Worn keyway on crankshaft

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I would source a new sprocket and see how worn the shaft is with it, What do you have to lose? Your going to need one anyway. If the new sprocket sits proud on the shaft just make sure you tighten it real good and give it a go, leave the key out. OK go ahead and roast me guys. I'm going for a ride now. Chuck. p.s. and then fix it next winter.
 
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Lots of replies, no consensus. So, here's what I would and wouldn't do.

Option 1: PM comoz and ask him what to do and what it would cost.
Option 2: Self-help:
  1. Buy a new sprocket
  2. Remove the crankshaft from the engine, split it, take the offending part to a machine shop along with the new sprocket.
  3. Ask the machinist to cleanup around the existing keyway and to inspect the taper. If the taper needs more that minimal lapping, buy a new crank - if not, continue.
  4. Ask the machinist whether it's best to cut a new keyway 180 degrees from the existing one, widen the existing one and make a stepped key, or widen the existing one and the one in the new sprocket.
You may find that the machine shop wants more than the cost of a good used crank.

Option 3: Be a big dummy, assemble with or without the existing key/keyway, and ignore it!
 
swooshdave said:

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.
Click to expand...

If you click on the link you'll see how I shimmed the tapered shaft and resolved my issue.

Everyone is correct, the key on the pulley/sprocket doesn't align to anything.
 
marshg246 said:
Lots of replies, no consensus. So, here's what I would and wouldn't do.

Option 1: PM comoz and ask him what to do and what it would cost.
Option 2: Self-help:
  1. Buy a new sprocket
  2. Remove the crankshaft from the engine, split it, take the offending part to a machine shop along with the new sprocket.
  3. Ask the machinist to cleanup around the existing keyway and to inspect the taper. If the taper needs more that minimal lapping, buy a new crank - if not, continue.
  4. Ask the machinist whether it's best to cut a new keyway 180 degrees from the existing one, widen the existing one and make a stepped key, or widen the existing one and the one in the new sprocket.
You may find that the machine shop wants more than the cost of a good used crank.

Option 3: Be a big dummy, assemble with or without the existing key/keyway, and ignore it!
Click to expand...

I asked Jim and he said to shim it. I did. It worked.
 
I was told by a pal many years back that the key is a safety item in the event of serious primary catastrophe. The key would shear off leading to a spinning situation instead of a lockup. Don't know if that was true as I've never tested the theory.
 
marshg246 said:
We don't know if his taper needs to be shimmed - we know is keyway is bad.
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Based on the condition of the keyway it would be hard to assume the taper is also bad. Regardless the keyway area needs to get cleaned up so the sprocket/pulley can be checked for fit. If the taper is good then even if the keyway is loose it shouldn't make a big difference, the taper would suffice. But if my assumption is correct the taper is also boogered so that needs to be addressed.
 
Holy guacamole guys! I guess I am not getting my post notifications as I had over two pages to catch up on! Thanks to everyone that has chimed in.

I’ll be taking this one step at a time and make decisions as things unfold. I have ordered up a brand new key, new sprocket, new star washer, and some machinist layout dye. Once everything shows up, I’ll have a look with the layout dye, post some pictures and we can continue forward.

Shimming does sound very appealing if it is a viable option. I’ll have to do some research on that one. Also probably best to contact Jim and get his thoughts once I have pictures to present to him.

I agree that a replacing the crank may be an option IF I do end up having to pull apart the bottom end. I know where I can track one down for a couple hundred dollars (Canadian $) and i would imagine it would be cheaper than the machine work. Of course you’re always rolling the dice with used. But I’m notquite at that point to have to make that decision.

I have worked as a machinist for a couple years, went to school for it as well. In my opinion IF the shaft and sprocket tapers are a perfect mate then I believe there is no need for the key. But that’s in a perfect world. I can’t imagine the force of that crank being transferred through that small key. That being said, I’m not going to toss that key out like some psychopath. I’m just hoping I can create a good tight mating.

keep you all posted!
Dan
 
The best of luck with it, and really hope you find the taper to still be serviceable...... Summer is upon you and you need all of the luck you can get to get on the road.
 
Torontonian said:
I was told by a pal many years back that the key is a safety item in the event of serious primary catastrophe. The key would shear off leading to a spinning situation instead of a lockup. Don't know if that was true as I've never tested the theory.
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Would assume the key would have to made of some other material, like brass, were that the case.
 
It looks like the sprocket has been trying to slip on the tapper and the key has worn the keyway depends on how far the keyway damage is on the crank I would shim the tapper locktite a new key in the keyway and new lock washer and tighten it all down and go for a ride.

Ashley
 
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jbruney said:
The best of luck with it, and really hope you find the taper to still be serviceable...... Summer is upon you and you need all of the luck you can get to get on the road.
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Actually my partner and I are expecting our first kid in ten weeks, so I was hoping to get it buttoned up before then
 
ashman said:
It looks like the sprocket has been trying to slip on the tapper and the key has worn the keyway depends on how far the keyway damage is on the crank I would shim the tapper lock tight a new key in the keyway and new lock washer and tighten it all down and go for a ride.

Ashley
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Judging by the wear on the taper and the keyway, I would imagine that the sprocket was slipping for some time.
 
texasSlick said:
+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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My 143 H.P. Rotax snowmobile crankshaft relies on a taper to transmit power through the primary clutch. No key.
 
The keyway is to stop it from slipping and as you say it looks like its been doing it for some time hence the wear to the keyway cutting, the keyway has stopped the sprocket from rotating completely, as I said before put a new key in and shim the tapper and it will be all good again.
This will be the cheapest fix for you and it will last a long time without any problems and save your money for what is coming in 10 weeks lol, you will need it, good luck.

Ashley
 
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