Wednesday, December 10, 2008

Waking Up the Sleepy Twin Cam

I just finished an installation of S&S Cycles’ gear drive cam shafts on my 2004 Electra Glide Standard. So far I am highly pleased with the results. The engine which was a little sleepy has had a wakeup call. Acceleration is up and the exhaust note is much crisper.
Harley Davidson’s Twin Cam engine was introduced for the 1999 model year. As the name implies, the engine has two cams with two lobes each, the earlier Evolution engine has a single cam with four lobes.
The Twin Cam engine uses chains to drive the cams. Think bicycle chain, on a bicycle the chain droops and when you start to pedal, the chain snaps tight. The action is the same on the chains driving the cams, so Harley Davidson added little nylon pads that are spring loaded and push on the chains to keep them taunt. This system is not the best for accurate cam timing.
The tensioner pads are also a weak point in the system. The nylon pads wear as the chains run over them and it is nearly impossible to tell how much they are worn without pulling the engine apart. Allowing the tensioner to wear out means metal on metal contact and metal particles inside the engine, not good.
S&S Cycle manufactures a gear drive replacement for Harley Davidson’s Twin Cam engines. The gear drive replacement provides increased performance by more precise cam timing and by eliminating much of the parasitic drag that is part and parcel of the old chain system.
The replacement cams, which because they are gear driven run backwards as compared to chain driven cams, are ground with a slightly higher lift and longer duration. This appears to me to move torque further up in the RPM band where it is most appreciated. With increased performance and no worries about tension pad debris or metal shavings contaminating the oil, I think this was money well spent.

Harley Davidson should have done gear drive cams in the first place.

1 comment:

joke said...

Hey Ray, how long did it take to change out the OEM cam tensioner to a cam gear unit? Was it fairly straight forward to do? I'm handy but no expert.