As some of you know, I once lived a normal life of the consistent toil and work needed to maintain many possessions. In time I established a way of life, on the road, almost completely devoid of these pressures. I believe that, aside from the elimination of ANY unnecessary possessions, this ideal is achieved by keeping things extremely simple. For the very definition of the word simple is EASIER, while the definition of complicated is undeniably HARDER.
So, did I want an easy life or a hard one? The choice became simple, and this ideal is probably what has kept me so loyal to Harley’s Evo engine for so long. For not only does the Evo offer the durability and longevity, it is also (aside for some of the very early stuff) the simplest design Harley ever built. Less moving parts and far easier to rebuild than a Knuckle or Panhead, and even easier is some ways to work on that a Shovelhead—which is what it was based on.
But lets move on to what I really want to say here…
I’m gonna get into the cam design for the Evo as well as the Twin Cam and show, in simple layman’s terms, what the actual benefits of the new design was. As you will see, although there are changes to the Twin Cam making it a far better performer, the Twin Cam design itself is not one of them. So why then did they build it? Well, I’m gonna show you…
Although there are plenty of you gear-heads out there who already know this stuff, if you tolerate my baby talk through the first photos, I’m gonna eventually get to the actual reason the Twin Cam design was built.
I’m gonna keep the beginning of this chat geared exclusively toward the non-gear-head. Although you non-gear-head guys may not be interested in tech stuff, if you bear with me for a minute you will also see, easily and obviously what the real advantages to the new Twin Cams are, and are not.
The stuff I’m gonna get into here is not rocket science. In reality, it’s only super simple, Jethro and Elly May hillbilly engineering.
Let’s get started…
Note: I have other photos of the inside of these lifter blocks that shows them being badly pitted up inside. And although they’ll work for now, I’ll keep an eye out to pick another set up some day and replace them if I’m ever in there again.
All Evo and older H-D engines have easily removable lifter blocks similar to this–All but the Twin Cam. The TC’s lifter blocks are machined directly into the right engine case and if there’s a problem with them you must replace that entire engine case.
The engine’s job is to turn a shaft that sticks out either side of it. The left side is ultimately hooked to the rear wheel through the transmission and clutch, while this side is used to turn things the engine needs—like the cam. Anyway, that little gear shown here on the bottom comes straight out of the engine and simply turns that cam above it. Pretty simple huh? That gear on the left is the breather which is also simple, but we ain’t gonna get into that right now.
Here’s the catch, that little bottom gear coming off the lower-end (called a pinion shaft) has to be turning completely straight. It can’t be wobbling back and forth and up and down or it’ll break the gear above it—obviously.
Because of this the crank inside the engine must be trued or aligned to very strict tolerances by an actual human being, who must fight with it until it’s almost completely straight. Also, because the machining is not always exact on each engine, the big gear above on the cam comes in different sizes (indefinable to the naked eye) that must be fitted again by a human being to each engine.
All Harley engines but the Twin Cam have been like this. This procedure probably costs extra money and H-D has eliminated the need for it by taking a couple of cheap shots on the TC engine. I’ll show you that in a few minutes.
For now I’m simply gonna reach in there and pull that cam out…
Now, in the next photo, we’re gonna take a look at the exact same thing—only in the Twin Cam…
Never before in H-D’s history have they used bicycle chains inside an engine. Why’d they do it now? Well…let me tell you…
Remember how I said that the crank inside the engine must be made completely straight by a human being? It no longer works like that.
Nowadays the cranks are pressed together by a robot which, although I’m sure it can knock cranks out like gangbusters and save a whole lot of money, seems seldom to be able to get them perfectly straight. Because of this misalignment, the pinion shaft often wobbles round and round and up and down. This is called run-out, and if it’s to far out of whack it’ll break gears. But it won’t break a bicycle chain. Likewise, the cam gear no longer needs to be sized by a human being as it does on the older engines.
Note, the little red cam chain tensioner on the left. These parts gave engines many problems between the years of 1999 and 2006. Gear drive systems and hydraulic tensioner fixed this issue–expensive.
Note: The second little red cam chain tensioner.
Push-rod systems will not work at high RPM, especially if they’re not straight up and down, which is why the Japs use overhead cams so they can rev their engines up to 10.000 RPM. But most of us Harley guys don’t give a shit about that. We like the slow turning, lazy, V-Twin engines thumping us up the hills and across the land.
Still, straight push-rod tubes are at least better than crooked ones—especially if you wanna rev it up. So the complex twin cam design was supposedly built so they could get them lifter blocks farther apart and tweak them push-rod tubes into a straighter angel. Well let’s take a look at the twin cam in the next photo and see how that worked out…
Let’s take a look at some of the older designs that they actually did get the push-rods straight, and see how they did it…
To answer, I’ll need to tell a chunk of H-D, or motorcycle in general, history:
As with all motorcycle manufactures, Harley- Davidson has always been in fierce competition with, well, their competitors. In fact, in the last century there was originally over 130 American motorcycle manufactures; all but one eventually buckled under the pressure.
For H-D competition came most often from Indian. After Indian’s demise in the early 1950s the British came on the scene (Triumph, Norton, and BSA) and the Sportster was born to compete with these smaller, nimbler bikes.
Next it was the Japanese who introduced reliability and longevity to modern motorcycles in the late ‘60s and especially the ‘70s. This development snuffed Norton, Triumph, and BSA out of business rather quickly and became the closest thing in history to almost put Harley-Davidson out of business.
Then, in the mid ‘80s, H-D countered with the Evolution engine (so named because it was supposed to have evolved to compete with the new era of motorcycles). Evo advertising offered greatly enhanced longevity, no overheating, and no leaks—problems plaguing almost all older bikes throughout history.
Yet Evo advertising said almost nothing of added horsepower; for that was not an important factor at the time, and not what the Evo engine was built to do—it was built to last.
Being of very early design the H-D has always been one of the simplest machines on the market. One of my main concerns for the Evo was: Would it carry on this tradition? Well, as I’ve already stated, the Evo engine and 5-speed transmission are both some of the simplest stuff H-D ever built.
Modern longevity coupled with extreme simplicity; a very big plus in my book.
But let’s get back to why the Twin Cam design was built:
The Evo debuted in 1984 and by 1989 had grown in sales to dwarf all the Japanese manufactures combined in sales for bikes over 800ccs, which is what H-D sells.
Problem was people wanted more power. Then, in the early ‘90s, S&S came out with a big 96-inch Evo clone (before that S&S had only made parts. Suddenly, they built complete engines). In time others began to make big Evo engines as well; for you see, the patent on the Evo had never been strong. Aftermarket companies quickly became, and remain to this day, Harley- Davidson’s newest form of stiff competition (although Polaris is trying to horn in on H-D’s game as well).
H-D had a choice: either build a bigger Evo and go into competition with the aftermarket boys, or come out with something completely new and put better patents on it. And so the Twin Cam was born. In reality, it had little or nothing to do with cam design improvements.
So what are the Twin Cam’s real advantages? First off the compression ratio was raised by one entire point, while cylinder to head surfaces were increased to lessen the possibility of blown head gaskets associated with higher compression.
Next, consideration was taken to make sure the twinky’s heads flowed better. Piston stroke was shortened by ¼-inch (a considerable distance), which probably contributes to a smoother ride.
But the greatest advantage was in moving farther apart the eight studs that protrude from the thicker, more robust cases to hold the heads and cylinders onto the engine. This simply allowed for the use of bigger cylinders, to added much larger displacements. Increasing Evo displacement by much was simply impossible due to the cases and stud placement.
Other advantages are a larger wrist and crank pin to help handle the extra power. Aside from that there’s not much. Flywheels are actually lighter (granting quicker revving, although possibly at the cost of a little torque) while crank bearings remain the same.
So you see, the twin cams have nothing to do with performance enhancement. In fact, S&S now makes their V-111 engine in both Twin Cam and Evo configurations and both put out exactly the same power and torque specs.
Because of my long history of riding these motorcycles and so much time spent traveling, I’m often asked what engine a person should go with. To this I almost always answer an ‘07 or up twin cam.
For most simply wouldn’t be happy with performance of the older bikes. Under normal use, where the bike will spend most of its time in town and seldom see more than 50 or 100 thousand miles in its lifetime, the twinky is a far more satisfying ride. But they are now very complex, expensive to repair, and all but impossible to fix on the side of the road. But how many folks repair their own bikes these days anyway?
Although the Twin Cam has gained improvements, it is designed more for those who do not mind spending a lot of money, but do not really ride crazy miles. The Evo was designed (possibly by accident) to go a lot of miles for very little money.
In my weird gypsy world there you have …
This engine is rumored to come in 107-inch and use four valves per head. Unlike Harleys of today, these will require periodic maintenance valve adjustments that must be made by removing the rocker boxes. This system sounds like it will be something akin to the old 750 Honda valve adjustments.
This engine will undoubtedly offer great power and smoothness; both things I will probably never get to enjoy because one of my main concerns is also simplicity. And let’s face it: the most common America (and H-D too) belief these days is “More complicated is always more better!”
–Scooter Tramp Scotty
Editor’s Note: Some would not agree with Scotty on some of his issues. Some will recommend Twin Cams before 2006. Earlier Twin Cams had Timken bearings in the left case. They didn’t have out-of-true lower ends. The 5-speed Transmissions had strong, better quality main bearings. You will need to upgrade the cam tensioner system, but then it might hold together.
