A break-in at Jesel’s shop cut the Cosworth project short, but the notion of driving camshafts by way of a belt stuck. And you could never determine exactly when the nylon gear would decide to take a vacation, so the results were sometimes catastrophic (and sometimes spectacular).ĭuring that era, Dan Jesel was knee-deep in high rpm, small displacement Chevy drag race engines builds. While messing with a pair of OHC Cosworth Vega cylinder heads (mounted on a small block Chevy, no less), Dan more or less discovered the benefits of belt drives. As a result, maintenance was often heavy, and you usually had to replace both the gears and the chain on a regular basis. It solved the problem, at least to a degree, but these nylon gears weren’t exactly known for being robust. The initial race engine builder solution (championed by the late Bill Jenkins, no less) was to use a timing chain set with a nylon upper gear (this was pretty much a standard Chevy production line piece). Plus, the damper is outboard of the lower cam or gear drive gear, so the cam drive is still forced to deal with a bunch of harmonics. You may ask: “Doesn’t a harmonic damperfix some or all of this ‘noise’ transmitted to the valve train?” Not exactly. The camshaft simultaneously witnessed every creak and groan witnessed by the crankshaft. And gear drives often made things worse because a gear drive physically ties the cam to the crank in a rather rigid fashion. At the time, the issue was so bad that engine builders were having difficulty maintaining stable engine timing. Obviously, this vibration, and the associated harmonics that went with it, had a serious effect on both valve and ignition timing. It was no secret to racers many years ago that a tremendous amount of harmonics, vibration, and resonance was transmitted to the camshaft by way of the crankshaft. So why have belt drives become so common in motorsports? Within drag racing, for example, they see use in everything from Super Stockers to Pro Stockers. While timing chains and gear drives are still in use today, they have been pretty much been eclipsed by belt drives in hardcore racing competition. Not that long ago, you had two choices when it came to driving a camshaft: timing chain or gear drive.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |