I was pulling out of a junction and my chain snapped and wrapped round the front sprocket. Ruined the rear chain guide aswell. 5000 miles and properly lubed and adjusted. I didnt take a picture but found one on advrider with almost identical damage. I hope i can get it welded.
Your chain may have been properly lubed and adjusted, but that one wasn't. That is one very worn sprocket.
Might be fixable, but it looks cracked all the way up to the clutch lever... This is why companies make case savers...
The picture has similar damage but my case just has a hole punched through, no cracks. The top part where the bearing seats is fully intact, luckily. I forgot to say in my first post that my friend and i believe the chain snapped at the split link. I dont think a piece of metal bolted to two flimsy casing mounts would have held up well. It would have to be mounted very robustly to take the hit my casing took.
Glad it didn't result in you having an accident- gotta admit chain breakage is always a concern of mine (I keep it maintained and have never had one break loose, but we all have things we think of. )
They are designed so the chain never has a chance to double over itself and get stuck ( which is what caused the case hit you took ), the chain instead just runs through and out the bottom hopefully dumping it on the ground.
Yep, the point of a case saver isn't to act as a shield, but as a guide to keep the chain from bunching up, because the damage happens when the chain whips into a bind and gets wedged between the sprocket and case.
I'm on the fence with the case savers as I have seen many snap the tabs off and cause as much or more damage. The best ones IMHO are the ones made from a delron like material and butt up against the case in front of it for support. Looks like that one took out the factory steel case saver as well as indicated by the snapped off mount. 5000 miles is a lot for a 520 chain and that sprocket is well worn out. All that said I would clean that area well, sand it some and JB weld it up.
Finally got some time to go and take a picture the damage done to my bike. Ive had my license 10 years and never had a chain snap. I have done 2500 miles since the beginning of November on this bike and only needed to adjust the chain a small amount, regulary oiled and cleaned.
I'd say that's plenty repairable. My factory chain was fine up to around 8k miles, didn't stretch much at all, then it started getting stiff and notchy. Sprockets were still fine. Went ahead and threw a kush sprocket on the rear and a new chain, but the front shows hardly any wear at 13k miles.
First of all, thank you for having shared your experience. IMO it's fixable with welding, since I don't think that the area damaged is much mechanically stressed, so if it doesn't leaks oil after the welding it should be fine because the upper and the lower areas should bear the stress. Was the plastic sprocket cover installed when it happened?
BTW, I had a similar (but less grave and difficult) repairing on my Husky some years ago, when the bolts of the rear sprocket became loose while riding: they dig a little furrow in the swingarm! The mechanic fixed it with a welder and this is the result:
The plastic sprocket cover was installed, just like it left the factory. Me and the friend i was riding with believe it failed in the area of the master link, we found pieces of it loose in the bunched up chain. Thanks for the heads up Theo, I will be keeping a check on my sprocket bolts regularly now. Ive talked to the foreman at a local engineering shop and he told me to bring the bike in for a look, hes done case welding before.
Which I believe has a metal case saver behind it. - Could be your master clip came loose and let the chain go. I have seen this happen when the rear chain guide gets bend in slightly causing it to wear out the masterlink clip.
No case saver behind Heres a couple of pics of my damaged rear chain guide insert I think the faulty part of the chain was sticking out before it went through and gouged into the insert and jammed, causing it to break. One end of the chain was jammed through it and stuck and the other end got pulled into the rest of the bunch in the sprocket.
It looks weldable to me. The sprocket on the other hand looks like it was made for catching fish. It's nothing but a ring of fishhooks. You should be able to weld it with the engine assembled and in the frame, no problem. May need to extract the clutch arm pivot bearing first to keep it from being damaged. A pocket reamer should be used or a good substitute for same to clean up that pivot hole before reinstalling the bearing and clutch actuator arm.
If it were my bike I think i would JB weld it instead of have someone weld it. My buddy had one welded (Wr250 but same issue), melted a nylon bushing in the arm area, this failed and caused the needle bearing to fall into his cases and destroy stuff. Make sure you know what your welding, what is inside the cases etc. JB weld should hold up forever there if done right. No stress just sealing a hole.
^^ that, no welding unless you are going to remove it and gut it. clean the oil off with some carb cleaner, jb weld, forget it.
