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Feb 06 2012

Installing a Milodon Gear Drive on a Big Block Chevy

If you’re thinking of buying a gear drive, chances are it’s for one of two reasons: you want more accurate cam timing than a chain can provide or you want that cool gear whine. Both are good, logical rationalizations for spending the grocery money on a car part.

Milodon makes some nice gear drives worthy of your hard-earned cash. All Milodon gear drives are three-gear, “fixed idler” models. The idler gear mounts solidly to the block (Under Cover) or to the cover (Full Cover). This system does not rob any power from the engine, and more importantly, will not allow cam timing to vary. When you dial in a cam connected to a Milodon gear drive, that cam timing stays where you set it.

We used a Full Cover gear drive on a 496 cubic inch big block Chevy. The drive uses an adjustable cam gear and hub assembly to set cam timing, accessible through the removable cam cover. The cam itself is bolted to the hub. When you combine that with rock-solid cam timing and near indestructibility, choosing a Milodon gear drive over a timing chain for your race engine quickly becomes a no-brainer.

You can follow our own install by click on the photo gallery below.

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This Milodon Full Cover gear drive is a three-gear, "fixed idler" drive with the idler gear mounted solidly to the cast aluminum cover. This setup will not allow cam timing to vary, does not rob power from the engine, and is virtually impervious to wear. The Milodon gear drive also uses an adjustable cam gear and hub assembly to set cam timing (accessible through the removable cam cover) and a three-piece roller bearing behind the cam gear to control cam movement, reduce drag, and eliminate block wear.

We installed the gear drive on a 496 cubic inch big block Chevy. Before we began bolting on parts, we drilled an extra oiling hole in the block (indicated by the pointer) to direct more lube to the gear drive. We also cleaned the block face thoroughly with solvent to remove any stray grease and oil.

The gear drive does not use the stock timing cover dowel pins, so they need to be removed. You can do this with a pair of vise grips, but it will take a little grunt to get the dowels out.

The three-piece roller thrust bearing is installed first; the bearing is sandwiched between two washers. The cam hub is then bolted on the cam with three Allen bolts. The crank gear is also installed at this point.

Milodon's instructions call for the cam gear to be installed before the cover is bolted on, but we did it the opposite way—it doesn't matter which way you do it. We ran a bead of RTV silicone around the inside perimeter of the cover, then bolted it to the block. The bolts were tightened just enough to hold the cover in place.

The cam gear is secured to the hub with seven Allen bolts. Gear position doesn't matter at this point—cam timing will be set later. To establish proper gear clearance, place a long strip of newspaper between the idler gear and the crank and cam gears, and tighten the cover bolts. Make sure pressure is applied to the idler side of the cover to keep the newspaper in place. Then, rotate the gear drive to remove the paper and make sure the gears mesh smoothly.

The block needs to be drilled and reamed for the gear drive's dowel pins. Use a 5/16-inch bit and drill through the hardened drill bushings in the cover (the bushings stay in place). Remove the cover and tap the dowels into the block, large end first. Now you can remove and reinstall the gear drive without disturbing the gear lash. The tape on the drill bit marks how far the bit has to go in so we don't drill in too far.

The next step is setting cam timing. The cam needs to be installed straight up, with no advance or retard dialed in. Remove the cam gear and use a degree wheel to find Top Dead Center for number one cylinder. Turn the crank until the degree wheel indicates the intake valve opening per the cam specs. Put a dial indicator on the intake valve and turn the crank until the valve opens to the cam maker's recommended checking clearance, usually .050 inches of lift. The cam is now installed straight up.

The cam gear bolt holes are used to set cam timing. Milodon suggests putting an indicator mark on the cam hub, then labeling an adjacent gear hole as Position One. This is the straight up position. The rest of the holes are then marked two through seven, going in a clockwise direction. This is how the marks look on our gear drive.

Each gear bolt hole has two degree settings—one for advance and one for retard. The illustration shows the cam gear set in the straight up position. To advance the cam, turn it clockwise to the appropriate bolt hole. To retard the cam, turn it counterclockwise. The chart shows the advance and retard specifications for each bolt hole.

With cam timing set, the removable cam cover is bolted on. Our new Milodon gear drive is ready to keep our big block's cam timing rock solid.

Parts List
Milodon Full Cover Gear Drive, 1965-90 (MIL-12600)
Milodon Gear Drive Installation Video (MIL-14900)

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