Lost Drive Power

concours said:

@KirkJ
As mentioned above, the scoring/galling on the two tapered surfaces must be closely inspected. A talented mechanic with a polishing stone may be able to save the crankshaft.
The sprocket should be replaced.

Pictures please.

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That's the reason I asked the history
Some well meaning person may have fitted a new crankshaft sprocket without even giving it a gental lap with fine paste
Just to see what the contact area is like

baz said:

And you absolutely must lap the two surfaces back in again until you have perfect contact

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Agreed, but need to add one word: And you absolutely must lap the two surfaces back in again until you just have perfect contact

It's relatively easy to overdo it and have the sprocket too close to the crankshaft seal. Also, before lapping, make sure any "lip" on the sides of the keyway in both the crank and sprocket is removed.

marshg246 said:

Agreed, but need to add one word: And you absolutely must lap the two surfaces back in again until you just have perfect contact

It's relatively easy to overdo it and have the sprocket too close to the crankshaft seal. Also, before lapping, make sure any "lip" on the sides of the keyway in both the crank and sprocket is removed.

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Yep
I guess I just take it as read that nobody would lap further than needed
But I take the point
Having seen some valves lapped in so far they'll end up in Narnia!!!

Why is there a key on this aprocket as there is no alignment requirement for it?

I had the rotor nut come loose 1st ride after getting bike back from a "pro" builder that had reassembled bike...the serated washer was absent. The shfting rotor messed up the timing scale but nothing more as far as I could determine.

Tornado said:

Why is there a key on this aprocket as there is no alignment requirement for it?

I had the rotor nut come loose 1st ride after getting bike back from a "pro" builder that had reassembled bike...the serated washer was absent. The shfting rotor messed up the timing scale but nothing more as far as I could determine.

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As I said earlier in a perfect world the woodruff key shouldn't take the load but in the real world sometimes they do
Take a look at the key and see if there are any witnesses marks
Yes on a commando there's no alignment needed on the engine sprocket
Feel free to remove your woodruff key but make sure you keep that alternator nut really tight at all times and the mating surfaces are tip top