Why a single cam?

[rbabos]

The most recent American Iron magazine has a review of the new M8 bikes, and the author, Steve Lita, states...

"With the inception of the Twin Cam, the valvetrain required the use of two cams because of the necessary pushrod angle with the old two-valve heads.  But now, with the transition to 4 valves, the single cam comes back into play."

Does this sentence make any sense?

Only shows the twin cam wasn't needed in the first place or was it? Depends on how you twist words around on a new product when advertised.
Ron

[PoorUB]

The comment makes some sense, but it is kind of like the chicken or the egg delema. HD probably could have done something similar to the two valve heads, but with wider valve angles and more lift it would have been harder to do. Narrow valve angles and lower lift made it easier on the M8.

[Sunny Jim]

And the lifters? Are they the same old crappy lifters?

[FSG]

And the lifters? Are they the same old crappy lifters?

yes

[rbabos]

And the lifters? Are they the same old crappy lifters?

yes

Ah come on. They must have been tested for a million miles, right? Well, one good thing is they should have an easier life with reduced spring pressures.
Ron

[Ohio HD]

And the lifters? Are they the same old crappy lifters?

yes

Ah come on. They must have been tested for a million miles, right? Well, one good thing is they should have an easier life with reduced spring pressures.
Ron

Is pressure reduced in total? Smaller, but smaller x 2.   

[rbabos]

And the lifters? Are they the same old crappy lifters?

yes

Ah come on. They must have been tested for a million miles, right? Well, one good thing is they should have an easier life with reduced spring pressures.
Ron

Is pressure reduced in total? Smaller, but smaller x 2.   

I'm guessing of course at x2 per lobe would still be less. In time we should have some real figures to compare with. If more, well that just adds fuel to the lifter fire, right?
Ron

[Ohio HD]

And the lifters? Are they the same old crappy lifters?

yes

Ah come on. They must have been tested for a million miles, right? Well, one good thing is they should have an easier life with reduced spring pressures.
Ron

Is pressure reduced in total? Smaller, but smaller x 2.   

I'm guessing of course at x2 per lobe would still be less. In time we should have some real figures to compare with. If more, well that just adds fuel to the lifter fire, right?
Ron

Yes    

And I wasn't poking at you, just wondering if they will be less.   

[gregm]

C'mon, people, this is Harley-Davidson we're talking about. The single cam is there for reasons of style, and anything anybody says about mechanical reasons for it is just rationalization.

Line up all the Harley Big Twins, from Knuckle to M8, and it's clear the TC is the odd one. All the others make a powerful visual statement with the four chromed pushrod tubes converging on the timer cover. It's distinctive, it's "muscular" looking, and it's uniquely Harley. You might even call it "iconic." (You might also be able to protect it with trademark or design patent registration, as nobody else has this look.) Back in the late '90s, when the TC was designed, this wasn't as important because Harley had the nostalgic-cruiser market to itself. The TC was more about performance and emissions than maintaining the classic look.

That was then. These days, Harley is facing competition from Polaris/Indian, which has launched a frontal assault on Harley's dominance of the nostalgia market. The Thunderstroke engine was specifically designed to look like the flathead motors of Indian's heyday. That's why it has that otherwise goofy three-cam system (allows the pushrod covers to be parallel to the cylinder, as in a flathead), and the heads hang out to swallow the top third of the pushrods, and of course the rocker covers have bas-relief fins cast into them. And it seems to be working--Indian's still not selling anywhere near as many bikes as Harley, but their sales are growing, Harley's are more or less flat, and there are a lot of used Harleys for sale at Indian dealerships.

So now Harley plays that game. The M8 delivers four valves, two sparks, a counterbalancer, etc., etc., in an engine that looks "older" than the Twin Cam. Notice how many people are comparing the M8's lumpy rocker covers to the Knucklehead? I doubt this is an accident.

There may be good technical reasons why two cams are better than one. But style and "heritage" are more important to selling bikes. And the engineers will figure out how to make it work.

[gregm]

ScottFree, my 2005 TC has four chromed pushrod tubes converging on the "timer" cover. Am I missing something?

[Piston Broke]

Perhaps it's in the look and the 'back to roots' concept?

The TC cost them a bit in bad PR and warranty ... and consumers double in replacement.