Harley Twin Cam Years To Avoid

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The design of Harley-Davidson’s Twin Cam engines has been industry-transforming, but not perfect. There are a few Twim Cam years that you may want to avoid.

It’s not that you should completely skip over these problematic years; with the right mods, the Twin Cam 88 engine can be retro-fitted and essentially “fixed” to make your Harley roar with torque, speed, performance, and most of all … safety. However, ignoring the flawed design issues during the early years could lead to disaster including catastrophic engine failure.

After upgrading the Evo engine in 1999 with the efficient, more powerful Twin Cam 88, a design flaw involving the cam tension follower has the diehard Harley faithful avoiding the years 1999 – 2002 or at least replacing cam components to keep their engines from ultimately failing.

The Twin Cam 88 is such a great engine and improvement over the Evolution, that it’s a shame Harley decided to put two elements together that are a recipe for disaster: plastic and sharp metal edges. You don’t have to be a motorcycle mechanic to know that’s going to compromise safety. Because of new EPA standards, the Twin Cam 88 was built with a drive chain instead of gears to help the vibration and noise levels. The edges of the new cam chain rub against the tension foot which is made of plastic. Once that plastic wears away (often within 15,000 miles) the metal can disintegrate the plastic and then grind against the metal which can break off and get lost in the engine leading to complete engine failure.

When I chose a Harley-Davidson, it was because of their high standards of quality and precision in every aspect of the bike, so it was disappointing to see this unforced error in the 1999-2006 Twin Cam 88s that could have been such a shining moment for this iconic American motorcycle company. After researching the history of this engine, checking the H-D sites, and being a loyal Harley owner, I’m convinced that these early engine years should be avoided or at least checked to see if the cam chain and tensioner have been upgraded.

In this article...


The Genesis of the Twin Cam 88

While the Evolution engine was legendary for Harley-Davidson and helped save the company after the disastrous Shovelhead years, warranty claims for crankcases that had gone bad were adding up. Reliability was a priority for Harley. Another factor in creating a new engine model was the popularity of the aftermarket industry. Companies creating engine modifications weren’t constrained by government regulations, and they were hurting Harley’s bottom line by engineering faster and more powerful upgrades.

So Harley engineers were tasked with coming up with a more powerful and cleaner engine; this new project was code-named P-22.

The EPA required exhaust emissions and noise levels to be lowered. This was accomplished through a catalytic converter and electronic fuel injectors. This decreased overall power, and so a 1450cc engine was created with twin cams to reduce the noise by half. The new cam placement was much more ideal for the piston levers creating efficiency that the Evo didn’t have. Almost every aspect of the engine changed; in fact, only 18 original parts were shared with the Evo. Harley-Davidson was changing directions completely.

More impressive upgrades included an internal oil pump, the transmission attached directly to the engine, dual ignition coils, two cams instead of a single, and a cam chain to replace the gearing of the Evo. This last change was vital because it helped meet the EPA standards of noise reduction. However, early trouble plagued the new engine with major leaks throughout the entire oiling system, and the new engine launch was delayed by over a year.

Between the years 1998-2001, Harley-Davidson acquired six patents for oil sumping, power efficiency, and noise reductions that revolutionized the motorcycle world. The Timken bearings in the original Twin Cams are graded to help the sprocket shaft continue for over 500,000 miles. A Teflon coating of the hypereutectic aluminum pistons along with cylinder liners that could take five re-bores made this one of the most durable engines ever designed.

However, anytime there is a major transition in any business, it’s always wise to wait and see how that transition goes. So it was with the engine changes from the Evolution to the Twin Cam 88. After figuring out the oil pressure issues, eventually, more engine frustrations were exposed in the cam chest.

Harley had several options for their EPA-approved cam system. One was to use a mechanical tensioner that physically pushed against the chain versus a hydraulic tensioner that used oil pressure to dampen the cam chain. Another choice was the quality of parts involved. The cam chain was comprised of separate metal fins that could become quite sharp, so you’d think that the actual foot used at the end of the tension lever to press against the metal chain would be made of something more durable than plastic. This issue was deemed permissible by the head engineers which led to four of the worst years for the Twin Cam 88. Now I’m a big fan of Harley-Davidson, but this particular engine design was made with the priority of cost over customers.

History of the Twin Cam Engine

1999 – 2002: Worst Twin Cam Years

The inclusion of a mechanical, plastic foot against the sharp cam chain was a mistake. Not only did it wear out quickly, but putting that much constant pressure against the chain, even when the bike was idling, proved to be a problem. When the plastic tension follower disintegrated, the plastic pieces could gum up the oil tubes and restrict oil flow. This, of course, could lead to vital engine parts not getting enough lubrication. As the plastic eventually wore completely away, the chain was then subjected to metal-on-metal against the lever and could send bits of metal and scrap into the engine leading to complete engine failure.

Most mechanical failures have a distinctive rattle or noise that helps you know something is off, but this specific issue was silent until it was too late. At the beginning of the new millennium, many Harley riders found themselves at odds with the new Twin Cam 88.

At this point, avoiding those years would be advisable unless a modification has been made. Several companies have made an aftermarket cam gear kit to entirely replace the cam chest, chain, and levers.

Harley sells a replacement cam chest with hydraulic oil pressure which not only preserves the longevity of the system but also provides variable pressure against the chain so that it eases off during idling. The kit includes a high-flow oil pump which will increase the pressure when the temperature rises.

Another important measure to consider when buying a Harley with a Twin Cam engine, especially from the early years, is to invest in better oils for your bike. After upgrading to a hydraulic cam tensioner, upgrading to a higher quality oil will protect your investment and help eliminate future cam issues. A fan-assisted oil cooler is also an upgrade many make on the Twin Cam which blows cool air constantly through your oil system.

Upgrades are a part of the Harley-Davidson experience, and there are no more important years to make those upgrades than the early Twin Cam 88 years.

2003 – 2006: Improved But Suspect Years of the Twin Cam

Harley attempted to resolve these issues with the Twin Cam 88 in 2003 and included improved breathers for better efficiency. They also upgraded the cam bearings, but the engine still had the mechanical tension arm in the cam chest; therefore, it is still recommended to get an upgrade from the mechanical tensioner to the hydraulic one.

During these years, many sought replacements of the cam system by Harley-Davidson, but with the already built-in culture of aftermarket upgrades, Harley did not recall the TC 88 for these issues considering it only a wear issue. Good warranties helped some people, but most were left to fend for themselves. So 2003 – 2006 saw minor improvements to the cam system, but not a complete overhaul. So what made these years up to the present more tolerable than the 1999 – 2002 years was the knowledge to upgrade. Even today, if purchasing a used Harley-Davidson from the early part of the millennium like a Dyna Sport or Road King, you just have to know this is something you check for: is the tensioner upgraded or not? Most of the Twin Cam 88s have been, but some still aren’t.

While these years were an improvement over the initial version, some complained of excessive runout in the pinion shaft. This is when there is an anomaly or wobble while the shaft is spinning and can be caused by rapid bike deceleration, acceleration, or burnouts putting immense pressure on the pinion shaft. Harley recommended a tolerance level of .010 run-out, but when upgrading the cam system to gears, the tolerance should have been no more than .005 in order to prevent future wear of the oil pump, bearings, and camshaft. Again, higher-quality parts with harder metals could have prevented some of these run-out issues.

A New Twin Cam Engine Design

2007 – 2009: Good Years for the Twin Cam 96

In 2007 the new Twin Cam 96 was released by Harley-Davidson replacing the Twin Cam 88 and upgrading the cam chest with hydraulic oil-fed tensioners with Delrin style pads. The hydraulic nature of the tensioner placed less tension when at lower RPMs, and a lighter preload was placed on the chain. This efficiency leads to a longer life of the cams. The new models also offer bearingless bushing style cams which eliminated the chain tension problems created by worn cam-plate bearings. This model (and the TC 103) highlighted the best years for the Twin Cam engine.

Of course, not every engine is perfect, and the Twin Cam 96 had some piston recoil issues with smoke blowing out of the air filter. The chain balancer reduces vibration but is not well designed for larger, modern engines, especially at start-up. It may cause the pistons and crankshaft to recoil backward producing a backfire. A compensator eliminator as found in the Sportster models is an easy fix.

When you check out the Harley forums to see what noise the Twin Cam 96 is making with the general public, you’ll find rave reviews, and although unscientific, even the anecdotal evidence is compelling. Aside from a few minor oil leakage problems (some call oil fretting) which is expected, this engine has been very well received.

2010 – 2016: The Best Years for the Twin Cam 103

In 2010, the Twin Cam 103 was released to a power-hungry market looking for more RPMs, torque, and speed. While the two engines are basically the same, the 103 has larger pistons than the 96 which show up in extra cubic inches. The increased compression range goes from 9.2:1 to 9.6:1 which allows for greater speeds. The Bore x Stroke is increased in the 103 from the 3.75 x 4.38 in of the TC 96 to the 3.876 x 4.38 in of the 103.

Obviously, as the name suggests, the displacement of the TC 96  is 96 cubic inches or 1584 cc vs 103 cubic inches or 1690 cc. Finally, the torque difference between the two is 92.6 lb-ft at 3500 rpm for the 96 and 102 lb-ft at 3500rpm for the 103. The latter also has an oil cooling system that the 96 doesn’t have.

Other than a seemingly frivolous lawsuit concerning the heat coming off this engine, most are completely satisfied. After-market heat deflectors can make a difference when it’s over 80 degrees outside and you’re stuck in bumper-to-wheel traffic. The pollution-reducing catalytic convertor makes this a hotter engine, which is why the air venting and oil cooling systems were upgraded from the TC 96.

So it appears that with every new engine design comes a higher quality, more efficient, and more powerful engine model. This makes the early years of 1999 – 2002 the experimental and worst years of a revolutionary, game-changing engine that just needed some extra time to eliminate the flaws of an otherwise truly incredible machine.