Twin Cam Engine Build Part 1 of 5

Mega-Horse

how to build a twin cam motor

Our setup consists of a few top-quality components from a few industry leaders, such as Dave Mackie Engineering, Darkhorse Crankworks, Zipper’s Performance, S&S Cycle, Carrillo, Harley-Davidson, Baisley, Cometic, JIMS USA, and more.

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We recently took a Twin Cam “A” motor from a 1999 FXDX out of its chassis at 100,000 miles, broke it down, inspected it, and then sent the lower end to Darkhorse Crankworks (DHC) so its squad of bottom-end experts could rework the tired components. Working with [Dave Mackie Engineering (DME)](Dave Mackie Engineering (DME)), we concocted a solid 107ci top end using bored H-D cylinders and some DME Mega-Sphere pistons, complemented by a DME cam. Both DME and DHC are known for their superior quality and attention to detail, so it was a pleasure to assemble this motor knowing the end result would be a powerful yet balanced blueprinted motor.

how to build a twin cam motor

Using a Feuling pinion-shaft runout measuring tool, the first thing we do is check our pinion-shaft runout. DHC is notorious for its commitment to perfection when building lower ends for any purpose from street to full race. The runout for this crank assembly after DHC rebuilt it is 0.00003, well within spec.

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how to build a twin cam motor

These are the components of the stock lower end that DHC sent back with our new, rebuilt, blueprinted, and balanced lower end. We replaced the rods due to their condition after 100,000 miles. We went with DHC “H” beam rods and DHC crankpin.

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how to build a twin cam motor

The piston rings are carefully installed over the DME piston. DME takes the time to measure the ring gap for each build and provides a sticker that states clearly which ring goes where.

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how to build a twin cam motor

Using an assembly lube, we coat each and every part that moves or comes in contact with another surface. This assures there are no dry surfaces contacting each other when the motor is initially fired up.

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how to build a twin cam motor

Place the wrist pin in the piston, and align the pin with the connecting rod hole.

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how to build a twin cam motor

Push the wrist pin through the piston and connecting rod. Make sure to cover your cylinder studs so you do not mar the piston surface or damage the rings when installing the wrist pin.

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how to build a twin cam motor

Using a wrist pin “C” clip installer tool, install the retaining clips in both sides of both pistons.

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how to build a twin cam motor

Align the piston ring gaps in an “X” pattern on the piston, and using a piston ring compressor tool, compress the rings and prepare to install the cylinders.

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how to build a twin cam motor

Install the base gasket or cylinder O-ring onto the cylinder. Make sure if you are using an O-ring-style base gasket that you remember to install the O-rings on the case as directed by the service manual.

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how to build a twin cam motor

Slide the cylinder over the studs and onto the piston. Be sure that all the piston rings are compressed and slide effortlessly into the cylinder bore.

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