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Discussion Starter #1
Does anybody know if the primary crank gear from an earlier version 860 - about 1977 - will fit a later Bosch type square case? If I pull the primary gear off the ignition rotor for the early model - will it fit up to the later Bosch style flywheel? I have found an early type flywheel and clutch basket and want to use them to replace the defective gear and basket on my 1981 model.
Thanks
 

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Does anybody know if the primary crank gear from an earlier version 860 - about 1977 - will fit a later Bosch type square case? If I pull the primary gear off the ignition rotor for the early model - will it fit up to the later Bosch style flywheel? I have found an early type flywheel and clutch basket and want to use them to replace the defective gear and basket on my 1981 model.
Thanks
So what your trying to do is get rid of the Ducati Electronica ignition stator set up with a later Bosch set up ? my under standing is that the crank is different
I'm about to change my set up in my 76 SS with a Kukosan Electronic Ignition Conversion Kit using late belt drive Transducers and pick-up coils

If you get stuck I have a Bosch set spare PM me if you get stuck

Cheers Mate
 

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Discussion Starter #3
MHR:

I am trying to replace the damaged primary gear on my 81' model (Bosch) using parts from the earlier model. So I am trying to see if the primary gear on the early model will fit the later model crank and solid flywheel. On both years the primary gear attaches to the flywheel using six bolts and two guide pins. If the internal taper on the gear, width and number of the teeth are the same - then my hope is that it will fit. I don't have the 77' model gear near me to measure it. Maybe the late model Bosch parts are hard to find because they made fewer bikes(?)
 

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The part number for the Bosch gear is 0799. 47. 10, but I can't find a part number for the earlier gear; it is just not listed in the earlier parts catalogue. I think that this is a case of checking it physically, or asking people like Phil Hitchcock or Gowanloch's. The problem may be that the taper was different between the two types, so that the earlier one may not slide on far enough (or too far).
 

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The only way to tell for sure is to physically compare the two.The parts book lists the earlier primary gear as the ignition flywheel unit.Probably because the magnets on the flywheel are indexed to maintain timing.The taper on the crank should be the same.The difference in the cranks is outboard of the pri. gear location.Things like gears and clutch baskets are pretty expensive to redesign and I'll bet Ducati used proven pieces where ever possible.The probable reason your old gear cracked is it was over tightened at some point and the taper spread the gear and caused a stress riser at the keyway slot edges.Use some heat and a good fitting allen socket with an impact driver to remove the screws from the gear they are usually loctited and are countersunk heads so the torque to break them loose is pretty high.
 

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Discussion Starter #6
Update:

Just an FYI: the early primary gear will fit the later Bosch era crank. I managed to exchange the flywheel and mount the early gear to it. Also, since the clutch gear looked to be damaged I also used the earlier clutch housing. The spacing was different (the later hub used more offset) so I used the earlier model clutch washer and everything fit up. The later clutch does have a larger diameter bearing that may be what causes the different offset. Now everything is quite and smooth. Thanks for the comments.
 

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I'm glad that everything worked out OK for you, without too much wallet draining! One thing I would warn you about is the reason that the factory changed to the larger rear bearing on the clutch housing, which is that the earlier bearings tend to 'lock' if the clutch is released at hgher revs when pulling away, and this leads to the centre races spinning against the rear spacer and loosening the clutch. So if you hear a rattle in the future, you may need to re-torque the clutch.
 

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Discussion Starter #8
Duccout:

FWIW - I had to change back to the late clutch. The basket offset is different and I would have had to use the old style springs and cups which are weaker. I tried using the later clutch pack and hub in the older basket and the clutch drug horribly because the offset caused the actuation geometry to fall into a range where it could not be adjusted. No doubt I could have changed the actuation rods and so forth - but I will just stick with the late style clutch and enjoy the superior clutch action. All of the horrible noise was caused by the cracked crank gear and I am glad to have it resolved.
 

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All these different clutch variations are a bit of a minefield. I found out the hard way years ago when I bought a used clutch from a Bosch engine 900 to fit to my round-case 750, because I was fed-up with the poor original clutch action. After spending a day changing everything and making up spacers to align everything, I found that the clutch cover would not go on, ecause the later clutch is wider. C'est la Vie!
 
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