Join Date: Feb 2004
Location: Rocklin, CA, USA
I split the cases on a 1994 Monster 900 about 1 month after I bought it used. Only 4,000 miles and the left main bearing failed. I had done this many times on my dirt bikes, mainly 2 strokes, and I found it to be very similar to the Ducati. It really didnt require any special tools although I had to buy a big puller to get a gear off the right side that had locked tapers. I would think that if you bought another case, you would need to make sure the preload of the main bearings are set properly. To do this I borrowed a long depth micrometer from work and found a long straight piece of tool steel to measure the distance between the two bearing seats and then measured the distance between the two shoulders on the crank shaft. I placed each case on a table and placed the flat bar on the edge of the case. I drilled a hole in the flat bar and placed the depth micrometer through the hole and down to the counterbore for the bearing. I did this on both cases and was able to get the total distance between the two bearing counterbores. I had to borrow a caliper that was big enough to measure the distance on the crank. The preload is actually calculated by the interference (meaning the distance between the outer side of the two main bearings is larger than the space it goes into. You get the right interference by installing thin flat shims (washers).
Other than that, everything went together the opposite way of pulling it apart. There are alot of pieces, but I just labeled boxes and for each major component, like the gearbox. Put it all back together and everything worked well for many thousands of miles.
It looks like your case was defective (porous). My ST4 case that cracked was due to the broken mounting bolt and allowing the drive chain to put undo stress on the case. If you buy another case I am sure you can find someone who can figure out if it is porous (maybe xray it). Or maybe just by looking at it.