you will have to get your crank welded and at this point but new bearings on I would think, that being said I would consider the 421 serval again since you have to split the cases. with the bigger serval you are able to ride them in a higher gear in the trail and with mine it kinda acts like a 4 stroke where you dont need to shift very much ( I have the 10mil serval) I think the 392 serval would be great for someone who just bought a new welded crank and now wants to do the topend