Introducing the Polaris Magnum 2x4 and 4x4 with the all new 425cc liquid cooled four
stroke engine, Polaris is building excitement. Features such as four valves per cylinder,
overhead cam shaft, automatic compression release, dry sump lubrication and liquid cooling
will help provide years of trouble free operation and easy maintenance. The Magnum engine is
coupled with other tried and true standard Polaris innovations such as PVT, on demand
all wheel drive, single lever hydraulic disc brakes and McPherson strut independent front
suspension. This video will provide you, the Polaris service technician, with a thorough
understanding of the Magnum four stroke engine operation and vehicle maintenance procedures.
In addition, you'll see some engine removal, disassembly and reassembly tips, but first
let's look at how the Magnum four stroke differs from the two stroke. Unlike the two stroke
engine, which relies on piston position to open and close the intake and exhaust ports,
the four stroke uses mechanically operated valves, precisely timed to crank shaft rotation
by a cam chain and sprocket. The valves are opened by the rotation of cam shaft lobes
against cam followers or rocker arms and are closed by spring pressure. The four stroke
engine completes the combustion cycle of intake, compression, power and exhaust in four strokes
of the piston. At the beginning of the intake stroke, the piston moves downward in the cylinder
and a fresh fuel air charge is drawn in around the open intake valve. Then, as the piston
begins to move upward in the cylinder, the intake valve closes, trapping the fresh fuel
air charge in the cylinder. Just before the piston reaches the top of the compression
stroke, a spark occurs and ignites the charge. The rapidly expanding gases force the piston
downward on the power stroke. The exhaust valve begins to open shortly before the piston
reaches bottom dead center. The upward movement of the piston forces the spent fuel air charge
out of the open exhaust valve. As the piston nears top dead center, the exhaust valve closes
and the intake valve starts to open, beginning another cycle. At the end of the combustion
cycle, there's a short period of time when both exhaust and intake valves are open. This
is referred to as valve overlap and is measured in degrees of crankshaft rotation. A small
amount of overlap helps scavenge the combustion chamber completely, increasing the efficiency
of the engine. One of the unique features of the Magnum four stroke engine is the automatic
compression release. The compression release mechanism consists of a small weight attached
to a release lever shaft installed in the camshaft. At cranking speeds such as electric
or manual starting, the weight is held against the stop by return spring pressure and a lack
of centrifugal force. With the weight in this position, a lobe on the end of the release
lever shaft pushes outward on an actuator ball located inside the camshaft. As the base
circle of the exhaust cam lobe passes under the cam follower, the exhaust valves are open
slightly for a brief period, releasing a small amount of compression for starting. When the
engine starts, centrifugal force swings the weight outward, rotating the release lever
shaft and the actuator ball retracts, automatically disabling the compression release feature.
To check the engine oil, unscrew the dipstick and wipe it clean. Screw the dipstick in completely,
remove it and read the oil level on the stick. The level should be between the add and the
full mark. If necessary, add Polaris Premium four all season synthetic engine oil to the
full mark on the stick. To change oil, place a drain pan beneath the oil tank and remove
the drain plug. The oil will drain more completely when the engine is warm. Wipe the magnetic
drain plug clean and install it using a new sealing washer. Torque the drain plug to 14
foot pounds. To remove the oil filter, position the drain pan beneath the oil filter area.
To minimize spills, place a shop towel directly under the oil filter and remove the oil filter
using an oil filter wrench. Be sure to wipe the gasket surface clean and apply a light
film of clean engine oil to the sealing O-ring of the new filter. Screw on the filter until
the O-ring touches the sealing surface and tightens securely by hand on about additional
quarter turn. Wipe the area around the oil filter clean. A little over a cup of engine
oil will remain in the sump of the crank case. This oil should be drained by removing the
drain plug found in the bottom right side of the crank case. Allow the oil to drain
completely and install the plug using a new sealing washer and torque to 14 foot pounds.
Install the oil tank with Polaris Premium 4 all season synthetic engine oil to the full
mark on the stick. The system holds approximately two quarts. Place the gear selector in neutral,
set the parking brake, and then start and run the engine for about two minutes, inspecting
for leaks. Shut off the engine and recheck the oil level and add if necessary. To service
the pre-cleaner and main air filter, remove the seat, then remove the pre-cleaner element.
Note the position of the duct support wire. It should be in line with the center line
of the ATV. Wash the element in high flash point solvent followed by hot soapy water
and rinse and dry thoroughly. Squeeze excess water out of the element and allow it to dry.
Apply foam air filter oil or clean engine oil and squeeze until the excess oil is removed.
The main air filter can be accessed by removing the two wing nuts and washers securing the
air box cover. Remove the wing nut and washer from the air filter cover and remove the main
air filter. Inspect the condition of the element, replace it if dirty, or contaminate with oil
or water. To check the gear case oil, remove the dipstick, wipe clean and reinstall, pushing
it in completely. Remove and read the level of the dipstick and add Polaris chain case
oil if necessary until the level is between the two marks. The auxiliary brake pedal deflection
should be one half inch prior to brake activation. To adjust, loosen the adjuster jam nut and
turn the adjuster bolt in or out to achieve proper pedal deflection. Tighten the jam nut
securely and recheck pedal free play. Periodically check the air box sediment tube for water
or sediments. Cut the tie strap and remove the drain plug to allow any deposits to drain.
Reinstall the plug and secure it with a new tie strap. Remove the seat and right hand
side panel to gain access to the spark plug. Disconnect the high tension lead and use a
spark plug wrench provided in the tool kit or any five eighths inch spark plug socket
to remove the spark plug. Inspect the plug and replace if necessary following the torque
procedures outlined in the magnum service manual. The valve clearance must be adjusted
with the engine at room temperature and the piston positioned at top dead center on the
compression stroke. To adjust the valves, remove the seat, remove the screws attaching
the left and right side panels and remove the panels. Remove the screws at the rear
of the fuel tank cover and disengage the tabs at the front of the cover. Remove the gas
cap and key and remove the cover. Reinstall the gas cap after the cover is removed. Remove
the pre-filter duct. Back out the headlight pod screws just enough to clear the bracket
and remove the fuel tank vent line. Remove the two bolts and spacers from the PVT air
outlet duct. Cut the tie strap and remove the duct. Be sure the fuel selector is turned
off and disconnect the fuel line from the valve. Remove the bolts with the brackets
and spacers at the rear of the tank and remove the noise baffle foam. Then lift the back
of the tank and carefully move the throttle cable out of the way. Pull out and hold the
fuel selector until it disengages the tank valve. Then lift and pull the tank back rotating
the rear of the tank to the left while lifting and remove the tank. While removing the tank,
take care not to damage the cables or fuel valve. Remove the spark plug high tension
lead and set it aside. Loosen the eight valve cover bolts evenly in a cross pattern and
remove the bolts. Tap the cover lightly with a soft phased hammer and remove the cover
and gasket. Remove the spark plug and place a shop towel in the spark plug cavity to prevent
dirt from entering. Remove the timing inspection plug from the recoil housing. Then using the
recoil starter, slowly rotate the engine watching intake valves open and close. At this point,
watch the cam shaft sprocket marks and continue rotating the engine until the marks are parallel
to the valve cover gasket surface. Verify accurate top dead center positioning by observing
the T mark aligned with the projection in the timing inspection hole. To adjust the
intake valves, insert a six thousandths or.15 millimeter thickness gauge between the
end of the intake valve stem and the clearance adjuster. Using a 10 millimeter wrench and
screwdriver, loosen the adjuster lock nut and turn the adjusting screw until there's
a slight drag on the thickness gauge. Then hold the adjuster screw and torque the lock
nut to 5.8 to 7.2 foot pounds using the 10 millimeter flank drive torque adapter at a
90 degree angle to the torque wrench. Recheck the valve clearance to be sure it is correct
and adjust the other intake valve using the same method. In the Magnum engine, the exhaust
valves share a common rocker arm. They must be adjusted at the same time using two thickness
gauges. Insert a six thousandths or.15 millimeter thickness gauge between each of the exhaust
valves and the adjuster screws. Using a 10 millimeter wrench and a screwdriver, loosen
the adjuster lock nuts on both valves and turn the adjusting screws until there's a
slight drag on both thickness gauges. Leave both gauges inserted during the adjustment
and torquing procedure. When the clearance is correct, hold one adjuster screw and torque
the lock nut using the 10 millimeter flank drive. Then repeat for the other adjuster.
Check for proper clearance on both valves. Remove all traces of gasket material from
the valve cover and cylinder head gasket surface. Then install the valve cover using a new gasket.
Torque the cover bolts evenly to 72 inch pounds. Remove the shop towel from the spark
plug cavity. Install the spark plug and high tension lead and install the fuel tank, tank
cover, side panels and the seat. If you need to adjust the choke, you'll have to take the
gas tank off to access the top of the carburetor. You'll then need to remove the diaphragm cover,
spring and diaphragm to see the choke plunger through the choke bypass hole. Flip the choke
lever to the half and to the full positions, observing the plunger in the hole. The plunger
should uncover exactly half the hole and the entire hole respectively. When the choke is
off, the entire hole must be closed. If the choke needs to be adjusted, loosen the lock
nut and turn the adjuster screw to position the plunger as needed. Choke adjustment is
important and must be done correctly. If you have any questions, consult your Magnum service
manual. To prepare for engine removal, disconnect the battery negative cable. Drain the oil
from the oil tank and engine sump and remove the seat, fuel tank and rear rack. Next, remove
the six bolts from the top of the rear cab, the mud flap attaching bolts at the back of
the foot rest and the two screws located at the front of the exhaust heat shield. Then,
remove the rear fender assembly. Remove the five springs attaching the exhaust pipe and
remove the pipe. Remove the auxiliary brake arm and on the Magnum 4x4, the center drive
chain guard, chain and sprockets. Disconnect the shift linkage rods and the crank case
breather line. The recoil housing, alternator components and starter drive can be removed
at this time to provide additional clearance for engine removal. When removing the starter
drive assembly, note the location of the thrust washer on the back of the drive gear. Remove
the flywheel nut, install the puller and remove the flywheel. Note the location of the stator
alignment marks. The mark on the stator plate should align with the crank case projection.
When you remove the stator assembly, be careful not to damage the crankshaft oil seal or bearing
surface with the flywheel key. Now, wrap the stator in a shop towel and secure it to the
top of the frame. Remove the oil passage O-ring and shim washer. Place shop towels in the
cam chain and crankshaft bearing area to prevent dirt from entering. To remove the carburetor,
disconnect the vent lines, the fuel pump impulse line, the front flange clamp and the rear
duct clamp. Remove the carburetor and disconnect the fuel line. Remove the two tie straps from
the frame and set the carburetor aside with cables attached. Do not hang the carburetor
by the cables or damage may result. Be careful not to damage the cables and be sure to cover
the carburetor to prevent dirt from entering. Cover the end of the carburetor mounting flange
with a shop towel and remove the spark plug high tension lead. Remove the PVT outer cover
retaining clips and screws and remove the cover. Mark the direction of the rotation
of the drive belt and remove the belt. Remove the drive clutch retaining bolt, install the
puller and remove the clutch. Remove the driven clutch using a driven clutch puller and remove
the spacers from the transmission input shaft. Bend back the retainer tabs and remove the
three screws securing the front of the inner PVT cover and the bolts at the rear of the
cover. The spacers on the back of the cover are held on the bolts with O-rings. Remove
the two bolts and loosen the clamp that holds the PVT air inlet duct and remove the duct.
Remove the starter motor retaining bolts and remove the starter. Disconnect the wire for
the temperature light and drain coolant into a suitable container. Remove the oil lines
from the fittings. The top line is the feed to the engine and the bottom line is return
line to the oil tank. Remove the oil tank mounting bolts and the oil tank breather line
from the air box. Be sure to hold the fitting with a wrench as you remove the line. Move
the oil tank forward and secure it out of the way. Remove the coolant recovery tank
with the spacers and secure away from the engine area. Remove the upper engine mount
nut and ground cable from the outside of the frame and remove the upper mounting bracket
from the engine. Remove the front left engine mount nut and washer and loosen the nut on
the slotted rear engine mount plate. Move the top of the engine to the left until the
coolant supply line clamp clears the frame tube. While lifting the rear of the engine,
tip the front down and rotate the engine until both coolant hoses are accessible. Support
the engine in this position with a 2x4 or similar brace and with the coolant hoses removed,
take the engine out of the left side of the frame. To begin engine disassembly, remove
the valve cover and position the crankshaft at top dead center on the compression stroke.
That's where we leave any valve spring load from the rocker arms and make the removal
process easier. Remove the camshaft cover along with the gasket. The crankshaft slotted
nut has a left hand thread. Remove the nut using the slotted nut tool. Loosen the clamps
on the coolant supply hose and remove the hose. Loosen the cam chain tensioner cap bolt,
apply inward pressure while unscrewing the cap bolt to offset spring tension and remove
the bolt, sealing washer and spring. Remove the bolts from the tensioner body, tap lightly
if necessary and remove. Inspect the ratchet teeth on the tensioner plunger and the ratchet
paw for wear or damage. Remove the bolts from the rocker arm shaft towers and remove the
towers, rocker arms and shaft as an assembly. Loosen the cam sprocket bolts about two turns.
Remove the thermostat cover and thermostat. Note the location of the air bleed holes in
the thermostat. They should be positioned next to the holes for the thermostat cover
bolts. Remove the camshaft thruster cap and the cam sprocket bolts. Then remove the sprocket
from the end of the cam and secure the chain to the cylinder head with a wire. Carefully
remove the camshaft from the cylinder head. Remove the two six millimeter bolts and loosen
the four cylinder head bolts evenly in a crisscross pattern, an eighth of a turn at a time until
completely loose. Then remove the bolts. Tap the cylinder head on the reinforced area only
to break it loose. Disconnect the cam chain wire and remove the cylinder head being careful
not to lose the dowel pins. Remove the dowel pins. Remove the cam chain guide and the two
six millimeter cylinder base bolts. Remove the upper and lower oil lines and ceiling
washers. There are four cylinder base bolts located inside the water jacket of the cylinder.
Loosen these bolts evenly in a crisscross pattern about an eighth turn at a time and
remove them. Tap the cylinder in the reinforced area until loose. Rock the cylinder back and
forth while lifting and place the piston support block under the cylinders to support the piston.
Remove the piston pin circlip. The piston pin is a push fit at room temperature and
can be removed without the aid of a piston pin puller. Remove the cam chain and the water
pump cover. Also remove the crown lock nut, the impeller, and washer from the pump shaft.
Remove the shoulder bolt and tensioner blade from the crankcase. Remove the one way oil
check valve from the PTO side crankcase along with the spring and ceiling washer. This valve
prevents oil in the tank from draining into the crankcase when the engine is off. Remove
the bolts from the magneto side crankcase evenly in a crisscross pattern. Tap the reinforced
areas of the crankcase with a soft faced hammer until the cases are separated and remove the
crankcase. Remove the pump drive gear from the shaft with the bearing and thrust washer.
The thrust washer is positioned between the gear and the bearing. Remove the three retaining
bolts and the oil pump from the PTO side crankcase. Note the alignment marks in the crankshaft
and counter balancer gears. The marks must be aligned during assembly. Remove the counter
balancer shaft. To remove the crankshaft from the crankcase, it is recommended to use a
hydraulic press. Check the oil pump and oil gallery mating surfaces. Be sure they are
clean and not damaged. The surfaces of the crankcase must be clean and free of burrs,
nicks, or damage. Pull the crankshaft into the PTO crankcase using the crankshaft installation
tool. Draw the crankshaft until it is firmly seated. Install the counter balancer shaft.
Align the marks in the crankshaft and balancer gears. Install the shims in the balancer shaft
and crankshaft. After installing the oil pump, align the slot in the drive gear with the
drive pin on the oil pump shaft and install the gear. Make sure the gear is fully seated
on the shaft and install the thrust washer. The pump shaft bearing should be installed
in the magneto side crankcase. Apply Loctite 515 or 518 gasket eliminator to both crankcase
halves. Be sure the alignment pins are in place. Set the crankcase in position and install
the magneto end crankshaft installation tool. Draw the crankcase halves together, tapping
lightly on the pump shaft area to maintain alignment. When the crankcase is fully seated,
install the bolts and torque to 14 foot pounds. To install a new water pump mechanical seal,
place the seal in the seal holder. Install the guide end nut and tighten the nut to press
the seal into place. Place the dowel pins in the crankcase and install the base gasket.
The top rail of the oil control ring has a locating tab to prevent rotation. The tab
must be positioned in the notch on the side of the piston. The arrow on the piston must
point to the magneto end of the crankshaft. Lubricate the rings and separate the top and
second ring end gaps at least 120 degrees from the oil ring end gap and from each other.
Lubricate the piston pin and connecting rod and install the piston. The circlip should
be installed with the end gap at the top or bottom of the groove. Fit the ring compressor
tightly on the piston, lubricate the cylinder and install it pushing squarely down on the
piston. Remove the ring compressor and support block and install the cylinder completely.
To install the cylinder head, place the cam chain guide in the cylinder. Install the dowel
pins, the gasket and the cylinder head. Follow the procedure outlined in the Magnum Service
Manual to torque the cylinder head bolts. Lubricate and install the camshaft. Turn the
crankshaft until a dot on the cam chain drive sprocket is facing downward and aligned with
the crankcase projection. Align the single plated link on the cam chain with the dot
on the sprocket. Pull the cam chain tight and slip the cam chain over the sprocket,
align the two dots with the two plated links. Install the sprocket and torque the bolts
to 72 inch pounds. Before installing the cam chain tensioner, push and hold the ratchet
pull in the unlocked position. Then push the plunger all the way into the tensioner body.
Mount the tensioner to the cylinder and install the spring and tensioner cap. Recheck all
alignment marks and verify proper cam timing. Install the rocker shaft assembly and adjust
the valve clearance. This video has been intended as a brief overview of the new Polaris Magnum
4-stroke. For additional information, refer to the Magnum Service Manual.