Does Harley’s Twin Cam Engine Deserve Its Bad Reputation?
A veteran mechanic on YouTube defends Harley’s controversial Twin Cam.
There’s no shortage of criticism surrounding Harley-Davidson’s Twin Cam engine. This design powered most big-twins from the model year 1999 up until 2017. However, a recent video from David Thompson treats the controversial powerplant with a little more balance than many, who simply trash it.
Thompson, who runs the YouTube channel DeathProof Productions, experienced an early example of this motor in a brand-new 1999 Dyna Super Glide. Remarkably, he still owns that bike today and clearly has an affection for it and the many adventures the pair have enjoyed over the years. Thompson, who was a certified Harley-Davidson dealership mechanic, points out the following perceived shortcomings — some of which have more merit than others.
The Twin Cam’s pressed crankshaft isn’t great
To begin, Thompson points out concerns over the Twin Cam’s pressed crankshaft/flywheel assembly. The new one-piece construction basically rendered the entire rotating assembly as unserviceable. That’s as opposed to the outgoing Evolution motors, which could be rebuilt and fitted with new connecting rod bearings, as well as the rods themselves.
Beyond that, many of the pressed cranks also had excessive runout due to inferior bearings. The definition of runout is a side-to-side movement of the crankshaft, which can lead to extra vibration or even crankshaft failure.
Lifter bores are cast into the case
Next, the video points out that the Twin Cam doesn’t have replaceable tappet blocks to house the lifters like the Evolution engines did. Instead, the holes for the lifters are cast into the case itself. Thompson mentions that he spoke with engineers who assured him that metallurgy had advanced to where this setup was reliable.
That’s not to mention that many American V-8 engines from the golden era of muscle cars had cast lifter bores. Lifter bore issues with those iconic engines are seldom, if any. In the unlikely event that a Twin Cam lifter bore does get wallered out, aftermarket vendors now offer kits to sleeve the bore back to new.
Cam bearings and tensioners can self-destruct
Finally, Thompson gets to the biggest criticism of the Twin Cam engines, which is, well, the twin camshafts. More specifically, the cam bearings and cam chain tensioners have caused headaches for many riders. The YouTuber recollects from his time as a dealership mechanic that the Motor Company was willing to upgrade bearings for customers free of charge. Some customers chose to abandon cam bearings altogether for bushings.
Perhaps a more notorious problem was the plastic cam chain tensioners. These inferior pieces had a reputation for rapid wear and even self-destructing. When this happened, shards of plastic were sent into the oil pump and could cause catastrophic engine damage.
One solution for the faulty cam tensioners is frequent observation and replacement. Other riders opt for gear drives to replace the chain altogether, a pricey conversion offered by S&S, among others. Note that later years, like 2007-onward, had an improved hydraulic tensioner system.
Early Evos had teething problems, too
Cycle World tested an early Twin Cam 88 in a 1999 Road King and was impressed. The new engine was claimed to produce 8% more horsepower and 10% more torque than the outgoing Evolution. On the road, that translated into “unquestionably better acceleration” and reduced the need to downshift in order to pass. But the new Twin Cam 88 wasn’t only more powerful. It was also less prone to oil leaks and featured improved cooling over the Evo.
The Twin Cam powerplant gets a bad rap and indeed, some of the damage was self-inflicted by Harley-Davidson. But early Evos weren’t without issues either, like leaking cylinder base gaskets. By now, the Twin Cams have been around a while. The issues are more well known and proper inspection and correction measures are in place.
Images: Deathproof Productions/YouTube