Worn keyway on crankshaft

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danfr

danfr

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Hey all, I’m reassembling my bike after being tucked away for a few years. I noticed the notch for the key on the end of the crankshaft is very worn. Has anyone had experience with this?

Video of crank play

Dan
 
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Is the keyslot and taper of the crankshaft still ok ? if so, I would replace the key and the pinion . It is the taper and not the key that holds the pinion in place.
 
The key itself is in fairly good condition. A bit more wear on one side as expected. The taper isn't holding anything unfortunately. I would imagine the sprocket would eventually wear through the crank seal. I'm wondering if its the sprocket that is worn or the taper. If its just the sprocket, I could replace it, have a friction fit, install a new woodruff key and jb it in and finally a new lock washer on the end of the crank to make sure nothing slips off.....

Here's another video and some follow up photos. This poor bike has really been beat on:

Worn Keyway

Worn keyway on crankshaft


Worn keyway on crankshaft


Worn keyway on crankshaft
 
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Those areas of raised metal around the key way will hold the sprocket off of the taper.

Difficult to be sure from your pictures, but sumthin don’t look right about the crank taper to my eye, it looks too shallow?

Now, why is the sprocket fouling the seal... is the seal all the way home? If so I’m thinking someone has lapped in the sprocket in the past in order to try and fix it, and the sprocket is now too far in board.
 
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Fast Eddie said:
Those areas of raised metal around the key way will hold the sprocket off of the taper.

Difficult to be sure from your pictures, but sumthin don’t look right about the crank taper to my eye, it looks to shallow?

Now, why is the sprocket fouling the seal... is the seal all the way home? If so I’m thinking someone has lapped in the sprocket in the past in order to try and fix it, and the sprocket is now too far in board.
Click to expand...

I don’t think any raised areas are catching. The sprocket is lipped inboard and is where it makes contact first. You can see on the seal the wear.

I took a straight edge over the seal and it is a little proud of engine case. I’m guessing 30 thou. So maybe if the seal is Pressed in a bit tighter the taper will grab. Here’s hoping!
 
I concur with what Eddie said, It looks like there is no taper on the crankshaft, or is the taper very shallow ? or is the picture just deceiving ?
Loose fit of the crankshaft pinion must have caused the damage that we see here, It looks like you have a serious problem here.
 
Dan, You can buy wider keys, but you are going to have issues cleaning up keyway to accept it due to it's proximity to the case / seal. Also I agree, there doesn't look as though there is any taper, which would explain the hammering the keyway has received. Can you measure the outer and inner of the shaft and see if there's any difference?

[EDIT]

Perhaps there is a taper and the camera angle is disguising it?

With a file I would carefully remove all the raised metal around the keyway, then put the sprocket on without the key and see if it locks on a taper. Of course the sprocket is likely to be worn as well, so may pass too far down the shaft before hitting a taper (if it exists)

Cheers,

cliffa.
 
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When you look at the vid, it looks like with the sprocket installed the end of the taper (shoulder) on the crank is protruding above the sprocket....it may only be a fraction, but if this is the case you have a worn out sprocket, crank or both. The end of the taper must be below the face of the sprocket
Can you confirm that this is the case, as it may be the camera giving the wrong impression
 
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Like others have said, there should be a very definite taper to the crank, yours looks straight. The taper does all the work, without it, all the stress is on the key. Look inside the sprocket, it should be tapered to match the crank. If your crank has been modified, you’d be best to replace it rather than try to just fix the key way.
 
Paint your crank ’taper’ with a sharpie permanent marker, then fit the sprocket without the woodruff key.

Turn the sprocket backwards and forwards like you are grinding in new valves.

When you take the sprocket off the crankshaft, there should be no marker left at all.

This is a great way to confirm the fit, and tells you if you need to start digging deeper.
 
How about more pictures of the engine? Are those welds on the crankcase? The taper isn't pronounced so it might be the camera lens that's distorting it.

I had to shim my sprocket to get it to work. Not sure if that will work with yours.
 
It looks like someone turned down the taper on your crankshaft. The result is exactly what you see in the pictures. The sprocket and key hammered the living shit out of the key-way in the crankshaft.

Most people would replace the crankshaft. Perhaps there's some other process to restore the taper (metal spraying?) and dress the keyway, but somehow I doubt it. I wish I had a better suggestion Dan, but that doesn't look fixable to me, but it would be best to ask a knowledgeable Norton savvy machinist if it's fixable...
 
If the taper is there and matches the sprocket (doesn't look like it) , there are three ways I know to fix the keyway. Weld and recut, cut a new keyway on the other side, cut for a wider key and cut the sprocket match.
 
Wow! Thanks for all the replies!

Yes there is a taper to both the crank and the sprocket. If I remove the keyway and rotate the sprocket, there is a friction fit when I tap in the sprocket. So I'm curious which will wear first, the sprocket or the crankshaft. I would assume they are both hardened steel.

I think the best route to go is to pick up a new sprocket and machine a new keyway 180 degrees from the existing one, like Greg said.

Worn keyway on crankshaft
 
Once you have the new sprocket & confirmed everything is correct....taper below the surface
1. I would suggest the crank is dressed around the key way slot
2. Apply a small amount of fine grinding paste and gently lap the two together
3. Get some engineers blue and check that the full surface of the sprocket is in contact with the crank taper
4. Get some key stock and make a stepped key to suit the different width holes to the two component.
A fair amount of work but certainly do able
 
olympus said:
Once you have the new sprocket & confirmed everything is correct....taper below the surface
1. I would suggest the crank is dressed around the key way slot
2. Apply a small amount of fine grinding paste and gently lap the two together
3. Get some engineers blue and check that the full surface of the sprocket is in contact with the crank taper
4. Get some key stock and make a stepped key to suit the different width holes to the two component.
A fair amount of work but certainly do able
Click to expand...


I have some valve lapping compound and can pick up some layout dye. Great idea.

You earlier asked about the depth of the sprocket and yes its face is a little raised of the crankshaft face.
 
I like the new keyway thoughts. Don't believe I'd wish to play with a patch job right there. ... I've another sprocket which is pretty decent out back that's not boogered with a lot of life left in it.
 
I would buy a new sprocket to see if it sits higher out on the taper. If you are going to lap the sprocket and shaft, then the sprocket is going to recede. As was mentioned, that sprocket needs to be proud of the taper. If you get an excellent taper fit, perhaps there's not much need to do anything to the keyway except dress the high spots off. That may sound "hair-brained", and it might actually be... That's why I would private message Jim Comstock and ask him for advise... Machinists are the people who fix this kind of thing, who better to ask than Jim?...
 
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