have you actually pulled the swingarm off and verified that the bearings are indeed good? While going through my bike last winter I checked mine just for the hell of it, and when I slid the pivot bolt out, all the needles in the bearing fell into my hand. I thought they were fine, when they were not.

 

No Dill, I haven't pulled the swingarm off and checked, but there is absolutly no play what-so-ever in my swingarm. Thanks for the tip too!

Now, I got my chain and sprockets today, so where can I find a case? There's a used cycle shop down the road from my house, so I'll check there for a used one. If not, where can I get one besides Service Honda? Does Ronnies sell them? Thanks alot!!

 

Is it the inside or outside case? IF it's the outside then you can get one just about anywhere, if it's the inner case you have to buy a machining set or else it will leak. My inner case got a hole in it but I got it welded and now it's fine. You can get the matched inner case set form Honda OR you could save up soem $$$$$ and go to ESR and buy there matched cases that are bored out to take there 370 kit !!!

 

Is that true? If so, I'm not so sure how I'm going to do this, because the chain cut the metal plate that had the number on it. And yes, I need the left case half.

 

well, first off, I am betting that your swingarm pivot and bearings are shot. If you had movement in them and just tightened the bolt, then the bearings were in fact, toast. What you did was just "clamp" the swingarm in the frame so that you could not move it, but when you gas it, the torque pulls it to the left. Probably why you threw chain to begin with.
Second, you need a new case. The case supports the countershaft and keeps it in line the way it should be. If you case is broken, which it sounds like it is, then it could be flexing, causing accellerated wear on the rest of the tranny. You need to stop riding this machine and take it all the way down to the bare frame and rebuild it. Otherwise, you are going to nickle and dime it to keep it running. It is going to go further down the trail that leads it to an early grave and parts machine status.
As for the "matched" case issue, I have never seen it to be so. These are machined pieces from Honda that come with bearings and seals installed and ready to go. I have never seen one leak. I have seen Suzuki cases that had issues of not matching up, but never a Honda. I may be wrong, but I personally have owned and been around a lot of these bikes. I have seen swingarm bearings that were "good" come out in pieces, exactly what I think you have here. You are going to have to treat this machine like it is an 88, not a 98.

 

I rebuilt my friends 87 bottom end with an 88 case half, and it leaked all around the center seal because the gasket surfaces did not match up.

Sometimes you win, sometimes you lose.

 

I'd make sure that your countershaft isnt slopy. If for some odd reason a bearing or a gear is going or has went and your shaft is moving all over the place when tension is place on it for example suspension compressing like you described earlier that might cause the shaft to move and the chain to jump off the sprocket. Just an idea, but it might be worth checking out.