The caller was inquiring about the cost of a bottom end rebuild on his Evo.

"How do you know it needs rebuilding?" I asked.

"She’s hammering away in there." He replied. "My drag pipes don’t even cover up the knocking."

Already, I knew from experience that it was a loose or worn compensating sprocket assembly.

I told the caller that I had good news for him or at least better news than he was expecting.

Over the years, I can’t think of a noise that’s raised more blood pressure than the dreaded bottom end knock, but the long and short of it is that in most cases, the culprit is something else entirely.

Truth is, a lot of mechanics can’t even detect this noise, especially in its early stages.

But being typical Harley riders, they immediately bypass all the simple, easy-to-fix inexpensive solutions and proceed to the most complicated, hard to get at and most costly-to-fix solutions.

Your first question should be "Can you tell me what’s causing this noise?", not "How much to do my bottom end? "Well, if you can hear your bottom end over the staccato of drag pipes, that sound would almost have to be the shattering of engine cases bouncing off the pavement as a broken connecting rod did its Grim Reaper" routine.

On the streets, I’ve only seen that scenario a few times in the last decade.

So, why don’t we examine what’s really causing this heart-palpitating noise?

Outside of a collapsed hydraulic lifter, nothing else can cause this much internal noise.

The lifter noise will come from the right side of the engine so it is easy to isolate or eliminate the problem. That leaves only one area to check, and that is the primary system, which is on the left side and connects the motor to the transmission delivering power back via the clutch to the rear wheel.

Now, the noises emanating form the primary are serious and require immediate attention, but they do not cost anywhere near that of bottom end work.

Check the simple and inexpensive solutions first

If you’re lucky, your primary chain could be too loose, and all that’s happening is that it’s constantly slapping against the inside of the primary case. That would take 15 minutes to repair. You may want to change the fluid since aluminum filings from the casing will not be attracted to the drain plug magnet. A loose or stretched chain can be whipsawing on and off the front sprocket, which also would make lots of noise and a jerking sensation, especially in high gear. That may simply be a loose chain but more likely it would be an unevenly worn one with tight and loose spots and/or worn out hooked sprocket.

Too tight a chain (or a worn one with tight spots) will cause a whine as opposed to a slapping or knocking and might cause the clutch to drag. this condition lessens the life of all components parts, including bearings.

No lubrication causes all kinds of havoc and noise and is evidenced by an orange rusty color evenly dispensed throughout the primary,. The chain must be inspected for a broken or missing (disintegrated) roller that can emit a grinding noise.

A constant grinding sound can be caused by a misaligned chain as it tries to re-cut teeth to accommodate its path more easily. I don’t even want to get into all the damage all those fine cuttings will initiate.

Also, a new chain should be broken in and checked after 500 miles. Consider changing oil as the break-in period generates lots of filings.

Loose nuts on the primary adjuster will allow it to flop up and down. After these chain-related problems are checked, examine the compensating sprocket assembly.

Compensating Sprockets

Big Twins since 1955 and Sportsters from 1957 to the mid-70s used four basic types of engine-to-transmission power shock absorption devices. The pulsing energy of the motor is cushioned to protect the power train back through the transmission.

The downside to these various mechanisms is that they suffer some power transfer loss from the engine to the rear well as it grabs the asphalt. This is another reason that the Sportster is faster than the Big Twin since many models are direct drive with only a sprocket and not the added compensating sprocket assembly

Bottom End Grenade

Although I recommend checking primary chain problems first, the bottom end knock invariably comes from a malfunctioning compensator. A mechanic can easily tell the difference between the two noises with a stethoscope, but this requires experience. Why would it sound like a bottom end knock? Because it’s attached to a bottom end component - the flywheel sprocket shaft. Although sprocket shaft bearing assembly spacing determines end play of the flywheels and their positioning inside the motor cases----- 35lb. flywheels rotating up to 6500 RPM would turn into a grenade if allowed to rotate into the motor case housing-----the compensating sprocket package ensures that this crucial end play is maintained.

So, when this assembly malfunctions through improper torque or wear, the accompanying noise transfers along the sprocket shaft into the bottom end, leading the rider to think the connecting rods, crank pin and associated bearing are worn beyond tolerance and therefore causing the insidious knock.

But not so.

IS THE SPRING STILL SPRINGING?

There are four main compensating assemblies used in Harley. Only one, which incorporates a coiled spring looks like an absorption device. The 1955-69 Big Twin and all Sportster compensators use this spring type device.

Two interlocking cams (#1 & #2) ride up on each other, transferring the power surge and compressing the attached spring to absorb the initial shock while the main thrust goes back along the primary chain through the transmission and the clutch to the rear wheel. After the shock, the cams are forced to rotate back to their resting position by the decompressing spring.

The three remaining types of compensators are similar in that they still used the rotating cams but they differ in they use diaphragm springs enclosed in a round metal housing (#4). To the uninitiated, these springs look like flat pieces of steel and it is difficult to see how they would compress let alone absorb shock---but they do. The nut (#5). and it’s a big one that holds the package together at 80 to100 ft. lb.. torque, may come loose or may bottom out, fooling the wrench into thinking that the proper torque has been achieved although the knocking noise will belie that.

A simple test is to grab the diaphragm spring package (#4) firmly and try to rotate it. If you can, something is wrong because your hands can not generate horsepower. Replace the nut if it is bottoming out on the shaft. This culprit is sneaky, and most people don’t check it out.

Knocking Cams

If the nut is not at fault, on 1970 to 1982 models a cup is used as a thrust washer between the spring package. As the cup between the spring package (#3) wears, it gets thinner and exerts less pressure, allowing the cams to rattle by slapping each other, causing the "knock"

The two remaining assemblies since 1983 eliminate this cup and incorporate it in hardened metal to resist wear with the outer sliding cam (#1 with #3). The 1991 and up unit eliminated the blind hole on the end of the nut (#5) i.e., put the hole in the end and added a space. Both later units thinned the number of diaphragm springs to four in the steel housing (#4).

If compensator parts become worn an other noise may occur and that is a rattling rotor. The alternator is comprised of a stator and rotor and is sandwiched between the sprocket shaft extension (#6) and the outer motor case. The rotor’s splined inner fits on the corresponding sprocket shaft spline and rotates with the flywheels and the compensator. If excess play occurs it can cause a knock of it’s own. This must be fixed immediately because the stator can be damaged and make the charging system malfunction.

If on the road and a compensatory noise is diagnosed-- -most easily heard when taking off in first gear-- - you may proceed home at a steady speed if close by. However, if temporary repairs are required, you may add a diaphragm spring to the compensator package to beef it up. Of course, going to all this trouble you might as well replace the offending part or parts since the same amount of effort is required. An easy roadside fix is to put a washer under the compensator nut to take up excess play and increase spring tension. Another method is to get rid of the compensating unit altogether and go direct drive with a corresponding performance gain because a higher percentage of power will be transferred. Simply use an aftermarket splined motor sprocket or an original Harley one (40211-55) used on some early models.

"How do you know it needs rebuilding?" I asked.

"She’s hammering away in there." He replied. "My drag pipes don’t even cover up the knocking."

Already, I knew from experience that it was a loose or worn compensating sprocket assembly.

I told the caller that I had good news for him or at least better news than he was expecting.

Over the years, I can’t think of a noise that’s raised more blood pressure than the dreaded bottom end knock, but the long and short of it is that in most cases, the culprit is something else entirely.

Truth is, a lot of mechanics can’t even detect this noise, especially in its early stages.

But being typical Harley riders, they immediately bypass all the simple, easy-to-fix inexpensive solutions and proceed to the most complicated, hard to get at and most costly-to-fix solutions.

Your first question should be "Can you tell me what’s causing this noise?", not "How much to do my bottom end? "Well, if you can hear your bottom end over the staccato of drag pipes, that sound would almost have to be the shattering of engine cases bouncing off the pavement as a broken connecting rod did its Grim Reaper" routine.

On the streets, I’ve only seen that scenario a few times in the last decade.

So, why don’t we examine what’s really causing this heart-palpitating noise?

Outside of a collapsed hydraulic lifter, nothing else can cause this much internal noise.

The lifter noise will come from the right side of the engine so it is easy to isolate or eliminate the problem. That leaves only one area to check, and that is the primary system, which is on the left side and connects the motor to the transmission delivering power back via the clutch to the rear wheel.

Now, the noises emanating form the primary are serious and require immediate attention, but they do not cost anywhere near that of bottom end work.

Check the simple and inexpensive solutions first

If you’re lucky, your primary chain could be too loose, and all that’s happening is that it’s constantly slapping against the inside of the primary case. That would take 15 minutes to repair. You may want to change the fluid since aluminum filings from the casing will not be attracted to the drain plug magnet. A loose or stretched chain can be whipsawing on and off the front sprocket, which also would make lots of noise and a jerking sensation, especially in high gear. That may simply be a loose chain but more likely it would be an unevenly worn one with tight and loose spots and/or worn out hooked sprocket.

Too tight a chain (or a worn one with tight spots) will cause a whine as opposed to a slapping or knocking and might cause the clutch to drag. this condition lessens the life of all components parts, including bearings.

No lubrication causes all kinds of havoc and noise and is evidenced by an orange rusty color evenly dispensed throughout the primary,. The chain must be inspected for a broken or missing (disintegrated) roller that can emit a grinding noise.

A constant grinding sound can be caused by a misaligned chain as it tries to re-cut teeth to accommodate its path more easily. I don’t even want to get into all the damage all those fine cuttings will initiate.

Also, a new chain should be broken in and checked after 500 miles. Consider changing oil as the break-in period generates lots of filings.

Loose nuts on the primary adjuster will allow it to flop up and down. After these chain-related problems are checked, examine the compensating sprocket assembly.

Compensating Sprockets

Big Twins since 1955 and Sportsters from 1957 to the mid-70s used four basic types of engine-to-transmission power shock absorption devices. The pulsing energy of the motor is cushioned to protect the power train back through the transmission.

The downside to these various mechanisms is that they suffer some power transfer loss from the engine to the rear well as it grabs the asphalt. This is another reason that the Sportster is faster than the Big Twin since many models are direct drive with only a sprocket and not the added compensating sprocket assembly

Bottom End Grenade

Although I recommend checking primary chain problems first, the bottom end knock invariably comes from a malfunctioning compensator. A mechanic can easily tell the difference between the two noises with a stethoscope, but this requires experience. Why would it sound like a bottom end knock? Because it’s attached to a bottom end component - the flywheel sprocket shaft. Although sprocket shaft bearing assembly spacing determines end play of the flywheels and their positioning inside the motor cases----- 35lb. flywheels rotating up to 6500 RPM would turn into a grenade if allowed to rotate into the motor case housing-----the compensating sprocket package ensures that this crucial end play is maintained.

So, when this assembly malfunctions through improper torque or wear, the accompanying noise transfers along the sprocket shaft into the bottom end, leading the rider to think the connecting rods, crank pin and associated bearing are worn beyond tolerance and therefore causing the insidious knock.

But not so.

IS THE SPRING STILL SPRINGING?

There are four main compensating assemblies used in Harley. Only one, which incorporates a coiled spring looks like an absorption device. The 1955-69 Big Twin and all Sportster compensators use this spring type device.

Two interlocking cams (#1 & #2) ride up on each other, transferring the power surge and compressing the attached spring to absorb the initial shock while the main thrust goes back along the primary chain through the transmission and the clutch to the rear wheel. After the shock, the cams are forced to rotate back to their resting position by the decompressing spring.

The three remaining types of compensators are similar in that they still used the rotating cams but they differ in they use diaphragm springs enclosed in a round metal housing (#4). To the uninitiated, these springs look like flat pieces of steel and it is difficult to see how they would compress let alone absorb shock---but they do. The nut (#5). and it’s a big one that holds the package together at 80 to100 ft. lb.. torque, may come loose or may bottom out, fooling the wrench into thinking that the proper torque has been achieved although the knocking noise will belie that.

A simple test is to grab the diaphragm spring package (#4) firmly and try to rotate it. If you can, something is wrong because your hands can not generate horsepower. Replace the nut if it is bottoming out on the shaft. This culprit is sneaky, and most people don’t check it out.

Knocking Cams

If the nut is not at fault, on 1970 to 1982 models a cup is used as a thrust washer between the spring package. As the cup between the spring package (#3) wears, it gets thinner and exerts less pressure, allowing the cams to rattle by slapping each other, causing the "knock"

The two remaining assemblies since 1983 eliminate this cup and incorporate it in hardened metal to resist wear with the outer sliding cam (#1 with #3). The 1991 and up unit eliminated the blind hole on the end of the nut (#5) i.e., put the hole in the end and added a space. Both later units thinned the number of diaphragm springs to four in the steel housing (#4).

If compensator parts become worn an other noise may occur and that is a rattling rotor. The alternator is comprised of a stator and rotor and is sandwiched between the sprocket shaft extension (#6) and the outer motor case. The rotor’s splined inner fits on the corresponding sprocket shaft spline and rotates with the flywheels and the compensator. If excess play occurs it can cause a knock of it’s own. This must be fixed immediately because the stator can be damaged and make the charging system malfunction.

If on the road and a compensatory noise is diagnosed-- -most easily heard when taking off in first gear-- - you may proceed home at a steady speed if close by. However, if temporary repairs are required, you may add a diaphragm spring to the compensator package to beef it up. Of course, going to all this trouble you might as well replace the offending part or parts since the same amount of effort is required. An easy roadside fix is to put a washer under the compensator nut to take up excess play and increase spring tension. Another method is to get rid of the compensating unit altogether and go direct drive with a corresponding performance gain because a higher percentage of power will be transferred. Simply use an aftermarket splined motor sprocket or an original Harley one (40211-55) used on some early models.

"How do you know it needs rebuilding?" I asked.

"She’s hammering away in there." He replied. "My drag pipes don’t even cover up the knocking."

Already, I knew from experience that it was a loose or worn compensating sprocket assembly.

I told the caller that I had good news for him or at least better news than he was expecting.

Over the years, I can’t think of a noise that’s raised more blood pressure than the dreaded bottom end knock, but the long and short of it is that in most cases, the culprit is something else entirely.

Truth is, a lot of mechanics can’t even detect this noise, especially in its early stages.

But being typical Harley riders, they immediately bypass all the simple, easy-to-fix inexpensive solutions and proceed to the most complicated, hard to get at and most costly-to-fix solutions.

Your first question should be "Can you tell me what’s causing this noise?", not "How much to do my bottom end? "Well, if you can hear your bottom end over the staccato of drag pipes, that sound would almost have to be the shattering of engine cases bouncing off the pavement as a broken connecting rod did its Grim Reaper" routine.

On the streets, I’ve only seen that scenario a few times in the last decade.

So, why don’t we examine what’s really causing this heart-palpitating noise?

Outside of a collapsed hydraulic lifter, nothing else can cause this much internal noise.

The lifter noise will come from the right side of the engine so it is easy to isolate or eliminate the problem. That leaves only one area to check, and that is the primary system, which is on the left side and connects the motor to the transmission delivering power back via the clutch to the rear wheel.

Now, the noises emanating form the primary are serious and require immediate attention, but they do not cost anywhere near that of bottom end work.

Check the simple and inexpensive solutions first

If you’re lucky, your primary chain could be too loose, and all that’s happening is that it’s constantly slapping against the inside of the primary case. That would take 15 minutes to repair. You may want to change the fluid since aluminum filings from the casing will not be attracted to the drain plug magnet. A loose or stretched chain can be whipsawing on and off the front sprocket, which also would make lots of noise and a jerking sensation, especially in high gear. That may simply be a loose chain but more likely it would be an unevenly worn one with tight and loose spots and/or worn out hooked sprocket.

Too tight a chain (or a worn one with tight spots) will cause a whine as opposed to a slapping or knocking and might cause the clutch to drag. this condition lessens the life of all components parts, including bearings.

No lubrication causes all kinds of havoc and noise and is evidenced by an orange rusty color evenly dispensed throughout the primary,. The chain must be inspected for a broken or missing (disintegrated) roller that can emit a grinding noise.

A constant grinding sound can be caused by a misaligned chain as it tries to re-cut teeth to accommodate its path more easily. I don’t even want to get into all the damage all those fine cuttings will initiate.

Also, a new chain should be broken in and checked after 500 miles. Consider changing oil as the break-in period generates lots of filings.

Loose nuts on the primary adjuster will allow it to flop up and down. After these chain-related problems are checked, examine the compensating sprocket assembly.

Compensating Sprockets

Big Twins since 1955 and Sportsters from 1957 to the mid-70s used four basic types of engine-to-transmission power shock absorption devices. The pulsing energy of the motor is cushioned to protect the power train back through the transmission.

The downside to these various mechanisms is that they suffer some power transfer loss from the engine to the rear well as it grabs the asphalt. This is another reason that the Sportster is faster than the Big Twin since many models are direct drive with only a sprocket and not the added compensating sprocket assembly

Bottom End Grenade

Although I recommend checking primary chain problems first, the bottom end knock invariably comes from a malfunctioning compensator. A mechanic can easily tell the difference between the two noises with a stethoscope, but this requires experience. Why would it sound like a bottom end knock? Because it’s attached to a bottom end component - the flywheel sprocket shaft. Although sprocket shaft bearing assembly spacing determines end play of the flywheels and their positioning inside the motor cases----- 35lb. flywheels rotating up to 6500 RPM would turn into a grenade if allowed to rotate into the motor case housing-----the compensating sprocket package ensures that this crucial end play is maintained.

So, when this assembly malfunctions through improper torque or wear, the accompanying noise transfers along the sprocket shaft into the bottom end, leading the rider to think the connecting rods, crank pin and associated bearing are worn beyond tolerance and therefore causing the insidious knock.

But not so.

IS THE SPRING STILL SPRINGING?

There are four main compensating assemblies used in Harley. Only one, which incorporates a coiled spring looks like an absorption device. The 1955-69 Big Twin and all Sportster compensators use this spring type device.

Two interlocking cams (#1 & #2) ride up on each other, transferring the power surge and compressing the attached spring to absorb the initial shock while the main thrust goes back along the primary chain through the transmission and the clutch to the rear wheel. After the shock, the cams are forced to rotate back to their resting position by the decompressing spring.

The three remaining types of compensators are similar in that they still used the rotating cams but they differ in they use diaphragm springs enclosed in a round metal housing (#4). To the uninitiated, these springs look like flat pieces of steel and it is difficult to see how they would compress let alone absorb shock---but they do. The nut (#5). and it’s a big one that holds the package together at 80 to100 ft. lb.. torque, may come loose or may bottom out, fooling the wrench into thinking that the proper torque has been achieved although the knocking noise will belie that.

A simple test is to grab the diaphragm spring package (#4) firmly and try to rotate it. If you can, something is wrong because your hands can not generate horsepower. Replace the nut if it is bottoming out on the shaft. This culprit is sneaky, and most people don’t check it out.

Knocking Cams

If the nut is not at fault, on 1970 to 1982 models a cup is used as a thrust washer between the spring package. As the cup between the spring package (#3) wears, it gets thinner and exerts less pressure, allowing the cams to rattle by slapping each other, causing the "knock"

The two remaining assemblies since 1983 eliminate this cup and incorporate it in hardened metal to resist wear with the outer sliding cam (#1 with #3). The 1991 and up unit eliminated the blind hole on the end of the nut (#5) i.e., put the hole in the end and added a space. Both later units thinned the number of diaphragm springs to four in the steel housing (#4).

If compensator parts become worn an other noise may occur and that is a rattling rotor. The alternator is comprised of a stator and rotor and is sandwiched between the sprocket shaft extension (#6) and the outer motor case. The rotor’s splined inner fits on the corresponding sprocket shaft spline and rotates with the flywheels and the compensator. If excess play occurs it can cause a knock of it’s own. This must be fixed immediately because the stator can be damaged and make the charging system malfunction.

If on the road and a compensatory noise is diagnosed-- -most easily heard when taking off in first gear-- - you may proceed home at a steady speed if close by. However, if temporary repairs are required, you may add a diaphragm spring to the compensator package to beef it up. Of course, going to all this trouble you might as well replace the offending part or parts since the same amount of effort is required. An easy roadside fix is to put a washer under the compensator nut to take up excess play and increase spring tension. Another method is to get rid of the compensating unit altogether and go direct drive with a corresponding performance gain because a higher percentage of power will be transferred. Simply use an aftermarket splined motor sprocket or an original Harley one (40211-55) used on some early models.

"How do you know it needs rebuilding?" I asked.

"She’s hammering away in there." He replied. "My drag pipes don’t even cover up the knocking."

Already, I knew from experience that it was a loose or worn compensating sprocket assembly.

I told the caller that I had good news for him or at least better news than he was expecting.

Over the years, I can’t think of a noise that’s raised more blood pressure than the dreaded bottom end knock, but the long and short of it is that in most cases, the culprit is something else entirely.

Truth is, a lot of mechanics can’t even detect this noise, especially in its early stages.

But being typical Harley riders, they immediately bypass all the simple, easy-to-fix inexpensive solutions and proceed to the most complicated, hard to get at and most costly-to-fix solutions.

Your first question should be "Can you tell me what’s causing this noise?", not "How much to do my bottom end? "Well, if you can hear your bottom end over the staccato of drag pipes, that sound would almost have to be the shattering of engine cases bouncing off the pavement as a broken connecting rod did its Grim Reaper" routine.

On the streets, I’ve only seen that scenario a few times in the last decade.

So, why don’t we examine what’s really causing this heart-palpitating noise?

Outside of a collapsed hydraulic lifter, nothing else can cause this much internal noise.

The lifter noise will come from the right side of the engine so it is easy to isolate or eliminate the problem. That leaves only one area to check, and that is the primary system, which is on the left side and connects the motor to the transmission delivering power back via the clutch to the rear wheel.

Now, the noises emanating form the primary are serious and require immediate attention, but they do not cost anywhere near that of bottom end work.

Check the simple and inexpensive solutions first

If you’re lucky, your primary chain could be too loose, and all that’s happening is that it’s constantly slapping against the inside of the primary case. That would take 15 minutes to repair. You may want to change the fluid since aluminum filings from the casing will not be attracted to the drain plug magnet. A loose or stretched chain can be whipsawing on and off the front sprocket, which also would make lots of noise and a jerking sensation, especially in high gear. That may simply be a loose chain but more likely it would be an unevenly worn one with tight and loose spots and/or worn out hooked sprocket.

Too tight a chain (or a worn one with tight spots) will cause a whine as opposed to a slapping or knocking and might cause the clutch to drag. this condition lessens the life of all components parts, including bearings.

No lubrication causes all kinds of havoc and noise and is evidenced by an orange rusty color evenly dispensed throughout the primary,. The chain must be inspected for a broken or missing (disintegrated) roller that can emit a grinding noise.

A constant grinding sound can be caused by a misaligned chain as it tries to re-cut teeth to accommodate its path more easily. I don’t even want to get into all the damage all those fine cuttings will initiate.

Also, a new chain should be broken in and checked after 500 miles. Consider changing oil as the break-in period generates lots of filings.

Loose nuts on the primary adjuster will allow it to flop up and down. After these chain-related problems are checked, examine the compensating sprocket assembly.

Compensating Sprockets

Big Twins since 1955 and Sportsters from 1957 to the mid-70s used four basic types of engine-to-transmission power shock absorption devices. The pulsing energy of the motor is cushioned to protect the power train back through the transmission.

The downside to these various mechanisms is that they suffer some power transfer loss from the engine to the rear well as it grabs the asphalt. This is another reason that the Sportster is faster than the Big Twin since many models are direct drive with only a sprocket and not the added compensating sprocket assembly

Bottom End Grenade

Although I recommend checking primary chain problems first, the bottom end knock invariably comes from a malfunctioning compensator. A mechanic can easily tell the difference between the two noises with a stethoscope, but this requires experience. Why would it sound like a bottom end knock? Because it’s attached to a bottom end component - the flywheel sprocket shaft. Although sprocket shaft bearing assembly spacing determines end play of the flywheels and their positioning inside the motor cases----- 35lb. flywheels rotating up to 6500 RPM would turn into a grenade if allowed to rotate into the motor case housing-----the compensating sprocket package ensures that this crucial end play is maintained.

So, when this assembly malfunctions through improper torque or wear, the accompanying noise transfers along the sprocket shaft into the bottom end, leading the rider to think the connecting rods, crank pin and associated bearing are worn beyond tolerance and therefore causing the insidious knock.

But not so.

IS THE SPRING STILL SPRINGING?

There are four main compensating assemblies used in Harley. Only one, which incorporates a coiled spring looks like an absorption device. The 1955-69 Big Twin and all Sportster compensators use this spring type device.

Two interlocking cams (#1 & #2) ride up on each other, transferring the power surge and compressing the attached spring to absorb the initial shock while the main thrust goes back along the primary chain through the transmission and the clutch to the rear wheel. After the shock, the cams are forced to rotate back to their resting position by the decompressing spring.

The three remaining types of compensators are similar in that they still used the rotating cams but they differ in they use diaphragm springs enclosed in a round metal housing (#4). To the uninitiated, these springs look like flat pieces of steel and it is difficult to see how they would compress let alone absorb shock---but they do. The nut (#5). and it’s a big one that holds the package together at 80 to100 ft. lb.. torque, may come loose or may bottom out, fooling the wrench into thinking that the proper torque has been achieved although the knocking noise will belie that.

A simple test is to grab the diaphragm spring package (#4) firmly and try to rotate it. If you can, something is wrong because your hands can not generate horsepower. Replace the nut if it is bottoming out on the shaft. This culprit is sneaky, and most people don’t check it out.

Knocking Cams

If the nut is not at fault, on 1970 to 1982 models a cup is used as a thrust washer between the spring package. As the cup between the spring package (#3) wears, it gets thinner and exerts less pressure, allowing the cams to rattle by slapping each other, causing the "knock"

The two remaining assemblies since 1983 eliminate this cup and incorporate it in hardened metal to resist wear with the outer sliding cam (#1 with #3). The 1991 and up unit eliminated the blind hole on the end of the nut (#5) i.e., put the hole in the end and added a space. Both later units thinned the number of diaphragm springs to four in the steel housing (#4).

If compensator parts become worn an other noise may occur and that is a rattling rotor. The alternator is comprised of a stator and rotor and is sandwiched between the sprocket shaft extension (#6) and the outer motor case. The rotor’s splined inner fits on the corresponding sprocket shaft spline and rotates with the flywheels and the compensator. If excess play occurs it can cause a knock of it’s own. This must be fixed immediately because the stator can be damaged and make the charging system malfunction.

If on the road and a compensatory noise is diagnosed-- -most easily heard when taking off in first gear-- - you may proceed home at a steady speed if close by. However, if temporary repairs are required, you may add a diaphragm spring to the compensator package to beef it up. Of course, going to all this trouble you might as well replace the offending part or parts since the same amount of effort is required. An easy roadside fix is to put a washer under the compensator nut to take up excess play and increase spring tension. Another method is to get rid of the compensating unit altogether and go direct drive with a corresponding performance gain because a higher percentage of power will be transferred. Simply use an aftermarket splined motor sprocket or an original Harley one (40211-55) used on some early models.