Classic Motorcycle Build

900cc Ironhead Engine Build

Rebuilding a Sportster motor is challenging, and an early 900cc motor will present a few more challenges. Difficulties will include limited parts availability as well as quite a few specialty tools needed. After learning the proper skills, knowledge and patience can overcome these obstacles.

900cc Ironhead engine build

In it's 26-year production run, the Ironhead Sportster was offered in two just engine displacements. When it debuted in 1957, engine displacement was at 883cc, which was rounded up to 900cc. In 1972, displacement increased to 1000cc.

When Evo Sportsters debuted in 1986, they were offered in 1100cc and 883cc displacements (and later in 1200cc). As to not be confused with 883 Evo models, the early Sportster engines are usually referred to as the 900 Ironhead.

900cc Ironhead Cases

As with all motorcycles, the engine cases are the foundation upon which all else is built. Although very early Sportster cases (1957-1958) have different casting numbers than later cases, all 900cc engine cases from 1957 through 1966 are interchangeable.

900cc Ironhead Sportster Project

Starting in 1967, a second set of cases were produced to accommodate electric start. From 1967 to 1971, there were two sets of cases for the Ironhead 900.

Damaged Engine Cases

All Ironhead motors had cast aluminum engine cases, which can be repaired as good as new - provided the repair was done right. If you are not proficient at welding dirty cast aluminum, find someone who is.

Irnonhead Case Repair

Read: Repair Cracked Cases

900cc Ironhead Cylinder Heads

Finding good 900cc heads get harder with each passing year. Availability is nowhere near as good as 1000cc Ironhead heads.

900cc Ironhead Sportster build

900cc Ironhead Cams

There are two styles of Ironhead cams, early (1957-1970) and late (1971-1985). Early Sportsters had an external distributor, which ran off the cam. This was no longer needed when points were moved to inside the right case in 1971.

Ironhead Sportster cam set

Read: Install Sportster Cams

Ironhead Sportster Project

Truing Flywheels

Due to their 45-degree configuration, V-twin motors such as Harley Sportsters are inherently out of balance to begin with. It is essential that the flywheel assembly to be trued, or not only will engine vibration numb your hands and feet while riding, it may cause internal engine damage.

900cc Ironhead

Read: Ironhead Flywheel Rebuild

Install Main Race

1957 to early 1976 Sportsters had a one-piece sprocket shaft race. These are sold as a matched set; two bearings, one-piece double bearing race, and one spacer. The race needs to be pressed in with a hydraulic press.

Ironhead Sportster Project

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.

900cc Ironhead Engine Build

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

During installation, I use a dab of wheel bearing grease to hold the roller bearings into the cage. The grease dissolves and assimilates into the engine oil upon start up/running.

900cc Ironhead

900cc Ironhead Gasket Kit

If possible, engine gaskets should be matched up to old ones. Don't skimp here; buy top-name, quality gaskets.

900cc Ironhead Sportster engine gasket kit

900cc Ironhead Transmission

Rebuilding an Ironhead transmission is a project within a project.


Read: Remove and Install Ironhead Transmission

A Word About VIN Numbers

Up until 1969, VIN numbers on Harley-Davidson motorcycles appeared only on the engine case and usually started at 1000 each new year. Starting in 1970, the VIN appeared on both the engine and the frame.

If you are looking at an Ironhead Sportster project and there are no numbers on the base of a motor, beware. It's likely they were ground off intentionally (stolen motor).

If you are looking to buy a 1970 or later Harley motor with no frame and registering it with the engine's VIN, it's not going to be the true Harley title. Someone else may be riding around in the frame with a different or aftermarket motor, and that bike is correctly titled from the frame number. If you get stopped and they run your VIN number, your bike could get impounded because there's another bike out there that is correctly registered with the same VIN.

Early Ironhead Sportster Build

Read: Early Sportster History (1957-1965)