Engine Tech, Building the Nissan VG30DETT part 1

The Crank

Although the stock Nissan crank is a very strong, heavy duty forged steel part, which would be the envy of any domestic V-8 engine designer, we feel that to get the most reliability from our 600 hp monster we will need to do some massaging to it.  However crank failures in even highly modified Z’s are rare but we are careful and would rather spend a little more time and money now than later getting it right!

We had sent our crankshaft out to be cyro treated with our block.  It is perhaps the crankshaft more than the block that can most benefit from the increase in wear resistance, lubricity and strength that cryo treating can provide.  It can improve the wear to the crank's bearing journals and also provide up to 100% more fatigue strength.  Cryo treating also increases the tensile strength.  All of these properties are highly desirable to improve on the crankshaft!

The center counter weight on the VG30DETT crank is bolted in place.  This is unusual and is one of the engine's weak points.  The counter weight is known to come loose which destroys the engine.  We used loctite red on the bolts, then welded their heads in place.

After cyro treating, JWT’s fabricator Mike Smith tack welded the bolts of our crankshaft’s center counterweight in place.   The VG30DETT crankshaft has an unusual bolted in place center counterweight.  Under extreme racing use, these have been known to work loose and fly off resulting in complete engine destruction.  Mike TIG (tungsten electrode, inert gas) welded the bolt heads of the cap screws holding the counterweights in place ensuring that they will never come loose.

After the cryo treatment and welding, the crank was given a precision dynamic balance job.  As a final touch, the crank bearing journals were micropolished to reduce friction and improve bearing wear.  This is an extra step that late model Nissan motors uses to reduce internal friction on all production engines.

Normally when building a high powered motor, we would be getting the crankshaft shotpeened.  Shotpeening is the bombardment of the part with steel shot at high velocities.  This creates a tough microforged skin over the outside of the parts which makes it difficult for cracks to form in the part.  Shotpeening usually improves the fatigue strength of a part by over 100%.  Fortunately for us Nissan shotpeens both the crank and rods on the VG30DETT from the factory, sparing us the time and expense of having to get it done ourselves.

The stock press in oil plugs were replaced with these screw in parts.  The press in plugs have a nasty tendency to come loose causing the engine to lose oil pressure.

Smith removed a calculated amount of weight from the crank's counterweights in proportion to the amount lighter that the Cunningham rods and JWT pistons are over the stock components.  This weight ended up being slightly more than a pound of steel. On a super high power motor, not going crazy by shaving too much weight from the crank is a good approach versus simply lightening the crank as much as possible.  By doing this, vibrational stresses to the motor are reduced.  The weight reduction was accomplished by bullnosing the crank counterweights and polishing all parts of the crank to remove forging flash and any sharp edges that could act as a stress riser.  The bullnosing helps the counterweights cut through the oil mist in the crankcase reducing windage losses. 

Next all of the pressed in ball oil passage plugs were drilled out. The passages were tapped and countersunk to receive allen screw in plugs.  The crank journal oil passage’s exit holes were given a teardrop contour to help disperse the oil film more evenly across the bearing and to act as a small oil reservoir while the crank rotates.  Finally the journals themselves were micropolished to reduce friction and the oil passages thoroughly cleaned. This is critical because dirt and debris tend to be centrifuged into blind holes on a rapidly rotating crank.  The oil passage plugs were installed with loctite red.

Our completed crank looks pretty, almost like a billet crank!

After the polishing and shaping, the crank was given a close tolerance balance job which was done by balancing the crank, flywheel, clutch and clutch disc separately, then together as a unit.  The completed prepared crank is amazing, at a first glance, the rework job is so thorough and careful that we mistook our crank for a billet Crower crank.