Motorcycle Engine Tools
(text and pictures by Mark Trotta)
Aside from basic hand tools and a torque wrench, other tools needed to rebuild a motorcycle engine include a micrometer, dial indicator, feeler gauge, piston ring installer, and some specialty tools for your make and model. Other things to have is a digital camera, curiosity, time, and common sense.
Engine Measuring Tools
One of the first steps of proper engine repair is accurately inspecting and measuring worn parts. Although most of us are more mechanics than machinists, the need arises during a motorcycle engine build to precisely measure wear and play.
I cannot over-stress the importance of having good measuring equipment, as well as the skill to use those tools correctly. These include measuring devices such as a micrometer, dial indicator, dial bore gauge, and a feeler gauge.
Essential to engine building is a quality micrometer (also known as a caliper). You can buy a digital micrometer really cheap, but I recommend buying a good name brand, such as Mitutoyo.
Shop: Digital Caliper
Digital micrometers are more expensive than dial calipers, but they are quicker and have an LCD display for easy reading.
Dial Indicator With Magnetic Base
Having a dial indicator allows you to check end play, flywheel run-out, up-and-down movement on connecting rods, and many others. Most have increments of .001" on a 0" to 1" scale. They can be mounted by clamp or magnetic base.
Checking thrust clearance on a Harley 45 Flathead with magnetic-base dial indicator.
Shop: Magnetic Base with Dial Indicator
Engine clearances are crucial, and learning to correctly read precision instruments takes some time. Experienced mechanics always double-check their specs. First-time builders should measure a dozen times (or more) before trusting their readings.
Small Hole Gauge
To accurately measure the inside diameter of valve guides and other small bores, a small-hole gauge is needed. These are also called telescoping or small-bore gauges, and come in varying sizes.
Shop: Small Hole Gauges
A feeler gauge, or gap gauge, is needed for checking valve tolerances, ignition point gaps and other critical measurements. They're made up of thin metal blades. Each blade is a different width of precise thickness, and will be marked in either thousandths of an inch, or millimeters, or both.
Shop: Feeler Gauge
The blades usually range from .0015" to .035" (.038 to .889mm). Long feeler gauges may be needed for valve adjustments on some engines.
Tap And Die Set
If you're rebuilding an old engine that's been neglected, I would rate a tap and die set as a necessity. With proper technique and lubricant, taps and dies will cut mild carbon and alloy steel, cast iron, aluminum, brass, and bronze.
Shop: Tap and Die Set
Dial Bore Gauge
To accurately measure the inside diameter of a cylinder, a bore gauge is needed. The one I have is a ToolUSA TM-34260. It has a range of two to six inches, a depth of six inches, and the round dial has .001" increments.
Shop: Dial Bore Gauge
Remember that micrometers, dial indicators, and dial bore gauges are precision measurements, and need to be treated as such. For consistent and reliable results, keep them clean and out of harm's way.
Cylinder Boring and Honing
If you're restoring an old engine, boring a cylinder back to round requires removing anywhere from .003" to .010" or more of metal. Professional machine shops have large, expensive, dedicated machines to perform all kinds of cylinder boring. The same process can be done in your home garage, but will take considerably more time. By using a rigid honing device and a slow-speed drill, high-quality motorcycle engine cylinder boring is possible.
Read: DIY Motorcycle Cylinder Boring
Piston Ring Expander
Do not be tempted to install rings into the piston grooves by hand. It's a bad idea, because rings get deformed by the twisting action, which may cause sealing problems. A piston ring expander is an inexpensive tool.
Shop: Piston Ring Spreader Tool
Piston Ring Installer
To install pistons back into the cylinders, a piston ring installation tool is needed. A clamp-style ring compressor is the least expensive style, but consider investing in a piston ring installer set. Most sets includes a half a dozen popular sizes you can use for other engine projects.
Shop: Piston Ring Compressor Set
Valve Spring Compressor
This is the tool you need for removing and installing valve springs. The one I have is a copy of Harley-Davidson #96600-36. Although it was designed to fit pre-Evo Big-Twins and Sportsters, it's really a universal tool.
Shop: Valve Spring Compressor
Vintage British motorcycles were assembled from the factory with Whitworth-sized nuts and bolts. These are often confused for, and not the same as, fractional or metric sizes. Many British motorcycles continued using Whitworth sizing into the late sixties, and to make things more confusing, some seventies British bikes had a combination of sizings!
Shop: British Whitworth Tools
Every type of motorcycle engine will require a specialty tool or two. The tool in the picture below is for installing piston lock-rings in early Harley-Davidson 45 flatheads. It lightly stretches the lock ring just enough to fit into the groove. The factory part number for this tool is 12052-32, and it's primary use is for 1932-1956 Harley-Davidson 45 models.
DIY Engine Tools
If you don't have all the tools needed for your motorcycle engine build, you can either borrow them or buy them (new or used), but many can be fabricated. If you can cut, drill, and weld metal, consider making some the tools yourself.
After a flywheel assembly is rebuilt, it needs to be trued before being reinstalled in the cases. For this, you'll need either a lathe or a flywheel truing stand. A $900 truing stand is a nice luxury, but homemade units work just as well.