will interfere with the pinion shaft and dog. I keep the extra length to a minimum, since you can only get about 1/8 turn from each application of the wrench in those tight quarters.
NOTE: Steps 2 through 4 under Removal above can be omitted, if instead you remove the spark plug and feed a length of lint-free rope into the cylinder to stop piston travel. The person who gave me this tip recommended cotton-sheathed clothesline over nylon or other plastic ropes.
Maintained by James VanBokkelen.