Harley-Davidson's 1988 Sportster-series motorcycle were powered by a then-new Evolution engine. Unlike the Twin-Cam engines used by the newer Softail and Touring models, which used separate transmission and primary chain-drive components, the Sportster housed both components in the primary chain case. This eliminated the need to replace a transmission-specific lubricant during routine oil changes. However, the fluid contained with the primary chain case must be changed every 2,500 miles to ensure smooth operation from the transmission.
Tools Used: T-27 and T-40 Torx screwdriver, Oil drain pan, Shop rag, Primary cover drain plug O-ring, 1 quart, Harley-Davidson Formula+ Primary Chaincase fluid
Change Primary Case Oil
Start the Sportster and take it for a brief 5 to 10 minute ride to warm the primary fluid to its operating temperature. Park the Sportster on its sidestand and let it cool for 10 minutes, once the motorcycle has warmed.
Mount the Sportster on a motorcycle-specific jack or stand to support it in an upright position.
Unscrew all six bolts from the clutch inspection cover, located at the rear portion of the outer primary chaincase cover on the left side of the engine, using a T-27 Torx screwdriver. Pull the cover and gasket away from the outer primary chaincase cover.
Unscrew the primary chaincase drain bolt, located along the bottom edge of the cover and directly below the clutch inspection port, using a T-40 Torx screwdriver. Drain the primary fluid into an oil drain pan.
Pull the O-ring off of the drain plug threads and replace it with a new O-ring. Clean the drain plug with a lint-free shop rag, then screw the drain plug into the bottom of the primary chaincase by hand. Tighten the drain plug to 6 foot-pounds, using a torque wrench and a T-40 Torx socket.
Pour up to 1 quart of Harley-Davidson Formula+ Primary Chaincase fluid into the primary chaincase through the clutch inspection port. Stop filling when the primary fluid is level with the bottom edge of the clutch basket held within the chaincase.
Wipe away any spilled primary fluid with a shop rag, then reinstall the clutch inspection cover and gasket onto the outer primary chaincase cover. Loosely tighten the clutch inspection cover bolts with a T-27 Torx screwdriver. Tighten the bolts to 10 foot-pounds, using a torque wrench and a T-40 Torx socket. Start at the uppermost bolt, then alternate between the remaining bolts in a star-shaped pattern.
Remove the Sportster from the jack or stand, then lower it onto its sidestand.
Tips & Warnings
You may use a Type D or F automotive automatic transmission fluid, in place of Harley-Davidson's Formula + primary fluid, if desired. Be sure the ATF fluid does not contain friction modifiers that can cause clutch slippage.
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