Pushrod length question-Magnum engine

[hemidart1]

I'm building a 318 magnum with a REGRIND cam that specs out at '512 lift. What length do I have to change the pushrods to if any?
A friend said that since it is a regrind cam-the stock pushrods won't have enough preload.

thanks

Al.

 

[street demon]

A cheap way out is to measure the base circle of the reground cam then measure the base circle of the same spec stock cam then see how much they have taken off and add that to your current pushrod length and order some new ones. This only works if you haven't changed head gasket size or had the heads milled.

 

[street demon]

Also I'm pretty sure your going to have retainer to seal issues with stock magnum heads with that much lift.

 

[dgc333]

Is the .512 lift based on the 1.6 magnum rockers or the more typical 1.5 ratio rockers? If it's based on the 1.6 ratio magnum rockers then you should be OK with .512 but certainly check clearances. I am running .509/.512 without guide clearance issues, the general accepted number is .525 on a magnum head before the need to cut the guides down.

You will need to measure what you need for push rods and will likely need to order custom length ones.

 

[hemidart1]

the cam is the 509/512 based on the 1.6. The problem is I installed the cam already not thinking ahead about the pushrod lengths. How do I measure now?

 

[dgc333]

Buy a checking push rod from Summit or Jegs. These are adjustable and you adjust the length to get the proper preload (and geometry if you are using adjustable stud mount rockers).

If you have the provisions to measure it you can order custom length pushrods. If you don't have the means to measure send the push rod back adjusted to the length and they will do the measuring.

 

[hemidart1]

I ordered a set of adjustable pushrods from Hughes today. It was easier than trying to figure out the length I needed-plus it is going to my mechanic this weekend to be finished off.

thanks for the the help-I needed it!