Cylinder And Piston

REMOVING (Figure 3-12)


See Figure 3-12, and proceed as follows: Clean crankcase around cylinder base to prevent dirt from falling into crankcase when lifting cylinders. Remove cylinder base stud nuts (1 ). Raise cylinder and piston just high enough to permit placing a rag over crankcase opening; this will prevent dirt and possibly pieces of broken ring from falling into crankcase. With piston at bottom of stroke, remove cylinder (2), discard cylinder base gasket (3). Using a piston ring expander (Figure 3-19) spring piston rings (4) outward until they clear grooves in piston (7) and lift off. Remove piston pin lock rings (5, 5A) from piston (7) groove. For 1976 and earlier models, use two sharp pointed instruments such as awls to remove ring. For 1977 and 1978 models, use Internal Lock Ring Pliers, Part No. 96215-49. Support piston and tap out piston pin (6) with a suitable drift.

Remove piston pin bushing (8) if necessary (see "CLEANING AND INSPECTION") using Piston Pin Bushing Tool, Part No. 95970-32A. Do not drive bushing out with a drift.

1. Cylinder base nut (4) 5A. Piston pin lock ring (2)

2. Cylinder

3. Cylinder base gasket 6.

4. Set piston rings 7.

5. Piston pin lock ring (2) 8. (early 1977 and earlier) 9.

(late 1977 and later)

Piston pin


Piston pin bushing Connecting rod


Place piston and cylinder in solvent or other carbon and gum dissolving agent until deposits are soft. Then thoroughly scrub piston and cylinder in solvent to remove deposits. Where carbon deposit is thick or hard, it is advisable to use a wire wheel to scrape carbon before cleaning. Use extreme care to avoid scraping into aluminum of pistons.

After parts are thoroughly washed, blow dry with compressed air. Force air through oil holes in cylinder. Clean piston ring grooves with a tool for cleaning ring grooves. Avoid scratching or damaging sides of ring grooves.

Examine piston pin to see that it is not loose in connecting rod, grooved, pitted or scored. If necessary, remove bushing as described in "DISASSEMBLING CYLINDER AND PISTON."

A piston pin, properly fitted, is a light hand press fit in piston and has .001 in. clearance in connecting rod upper bearing.

If difference in diameter of hole in piston pin bushing and diameter of piston pin exceeds a .002 in. fit, replace worn parts.

Replace piston pin lock ring with a new ring whenever it is removed from piston groove. If opposite side ring has not been removed and is undamaged, it is not necessary to disturb it.

Examine piston and cylinder for cracks, burrs, burned spots on piston dome, grooves and gouges.

On motorcycles using rod bearings with steel retainers (1976 and Earlier) check rods for end side shake (Figure 3-13). To make this check with accuracy, pistons should first be removed. When side shake (rod tip) at extreme upper end is 3/64 in. or more for front rod or 1 /64 in. or more for rear rod, lower bearing should be refitted.

On motorcycles using rod bearings with aluminum retainers (1977 and 1978) side shake cannot be used to determine bearing wear. Instead, carefully check rod for up-and-down movement. To make this check accurately, pistons should be removed first. When appreciable up-and-down movement is found, lower bearing should be refitted.

These two procedures require removing and disassembling engine crankcase. See "CRANKCASE".


Piston and cylinders must be measured to see if they are worn to the point where cylinders must be refinished and oversize pistons installed.

Inside and outside micrometers used for cylinder-piston fitting should be checked together to be sure they are adjusted to read exactly the same. By subtracting piston measurement from bore measurement, amount of piston-cylinder clearance is obtained.

Figure 3-12. Cylinder and Piston - Exploded View

Figure 3-13. Checking Connecting Rod for Crankpin Bearing Wear on Engines With Steel Bearing Retainers (1976 and Earlier)

Figure 3-14. Measuring Cylinder

Bore measurement of a used and worn cylinder should be taken in ring path, starting about 1/2 in. from the top 01 cylinder, measuring front to rear then side to side. Repeat procedure at the center and at the bottom of the ring travel (see Figure 3-14). This process will determine if cylinder is out-of-round or "egged" and will also show any cylinder taper.

Piston measurement should be taken at extreme bottom of skirt, measured front to rear, 90° from center line of piston pin (see Figure 3-15).

If cylinders are not scored and above measurements do not vary more than .002 in., it is not usual practice to refinish oversize. If the total piston clearance is more than .006 in., a new standard piston, or piston of the same oversize to which the cylinder was last refinished, should be fitted to reduce clearance and effect reasonably quiet operation.

If cylinders show more than .002 in. variance, they should be refinished to the next oversize step and fitted with new corresponding pistons and rings.

Exact final size of the cylinder bore is determined by size of the piston to be used in that cylinder. Measure piston diameter accurately as described previously, then add desired piston clearance in cylinder. This will equal the exact final size to which cylinder bore should be refinished. Example: The .020 inch oversize 1971 piston to be used measures 3.0190 inches, adding .0025 inch (desired clearance) equals 3.0215 inches (finish-honed size). When cylinders require reboring to beyond oversize limit to clean up, (.030 in. for 1972 to early 1973 models; .070 in. for all other models) cylinder oversize limit has been exceeded and the cylinder must be replaced.

Pistons are available in the following oversizes: .010, .020, and .030 for 1972 to early 1973 models, .010, .020, .030, .040, .050, .060, .070 fo other year models. Oversize pistons have their size stamped on head; for example: 10, 20, etc.

In general practice only cylinders not scored and not badly worn are refinished using only a hone. Cylinders badly worn or deeply scored are first rebored to nearly the required oversize and then are finish-honed to exact size.

Figure 3-15. Measuring Piston

Figure 3-14. Measuring Cylinder

Figure 3-15. Measuring Piston


If cylinders are worn less than the .002 in. maximum and refinishing is not necessary (unless they are scuffed or grooved), the same pistons may be used with the replacement of rings. However, before reassembling it is a good ractice to rough up the cylinder wall with No. 150 Carbo-rundrum emery paper or a No. 300 hone. This will remove any high spots, carbon or foreign material from the cylinder wall and at the same time provide a surface suitable for proper lubrication and ring seating.

Piston rings are of two types - Compression (plain face) and oil control. The two compression rings are positioned in the two upper piston ring grooves, chamfered side up. Rings are available in following oversizes to fit standard oversize pistons: .010, .020, .030, .040, .050, .060 and .070 in.

The rings must have proper side clearance in ring grooves. See "SPECIFICATIONS." Check with thickness gauge as shown in Figure 3-16. Gap between ends of rings when inserted squarely in cylinder bore must also be as specified under "SPECIFICATIONS."

Figure 3-16. Measuring Ring Clearance in Grooves

The oil control ring is a full width slotted ring using a spring expander.

To check ring gap place a piston in cylinder with top end of piston about 1/2 in. from top end of cylinder.

Set the ring to be checked in cylinder bore squarely against piston. With a thickness gauge, check ring gap as shown in Figure 3-17.

Use only standard size rings and piston in standard bore, and only matching oversize rings and pistons in same oversize bore.

If cylinder has been refinished oversize, use the correct oversize rings, fitting rings to give standard gap.

If gap is less than specified, ring ends may butt under expansion, and rings may be scored or broken. Gap may be increased by filing with a fine-cut filfe.

The two chrome plated compression rings, recognized by bright finish, are used in top and second ring grooves, with chamfer on one edge of the inside diameter facing top of piston when installed. Slotted oil control ring is used in bottom ring groove.

Figure 3-17. Measuring Piston Compression Ring Gap

Slip compression rings over piston into their respective grooves as shown in Figure 3-18. Be extremely careful not to overexpand, twist rings or damage the finely finished piston surface when slipping them into place.

Figure 3-18. Installing Piston Rings



When connecting rod bushing is found tight in rod but is worn to excessive pin clearance (.002 in. or more) it is, of course, possible to repair it by reaming oversize and fitting an oversize pin. However, it is better practice to install a new bushing and ream it to fit a standard pin, except when piston to be used had previously been fitted with oversize pin or pin is loose in bosses, necessitating fitting with larger pin. The principal objection to fitting upper end oversize is that considerably more time is required for the job. New pistons obtained from factory are supplied correctly fitted with standard pin, and installing one is not difficult if the rod bushing is already reamed to standard size. If bushing has been reamed oversize, either new bushing must be installed and reamed to standard size or piston must be reamed oversize to fit an oversize pin, which involves extra time.

When removing bushings in connection with only a top overhaul, use special tools as shown in Figure 3-19, Bushing Tool, Part No. 95970-32A, and Connecting Rod Clamping Fixture, Part No. 95952-33.

Connecting Rod Bushing

CAUTION — Oil slot in bushing must be in alignment with oil slot in rod.

Ream new bushing to size, or preferably, ream nearly to size and finish to exact size with a hone (Reamer, Part No.94800-26). A properly fitted pin should have .001 in. clearance; with this clearance, pin will have just noticeable shake in bushing. Fitting tighter is likely to result in a seized pin or bushing loosened in rod.

Oversize piston pins are available in .004 in. oversize.

After installing new piston pin bushings connecting rod alignment must be checked.

In refitting and reassembling connecting rods, and finally fitting pistons, rods may possibly be bent or twisted, throwing upper bearing and lower bearing out of alignment with each other to some extent. Therefore, after pistons have been installed, rods must be checked and re-aligned as may be necessary. If a rod is left bent or twisted, piston has a "cocked" relation to cylinder bore and the result is excessive noise and rapid wear.

Check rod alignment by means of Piston Squaring Plate, Part No. 96181-26, as shown in Figure 3-20. Be sure crankcase face is clean and free from burrs so that squaring plate seats fully. On 1972 and later 61 OHV engine, use 2 spacers on studs to center the plate over cylinder hole in crankcase.

If a rod is in perfect alignment, piston bottom will rest squarely on plate with flywheels turned so that crank pin is in either forward or rear position. Keep in mind that this check, to be accurate, depends upon checking with crank pin in both forward and rear positions. It is the change of rod angle, resulting from changing crank pin from one position to the other, that influences the seat of piston on squaring plate and thus indicates whether or not rod is in alignment.

Insert narrow strips of very thin paper of equal thickness underneath piston, one on each side, below piston pin, as shown in Figure 3-20. Press piston down lightly with fingertips resting on center of piston head and pull first one paper, then the other, partially from underneath piston. If piston is perfectly square (rod in alignment), both will have the same amount of drag.

Figure 3-20. Checking Connecting Rod Alignment

If rod proves to be out of alignment, it can be straightened by means of a bar inserted through piston pin, as shown in Figure 3-21. Use a bar with a diameter as close to the hole diameter in the piston pin as possible. The manner in ~><vhich piston seats on squaring plate indicates as follows:

. Piston high on same side, both crank pin positions; rod is bent.

Figure 3-21. Straightening Connecting Rod

■^2. Piston high on opposite sides as crank pin position is > changed; rod is twisted.

3. Piston square or nearly square with crank pin in one position and high on one side with crank pin in other position; rod is bent and twisted.

Correct as follows:

1. To straighten a bent rod, insert straightening bar through piston pin hole on low side of piston and apply upward force.

2. To straighten a twisted rod, insert straightening bar through piston pin hole on high side of piston, and if crank pin position is to front, apply force to rear - if crank pin position is to rear, apply force to front.

3. To straighten a bent and twisted rod, remove bend first and then remove twist. See above paragraphs, Nos. 4 and 5.

After rods have been aligned, check to see that pistons center in crankcase cylinder opening, without side pressure on upper rod ends. If further realigning is necessary to center pistons, correct by dressing off end of rod bushing on interfering side with a file. This allows the piston to shift slightly on rod to find a more suitable alignment of rod, piston and cylinder.

ward intake valve when head is installed. Be sure one piston pin lock ring is in place. If the piston is heated the piston pin may be inserted into piston with a slip or light press fit.

After pin is in place, install new piston pin lock ring. Use special Lock Ring Tool, Part No. 96780-58A, as shown in Figures 3-22 and 3-23 for 1976 and earlier models. 1972 engine requires Part No. 96781-72 tool plug. 1977 and 1978 models require Internal Lock Ring Pliers, Part No. 96215-49. Make sure ring groove is clean and that ring seats firmly in groove. If it doesn't, discard the ring and install a new one. A lock ring loosely installed will rapidly' loosen further in service and finally will come out of piston groove, resulting in both piston and cylinder soon being damaged beyond repair. Never install a used lock ring or a new one if it has been installed and then removed for any reason, always use a new lock ring.

Piston Pin Lock Ring Tool
Figure 3-22. Inserting Piston Pin Lock Ring in Tool (1976 and Earlier)


hen connecting rod is true, remove squaring plate and Figure 3-23. Installing Piston Pin Lock ittach piston so relief on piston dome for intake valve is to- Ring in Piston (1976 and Earlier)

Luuncaie cynnaer wans, pistons, rings, pins and rod bushings with engine oil. Space ring gaps about equidistant around piston. Turn engine until crank pin is at bottom center. Install new cylinder base gasket. Position Piston Inserter Ring Tool, Part No. 96331 -57, on piston and slip cylinder down over piston as shown in Figure 3-24. Install flat washers and nuts and torque nuts to 30 ft-lbs. Repeat process for other cylinder.

Assemble cylinder head and remaining parts of motorcycle as indicated in "INSTALLING CYLINDER HEAD ASSEMBLY."

Figure 3-24. Installing Cylinder on Piston




The oil feed and scavenger (oil return) pumps are gear-type pumps incorporated in one pump body with a check valve on the oil feed side. The feed section forces oil to the engine and the scavenging section returns oil to the tank.

The oil pump seldom needs servicing; therefore, before disassembling the pump for any repairs because of no oil pressure, be absolutely certain that all possible related malfunctions have been eliminated:

Check the level and condition of oil in the tank. If oil is diluted, pressure will be affected. In freezing weather, the oil feed line may clog with ice and sludge, preventing circulation of oil.

Check for a grounded oil pressure switch wire or a faulty switch if oil indicator light fails to go out with engine running. See "ENGINE LUBRICATION," for additional information.

Inspect the oil pump check valve. The check valve prevents the gravity flow of oil into the crankcase when the engine is not running and provides correct oil pressure for operation of the oil signal light switch. If the check valve is not seating correctly oil will bypass the valve and drain oil from the tank into the crankcase and on starting the engine, a considerable amount of accumulated oil will be blown through the crankcase breather pipe. If this condition exists, disassemble and inspect the check valve. See "DISASSEMBLING OIL PUMP CHECK VALVE."

If no oil pressure or return oil is indicated at the oil tank (return line) when engine is running, or an excessive amount of oil is blown from the breather pipe, (after all other possible troubles have been eliminated, including inspection of the oil pump check valve), disassemble the oil pump for further inspection and repair. See "DISASSEMBLING OIL PUMP."

When an oil pump has to be disassembled for repair, damage is usually caused by a foreign particle, such as a metal fragment, that has worked its way into the oil circulatory system. If this particle passes through the pump's protective screening, damage will result when it enters the pump. Primarily, the damage consists of a sheared oil pump drive lock pin (18, Figure 3-25), broken retaining ring (7, Figure 3-25) or subsequent damage to gears and other parts.


Thoroughly clean exterior of pump in cleaning solvent before disassembly. Disconnect oil pressure switch wire and disassemble switch (1) from motorcycle. Remove oil pump nipple (2). Free check valve spring (3) and valve (4) from pump body.


Clean all parts in cleaning solvent. Blow out pump nipple (2) oil passage and the nipple valve spring guide. Examine the nipple for any damage that would bind or hinder the free operation of spring (3). Carefully examine the nipple threads for wear; if badly worn replace nipple.

Inspect spring (3) for breakage and rusted condition. Replace if worn or damaged. Free length of new check valve spring (3) is approximately 1 -15/64 in.

Carefully inspect the oil pump check valve ball (4) for wear and rusted condition. Valve may have rings formed by action on valve seat. Valve balls not perfectly smooth and round should be replaced.

Using a light, inspect valve seat in pump body (16) for pits and for dirty condition. A small particle of foreign matter lodged on valve seat will prevent check valve ball from seating. If seat is only slightly damaged place check valve ball on seat and with a drift lightly tap against its seat to remove slight marks or pits. Replace pump body if valve seat is badly damaged. See "DISASSEMBLING OIL PUMP."


Assembly is essentially the reverse order of disassembly. Apply a light coating of oil to all moving parts. Make sure that check valve ball (4) is correctly seated and valve action is free. Be extremely careful to prevent dust, dirt or other foreign particles from getting on the parts when reassembling.


Because of interference from motorcycle frame it is necessary to remove engine to disassemble pump. First, remove the engine complete from the chassis and position on workbench. See "STRIPPING MOTORCYCLE FOR ENGINE REPAIR."


It is not necessary to remove valve tappets and valve tappet guides to service the oil pump.

The breather is a part of and drives the oil pump. When removing the oil pump, the breather will of course come out with it. Removing the pump does not require removing the circuit breaker, gearcase cover or removing timing gears. However, it must be remembered that in order to correctly time breather and to check oil pump alignment, it is necessary to remove these parts.

See Figure 3-25. Thoroughly clean exterior of pump with cleaning solvent before further disassembly. Remove the five crankcase stud nuts that secure the oil pump to the crankcase. Slip the pump off the studs as one unit. If difficult to remove, take a piece of brass and tap on breather sleeve that extends into gearcase compartment. To disassemble the check valve see "DISASSEMBLING OIL PUMP CHECK VALVE."


Figure 3-25. Oil Pump - Exploded View (1976 and Earlier)

1. Oil pressure switch

2. Oil pump nipple

3. Check valve spring

4. Ball valve

5. Body plate

6. Body plate gasket

8. Scavenger pump gear

9. Scavenger pump idler gear

10. Breather valve key

11. Oil pump cover

12. Body cover gasket

13. Pump gear

14. Pump idler gear

15. Oil pump seal

16. Oil pump body

17. Body gasket

18. Drive lock pin

19. Breather valve gear and shaft

20. Crankcase breather valve screen

21. Idler gear shaft

22. Feed line nipple

Free the oil pump body plate (5) from pump body. Discard gasket (6). Remove split key (7), remove scavenger gears (8) and (9). Remove key (10). Free oil feed pump cover (11) and breather valve (19) as one assembly from pump body. Discard gasket (12). Free gears (13 and 14) from pump body. Pry oil seal (15) from pump body (16) and discard seal. Discard gasket (17).

With a punch remove lock pin (18) and free oil pump breather valve gear and shaft (19) from oil pump cover (11).

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