What is the cause for a inner primary leak in a 2003 dyna superglide?

Answer 1

There are several places where the chaincase can leak, and all involve a worn or damaged gasket, o-ring or seal.

There's the large gasket that seals the two chaincase halves together, there's a large o-ring where the inner primary cover meets the motor at the alternator, there's an oil seal where the transmission shaft enters the chaincase, there's an oil seal where the starter jackshaft enters the chaincase, there's a gasket behind the derby (clutch cover), there's a gasket behind the chain inspection cover and of course there's the drain plug.

Also it's possible that the chaincase has a hairline crack near the motor, not as uncommon as you might think, especially on Dyna models that have been abused.

Virtually any oil leak on a Harley Big Twin will manifest itself as a leak dripping from the bottom of the chaincase (near the drain plug) because that's the lowest part of the entire powertrain.

A cylinder base gasket leak, a transmission main seal leak and even a pushrod cover leak will all cause oil to drip from the bottom of the chaincase (if the bike is ridden).

First inspect the oil that's dripping. If it's very clean-looking, it's unlikely that it's motor oil (which is usually quite dark) and there's a chance it's coming from the transmission, whose oil always stays clean. The most likely transmission leak is from the mainshaft seal, behind the belt pulley.

The most likely chaincase leak would be the starter jackshaft seal, which can sometimes become loose in its seat.

To pinpoint any kind of oil leak on a Harley, first clean the bike thoroughly, then use masking tape to secure folded paper towels at all suspected leak points and go for a ride. The paper towel that gets a wet spot is the one covering the leak.