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Here is a strange fault that I can't understand why it occurred or why it disappeared.

You may recall I had issues with the transmission and shimming.
Sorted that with the help of you lot and the links to parts manuals.

Test the transmission without the crank, and end float of the 2 shafts. All happy...
Split cases and fit crank and check end float clearances. All good.
Changes gears, finds neutral,,, All good.
Fit clutch, sprocket and test gears, all good.
Fit cylinder and head. Set timing with new Electrex ignition and alternator.
Fit clutch cover and oil pump and ignition.
Test gear selection and neutral. All Good.
Install engine in frame.

A week later I go to fit the drive chain.
Can't turn the sprocket without the crank turning,,,, Must be in gear
Find neutral, still same as if it is in gear.
If I use a 24mm socket on the sprocket nut I can (with considerable force) turn the sprocket without the crank moving.

Remove the engine, remove head and cylinder.
Remove the clutch.
Clutch and sprocket shafts both turn freely but NOT independently !
I can see the gear dogs are not engaged on any gear.
If I hold the clutch with the clutch holding tool I can turn the sprocket independently with a socket but it is very hard to turn.
As if one of the freewheeling gears is stuck on the shaft not letting the shafts turn independently.

Call everyone I know that has experience in building singles. No answers that I haven't thought of.
I had the engine laying on the clutch side to remove the sprocket.
Rolled it back upright and the two shafts are now free of each other,,,,
And I can't replicate the problem again. WTF,,,

I don't want to split the cases and find nothing.
It changes gears and finds neutral.
I've rolled the engine over several times in all directions and all is as it should be.
Don't want to build the engine again and fit it in the frame and have it happen again, or worse when it is doing 100km per hour.

Any ideas ?
Sorry for the long winded story.

Regards
Graeme

Hi Graham,

What an absolute pain. Did the shafts free off after you removed the sprocket? If so, I am wondering if tightening the sprocket has introduced some binding somewhere. I think that you have to hope that Nigel sees your post; I would guess that he has built more Ducati Singles than anybody and will be bound to have come across this problem.

Something else comes to mind - with the barrel off, and if you go through the gear selection, can you get end-float on the gears where they butt up against the bearings? You can check this with a screwdriver moving the gears from side-to-side - I think that it may be possible to have end-float on the shafts, but still have a gear sandwiched tightly against the bearing..... Possibly.

Good luck,

Colin

Hello Colin,

Rolled the cases with the sprocket still on and tight and the clutch inner on and tight.
Maybe .03 or .04 end float on both shafts. Should be loose enough.
The gears at each end of the input and output of both shafts are free.
I have laid the cases on the clutch side and the timing side and changed through all 5 gears. Then vertical and same result. All good.
Got me fuc*ed,,,,,
Nigel may have seen this, I hope.
Trouble is I can't get it to do it again.
Was as if one of the free wheeling gears was glued in place?
When I assembled the trans I used Nulon assembly lube.
I've used that before and never had an issue.

graeme

Sounds like the kickstart mechanism is moving accross . tipping the bike over towards the drive side used to be the way to get the KS to engage on the NC models.

Might be totally unrelated, but when I built my 4-speed gearbox, I fitted one of the gears back to front on the shaft. It all assembled and the 2 crankcase halves went together but it was very hard to rotate the output shaft due to binding against the case.
I should have looked at my stripdown photos before I put it together, but it was easy to see when I took it apart again.

I think I found the problem.
With the sprocket removed all is happy.
Once the sprocket is tightened and pulls the output shaft towards the sprocket it binds up.
I added an extra spline shim under the 5th gear, the gear directly inboard of the sprocket.
I did this to line up the gear teeth with its gear on the input shaft.
But,,,,
The extra spline shim (0.5mm thick) lifts the 5th gear enough that the shoulder of the spline is slightly less protruding above the gear.
Thus when the sprocket is tightened it pushes the 5th gear against the 2mm shim that touches the bearing and squeezes it against 5th gear.
Remove the extra spline shim, lets the shaft shoulder sit against the 2mm shim and gives clearance when the sprocket is tightened.
(at least that is what I found)
(the joys of building an engine from parts !!!!)



Spline shim 16.170, I removed 1 so the spline shaft shoulder is proud of the gear.
2mm shim 055 that sits against the shafts spline shoulder.

Now to reassemble and test gear changes, wish me luck.

Hope this makes sense,,,,

Thanks for all the suggestions

Graeme

Hi Graeme

could be the front sprocket to . i had to put sprockets on a old shaft and put in the lathe to clean them up

they are not 100% round at the labyrint a lot of times .

Regards Eldert

Hello Eldert,
Hope you are well.
It was the extra spline shim I put under 5th gear.
Making it squash on the 2mm spacer next to the bearing when the sprocket is tightened.
Remove the extra shim so the shafts shoulder now presses against the spacer and bearing.
All good now.
Appreciate your advice.

Regards
Graeme

Well done Graame,

Who knows what has been done to these engines in the past fifty years, not to mention the errors that they came out of the factory with.

Let us know how it goes when you get it running.

Cheers,

Colin