Classic Motorcycle Build

Ironhead Engine Assembly 1977-1985

Article and Pictures by Mark Trotta

The Sportster motor saw several revisions for 1977, including reworked engine cases, new oil pump, and new pinion bearing. Assembling these '77 and later Ironhead engines require slightly different procedures than earlier 1000cc models.

Ironhead Sportster engine assembly

After the flywheel assembly is back together and trued, engine re-assembly can begin. Here's what you should have ready:

Sprocket Shaft Timken Bearing Set

Whereas 1957-1976 Sportster engines have a single bearing race and two bearings, '77 and later models have two separate races and two bearings. The inner and outer sprocket shaft bearings are the same in both early and late styles, and should always be replaced as a set.

1980 Sportster engine assembly

Inner Sprocket Shaft Bearing

The inner sprocket shaft bearing is pressed on until it bottoms out against the shaft shoulder. A shop press is most often used for this procedure, but the bearing can also be installed by heating it up and slipping it over the shaft.

1979 Sportster engine assembly

Install Flywheel Assembly

Place the flywheel assembly in a sturdy vice, so that the flywheel assembly sits with the sprocket shaft pointing straight up.

1978 Ironhead engine case assembly

Lay the left engine case over the sprocket shaft, propping the back end up. Install the spacer, and then the outer sprocket shaft bearing.

Ironhead engine case reassembly

Installing the outer bearing is best done with the factory-type tool #97081-54 (or equivalent). Crank down on the tool until the bearing is completely seated.

1981 Sportster engine case assembly

Many DIY mechanics heat up the bearing and then slip it on the sprocket shaft. The trouble with this method is, it's hard to tell if it's on all the way. When you use the tool, you can feel the new bearing "bottom out" on the shoulder of the sprocket shaft.

special tools needed for Sportster engine

Outer Sprocket Seal

The outer sprocket seal can be installed with the 97081-54 tool.

With the flywheel assembly installed back into the left engine case, prop it up on blocks of wood.

Sportster left engine case

Right-Side Engine Case (1977-1985)

One of the updates to the 1977 Sportster was the pinion shaft bearing assembly. The 1977-1985 assembly (HD #24648-77) is "caged" and is a whole lot easier to install than 1957-1976 engines with 13 loose roller bearings.

right-side Sportster engine case

When replacing, the pinion bearing gets pressed in and out of the right-side engine case. When done, the bearing should be flush with the inside boss.

Engine Case Sealant

There are dozens of products to seal engine cases, and the ones that are sold at automotive parts stores are almost always wrong for your motorcycle. For several reasons, I prefer anaerobic gasket sealant.

best sealant for engine cases

Read: Anaerobic Gasket Sealer Review

After spreading a thin coat of sealant on both case halves, wait a few minutes for them to get "sticky".

Install Rear Motor Mount

I did not remove the three rear motor mount studs from the case during this rebuild, so before placing the right case on top of the left case, I had to install the rear motor mount first. If you forget this step you'll have to remove the three studs.

Harley Davidson Sportster rear motor mount

Install Engine Bolts

Once the cases are together, start installing the case bolts, just hand tight. Once they are all installed, tighten them evenly. On 1979 and later motors, there is one Allen-head engine case bolt. The others are 7/16" and 1/2" six-point hex head bolts.

Engine Assembly Lube

I pour a bit of engine assembly lube inside the connecting rods and anywhere else it can reach. I also lubricate the pinion shaft bearing with engine oil.

motorcycle engine assembly lube

Engine Stand

At this stage of reassembly, I put the motor onto an engine stand. If you don't have a stand, you can continue assembling the motor on blocks of wood.

1981 Ironhead engine assembly
1980 Ironhead engine assembly

Misc Notes

On early Ironhead motors (1957 thru 1976) the oil pump MUST be installed on the motor before mounting it on the frame. On 1977 and later motors, the oil pump can be installed after the motor is in the frame.

Pinion Shaft Race (1979-E1981)

On 1979 through early 1981 Sportsters, there is a pinion race that is pressed onto the pinion shaft. When replacing, the pinion race should be .031" from the edge of the pinion shaft shoulder.

engine assembly 1980 Harley Sportster

Related Articles:

Ironhead Engine Cases
Ironhead Special Tools
Remove And Install Ironhead Transmission
Four-Speed Sportster Transmission