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Has anyone experience fixing something like this?



I did google a bit. jb weld seems to be a dreamstuff???

forget JB find a talented welder or get a new head


there are compounds to fix but JB is not one of them, Alumiweld in a pinch as long as it is not a stressed component

or get a new head

?
At some point a chain must have snapped.

No idea how this happened... I guess there was an inpact from the chain....
Question is how to fix....

What normally happens when the chain either derails or breaks is that it rolls up on the front sprocket until the diameter is such that it pushes the crankcase out of the way ...... and yours is mild compared to some of the damage I have seen

A good engineering/welding shop will be able to repair that crack unfortunately it means that the motor will need to come out and stripped down to do it properly. Been there done that.

Mc tool wrote:What normally happens when the chain either derails or breaks is that it rolls up on the front sprocket until the diameter is such that it pushes the crankcase out of the way ....

I didn't know that, and it's an interesting theory, but it suggests to me that those metal case savers are totally useless unless they can just stop the motor from turning over when the diameter becomes such that . . .

I've only ever had one chain let go on me, and luckily that just split and came off the sprockets and fell down onto the road.

is it possible the caser saver (which does not fit on 750 engines btw) withstands the forces and stalls the engine instead (shredding the gearbox). Also it usually is quite close to the chain so maybe it prevents the chain to roll up between engine case and sprocket.

I think the real truth is that if your diligent enough to fit a case saver your probly diligent enough not to let your chain/adjustment get so bad that it could fail .Please don't refer me back to the sprocket bolt thread where I admitted to "chucking a chain thru the cases " ...........that must have been someone elses fault . Its ( the case saver ) like carrying a puncture repair kit.........your guaranteed not to need it as long as its on board .... soon as you leave it at home you get a puncture

MarkST wrote:

Mc tool wrote:What normally happens when the chain either derails or breaks is that it rolls up on the front sprocket until the diameter is such that it pushes the crankcase out of the way ....

I didn't know that, and it's an interesting theory, but it suggests to me that those metal case savers are totally useless unless they can just stop the motor from turning over when the diameter becomes such that . . .

I've only ever had one chain let go on me, and luckily that just split and came off the sprockets and fell down onto the road.

Me too, but nevertheless I have them installed on my 907 and my MTS. You can't be too careful.

The saver doesn't have to resist the force of the chain bunching up. It works by preventing it from lifting off the sprocket in the first place, so the chain should just feed through and exit out the bottom (hopefully).

Mc tool wrote:I think the real truth is that if your diligent enough to fit a case saver your probly diligent enough not to let your chain/adjustment get so bad that it could fail .Please don't refer me back to the sprocket bolt thread where I admitted to "chucking a chain thru the cases " ...........that must have been someone elses fault . Its ( the case saver ) like carrying a puncture repair kit.........your guaranteed not to need it as long as its on board .... soon as you leave it at home you get a puncture

There is a lot of truth in what Hamish says; in that the sort of people who fit them are usually maintenance enough savvy that they never need them anyway.

Some alloys are porous and take up oil over time. These cant be welded successfully. Found this out when I went to have a crankcase on my motocrosser welded.

Metal stitching is the best type of repair for this situation as it is done cold and so there is no shrinkage or contamination issues, but it is a specialist job which probably means it is very expensive.

Probably better to get some crank cases. Will probably end up costing the same as having your cracked one welded but the integrity will no longer be suspect.