Feel free to browse. Bare in mind that this site, like the project it
depicts, is currently.....
This is a page documenting how I built my Datsun 3.1 liter
stroker. I'm not an expert on these by any means, however, I have been working
on cars for about 30 years. In that time I have built many motors including
several Datsun L series. This is not intended to be a "How To Guide", it simply
contains some of the knowledge I have acquired while researching, along with
hands on experience with this particular project. Consider this just another
piece of the information puzzle.
This motor is definitely not for
everyone. It's expensive to build and, when finished, you won't end up with the
horsepower that can be achieved with a turbo or a V8 conversion for the same
amount of money. So why build a 3.1 stroker? One word....TORQUE!!! The stroker
is an extremely torquey motor. Unlike a turbo, which produces most of its torque
at higher rpm's, or a stock V8 that has a relatively steep torque curve, the
stroker when properly setup, has close to maximum torque from 2000 rpm all the
way through the rpm range. This makes for a car that is just flat "fun to
drive". If you enjoy "seat of your pants", "head snapping" driving, you might
consider the 3.1 stroker.
With that said, lets get our hands dirty.
Block Preperation
The block of choice for the 3.1 stroker is the F54. Although some people
have used the N42, the F54 block has webbing built in between the cylinders for
extra rigidity. The block will need to be bored 3mm over stock. It is strongly
recommended that the boring process is done with the main caps torqued to specs
and with the aid of a torque plate. This will ensure that the cylinders will
remain true after the engine is assembled. Don't shop around for the best price
on your machine work. Go with the best you can find.
Nissan used
press-in plugs to seal the front and rear main oil galleries. I'm using a higher
pressure turbo oil pump, therefore, I opted to remove them by using a slide
hammer, and drilling and tapping the hole to accept a standard threaded plug.
When installed with Lock-tight, it will eliminate the possibility of blowing out
a plug and loosing oil pressure under extreme conditions. This needs to be done
prior to the machine work so all the metal shavings are removed during the
cleaning process.
NOTE:
The front
plug will need to be shortened so that it doesn't close off the # 1 main bearing
oil passage and, at the same time, it will fit flush with the front face of the
block.
Ring Gap
To check the ring gap, insert the top ring into the cylinder and use a
piston to square the ring by pushing it down approximately 2 inches. Using a
feeler gauge, measure the gap to ensure that it is within spec. Use a good
quality flat file clamped in a vise to remove excess material. Be sure to deburr
the corners of the filed end. Repeat the procedure with the second ring. Because
this is a "non typical" set-up, you won't find a factory specification on this
in any Z service manual. If the manufacturer of your rings didn't supply the
ring gap specs, here is a good general rule to follow for compression rings.
Top Compression Ring.
0.005 end gap per one inch bore diameter.
Second Compression Ring.
0.004 end gap per one inch bore diameter.
Oil Ring.
Oil ring-rail gap is not as critical. They can have anywhere
from 0.0010 - 0.040 in. end gap.
This formula works well with
any L series engine, however, if you plan on racing your motor on a consistent
basis, it's a good idea to add .002 in. to the gap to cope with the increased
expansion due to the prolonged heat.
LD28 Crank
The heart of the 3.1 stroker is the LD28 crank. It has an 83mm stroke as
opposed to the 79mm stroke of the stock L28 crank. These cranks were used in the
81-84 diesel Maxima with the LD28 block. The LD28 crank, often referred to as
the "stroker crank", shares the same 49.97mm rod and 54.95mm main journal sizes
as all the L28 engines. It also has the same type snout, pulley-retaining bolt,
keys, front seal, rear register-flywheel flange-rear seal, and transmission
input shaft pilot bushing. This means that the dampers, pulleys, crank
sprockets, flywheels and drive gears are interchangeable among all of the L28
engines.
NOTE:
If your LD28 crank has a flywheel dowel installed, it will need to be
removed.
When installing the rear main cap, apply a sealant
such as Permatex in the area shown here. DO NOT use
silicone!!! After the main caps have been torqued to specs, (33 - 40 ft-lb),
check for proper crankshaft play by using the handle of a hammer to force the
crank towards the front of the block. Use a feeler gauge to measure the amount
of play.
Acceptable play is .0020 - .0071.
Pistons
When purchasing 89mm pistons for a 3.1 you have a few choices. One is the
LZ24 from the Nissan 720 truck, (Nissan part #12010-30W01). This is a 15cc
dished piston that will produce a 9.4:1 compression using a 2mm gasket and N42
head. Using this piston will require the removal of some material from the top
of the rod to achieve clearance between the rod and piston pin boss.
Second, and probably the most popular, is the KA24E piston from the
240SX. There are actually three versions of this piston. Part #12010-30R10 has a
2.8cc dish and uses a floating pin. This piston with a 2mm gasket and N42 head
will yield a 10.14:1 compression. Part # 12101-40F10 is the flat top version of
the same piston and will bump the compression up to 10.6:1. The third version,
and the one I went with, is the KA24E from the mid to late 90's model Hardbody
truck. It also has the 2.8cc dish but uses a pressed pin instead of the floating
pin and clips. All three of these pistons have the same 34.0mm pin height and
will result with a 0.6mm positive deck height.
When installing the
pistons, here's a couple tips. Turn the block on it's side. By doing this, you
lessen the chance of damage to the rod journals caused by the piston falling
through the bore once the pistons clear the ring compressor. For extra
protection, use fuel line to cover the rod bolts during installation.
Big End Play
When securing the rod caps, there are a couple items that need to be
addressed. First is the big end play. Like the crank shaft end play, there needs
to be proper clearance between the rod big end and the crank shaft. Factory
specs are 0.008 - 0.012 in.
Second is clearance between the block and
rod bolts. The combination of the longer stroke of the crank, coupled with the
larger 9mm rod bolts, can sometimes cause the rod bolt nuts to actually scrape
the side of the block. This picture shows
where to look for clearance. I personally didn't have a problem with them
clearing. I have heard that some people have, so check all of the rods for
clearance. If needed, remove some of the material on the block using a die
grinder.
Deck Height
When designing a stroker motor, one very important factor is the final
"deck height", or in other words, how far the piston is relative to the top of
the block with the piston at TDC. This number can be either positive or
negative. The block height of an un-shaven L28 block is 207.9. Next you need to
know the "installed piston height". This is calculated using the following
formula.
Installed Piston Height
Piston Pin Height + Rod Length + Stroke/2
Here is an example of how this formula works with a stock L28
motor.
38.1mm + 133.3mm + 79.0mm/2 = 207.9mm
The "Deck Height" is the "Installed Piston Height", minus the
"Block Height" or in this case...
207.9mm - 207.9mm = "0" Deck Height.
Here are the
numbers for a 3.1 stroker set up. As mentioned earlier, both of the KA24E and
LZ24 pistons have a pin height of 34.0mm. The 9mm 240Z rods have a length of
133.0mm and the stroke of the LD28 crank is 83mm. Using the formula above...
34.0mm + 133.0mm + 83mm/2 = 208.5mm
208.5mm - 207.9mm = 0.6mm
You'll notice that you end up
with a positive deck height of 0.6mm. This can be dealt with by, either, shaving
the tops of the pistons or by using a thicker head gasket to achieve the proper
piston to head clearance and compression ratio.
Head Gasket
Due to the 89mm bore required for the 3.1, you must use the "Big Bore"
head gasket in order for the pistons to clear the gasket. This gasket comes in
either a 1mm or 2mm thickness to allow for altering compression ratios. Both
have a 91mm bore and are made of multiple layers of steel and coated with
fluorine rubber. These gaskets are not cheap, however, they can be reused
several times. Courtesy Nissan has
the best price on these. (Sorry MSA, but $50.00 is $50.00)
Cam-Lobe Wipe
Pattern
Having the correct cam-lobe wipe pattern is extremely important to ensure
the longevity of your cam. This is accomplished by using the procedure below.
Coat the contact surface area of the rocker arms with lay-out fluid or
black magic marker. Install one rocker arm and set the clearance to the cold
specifications. (Intake .008 Exhaust .010) Using the cam sprocket bolt, rotate
the cam one complete revolution. Compress the valve spring and remove the
rocker, check the wipe pattern to see if it is centered and does not extend off
the rocker arm pad. Adjustments are made by using different-thickness lash pads.
These are available in 0.010 in. increments and range from 0.150 in. to 0.330
in. Stock lash pads are 0.118 in. (3mm). If the pattern is towards the valve end
of the rocker, a thinner lash pad is needed. If the pattern is closer to the
pivot end, a thicker lash pad is required. Continue this procedure until all the
rockers have been checked. It is not unusual to have as many as five or more
different size lash pads to achieve a correct setup.
Timing Chain
Installation
With the cam and the crank at their TDC positions, install the timing
chain, sprockets, guides and tension block. The chain should be positioned so
that the bright links are facing the front. Align one bright link to the
crankshaft-sprocket dot, which should be at about the 4 o'clock position. Align
the second bright link to the selected cam sprocket, start with dot 1. The link
position should be at approximately 2 o'clock with the corresponding dowel hole
in the sprocket hub aligned with the cam dowel. Install the cam sprocket to the
cam nose. Once everything is in place, there should be 42 link pins inbetween
the two timing marks, and the dash mark should be slightly to the left of the
cam sprocket notch as seen here.
Distributor/Oil Pump
Shaft
Assemble the oil pump and drive spindle, aligning shaft mark...(small
dot)...with the oil pump hole, and then rotate the shaft to the right one notch.
At this point, fill the pump with clean oil. With the motor at TDC, install the
pump and shaft as a unit. If done correctly the shaft tang should be at the
11:25 position and directed tangent to the backside of the top
distributor-adapter mounting bolt.