I am currently rebuilding a 1977 dt250. I have the crank completely removed from the case and the bearings off. I am ready to reinstall the bearings. I have a clymer manual but it does not give any information on this step and neither does the manual in the technical section here. I am curious if I put the bearing on the crankshaft first and then press that into the case or put the bearing into the case and then press the shaft into that. Additionally I measured the space from the flywheel on the shaft to the wall of the case before I removed it to get an idea on how deep it needs to be pressed. I'm worried though that I did this incorrectly.  Does anyone have any information on how to properly reinstall the crankshaft into the left hand side of the case? 

Just my idea & what i did last time long ago. Fit the bearing to both case.
They go right home.
Then i'd fit the crank to the right side "with shim" if it has one.
Then fit the crank nut & gear semi tightened to hold it over.
Then with the transmission & selectors in the case, it use the yamaha puller to pull the left case onto the right side--with caset cement of course--& don't forget the dowels.
That's my todays theory which might change tomorrow.
Just thinking that way because you have the bearings in your hand & the left bearing doesn't go hard against the crank like the right side.
Others may do it different

What RT325 just described is the method I use as well. There are many ways to "cheat" but that seems to be the best way without risking damage like knocking the crank out of alignment. 

Heat bearing to 100c. (Fizzling spit test, or bring bearing to the boil in a pan of water)  About 30 mins before this, put crank in freezer
Remove crank from freezer and position it ready to drop the bearing on.

Bearing will drop into place on crank under gravity.

Allow to cool

Heat crankcase to 110c ( water will just be starting to form a ball when you drip it on the case. Or a wax crayon mark will turn black).

Crank will drop into left case under gravity, no force required

What yamaha puller are you talking about? I looked up the part numbers to the special tools that are in the technical sections manual here and I couldnt find shit lol. 

Contact DEET for his crank puller set or some have used the Tusk crank puller.  www.rockymountainatvmc.com/parts/tusk-cr...ler-installer-tool-p

Here's a similar one to what i use. Man they're getting expensive to buy.

www.amazon.com/RYANSTAR-RACING-Installer...?crid=3080O0MRABUFP&
This one above looks like it has the tool for pushing the crank out included. Wording is confusing me but think it means 'that' & one pic shows both.

Looks like the Amazon one has three options...  puller for installing the crank, press for removing the crank, and both.  Good prices. Nice find RT325!

I use a standard two bolt steering wheel puller to press the crank out of case. 

Many years ago I made a puller to install the crank out of all thread, a section of thick wall aluminum tubing I had lying around, some flat washers, a nut that fit the all thread, and a threaded adapter I made to connect the all thread to the crank thread.  Back then the Tusk installation tool or this cheaper one on Amazon didn't exist or I would have just bought one.  The installers I found for sale were well over $100 back then (probably $200 in today's money LOL) so it made a lot of sense to cobble up one in my garage. 

Totally agree w/tinkicker's recommendation here. Use of heat & freezing things works really well and definitely reduces  stress on the bits. You can of course use an installation tool, but once you try heating the bearing/freezing the crank, you will be surprised how ell that goes.

I was taught the trick when I worked for a dealer who sold Bultacos. Worked a 'treat', as the Brits would say.

This also works well when installing wheel bearings.