Because
I'm particular about cleanliness on this project (you wouldn't know it
to look into my engine bay at the time), I cleaned off all of the remaining
bits of varnish (which was very little) using carb cleaner and an old toothbrush.
At this time I removed any remaining bits of liquid gasket from the block
using a single edge razor blade and great care. Houston
is known for incredible humidity, so I coated the fresh bores with STP
to keep them from rusting. The STP works well since it sticks a little
better than regular oil. It means I'll have to work harder when cleaning
the bores for piston installation though.
The old pistons and rings get discarded. I am using new pistons from a NA 300ZX. I had the domes milled off (resulting in a flat top) and the pistons balanced before sending them off to Jim Wolf Technology along with the block for boring. I also had JWT drill and tap the block for piston coolers from an SR20DET. The piston cooler is a really neat piece of work. The bolt that threads into the block is hollow and it has a spring loaded shaft that presses in when the oil pressure is high enough, letting oil flow through the bolt and into the jets that spray the bottom of the piston with oil.
After the block and pistons came back, I sent the pistons to Swain Technology for their Thermal Barrier Coating (TBC) on the crowns of the pistons and Poly Moly (PM) coatings on the skirts. The TBC coating keeps heat in the cylinder and out of the piston. This is good on two fronts. Keeping the heat in the cylinder makes the engine more efficient and keeping the heat out of the piston keeps it from expanding too much, and from causing hot spots on the surface of the piston that can lead to detonation. The TBC also helps spread the heat across the surface of the piston more evenly, again helping to resist detonation.
Now that we have the pistons covered, we need
to do something with the rods. The first order of business is to 
separate
the old pistons from the rods. The wrist pin is held in place by
two circlips. You need circlip pliers to remove them, and even using
them I found the task a bit frustrating since it was difficult to squeeze
the circlip together and pull it between 1/8" and 1/4" out of the wrist
pin bore. No worries. They still come out. Some just
take more time and patience than others. Once the circlips are out
of the way, you should use a wrist pin puller. It is a device
that wraps around the piston and has a threaded bolt that when you tighten
it, pushes the wrist pin out the other side of the pistons. What
I did was to place a 3/8" socket extension on the wrist pin and
tap it out with a hammer. If you choose
to do this, it is against my suggestion. As usual, I take responsibility
for my engine, but not for yours.
Once you remove the wrist pins, the pistons come right off the rods.
I also removed the rod bolts since I bought new ones and you should too.
To remove them I placed the nuts on the rod bolts, but not so far that
the threads were exposed, and tapped the nuts with a hammer until the bolts
came free of the rods. If you choose
to do this........ That leaves us with
one thing left to do with the rods before taking them to the shop - cleaning. 
I used a one gallon can of Berryman's B-9 Chem Dip. It comes with
a tray for parts and is not quite like a parts washer (I also have one
of those), but it cuts through grease with ease. I put the rods in
the dip for about 20 minutes and they came out nice and clean. That's
not to say shiny like new, but they are clean. The rods are now ready
for balancing.
At this point you would normally clean the crank and get it polished. The engine I have had a spun bearing so I decided to get a new crank instead. I took the rods, the crank, the main pulley, the flywheel, and the pressure plate into a machine shop to have the rotating and reciprocating mass balanced. Before the rods could be balanced, I had new bushings pressed into the wrist pin bores and honed to match the wrist pins. I debated polishing the rods and having them shot-peened. After much discussion with Mike Kojima and Mike Pahls, I decided to pass on these steps. The rods are shot-peened from the factory. It was the general consensus that additional shot-peening should not be necessary. Polishing and shot-peening can actually distort the rod, so I decided to just have them balanced and straightened if necessary.
To clean the oil galleys, I bought a gun cleaning rod with plenty of patches and brushes (or whatever they are called). I bought the pieces for a .30 caliber gun. These work great for getting inside the passages. Just make sure you clean them thoroughly. You don't want to go through this much work and expense only to cut corners now. Remember, preparation is everything.
While the engine is out having the machine work done, take the opportunity to clean all of the little parts that you took out of, and off of the engine.
The last steps before assembly can begin are sizing the bearings and checking the clearances. Nissan uses a matrix for determining the correct bearing size, but you still need to check the clearances. The engine is stamped with grades for the crank bores. The crank is stamped on the end counterweight with the journal and pin grades (pins are where the rods attach). Use the matrix in the Factory Service Manual (FSM) to determine the correct bearing grade. If the crank bore is grade 1 and the journal is grade 2, then a grade 3 bearing is used. Without fail, you should use the FSM to determine which bearings you need. You are not done yet, however. You must install the bearings in the block and the rods. Be sure to torque the bolts to spec. You must then measure the inside diameter of the bearings and the diameter of the journals and pins. Subtract from the corresponding ID of the bearings, the corresponding diameter of the pin or journal to determine the clearance. If you have any bearings that result in out of spec clearances, get larger or smaller grade bearings as necessary. Remeasure the bearing ID and when your clearances are within spec, you are ready to assemble the engine. Don't be alarmed if you have to get other bearings due to improper clearances. I had one that was out of spec.
One last thing I want to discuss here is the cylinder
head. I sent my head off to DPR Racing Development for Stage VI treatment.
The following is a list of modifications necessary to create a Stage VI
head (from DPR's website):
Competition Port & Polish Deshrouded & Polished Combustion Chambers
Back-Cut Valves
Radiused Blend Seats
Three-Angle Valve Job
Hand-lapped & Vacuum-Tested Valve Seats
Swirl Polish the Intake Valves
Cylinder Head Deburred & Blueprinted
Combustion Chambers C.C.'d
Detailed Matched Intake Manifold Fully Ported to Head
and Throttle Body
Match Port Exhaust Manifolds
Port Faces Lapped Flat (Studs removed and reinstalled)
Decks Milled & Lapped (At any amount with no additional charge)
Radiused Cut Seats
Combustion Chambers Welded & Reshaped, (clover-leaf pent-roof design)
Intake Valves Lightened
Includes Valve Spring Shims as Needed
In addition, I had my valve stems coated with an anti-friction coating from HPC. I would have preferred to use Swain coatings for the valves, but DPR currently uses HPC and time was becoming critical. I decided to stay with what DPR is familiar with. During the rebuilding process, I had DPR replace my valve guides and install DPR's valve springs. Their valve springs are all matched for rate for even pressure on all of the valves. In the end, I was sorry I didn't spec Swain coatings for the valves. HPC was supposed to coat the valves and return them to DPR in 3 days. I guess HPC doesn't quite know how to tell time yet since they were returned in a little over 3 weeks according to the folks at DPR.
Check back soon for the next installment when we cover the assembly process.
Copyright George D. Roffe 1999