Ironhead Engine Build

A vintage Sportster engine will take considerable time and money to rebuild properly. If you're thinking of having it done at a motorcycle shop, a complete Ironhead engine build could easily run $2,000 with some shops quoting over $3,000. And if you don't have a qualified shop in your area, factor in another $350-$500 for shipping (there and back).

1976 Ironhead Sportster Engine

Should I Rebuild A Sportster Engine Myself?

To get an idea of what a total Ironhead engine build would really cost, I contacted five motorcycle shops in my area. The local H-D Dealer said they couldn't help me, as did two of the Indie shops. Two of them offered to ship my motor from their shop to either V-Twin (Newburgh, NY) or Millennium (Plymouth, WI).

So, it seems that precious few shops actually rebuild Ironheads in-house any longer, and finding a good Harley mechanic that will work on older bikes gets harder with every passing year. So, should you rebuild an Ironhead engine yourself?

Ironhead engine build

DIY Engine Rebuilding Pros and Cons

On the plus side, every part is available (with few exceptions) for Ironhead Sportsters, either used, N.O.S., or reproduction. Also, any information you may need is easily found on internet forums, Youtube videos, or the good old factory manual.

There are two big negatives for first-time Sportster engine builders. First, special skills are required, which are no longer taught in today's vocational schools. These include flywheel rebuilding, flywheel truing, and honing main bearings (see below).

The second big negative is the cost of the tools. If you don't already have them, they may cost you more than having someone do the work for you. Hopefully you won't need every engine tool listed in the factory manual.

read Motorcycle Engine Tools

Bottom line - it's your bike, you decide. Remember that you are the best mechanic for your bike, and no shop employee could possibly care as much as you do. But if you don't feel comfortable in your abilities, consider farming out some things and stick with the ones you do feel comfortable with.

Ironhead engine build

Planning An Engine Build

An Ironhead engine build can be broken down into several categories. These include top end, bottom end, transmission, clutch, carb/fuel, oil pump, and electrics (distributor, generator). Because no two engine builds are alike, you won't know what tools and skills you'll need until a complete disassembly and careful inspection of parts.

read Remove and Install Ironhead Clutch

Check Bottom End Play

After the cylinder jugs are removed, check the connecting rods for up and down play. Some side to side play is normal and actually needed for when the engine gets hot and metals expand. Generally, a Sportster top end will get rebuilt twice before a bottom end rebuild is needed, but remember that you're dealing with a 50 year-old machine. It may be prudent to do a complete rebuild from the flywheels up.

Inspect The Cases Carefully

Always check carefully for cracks upon disassembly. Aluminum engine cases are repairable and can be made as good as new, provided the repair was done right.

read Repair Cracked Cases

Ironhead Cracked Cases

Mixing Ironhead Cases

If your Sportster engine was already running, the cases may be okay, but if they weren't, you won't know what problems you'll have until you put two mismatched cases together.

Mismatched cases usually mean a poor alignment in the shafts that ride in each case. It's also likely that the cylinder decks will have to be machined so they are dead-flat. A mismatch of case halves can also mean premature transmission problems, because the two transmission cavities aren't lined up correctly. Of course, all these problems can be overcome, but it will add considerable time and effort to your build.

Matching Belly Numbers

When that old Harley-Davidson left the factory, the engine halves were a matched set, with matching line-bore numbers stamped on the bottom of each case. Take for example, a set of XLCH cases stamped 765-1298. The '7' signifies it as being a Sportster, the '65' is the year the motor was manufactured, and the '1298' is a sequential assembly-line number. If you're building an old Harley motor from the cases up, belly numbers that match usually mean that line-boring may not be required, although its always a good idea to check.

Ironhead Bottom End

The most time-consuming part of an Ironhead engine build is the bottom end. Repairing the lower end requires special tools and skills, and can take considerable time to properly measure and rebuild. Aside from the labor, factor in the cost of lower end specialty tools.

Line Boring vs Line Honing

Line boring is the process of centering and re-fitting the bearing races in one or both cases. The objective is to have the crank assembly sitting parallel in the cases. In some cases, the races may need to be replaced.

Whereas line boring uses cutters with a boring bar, line honing uses abrasive stones, which removes less metal and leaves a smoother finish. Neither line-boring nor line-honing may be needed, but careful inspection and measurement is critical.

read Ironhead Flywheel Rebuild

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 engine vibration will not only and numb your hands and feet, it may inflict internal engine damage. Trueing flywheels is one of the most important steps in an Ironhead engine build.

Truing vs Balancing

Balancing is about the weight of the pistons, rods and other rotating/ reciprocating items. Truing is done at the factory, balance is not. Balancing may make it run smoother, but if the flywheels are trued and the run-out is within specs, re-using your original parts will have the engine running as it did when it left the factory.

Ironhead Top End

Compared to the bottom end, the top end of an Ironhead requires less time and less special tools. The two main obstacles will be if the cylinder jugs need boring and if the valve seats need to be cut. This is where careful inspection and measurement pays off. If you're lucky, you may get away with just honing the jugs and installing new piston rings.

Ironhead Specialty Tools

Aside from basic hand tools, you'll need a piston ring installer, torque wrench, dial caliper, feeler gauge, and most likely some specialty tools. Many of the special tools needed for a motorcycle engine build can be fabricated. If you can cut, drill, and weld metal, consider making some the tools yourself. Here's a few of the tools I've made to keep my old bikes on the road.

read Ironhead Special Tools

Tools for Ironhead Sportster engine build
1965 Ironhead Sportster Project

read 1976 Sportster Project

read Best Carburetor For Ironhead Sportster