I say go for it!  You can do it!

I was intimidated as all heck before the first time I split cases.  

My main "motivator" was I couldn't afford to pay someone at the time.  It was even scarier because all I had was a generic motorcycle manual (and Al Gore had not invented the Internet yet.  LOL )  I was a bit "unconventional" because I didn't have the right tools but I improvised and got it done without too much carnage and no leftover parts! 

Until a few years ago, I had never laced a wheel.  My buddy Scott (Scootern29) kept telling me it's not a big deal, just take pics and offset measurements (if the hub centerline is offset from the wheel centerline) BEFORE you take the wheel apart.  I actually had fun lacing my first wheel.  Sort of a "Zen-like" experience.  And it also wasn't nearly as difficult as I imagined it to be.  

 

My worry splitting cases is that the bikes I'm working on are so old and beloved. I need some parts bikes to practice on.

I copied below what you said--the shop said in an earlier post, as i'm worried.

"While the shop was putting in the new bearings they discovered that the reason why the bearing race was able to spin on the crank was it had the wrong bearing in it.The outer race fit correctly but the inner was not correct".

Call me a doubting thomas but that comment from the shop worries me--that the shaft has been spinning but has over time worn a thou or two out of the bearing.
But also worn the shaft. Bearings are true to size. When they say C3 C4 for instance, that's the clearance of the balls. not bearing to shaft.
Only hypothesizing that when its all together the new "to size" bearing will still revolve on the worn shaft.
That's when the bearing is fully home, as it will be tight "on the way down the shaft--until its not"-- when fully home. Sorry i had to say all that & hope i'm wrong but have seen it many times. That was refferencing post #9 i think. Now i'm confused what post i'm on.

Hi Morley, yes I have thought of that myself but am trying to tell myself that that everything will be alright and that it wasn't run long enough with that wrong bearing to cause any real damage. Time will tell...

"My worry splitting cases is that the bikes I'm working on are so old and beloved. I need some parts bikes to practice on."

I have thought of buying a complete lower end from ebay or FB market place for doing just that.  

Mark, I really thought about doing it myself and if I had the tool for splitting the case I may have. I have a friend with a press so pressing the bearings out wouldn't have been an issue.

I did lace the wheels for my DT400, it took me 4 attempts to get the rear wheel correct, I'd get partway done then realize I made a mistake and have to pull it all apart to start over. As for taking measurements, yeah I did that but either it was luck or divine intervention they just naturally fell into place.

I am fortunate that my current JT project does include a second complete but totally locked up JT engine. I have currently split that one open, but I am waiting for my son to oversee the tear down of the target engine I am rebuilding. He has done several and has all the right tools.