900cc Ironhead Engine Build

Text and Pictures by Mark Trotta

It's challenging enough rebuilding any Ironhead motor, and an early 900cc bike presents a few more challenges.

Difficulties will include limited parts availability, and more specialty tools.

*********

Early 900 Cases

As with all motorcycles, Ironhead engine cases are the foundation upon which all else is built.

Harley Sportster engine case restoration

All Ironhead motors have cast aluminum engine cases, which are prone to crack under abuse. Very often they can be repaired to as good as new - provided the repair was done right. The key is to find someone who has experience with welding dirty cast aluminum.

Read: Repair Cracked Cases

*********

Main Bearing Lap

Lapping the main bearing race assures precise alignment of flywheel shafts, allowing maximum power and engine life.

Read: Harley Crankcase Lapping Tool and Usage

*********

Truing Flywheels

Due to their 45-degree configuration, Harley V-twin motors are inherently out of balance to begin with.

It is essential that flywheel assemblies to be trued, Not only will engine vibration numb your hands and feet while riding, it could cause internal engine damage.

*********

Sprocket Shaft Bearings

From 1957 to early 1976, Sportsters had a one-piece sprocket shaft race. These are sold as a matched set, which should include two bearings, a one-piece double bearing race, and a spacer.

The race needs to be pressed in with a hydraulic press.

Pinion Roller Bearings

From 1957 to 1976, Sportsters used loose roller bearings on the pinion side. Later models (1977-1985) had fixed, or captured bearings.

Loose roller bearings require more attention than captured roller bearings. When in doubt on proper fitment, remember that a little too loose is always better than a little too tight.

*********

900 Cylinder Jugs

I bought and installed a set of aftermarket cylinders, but they are shipped undersized, so they need a slight bore even for standard sized pistons and rings.

Read: Ironhead Sportster Cylinders

Read: Cracked Cooling Fin Repair

*********

900 Ironhead Pistons and Rings

Eastern Motorcycle Parts offers a Replacement Piston Kit For 1957-1971 Harley Sportsters.

The kit includes two cast alloy pistons, genuine Hastings 3-piece ring set, 2 wrist pins and 4 circlips. Unfortunately, sizes are limited.

*********

Cylinder Heads

If you want to tackle rebuilding Ironhead heads yourself, you'll need a few specialty tools, and in the process learn some new skills. But you won't know how far you'll need to go until the heads are off and valves are out.