Project LA Thumper Gets A Milodon Gear Drive For Precise Timing

When discussing the best way to link your engine’s cam and crankshaft, the conversation always seems to be a topic that leads to varying opinions. Ask any engine builder or enthusiast their opinion — whether it be about a chain, belt, or a set of gears — each one solicits a strong argument.

We’re at a point in assembling Project LA Thumper where we need to make the cam/crankshaft connection. While a timing chain would suffice, we decided to step it up a notch and chose to use a Milodon gear drive (P/N: 13600). We’ve heard the statements about issues with gear drives being noisy and initiating harmonics in an engine, so we asked Steve Morrison at Milodon about these concerns. “The talk of harmonics has been going on forever. While there might be some validity to it, no one has ever tested the theory. As far as noise, these are straight-cut gears, so there will be a small amount of noise, but it is minimal.”

The Milodon gear drive uses a single fixed idler. Drilling and tapping of the engine block for one bolt (arrow) is required to complete this installation.

Many enthusiasts have the opinion that a gear drive is best suited for a race engine. While that is true to an extent, a good gear drive is just as “at home” in any performance engine. When properly installed, we’re told a Milodon gear drive will last almost indefinitely. This is because there is nearly zero wear — again, if properly installed. Since cam timing accuracy and consistency are key to accessing every bit of the cam’s available power-delivering capabilities, a gear drive is a perfect option.

Milodon gear drive

The idler gear and bracket are affixed to the block with the cam-plate bolts.

If you are looking for a gear drive to make more power, look elsewhere. A gear drive is not designed to increase power. What it is designed to do is create stable timing that does help with power production. As Steve stated, “anything flexible can stretch. “When a chain or belt stretches, that will affect your timing. With a gear drive, no stretch can occur.”

Gearing Up

The Milodon gear drive is made from billet steel. But, unlike other multi-gear sets, the Milodon drive uses a single idler gear that is rigidly mounted to a support bracket that affixes to the block. This rigid mounting does not allow any timing fluctuations like could possibly be found when using a flexible belt or chain that can, again, stretch over time.

Mounting the idler gear and its bracket is done via the cam-plate bolt holes along with a single bolt near the bottom of the bracket that you have to install. The new bolt threads into a hole you drill and tap into the front of the block. It protrudes into the interior wall of the engine block (crankshaft area). Unfortunately, if precautions are not taken, those drill particles can and will scatter throughout the engine interior.

milodon gear drive

The bottom of the bracket needs a mounting hole drilled into the block. We attached newspaper to the interior and exterior of the block to prevent drill particles from getting everywhere.

The instructions make no mention of this, but if your engine is assembled, proper care must be taken to ensure those filings do not get embedded in any bearing surfaces or the oil system. Before you drill, tape a piece of newspaper on the interior of the block, above where the new hole will protrude, to keep the particles from going everywhere. When done drilling, remove the tape and paper and then wipe the interior wall of the engine block.

If newspaper is not used, you might be able to — with the engine upright on a stand — thoroughly flush the internal area of the block after drilling. Honestly, even though we did our best to protect the internals, we felt we needed to disassemble the engine after installing the gear drive to make sure everything was thoroughly cleaned and no filings were present. Luckily, no debris was found.

The gear drive does not have any markings to aid with camshaft timing. You need to find top dead center of the piston's travel, the base circle of the camshaft, and then adjust per the cam card.

With the idler gear and mounting bracket loosely attached via the four top bolts, it’s time to set the gap/backlash between the gears. While a backlash of .003- to .006-inch is needed, Milodon also doesn’t recommend the use of a dial indicator to set backlash. Instead, use a single 1/2-inch by 6-inch strip of newsprint (not glossy magazine paper). First, take the strip of paper and feed it between the camshaft gear and the idler gear, following through the idler and crankshaft gear. With the strip of paper between the three gears, hold the idler gear tight against the upper and lower gear. This centers the idler gear between the other two gears as well as sets the backlash. Now you can mark, drill, and tap the lower bolt hole in the bracket.

Getting In Time

When it’s time to “time” the engine, things can get confusing. The Milodon gears have no timing marks to use, so you must find true Top Dead Center (TDC) and then install the gears with the cam in the proper position. To begin, with the idler in place, install the camshaft hub without the gear installed and the crank gear. Next, install a degree wheel on the crankshaft. There are several ways to locate TDC, but I used a dial indicator on a magnetic base. Once you have found TDC, set a pointer/indicator at T.D.C. on the degree wheel for the number one cylinder.

Next, place a dial indicator on the camshaft’s number one intake lobe. We used a lifter and a pushrod with the dial indicator mounted on the deck surface. Next, position the camshaft so the lifter is in the “valves closed” position (bottom of the ramp). The cam specs indicate the intake opens at 15.5 degrees Before Top Dead Center (BTDC). Therefore, we set the crankshaft-mounted degree wheel at 15.5 degrees BTDC and then spun the gearless camshaft until the dial indicator moved .050-inch. This establishes the camshaft and crankshaft are now in the “straight-up” position with zero degrees advance or retard.

With that done, the camshaft gear is now placed onto the cam hub making sure to align the bolt holes. Sliding the gear in place will engage idler gear teeth and allow the cam gear bolts to align with the hub bolt holes. (There are seven bolt holes and, therefore, seven possible positions).

Setting up clearances between the gears is a simple task accomplished with the help of an old newspaper. It’s simple and effective.

According to the instructions, the camshaft can be advanced or retarded by utilizing the gear’s bolt holes. This is done by simply rotating and reorienting the gear on the hub. For instance, there are two tooth locations possible for each bolt-hole position. Rotating the gear slightly counterclockwise to align bolt holes will advance the cam. Spinning the gear clockwise and aligning the holes will retard the cam. My initial install of the gear gave me a camshaft that is 1.5 degrees advanced. Once the correct cam-gear-to-hub position has been found, coat all seven cam gear bolts with thread locker, and then torque to 22 lb-ft.

With the installation of the Milodon gear drive complete, we are now one step closer to finishing LA Thumper and can’t wait to see how this mill turns out. You can check out the other articles published about this engine by clicking here. Also, stay tuned as there are more articles in the works as we continue assembly.

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Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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