Straight cut gears are noisy. If the profiles are hobbed correctly, though, they do not impart any accel/decel on the working parts. Straight cut gears are also strong.

Helical gears are used simply because they are quiet.


Harmonic dampers don't stop crankshaft twisting, they just keep the twisting from gathering momentum and amplifying to where it breaks the crank.

Cranks have harmonics in their flexing.
Cams have harmonics in their flexing.

The two parts have DIFFERENT harmonics that do not "jive" with each other.

In a constant speed application, you need something between them that insulates the two flexing "nonharmonius" pieces from each other.

Gears do not do that.

Some motorcycle applications that use gear driven cams do so by driving a vertical driveshaft off the crank and then driving the cam from the driveshaft. The torsionally flexible nature of the driveshaft acts as a damper.

Gear driven bike cranks that use gears all stacked up (like my 1986 VFR750F Honda) don't offer any damping in the cam drive, but are also driving cams that are 6" long - and on that bike it is driving the cams from the CENTER. This is in essence, a nonflexible cam. It is also driving from the center of a 8" long crank. While that application works alright, most bikes use side driven cams cause it allows the crankcases to be narrower. This is on the extreme ends of the crank and cams and is no longer suitable for the rigid gear setup.

Suzuki GSXR1100's have long had cam chain troubles when coupled with stiff springs and hotter Yosh camshafts. Since that time, Gixxer motors have been updated many times. If gears would have fixed the problem, they'd have used them.

What do they use on the 2004 GSXR's, FZR's, CBR's, ZXR's? Chains.

Thank you for the info. I added another wrinkle to the brain today.

I have a friend who lost a 1400 hp engine because of a jesel belt failure. The belt seperated (delaminated-whatever) and the cam went out of time and byby pistons and valves.

Yeah, nothing lasts forever.

Jesel belts, though, are usually trouble free. Chances are that his belt got nicked by something a few hours prior.

The service life on gilmer cogged tooth belts is short... Even on DOHC cars that use them... Ferrari... etc.. they recommend changing the belts every 30,000 miles... and they are three times as wide and twice and thick as jesel belts.. plus they are turning whimpy overhead cams that don't need anywhere the heavy valve springs like a BBC. Plus each "bank" has it's own belt... The first time I saw a Jesel set-up on a BBC I about fainted by how small it was. I can't imagine that they last for more than just a few hours. I'd be inclined to change them every time I took the boat out. I'm sure they last longer than that... but knowing how much bigger they are on even Ford Pinto motors.... it scares me. I think the big advantage of the jesel set-up is in development work... who wants to pull the front cover to change the timing on a cam while the engine is on the dyno... I'd be inclined to get the dyno figures and timing settings and then put in a high quality roller chain set-up before the engine was dropped into the boat.... just my .02

Just lost a Jesel belt on my 705 ci engine. It came apart but left a small 1/4 inch wide section working which saved my entire engine. I smelled burning rubber and noticed the engine laying down above 4500 rpm. Wish I had a pic of the small piece that was left on. It was scary to see how close I came to grenading the engine ($$).

We are replacing belts in both engines. Engine builder says they don't like salt water. If they get wet with salt water you need to replace. (???)

Call me lucky from now on.