another 6 speed harley transmission failure
#721
11-01-2017, 11:23 AM
When the MC went to the CD 6 speed they changed a few things. On the clutch hub, they moved the starter ring gear to the inside of the primary drive sprocket and moved the sprocket outward on the clutch hub. This was done so they could change the starter design and eliminate the whole "jackshaft" setup for the starter.
Also at some point prior to that, they started using a self-adjusting spring loaded wedge type tensioner that has a tendency to overtighten the primary chain whenever it gets a chance to do so if there is slack in the chain.
The thing is that the chain gets HOT and when it gets hot it expands and the tensioner takes up the slack. Couple that with the new location of the drive sprocket on the clutch hub which can cause the trans shaft to"flex" when under high load I can see why there is a problem.
On the last trans that I did due to this problem the MC has updated the design of the main bearing to a single row larger ball bearing (older 5 speed style) design and done away with the two-row f.a.g. corp bearing that was made in Canada. This was a "one-off" bearing that you could only buy from the MC that I know of anyway...I looked.
The problem with the two row bearing that was used up until recently was that the bearings were too small and the pressures on them due to flexing and the overtight chain was causing the hard facing on the bearings to come off eventually causing at first translucent oil due to metal in the oil and then a grinding sound from the trans.
If not fixed the bearings would eventually start coming out of the race after being ground down enough.
The outer bearings in the main bearing would take great pressures when there was any type of flexing as the outer row would take the brunt of the forces due to any flex or overtightening of the adjuster. Usually, the outer bearings come out first as the inner bearings have a real hard time getting past the main drive gear on the inside of the trans.
The flexing of the trans shaft can also cause the ends of the splines on the inside of the clutch hub to break or crush but that can also happen if the clutch hub nut is overtightened. The splines on the inside of clutch hub are "softer material" than the splines on the trans shaft so if you if you tighten the nut over 70 ft-lb tq they can be pushed into the mating splines and get crushed.
The new main bearing that the MC is using now look like the old main bearing in the 5-speed trans. Time will only tell if the trans issues will be solved by the use of the new bearing...
Also at some point prior to that, they started using a self-adjusting spring loaded wedge type tensioner that has a tendency to overtighten the primary chain whenever it gets a chance to do so if there is slack in the chain.
The thing is that the chain gets HOT and when it gets hot it expands and the tensioner takes up the slack. Couple that with the new location of the drive sprocket on the clutch hub which can cause the trans shaft to"flex" when under high load I can see why there is a problem.
On the last trans that I did due to this problem the MC has updated the design of the main bearing to a single row larger ball bearing (older 5 speed style) design and done away with the two-row f.a.g. corp bearing that was made in Canada. This was a "one-off" bearing that you could only buy from the MC that I know of anyway...I looked.
The problem with the two row bearing that was used up until recently was that the bearings were too small and the pressures on them due to flexing and the overtight chain was causing the hard facing on the bearings to come off eventually causing at first translucent oil due to metal in the oil and then a grinding sound from the trans.
If not fixed the bearings would eventually start coming out of the race after being ground down enough.
The outer bearings in the main bearing would take great pressures when there was any type of flexing as the outer row would take the brunt of the forces due to any flex or overtightening of the adjuster. Usually, the outer bearings come out first as the inner bearings have a real hard time getting past the main drive gear on the inside of the trans.
The flexing of the trans shaft can also cause the ends of the splines on the inside of the clutch hub to break or crush but that can also happen if the clutch hub nut is overtightened. The splines on the inside of clutch hub are "softer material" than the splines on the trans shaft so if you if you tighten the nut over 70 ft-lb tq they can be pushed into the mating splines and get crushed.
The new main bearing that the MC is using now look like the old main bearing in the 5-speed trans. Time will only tell if the trans issues will be solved by the use of the new bearing...
#723
11-02-2017, 07:31 AM
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