Nissan VG30 Adjustable Timing Gears by BDE

Until now there have never been any adjustable timing gears for the VG30DETT and VG30DE as found in the 300ZX and the 300ZXTT.  Brett Dempsey Engineering or BDE has come up with some excellent adjustable timing gears that solve some unique issues with V engines and the VG30 itself.

When freshening or rebuilding overhead cam cylinder heads and engine blocks, we normally machine the decks to assure that their head gasket surfaces are perfectly smooth and flat.  This is important for a good cylinder seal for turbo cars, especially with today’s MLS steel gaskets.  When machining the heads and deck, the cams are moved closer to the crankshaft and consequently, the cam timing relative to the crankshaft is changed, the cams get retarded as the material is removed. In addition, if the engine is a V-type (like the Z32’s VG30DE is), the cam timing will change differently for each side of the engine, getting cumulatively more retarded for the engine’s opposite bank.

This cam timing change usually necessitates degreeing the cams with an adjustable pulley to get the critical cam opening/closing events back in sync with the crankshaft. If the cams are degreed using the adjustable pulleys that have been available until now, the numbers on their scales would have no relevance whatsoever to their original zero marks when finished. To add to the confusion, a V-engine’s different bank-to-bank change typically leaves the final degreed setting of each pulley on a different number of their scales… that is “if” they ever came with a zero mark reference.

BDE Bullseye Adjustable Exhaust Pulleys have a unique feature to make tuning easy even with the cam timing variance from bank to bank. After the cams are degreed to the crankshaft, the BDE pulleys have an addional outer ring which adds a third timing element that is rotated to align with the scale’s zero mark so future adjustments can easily be made without the hassle of remembering where the original degreed setting was.  You can baseline the cam timing to a true zero for both banks, then adjust the cam timing using the other scale from there!

Now the vernier scale on the pulleys actually means something after the initial baseline cam degreeing process. For fresh builds, the pulleys can easily be set to true zero by visually centering the bullseye and then setting the scale’s zero to the ring’s timing mark!  This is a great innovation by BDE and we hope they can make some pullies for other engines like the VR38VETT, wink.

BDE also makes a unique adjustable intake pully that solves Nissan’s notorious VTC (Variable Cam Timing) issues which are erratic cam timing and a ticking noise at idle and in the mid-range.  By design, the VTC function is to advance the intake cams 20° (crankshaft) from just above idle to roughly 5800 RPM to increase torque in this RPM range. At idle and high RPM the VTC is in its static “zero advance” position which reduces valve overlap for smooth idle characteristics and increases torque at higher RPMs.  The VTC units only make noise and move around uncontrollably in the zero advance position. Our engine has Nissan’s countermeasure stiffer countermeasure springs and it still makes a ticking noise at idle.

Stock Nissan Variable Valve Timing Control (VTC) intake camshaft pulleys are non-serviceable units that are notorious for making noise and leaking oil. Oil leakage occurs because the rear cam seal plate can rotate independently from the pulley, this wears its internal o-ring seal and eventually leads to an internal oil leak. The noise is typical with high-mileage pulleys and/or aftermarket higher-pressure valve springs that cause the cams to over-rotate on every cylinder’s intake valve-closing event. This over-rotation causes the VTC piston to screw itself onto the VTC helix and overpower the piston return spring. As the cam continues to rotate, the valves close and the valve spring pressure diminishes to the point where the VTC return spring slams the piston back to its stop creating the audible tick that is indicative of a noisy VTC.

Leave a Reply

Your email address will not be published.

*
*