You have to assemble the engine sprocket, primary chain and clutch basket together, then put the whole thing on as one unit. The sprocket goes over the engine shaft at the same time the clutch drum goes on to its shaft.
Then you tighten both the clutch hub nut and the engine shaft nut up to 150ft lbs.
To dig this far into a Sportster engine, you need to have a good workshop manual and a factory parts book.
Also, try the xlforum.net Ironhead forum for advice.
engine and primary share the same oil on the 1976 sportster,due to engine oil sumps into primary.
In the primary case on the lefthand (gearshift) side of the engine.
The '99 Sportster uses three quarts of engine oil, and one quart of Sport-Trans in the Primary/Transmission.
Fig. 11 Valve Timing MarksRemove engine front cover as outlined previously.Remove crankshaft oil slinger.Crank engine until timing marks on sprockets are in alignment, Fig. 11.Remove three camshaft to sprocket bolts.Remove camshaft sprocket and timing chain together. Sprocket is a light press fit on camshaft for approximately 1/8 inch. If sprocket does not come off easily, a light blow with a plastic hammer on the lower edge of the sprocket should dislodge it.If crankshaft sprocket is to be replaced, remove it with a suitable gear puller. Install new sprocket, aligning key and keyway.Install chain on camshaft sprocket. Hold sprocket vertical with chain hanging below and shift around to align the timing marks on sprockets.Align dowel in camshaft with dowel hole in sprocket and install sprocket on camshaft. Do not attempt to drive sprocket on camshaft as welch plug at rear of engine can be dislodged.Draw sprocket onto camshaft, using the three mounting bolts. Tighten to specifications.Lubricate timing chain with engine oil and install cover.
The oil drain plug is at the bottom of the oil tank (for engine). Bottom rear of primary case for primary & transmission.
That plug is the drain plug for the primary and transmission oil supply.
Primary oil and transmission are the same. The crankcase is different. They are separated.
The engine oil supply holds three quarts. The primary/transmission holds one quart of Sport-Trans.
The transmission on a 2003 Sportster is to the rear of the cylinders, just below the starter motor. If you kneel down on the left side of the machine and face the engine, the transmission is in a direct line behind the "derby" cover (the large dome cover in the primary) to the other side of the engine.
The engine uses three quarts of oil, and the Primary/Transmission uses one quart of Sport-Trans.
If its anything like my 1996 1200 it should take three qts for the engine and one qt for the primary.
it's built in behind the engine compensating sprocket located inside primary cover, left hand side of the bike