Here the engine's out and ready for disassembly.  Due to circumstances beyond my control, it's rather dirty.

Normally, I'd take the whole bike to a 'do-it-yourself' high-pressure carwash, and after liberally dousing it with Gunk or the like, would attempt to wash off the caked-on grease.  This helps keep crud out of the delicate bearings and parts as you disassemble.  But, since this engine will be stripped right down to the bearings, I can get away with it this time.

When the engine is on the bench, as in the picture above, an old car mat can really facilitate moving it around!  The carpet slides nicely on the bench surface, while the rubber backing remains impervious to oil, dirt and crud.

Once serious disassembly is underway though, nothing beats an engine stand.

This one was made from a cheapie $35 car engine stand on sale. It bolts to my workbench top/edge.

Note the drainpan below...

Again, this engine is up for total disassembly, but if you're just doing a top-end job (a fairly frequent chore for small-bore 2-cycle bikes from this era) always stuff the crankcase mouth(s) with clean shoprags to prevent crud or small parts like circlips and the like from getting down around the crankshaft.

If they do, well, your job just got bigger than you originally intended.

One of the nicest things about an engine stand like this is you can rotate the block around at your convenience.

That can be surprisingly helpful.

If you're a mini-machinist, like most of our viewers, you might want to personally tackle some of the more esoteric tasks involved with rebuilding an engine.

By using dead centers in the mini lathe spindle and tailstock, I can easily check the runout on the little twin's crankshaft.

This is about as large a crank as I could do this with -- note the last half/inch of the tailstock!

Here, on my mini mill, I'm finishing up a precision ring fixture that will fit the bottom of the little Yamaha's cylinders,

which then will allow them to bolt securely to it.

In turn, that fixture allows me to remove the chuck from my mini-lathe and mount a faceplate instead.

That fixture can easily be clamped to the faceplate, and the cylinder then trued to the lathe centerline.

I was able to adjust this cylinder to spin true within .0005" TIR --

for any newcomers, that means it was within .00025" of perfectly centered. 

That's 1/20th of the thickness of a sheet of normal notepaper!

My mini is one of the smaller ones available.  It's a 7" swing by 10" bed.  The Yamaha cylinder is the top limit of its capacity --

it barely clears!

  The cylinder has apparently siezed many times, and is so badly worn that it will have to go up 2 or maybe 3 overbore sizes to be useable.

Here, a heavy-duty boring bar with an indexable carbide tip prepares for the first cuts.