I need help with my Predator push rods

#1
Right now I'm building a predator 212cc and the engine is a Hemi. Aside from the necessary flywheel, carb, exhaust mods...
It will have the original head, 1.2 ratio roller rockers, original valves, 26 lb springs, a lift for the valve cover, a mod 2 Dyno cam, and a flat top piston.

My issue is that I have no idea what the push rod length needs to be. I've read in the forum about using playdoe or clay to check for clearance, but I don't even know where to start with the rod length.

Secondary question: Does the valve lash stay the same with the mods I'm doing, or will it change.

Any help is much appreciated, and I'm open to any suggestions or improvements.

Thank you
 

delray

Well-Known Member
#2
first question:is the head milled and if so, how much. when you say original valves? are you running a retainer and keepers(automotive style)
what kind of head gasket/thickness. if you are using gage roller rockers? that will be real easy to figure out what kind of push rods you will need. maybe stock length or .100 shorter? but either way you will need after market push rods so the ball end fits correct in the roller rocker and you will not use the guide plates either on true roller rockers.
if everything is in the guide lines of building you engine correct you will not have to clay your motor at all. ever with the 1.2's it won't be enough lift to crash into piston and the cam will clear the crankshaft too. it should almost be a bolt in engine build if everything is done correct.
carb I would start out with a 22mm mikuni/china round slide with a 120 jet/15pilot and go up from there if need too.
and yes the valve lash stays at .004
 
#3
start with the pushrods that you have then with the roller rockers if the adjuster is on the pushrod end adjust the pushrod cup for .003 lash then see where the adjuster sits. it should have threads showing above the locknut. Then to check valve side geometry first measure total lift at the valve spring retainer, then divide by two and turn the motor over till you reach one half of the total lift. if you hold a machinist ruler in the center of the fulcrum and the center of the roller axle on the valve end it should be 90 degrees to the valve. You can eyeball it. I use flat neo magnets to hole the ruler against the fulcrum. If I have a pic Ill post it.
 

Attachments

Top