G: Gearbox (Twin) Cracked G4 final drive shaft

TouringGodet

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Not counting consumables like pistons and valve jobs, this is only the second failure for the Shadow. My father had an Alpha big end installed in the late 50’s but did not put the engine back together until the 80’s.
 

greg brillus

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Maybe it's simply a matter of the shaft being hardened too much, the G16 bush could have too much interference and the shaft has just let go on the weakest points at the base of each spline.
 

Bill Thomas

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I think Steve must have cleaned up the shaft a bit,
I would think it showed a bit of colour !!,
Would a tight rear chain stress it ?.

For me another reason to keep the full 2 UK pints of oil in there ?.
 

Peter Holmes

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Hello, I have had a G4 fail in the same manner, luckily not so catastrophically. The bushing looks like the correct oilite.
Just old age, much like many owners!
John.
A very good point, I suppose even our beloved Vincents are not totally immune from metal fatigue, and like most of their owners they are getting on a bit, and lets be honest, when the clutch has occasionally not functioned as it should who hasn't been a bit rough with the gear lever just to get you home, I certainly have been guilty of that over the last 56 years.
 

vibrac

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The twin gears are tough compared to most classics but perhaps they aint 'Burman tough'. 10,000 DR's boots stamping down throughout WW2 saw to that testing
 

craig

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Was there a modification to G4 to reduce issues with G3/G4 lubrication?
Maybe notches at G4/G6 end?
Or holes drilled in G4?
G3G4mod2.jpg
 

erik

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@ Bill . I would think About a rear chain with to much Tension is a Point to dicuss.Especially if the chain and sprockets are worn and the chain can run onto the teeth.Erik
 
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