Having some troubles with yamaha transmission. This applies to my XS1100 as well as my new FZR600 so I don't think I'm breaking this sub-forum rules.
Whenever I shift from 1st to 2nd when I'm really opening her up and accelerating quickly from stop I get a grinding noise and it seems like 2nd doesn't want to engage. I had the problem with my '78 XS1100 and now with my FZR600.
When I'm just beebopping around at regular rpms shifting goes smoothly and I don't get any gear clash but when I accelerate quickly and try to shift from 1st to 2nd I get issues about 60% of the time. I am fully disengaging the clutch and the clutch is properly adjusted so I know that it's not because power is still going to the countershaft. These are fast bikes and I can't imagine that they aren't capable of high rates of acceleration and quick shifting.
What I've seen reading through forum searches is that when you do a high rpm shift it takes longer for the countershaft to slow down enough for the next gear to engage. Also, that this problem is exclusive to 1st to 2nd gear upshifts and 2nd to 1st downshifts namely because they are the only gear changes that have a free spinning gear being engaged with the slots of a gear that's fixed to the countershaft. I guess let me explain that more:
Upshifting (slightly different for a six speed):
-1st to 2nd --> shift fork pulls 1st dogs off of 4th gear slots and pushes 2nd dogs onto 5th gear slots
-2nd to 3rd --> shift fork pulls first off and drive gear engages fixed 3rd gear
-3rd to 4th --> shift fork pushes drive gear onto fixed 4th gear
etc.
Downshifting (D0wn5h1ft'ing ) (again, slight different for six speed):
-3rd to 2nd --> shift fork pushes 2nd dogs into 5th slots
-2nd to 1st --> shift fork pushes 2nd dog out of 5th (fixed) slots and 1st dogs into 4th (fixed) slots
As you can see, I think the issues is only present with 1to2 and 2to1 is because they are the changes where free spinning gears are being meshed with the fixed gears on the countershaft.
So my question is how do I prevent the gear grinding, which is horrible for these old transmission, during fast acceleration at high rpms? I know one solution is hold the clutch in longer before shifting which allows the countershaft to slow down more allowing the gears to actually engage the countershaft without grinding. But this leads to granny shifting and I just refuse to believe that these high performance bikes are incapable of this kind of shifting.
Another question is would changing up the kind of oil I use possibly relieve some of these issues. I've heard of limited success with people who change over to a full synthetic without the friction modifiers of course since it promotes better transmission operation. Or even to a heavier oil because the higher viscosity slows the countershaft down faster when it's freespinning.
The engineer side of me wishes that the yamaha engineers would have thought of some kind of countershaft dampener that would slow the rotation speed of the countershaft when the clutch is disengaged on these unsynchronized transmission. Sort of like this:
http://www.google.com/patents/US3478615
Pretty interesting read actually. Next time I get my hands on a junk xs series bike I'm going to try my hand at a custom fabricated dampener like this and maybe come up with some cool results.
Whenever I shift from 1st to 2nd when I'm really opening her up and accelerating quickly from stop I get a grinding noise and it seems like 2nd doesn't want to engage. I had the problem with my '78 XS1100 and now with my FZR600.
When I'm just beebopping around at regular rpms shifting goes smoothly and I don't get any gear clash but when I accelerate quickly and try to shift from 1st to 2nd I get issues about 60% of the time. I am fully disengaging the clutch and the clutch is properly adjusted so I know that it's not because power is still going to the countershaft. These are fast bikes and I can't imagine that they aren't capable of high rates of acceleration and quick shifting.
What I've seen reading through forum searches is that when you do a high rpm shift it takes longer for the countershaft to slow down enough for the next gear to engage. Also, that this problem is exclusive to 1st to 2nd gear upshifts and 2nd to 1st downshifts namely because they are the only gear changes that have a free spinning gear being engaged with the slots of a gear that's fixed to the countershaft. I guess let me explain that more:
Upshifting (slightly different for a six speed):
-1st to 2nd --> shift fork pulls 1st dogs off of 4th gear slots and pushes 2nd dogs onto 5th gear slots
-2nd to 3rd --> shift fork pulls first off and drive gear engages fixed 3rd gear
-3rd to 4th --> shift fork pushes drive gear onto fixed 4th gear
etc.
Downshifting (D0wn5h1ft'ing ) (again, slight different for six speed):
-3rd to 2nd --> shift fork pushes 2nd dogs into 5th slots
-2nd to 1st --> shift fork pushes 2nd dog out of 5th (fixed) slots and 1st dogs into 4th (fixed) slots
As you can see, I think the issues is only present with 1to2 and 2to1 is because they are the changes where free spinning gears are being meshed with the fixed gears on the countershaft.
So my question is how do I prevent the gear grinding, which is horrible for these old transmission, during fast acceleration at high rpms? I know one solution is hold the clutch in longer before shifting which allows the countershaft to slow down more allowing the gears to actually engage the countershaft without grinding. But this leads to granny shifting and I just refuse to believe that these high performance bikes are incapable of this kind of shifting.
Another question is would changing up the kind of oil I use possibly relieve some of these issues. I've heard of limited success with people who change over to a full synthetic without the friction modifiers of course since it promotes better transmission operation. Or even to a heavier oil because the higher viscosity slows the countershaft down faster when it's freespinning.
The engineer side of me wishes that the yamaha engineers would have thought of some kind of countershaft dampener that would slow the rotation speed of the countershaft when the clutch is disengaged on these unsynchronized transmission. Sort of like this:
http://www.google.com/patents/US3478615
Pretty interesting read actually. Next time I get my hands on a junk xs series bike I'm going to try my hand at a custom fabricated dampener like this and maybe come up with some cool results.
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