Gearbox problem

crossflow
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Gearbox problem

Post by crossflow » Fri May 12, 2017 4:29 pm

Well, the bike went through its MOT today so, taxed and insured, I went out for a ride (in heavy rain and windy conditions) to see how it went. Not the best circumstances and for sure it's not perfect but I like the feeling of what it might be if the loose ends are tidied up. I definitely think it might need the head bearings looking at as there's something a little vague about the handling, the front brake is utterly wooden and I still have to deal with the popping on overrun but the main issue is that it doesn't seem to have a fifth gear.
I have since seen that there is a known issue with damage to the teeth of this gear pairing, but does this ever manifest itself in losing 5th altogether? There are no problems at any point through the gears but then when you go into 5th, it's like another neutral....the engine revs freely with no drive. Are there any known selection issues?
3yf by the way...
Cheers,
Rich

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xtzrick
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Re: Gearbox problem

Post by xtzrick » Sat May 13, 2017 12:12 am

Head bearing problems are common to all "oil in frame" bikes, make sure the bearings you buy have a rubber seal built in to the lower race.

I've not heard of any problems selecting gears that weren't caused by improper chain adjustment or dragging clutch.
Can you rock the bike through the gears with the engine off?

Rick

crossflow
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Re: Gearbox problem

Post by crossflow » Sat May 13, 2017 1:09 pm

xtzrick wrote:Head bearing problems are common to all "oil in frame" bikes, make sure the bearings you buy have a rubber seal built in to the lower race.

I've not heard of any problems selecting gears that weren't caused by improper chain adjustment or dragging clutch.
Can you rock the bike through the gears with the engine off?

Rick
Unfortunately it's not selecting 5th, either with the engine off or when riding. When I keep pressure up on the gear shift as if going into 5th, I can feel a slight pulsing feeling that I am guessing is rotation linked. Maybe this means that the selector is trying to slide the gear into mesh but either something is stopping it from moving or there is no dog engagement when 5th is selected due to previous damage. I hope this this is a selector problem so I'll put it up on the stand to get that cover off to have a look.
I did go out on it again this morning (sunshine) and really enjoyed it, but it's not very sensible considering that castastrophic engine failure might well be the least of your problems if a damaged box locks up. I have to sort it out.

crossflow
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Re: Gearbox problem

Post by crossflow » Sat May 13, 2017 2:32 pm

Back on the ramp, rear wheel in the air and it does now seem to select 5th. Going to remove clutch cover and see if I can see a selector issue.

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Re: Gearbox problem

Post by crossflow » Sun May 14, 2017 9:27 pm

Clutch cover off and the thing shifts effortlessly into every gear with me just rotating output shaft by hand. When moving into fifth, I cannot even get it to stay in a false neutral as the detent doesn't allow it. Goes straight through into gear. Output shaft spins freely in neutral..no obvious bearing issue and wasn't noisy in operation.
Obviously I'm not seeing the whole picture here and the comment about chain tension makes me wonder whether there is a possibility that I might have a slight bend in the output shaft that is only a problem when in use. The reason that I thought it might be a possibility is that when I bought the bike, I noticed that the previous owner had fitted a new chain but I didn't immediately check the tension. I'm sure that I sat on the bike before I checked the chain ...when I did, it was very tight. I just wouldn't have thought anybody would have set it up like that. I was wondering whether it was possible that this had slightly bent the shaft so that in operation, the selection of 5th was compromised. I have checked runout on the output shaft the best I can ( as there's not much to go on) but it's not showing anything much...a couple of thou maybe, but I'm not running the clock on a perfect surface so it's not really reliable info. Also, as its right up against the bearing I suppose any bend on the shaft would hardly show at all within the 1" projecting, but could well result in far more internally.
I don't know, maybe I'm barking up the wrong tree but I cannot see that I have actually done anything to fix a problem yet now I don't have one , and though I can't get it to do it at the moment, I'm pretty confident that it still won't shift in action.
Has anyone experience over bending an output shaft on these motors?

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Re: Gearbox problem

Post by jibber » Sun May 14, 2017 9:57 pm

On here, I have seen totally ruined bearings, broken drive dogs, shagged splines, knackered gear teeth etc, but can not remember reading about bent shafts.

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Re: Gearbox problem

Post by crossflow » Sun May 14, 2017 10:33 pm

jibber wrote:On here, I have seen totally ruined bearings, broken drive dogs, shagged splines, knackered gear teeth etc, but can not remember reading about bent shafts.
Well, it quite possibly isn't... I'm really appealing for insight because I don't want to have to drop the engine and split the cases unless I'm sure. Or surer than I am right now anyway.
How about a deteriorating bearing affecting shift on 5th?

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Re: Gearbox problem

Post by xtzrick » Sun May 14, 2017 11:44 pm

I think a bent shaft would knacker the output bearing and you would see lots of oil pumping past the seal, if you can't feel any play then it's probably ok.

The things that are 5th specific tend to be between the cases apart from the pins in the end of the selector drum, I think you need to take the clutch off to see if they are damaged.

Check your rear cush drive rubbers and bearings, they can knacker up quite quickly, would have thought they'd affect all gears but it's an easier 1st step than splitting your cases.

Rick

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Re: Gearbox problem

Post by crossflow » Mon May 15, 2017 12:26 am

xtzrick wrote:I think a bent shaft would knacker the output bearing and you would see lots of oil pumping past the seal, if you can't feel any play then it's probably ok.

The things that are 5th specific tend to be between the cases apart from the pins in the end of the selector drum, I think you need to take the clutch off to see if they are damaged.

Check your rear cush drive rubbers and bearings, they can knacker up quite quickly, would have thought they'd affect all gears but it's an easier 1st step than splitting your cases.

Rick
I'll get a clutch locking tool to get that off and I'll have a look at pins on the end of the drum. Certainly good enough to shift without load...
I can't see the rear bearings or Cush rubbers affecting the change on one gear but I understand what you mean. Rubbers have some play, bearings are fine.
The lack of 5th was so definite...into a neutral with no hint of going into a gear,regardless of speed or load.

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Re: Gearbox problem

Post by ActionManMelb » Mon May 15, 2017 1:20 pm

Forget the bent shaft theory!

Look for a piece of debris in or near the hairpin spring of the selector pawls (the claws that grab the pins on the drum).

Could also be a piece junk temporarily stuck in the track of the selector drum (where the fork rides).
"Don't worry," he said, "things could be worse ........."
So I stopped worrying and lo and behold, things did get worse!

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