Worn keyway on crankshaft

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If the existing keyway has two parallel sides, then I would agree with olympus's suggestion to make a stepped key to fit both the crank and sprocket. Not rocket science. Keystock is cheap so if you screwup you get lots of tries.
 
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If it were mine I would carefully dress down the area either side of the keyway
I would get a new sprocket and lap it on to the crank for a perfect fit
Then make a stepped key to fit
 
I've done this kind of repair before on flywheel magnetos, the biggest job here will be the accurate manufacture of the stepped key
 

Front Pulley Issues

Overly complex compared to shoving crap in the gap or getting a blank pulley machined to the right taper. I don’t agree. Any competent machinist with a lathe could do that in 15 mins. Way way way better that jamming bits of tin in there. Machine it back, put some engineers blue on it to identify...
www.accessnorton.com www.accessnorton.com

Remember that the key does not hold the pulley, it's just there to index the marks on the alternator rotor.
 
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Locomotive traction motors have no keyway on the taper for the coupling using only the taper to lock in after being heated and drawn into position.... so what does this fact communicate. We used an arc gouger to carefully remove them when the need arose to prevent damage to the DC motor shaft. I have to go with the gentleman's opinion on the key's use as an indexing tool after reflecting on this because if locked solidly onto a proper taper fit the sprocket is where it shall remain..... Getting old is hell on the memory.... Just more to roll around in the noggin.
 
baz said:
If it were mine I would carefully dress down the area either side of the keyway
I would get a new sprocket and lap it on to the crank for a perfect fit
Then make a stepped key to fit
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^^^ this.

I wonder if you could lap the two surfaces, then hard chrome the sprocket's taper to tighten the fit and move the sprocket back out on the shaft, then maybe lap it again so it's got both a good fit and is still proud of the shoulder on the shaft like it's supposed to be.... (another question for the jim comstocks of the world..)
 
o0norton0o said:
^^^ this.

I wonder if you could lap the two surfaces, then hard chrome the sprocket's taper to tighten the fit and move the sprocket back out on the shaft, then maybe lap it again so it's got both a good fit and is still proud of the shoulder on the shaft like it's supposed to be.... (another question for the jim comstocks of the world..)
Click to expand...
Hard chrome involves grinding down in a bore grinding machine as it will be a rough surface that requires finishing.
 
Since there's nothing to index, I don't agree with the key is there to index/register only.
 
marshg246 said:
Since there's nothing to index, I don't agree with the key is there to index/register only.
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+1. Without the key, the sprocket would most likely spin on the crankshaft.

I would cut a new key way 180 degrees opposite on the crank. I do not think it necessary to weld up the old key way and welding may create a distortion. Unfortunately, it means splitting the cases.

Slick
 
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Bernhard said:
Hard chrome involves grinding down in a bore grinding machine as it will be a rough surface that requires finishing.
Click to expand...

Perhaps I wasn't clear. I meant that if the surface of the sprocket taper could be built up with some sort of plating (hard chrome), then the sprocket could be lapped to the existing taper, and NOT be too far in on the shaft. Why would the chrome plating need to have any fine finishing if it's going to be lapped to the taper of the shaft again after chroming? (It's a question, not a solution I'm proposing)

I watched that metal spraying video the other day and that's essentially what the machinist did, except he did it to the shaft, then turned it back down to recieve the race. Why couldn't it be done the opposite way? build up the sprocket taper, then lap it to the shaft....
 
o0norton0o said:
Perhaps I wasn't clear. I meant that if the surface of the sprocket taper could be built up with some sort of plating (hard chrome), then the sprocket could be lapped to the existing taper, and NOT be too far in on the shaft. Why would the chrome plating need to have any fine finishing if it's going to be lapped to the taper of the shaft again after chroming? (It's a question, not a solution I'm proposing)

I watched that metal spraying video the other day and that's essentially what the machinist did, except he did it to the shaft, then turned it back down to recieve the race. Why couldn't it be done the opposite way? build up the sprocket taper, then lap it to the shaft....
Click to expand...
Hard chromeing and chrome plating are two entirely different processes, as you quoted the former, I realised you were not familiar with the former. Chrome plating on the other hand is unsuitable for such a job, best used to plate your wheels and other bright work that endures your machine.
In all honesty, you would be better off obtaining a new sprocket and lapping it onto the shaft with fine valve grinding pase it's the taper that transmits the load, you should need a Norton sprocket puller to remove it afterwards.
 
yeah, I wasn't sure what the process was to build up the taper inside the sprocket, because building up the taper on the shaft requires disassembly, and at that point, just getting a new crank is a better solution anyway.

I mentioned previously that he should get a new sprocket, but I think his shaft surface is so poor that once he laps his new sprocket, it's going to be too far inboard on the shaft,.... SO, my rookie idea was to take the sprocket after the first fitting and build the tapered surface up through some sort of plating, so it can be lapped a second time to make a perfect fit, and then not be too far inboard after the second lapping.

I would also buy 5 oversize keys, pull out my belt sanding table and carefully fit the key, like my life depended on it... With 5 chances, it would fit like a glove.
 
I agree, I think making a key to fit the damaged slot is a good idea, and widening the keyway should not be too difficult.
 
I have seen a similar problem years ago on a 750 shaft. As best I remember the cause of the problem was the deep nut for the shaft that holds everything together was not threaded all the way to the end. The nut would tighten on the shaft, run out of threads, before the gear engaged the taper with sufficient force to lock it in place.
 
It is certainly NOT uncommon for the alternator rotor nut to come loose. A lot of owners do not tighten them properly, and / or use correct locking washers.

When this happens on a Triumph, the sprocket rattles / clatters on the splines on the crank making an awful din but not doing too much damage unless the owner is totally deaf.

When it happens on a Norton, the sprocket and crank taper eat each other.

(The reverse being the case with the gearbox main shaft situation !)
 
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Correct me if I'm mistaken... First impression was chatter from being loose. First thoughts were toss crank pin & sprocket, but being the pin is such a PITA to change I'm hoping for the underdog owner to come out without going through the costly process....... So could one or more of you more learned gentlemen help him along with some possible %'s of potential failure rates he could expect pursuing the various patch jobs put forth.
Lots are sound, though still require a priest present and considerable time and luck. No aspersions cast on anyone's suggestions seeing as I've just paid for the front caliper ruined in a fixit dream..... It was a good solid sensible thought too, but Murphy stepped in. Anyway riding season is upon one of our brothers and my experience covers lower RPM high torque service. Virtually useless in this situation.
 
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