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Chevy Geardrive System - Keeping In Sync

With Milodon's Simple Geardrive

Seth Millhollin Oct 1, 2002
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This is Milodon's latest geardrive system. It features a single idler gear that is solidly attached to the back of the cover.

Choosing the correct system to link the cam and crank together in a stout performance engine has always been a topic that led to varying opinions. Engine builders and extreme enthusiasts have always had concerns surrounding the use of cam drives, whether it be a chain, a belt, or a set of gears. Each one has its own set of myths of the "do's" and "don'ts."

One of the biggest of all the myths was focused on the geardrive system. There was a common belief that using a solid gear-to-gear connection between the cam and crank sent major harmonics to all of the valvetrain components. There was even some concern about improper timing. To avoid this, legendary Chevy engine builder Bill "Grumpy" Jenkins would install stock nylon-coated link-style timing chain sets in his 600hp Pro Stock small-blocks, the thinking being that they would absorb the harmonics and were literally disposable after each race.

While most of us would never notice the distortion in our street machines or bracket race motors, this debate, nevertheless, still rages on. Today, many aftermarket firms produce state-of-the-art geardrives that offer a perfect sync between crank and cam. Milodon Engineering has been producing geardrives for years and are more than confident with the performance and integrity of their products.

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This is the idler gear mounted on the back of the cover. This is a cast cover that has been machined, and the single idler gear is pressed into a cast boss. The bearings used will ensure its strength in extreme-use conditions.

This particular geardrive uses a solid mounted idler gear that is located on the back of an aluminum timing cover. Once the crank and cam gear are correctly installed, you put the cover on the engine and the idler gear meshes into its proper location, providing an accurate link between the two.

With the cover secured to the block, backlash is then set between the gears by following simple instructions. It isn't complicated and can be done in any home shop or garage.

The cover that is used for this is a nicely crafted, large, aluminum piece, which has flanges that fit under the water pump to create the necessary clearance. The cover also has a removable center cover to allow you to adjust the cam timing. When you have the cam where you want it, just reinstall the middle section. It is much easier than removing the entire cover, as some timing devices require.

This is a quick, easy, and accurate install for anyone who wants to spruce up the look and/or the performance of his engine. With help from George Vrbancic of Vrbancic Brothers Racing and Dyno Shop, our install went fairly smoothly, and the finished product was what we had hoped for. One thing we didn't cover in the install was initial cam timing setup. When you have everything finished and the cover is on correctly, you will have to take it back off to set the cam timing. Using a degree wheel, set the crank on TDC for the No. 1 cylinder. Using the cam manufacturer's specs, find the No. 1 intake opening and move the crank to that position. Place a dial indicator on the No. 1 intake and open to what the cam manufacturer used for checking clearance.

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Once the crank has been installed in the motor, you will need to press the gear over the snout of the crank. This is one of the nicer tools made for this job, but any of them will work.

Here is an example: If the cam specs were intake opens at 39 degrees BTDC at .050-inch cam lift, then you would set the crank degree wheel at 39 degrees and the dial indicator on the No. 1 intake at .050 inch lift.

If you set this up and get the specs that you are supposed to, then the cam is in "straight up" or at 0. If you are plus or minus a degree or two, then the cam is advanced or retarded, advanced if you are over and retarded if you are under. Once you have the timing set, you will number the seven alignment holes, which can be used for future quick adjustments of cam timing.

This may sound a bit confusing, but it isn't. When you are looking at your own cam card, it will be much simpler. You have to use a degree wheel and dial indicator for this geardrive. It is the correct way to dial in a cam, no matter what you use. Once it is done correctly with this geardrive, you will have the most accurate timing possible.

All in all, the Milodon geardrive proved to be a quality system that is relatively easy to install-and accurate in keeping the cam and crank in perfect sync.


Vrbancic Bros. Racing



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