This is the "spider" mentioned in the text. As you can see, the design is such that it fits inside the upper belt drive pulley (on the four studs). The spider is keyed, which in turn, allows it to fit over the cam adapter. In this close up photo, you can see that the upper pulley is indexed, and of course, degreed for camshaft adjustment. You can advance or retard the cam by 10 degrees. And in case you forget which way is advanced and which way is retarded, they've machined an "A" and an "R" next to the degree marks.
A Cam Drive & More…
As mentioned earlier, a big benefit of a belt drive is the fact it allows for extremely easy (and rapid) cam adjustment. The drill is simple: Four nuts on the cam drive (spider) are loosened (for a closer look check out the accompanying photos). To retard the cam, turn the crank clockwise. To advance the cam, turn the crank counter-clockwise. The timing marks machined into the spider indicate two degrees of crankshaft degrees each. Re-tighten the nuts on the spider and you’re done. The actual range of adjustment is + or - 10 degrees, which, as most of you are well aware is more than sufficient for any drag race cam tuning operation. Keep in mind that without a dust cover in place (which is the case for the majority of drag race applications), almost everything is readily accessible. Aside from removing the water pump, this task takes minutes rather than hours.
Given the above, it's easy to see that changing the cam also proves to be an uncomplicated affair: Once you yank the water pump and peel out the lifters, there's nothing left to do except remove the belt and the retaining plate. Then the cam literally falls out. There's more too: Incorporated into the system is a camshaft thrust mechanism. Now, it's no big secret that roller camshafts tend to move fore and aft in the block. Some means of thwarting this movement is mandatory, and that's the purpose of this design. The removable thrust plate is also adjustable allowing easy endplay adjustment as well as cam removal through cover.
 Here's a close look at the belt and pulley tooth fit. As you can see, the belt is a special round tooth, high torque configuration. Jesel selected a round tooth belt for one major reason: The round shape of the “teeth” does a superior job of distributing the load across the tooth. The 25 mm belt is designed to run dry, and the overall design is resistant to wear from dirt and grit. |
How Good Is The Belt Drive?
When the belt drive system was first developed over two decades ago, some skeptics figured there wouldn't be much power gain from the system. They figured wrong. Initial testing on a 600 HP, aluminum rod, multiple carburetor engine (an old small block Chevy Modified Eliminator combination) showed gains of 12-14 horsepower. Independent back-to-back tests on a Super Stock style small block saw gains of 17 horsepower when compared to a conventional chain drive. Where did the gains come from? There were three probable areas: Reduced windage, increased timing accuracy (from the reduced harmonics transmitted to the cam) and of course, a lack of wasted motion (timing chains are noted for chordal action which can actually turn the chain into a "S" at high speed).
Source |
Jesel Valvetrain Innovation 1985 Cedarbridge Avenue Lakewood, NJ 08701 PH# 732-901-1800 Website: www.jesel.com |
OK. The belt makes more power and the drive system offers a number of advantages. How reliable is it? Very. The belt durability has proven to be greater than both gear drives and chain drives over thousands of race miles of competition in all types of race car applications. As mentioned previously, it sees considerable use in endurance applications. Remember too, there are literally tens of thousands of Harley Davidson motorcycles out there churning out equally large miles every year. And each and every one of those bikes is equipped with a drive belt rather than a drive chain.
When it comes to maintenance for a belt drive, it’s a simple job. Jesel recommends that the drive belt should be replaced annually (or following an inadvertent engine explosion). And the upper and lower seals should also be replaced annually. If operated in a severe dirt application (i.e.: sand drags), then it's a good idea to incorporate Jesel's optional dust cover. That's it. No fuss. No added maintenance. And it works. That's something any racer can appreciate.
For a closer look at the belt drive system, check out the accompanying photos.