Exploding sprocket!

[crumbobly]

Hey Guys,
Just had to tell someone about my nasty little supprise i had the other day.
Anyways i was riding home from work. And on passing a rather slow moving ute changed from 2nd to 3rd and ..... BANG.... My front sprocket exploded!!!!
Well i was about 2km from home so thought id push
Get home and pull the sprocket cover off to find half of the sprocket sitting in the cover and the rest of it im guessing in pieces over the road. On closer inspection i see that the sprocket had actually been welded to the shaft. I guess it serves me right for not checking all that out before purchasing.
But still thats pretty dangerous. I could have come off in a big way...
Is it actuall plausable to weld the sprocket to the shaft???
So ive managed to clean up the splines with a die grinder and have put a new sprocket on and didnt really like the idea of welding this sprocket on so i drilled a hole into the spline and tapped a thread and have put a bolt and washer to hold the sprocket on.
Im not too sure how they go on from factory as i dont have a manual for it.
So do you guys think thats suitable....?
Has anyone else come across a front sprocket welded on?
Bike is a '92 GSF250

[SS90]

Hey Guys,
Just had to tell someone about my nasty little supprise i had the other day.
Anyways i was riding home from work. And on passing a rather slow moving ute changed from 2nd to 3rd and ..... BANG.... My front sprocket exploded!!!!
Well i was about 2km from home so thought id push
Get home and pull the sprocket cover off to find half of the sprocket sitting in the cover and the rest of it im guessing in pieces over the road. On closer inspection i see that the sprocket had actually been welded to the shaft. I guess it serves me right for not checking all that out before purchasing.
But still thats pretty dangerous. I could have come off in a big way...
Is it actuall plausable to weld the sprocket to the shaft???
So ive managed to clean up the splines with a die grinder and have put a new sprocket on and didnt really like the idea of welding this sprocket on so i drilled a hole into the spline and tapped a thread and have put a bolt and washer to hold the sprocket on.
Im not too sure how they go on from factory as i dont have a manual for it.
So do you guys think thats suitable....?
Has anyone else come across a front sprocket welded on?
Bike is a '92 GSF250

I am impressed that you managed to 1) remove the weld, and repair the spline, and, 2) drill and tap the shaft.
Anynway,

The front sprocket is held on by a "locking plate", that sits in the (possibly now missing) groove of at the end of the spline, and, when turned, the two holes lone up with two holes on the front sprocket, which are threaded with M6.

And, simply 2 M6 cap screws hold the sprocket to the locking plate, which allows "free play" of the sprocket, but does not allow it to come off.

I suspect someone lost the plate, but had a welder.

[crumbobly]

Well i nearly gave up on trying to drill and tap the shaft as i tried an HSS drill bit. That went blunt in a split second. Tried with a cobalt drill bit. That lasted all of maybe 1 second and got about 2mm into the shaft. So off i went to find a harder drill bit. Went to two engineering shops and the best they could do offer was an overpriced cobalt bit to which i had already made blunt. So decided to see what Mitre 10 mega had to offer..... Not much... but they did have masonary bits..... hmmmm i pondered..... these are made of tungsten carbide. So i thought why not. They were cheaper than the cobalt bits. So i got it home and gave it a bit of a sharpen on the bench grinder. And what do ya know. It bloody worked.
Ill post a picture of what i have done if i remember tonight.
I can sort of see where the groove was supposed to be. But this new sprocket i have is wider than the old one and fits almost flush with the end of the spline.

[schrodingers cat]

How did you mage to tap the shaft? Or was it only case or flash hardened on the outside?

Masonary drills have their uses alright! LOTS o coolant!

[bogan]

good on ya mate, thats the kiwi diy attitude . Though sounds like that last owner had it too, but was missing some competence. As long as theres no play in it and its aligned properly (sounds like it is) I see no problems with this, just hope the guy who welded it on didn't damage the bearing in the process though.

[crumbobly]

To be honest i think it was just luck... i couldnt find my tap wrench so put the tap into my grunty drill and slowly went in and out taking little bites at a time with a heap of cutting fluid cleaning out the the flutes. I have a pretty steady hand haha. Would have made my day breaking the tap off.
Not sure if it was only case or flash hardend but its bloody hard material.

And i hope the bearings are fine too... i really dont want to pull it all apart.

Guess i opted for the quick fix. Just not quite as quick as welding. And hopefully my way is reliable.

[schrodingers cat]

Given that a beaing regularly survives 85 degree plus temperatures I doubt that the HEAT energy put into the shaft by the welding would have been sufficient to transfer to the bearing and get it to anything like that. Is the seal burnt? Is the grease cooked? Doubt it

Heat and temperature are two different animals

Ride on McDuff

[Ixion]

I've seen a good few welded on sprockets. Never done one, but I wouldn't expect any issues with bearings or seals, if an arc welder be used. Never heard of one breaking like that though, I suspect maybe the sprocket wasn't true to the shaft.

[bogan]

Given that a beaing regularly survives 85 degree plus temperatures I doubt that the HEAT energy put into the shaft by the welding would have been sufficient to transfer to the bearing and get it to anything like that. Is the seal burnt? Is the grease cooked? Doubt it

Heat and temperature are two different animals

Ride on McDuff

yeh I wouldn't expect the heat to do it, but if the guy put the earth lead on the frame instead of the shaft or sprocket, you'd get hundreds of amps going through path of least resistance, and a portion of that would be the bearing, which could fuck it up some lets just hope the guy managed to put the earth lead on the sprocket or shaft

[CookMySock]

Good on you with the masonry bit.

Yeah thats an old trick - I have seen a broken easy-out removed with a sharpened masonry bit. Nice work!


Steve

[sputnikMk2]

Im not too sure how they go on from factory as i dont have a manual for it.

My GSF has a circlip on the outside of the shaft which stops it falling off but still lets it align itself with the rear sprocket.

[crumbobly]

My GSF has a circlip on the outside of the shaft which stops it falling off but still lets it align itself with the rear sprocket.

I see.... So how much of a gap is there between the sprocket and the circlip?

[quickbuck]

I see.... So how much of a gap is there between the sprocket and the circlip?

I would say about 2 to 5 thou... what ever that is in metric... ie, not much but enough to allow a bit of float.

If the sprocket was indeed welded on, i would say it ran out of heat cycles, got too brittle, and BANG!
You are pretty lucky, because if the chain jams, guess what... No amount of pulling in the clutch, will let the rear wheel turn again...