off your rocker ?
Basic valvetrain tips
from the 50s if not earlier Mopars have been engineered with arguably the best valve train in the industry, the shaft rocker
by using a shaft the rocker is far more stable than other designs , it cannot twist away from the load doesn`t limit the lift it
can handle offers a larger surface area to pivot on & the shaft becomes an oil reservoir & distributes oil to the rockers which
simplifies the oiling system as well , the oiling to the shafts is controlled though a pulse system as the cam rotates , there
is a hole in the cam that directes oil up to the rockers briefly each rotation , this limits the oil to the heads & keeps most
of the oil down at the crank where it is needed more , the oil not only lubricates the rockers & valves but it controls spring
temperature as well. We have all bent a coat hangar between our thumbs & the faster you bend it the hotter it gets, a valve
spring is the same , with higher lift cams & higher RPM the valve spring heats up , so the oil takes the heat away & extends
the life of the spring
the shaft rocker system ahs proven to be very reliable & will take a lot of abuse even with just stock parts
The first upgrade availalbe is the shaft itself , the shaft is a thin walll design & should be torqued when tightened as over
torquing can crush the shaft & cause it to become oval, this can cause the rocker to gall or sieze on the shaft .
the torque spec is 25 ft lbs for small blocks big blocks & slant 6
the Hemi has a spec of 30 ftt lbs
By using a thick wall shaft , the valve train becomes more stable , when using aftermarket cams & higher valve spring loads the shaft
can defelect & decrease or possibly increase valve opening . Crane has the thick wall shafts available for under $100 / pair
the next upgrade is the hold down hardware , upgrading the bolts to grade 8 bolts will help & using billet holddown blocks
P5249714 B/RB
P5249712 LA
P 5249713 LA / W2
will increase stability under extreme loads such as roller cams with extreme spring pressures of 500+ lbs open
the most obvious up grade is the rocker arms themselves , the factory used stamped steel rockers in all but Hemi engines
the accuracy of these is ok but the actual raio will vary as low as approx 1.42 : 1 so even if you can has .460 lift , the actual lift
may be as low as .434 at the valve, so just upgrading the rockers can increase performance with no other changes
there are a number of choices in rocker arms from a lot of manufacturers
there are also 1.5 & 1.6 ratio rockers for the LA, B & RB engines
- the first choice is the HD stamped steel rockers from Mopar , these are stronger but the accuracy of the ratio could still be a problem
- next the ductile iron rocker these are great from a cost & durability stand point , Mopar used them on the 273 engines from the factory
they are fully adjustable & I have never see one break & use them a lot , they are available in both 1.5 & 1.6 ratios , on LA engine you
must be careful to check clearance to the valve spring as they can touch
- alum rockers are the next option , they offer the advantage of being accurate with the ratio & have the roller tip & are very light & help to
decrease the load on the valve spring , the roller tip prevents the valve from being pushed sideways against the valve guide as the valve
opens which helps increase valve guide life, the down side to the alum rocker is that the alum will often eventually fail & break so I generally
do not use these on street engines , these are available in 1.5 & 1.6 ratio also
Some alum rockers use roller brgs inside them to run on the rocker shaft , I see no advantage to this , the rockers float on a film of oil &
never touch the shaft so the oil creates the resistance to movement , if the aluminum contacted the shaft the alum would gall & fail vitually
immediatly also the surface area of a needle brg is minute compared to the area inide a rocker arm with no needles so the probablitiy of the
shaft wearing could be increased substantially , the last problem is if a rocker breaks you will be faced with not only replacing the broken
rocker but also retreiving numerous needle brgs from inside the engine
the last option is the Investment cast stainless rockers or the Crome Moly rockers , these are very light & accurate , come with roller tips
& are available in 1.5 & 1.6 ratio as well , these are great rocker , I do suggest you sit down before asking the cost though !!!
there are a number of other factors when setting up a valve train
you should be aware of the rocker being centered over the valve tip , also make sure the push rod is not rubbing against the head in either
full open or closed position I always grind extra clearance into the head where the pushrod gets close to the head when porting heads &
you may need to do this as well to keep the rocker arm centered , shims are available to correct this , P 3690896 in packs of 12
Pushrod length is also very critical , with hyd cams usually no one checks but the piston has to be preloaded but not excessively, the spec
should be at least .010 of preload , excessive preload is bad also as the lifter can pump up & not allow the valve to ever fully close
new pushrods may need to be ordered ,fi the pushrod is too short & no prelaod exists in a hyd lifter
things will go bad quickly , you can bend or break the pushrod or it may fall out or it can break the rocker arm , larger lift cams grind into
the base circle of the cam which lowers the lifter & can make the pushrod too short so this needs to be checked when swapping cams
With adjustable rocker arms & solid lifter cams the adjuster must
have 1-2 threads showing below the rocker arm, less & you do not have full thread engagement more & the end of the adjuster can be
subjected to to much side load & can break the adjuster screw off , the hyd lifters should be preloaded 1/2 turn from zero lash to prevent
lifter pump up . all cams have to have each valve adjusted on the back side of the cam lobe , exhaust should be a djusted 90* before TDC
firing & intake 90* after TDC firing for each cylinder , Mopar has an adjustment decal available P 4452989 to help set valves
Another thing to check before istalling a larger cam is the piston to valve clearance , if they touch the valve will be history immediatly
the last "trick " is Schubeck lifters, these have a composite face close to Diamond hardness, these are the last lifter you will ever buy ,
even if you swap cams every weekend you can keep using the same set of lifters , these are not lubrication sensitive & eliminate metal
to metal contact , better be sitting down for the price on these though , over $1000 for a set
food for thought.............. at 6000 rpm the piston is at TDC 100 times / second & weighs 2200-2400 grams in a 440 ,almost 5 lbs
& the valves are opening 50 times / second ... try bending a coat hangar 50 times / second
