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These quiet Donovan gear drives allow you to dial-in your cam with Vernier Accuracy* without any cam walk or float using three easy steps that appear below the video.

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Step 1 — Finding TDC on Donovan Engineering Gear Drive

1. Install the Donovan gear drive assembly, but leave the cam gear off for now.
2. Install a degree wheel on the crankshaft and a pointer on the block.
3. Put a dial indicator on the top of the #1 piston, and rotate assembly until the piston is at the highest point of travel. Set pointer to TDC.
4. Rotate crankshaft counter clockwise until piston has traveled dow 0.100″. Note reading on degree wheel.
5. Rotate crankshaft clockwise past TDC until piston has once again traveled down 0.100″, note reading on degree wheel.
6. The point half-way between the two readings is actual TDC. Rotate the crankshaft to this half-way point and re-adjust the pointer to read TDC.

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Step 2 — Establishing Starting Position

1. Note the manufacturer’s cam card listing for intake opening at 0.050″ lifter rise.
2. Rotate the crankshaft to this position on the degree wheel. (Usually between 45 degrees BTDC to TDC)
3. Move the dial indicator to read the lifter rise on the intake lifter of cylinder #1.
4. Rotate the camshaft until the lifter is on the heel of the cam. Set indicator to read Zero (0).
5. Rotate the camshaft clockwise until the indicator reads 0.050″ travel up.
6. You now have the camshaft positioned at 0.050″ rise on the intake #1 cylinder, and the crankshaft is positioned at the 0.050″ reading on the cam card.
7. Match the bolt holes in the cam gear to the holes in the cam hub for the closest alignment. Install and tighten the bolts.

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Step 3 — Change Valve Timing

1. Establish desired intake cam lobe position according to cam timing specs on cam card and using dial indicator readings.
2. Once cam is in position, remove cam gear carefully without moving cam.
3. Rotate crankshaft to desired TDC position.
4. Re-install cam gear by visually lining up the bolt holes in cam gear to the holes in the cam hub, at the same time meshing whatever teeth line up at this position.
5. Disregard any timing marks on gears. The vernier effect takes place when the cam gear is relocated on a different hole position due to an odd number of holes and an even number of teeth.

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