What pushrods?

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71valiant

71valiant

Make fast, break, repeat.
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73 318 with a Comp XE268H cam, Magnum heads with Mopar Per. .024-.028 head gaskets, flat tops with 4 valve relief
 
Your lifters are spec'd for use with Magnum heads, right? (meaning they are Comp's AMC lfiters) You will need hollow pushrods for rocker oiling. The important question is what length...And really, the only one who can determine that is the assembler. I would aquire some stock LA ones, and check to see what you have for lifter preload and rocker tip sweep. Then order the length you need.
 
I'm using the matching lifters for the cam. They are Comp hydraulic lifters. Not sure of the part number though.
 
I've used the Mopar Performance pushrods that are made for the Magnum heads on LA blocks three times with good results. These can be had for under $40 at Mancinis, They are 7.625" long and part # 5007477. Your lifters should work as long as they have the oiling hole in the top.
 
Thats the ones I was thinking I was needing. And yes, the lifters have the holes in the top.
 
Keep me posted on your performance with that combination. I am planning about the same. What intake/carb are you going to use? toolmanmike
 
My Magnum'd LA engine(318) required a 7.350 Push rods. I was using the same head gasket as you, .024-.028 compressed. I bought the 7.650 rods but they were way too long. There seems to be such varying deck heights on these LAs that you might be better off getting a adjustable to measure you length. Pushrods, even custom length are reasonably priced.
 
Smith Bros. charged me $116 for the set, custom cut. You can borrow, or buy for $25, an adjustable checker push rod.
 
I was going to use the cam you have but I was concerned about valve spring coil bind. Magnum heads can only take .525" lift without machining the spring pockets. The 1.6 ratio rockers on the magnum heads that make the difference. I bought the XE262H cam with less lift. (.462-.470) or
.493-.501 with the 1.6 rockers. The 7.625" pushrods should work.(I hope they do, that's what I bought) Mike
 
1.6 rockers would only take the lift to like .512. So I'm under the .525. The retainer will hit the valve stem seal at .530 inch lift.
 
Well I just put a couple of pushrods in and snugged down the headbolts. It seems like the pushrods may be too long. It's compressing the spring A LOT. How do you go about properly checking on what length of pushrod you need????
 
I am assuming you have none adjustable rockers. That being the case, this is what I did.

Bolt the head to the block with the gasket in place.
rotate the cam so that the lobe is facing away from the lifter.
place the lifter in it's bore.
place the pushrod down through the head and seat it on the lifter.
start to install the rocker until it meets the push rod and is seated properly on the valve spring.
set up a magnetic base dial indicator so the plunger is over the pushrod end of the rocker and reading about 1/2 an inch.
Finish tightening down the rocker to spec.
read the dial indicator again
the difference in the 2 readings is your lifter pre-load.
You want this to be .015 to .020
You can get away with .030 but I would never go more than that and in a performance engine never more than .020.
When you find your pre-load this is what you do.
Measure the lenght of your current pushrod, subtract the measurement you took and then add .015. That will give you the length of pushrod you need.

Jack
 
I have heard that Ford Boss 302 pushrods are the correct length for the magnum head/amc lifter swap.


Chuck
 
Well, heres the deal. I don't have a dial indicator. So that pretty much shoots that in the ***. How far down should the spring compress?
 
You don't want to check it at the valve spring. Turn the engine over until the cam lobe is pointing away from the lifter. What you are trying to measure is how much the pushrod push's down the plunger in the lifter when you tighten down the rocker.

Jack
 
Ok. I have to take the wife to the doctor real quick. I have a set of calipers, I can measuer inside the lifter............... STAY TUNED!!

Thanks guys!
 
Everything looks good. The motor cranks over smoothly with a 1.25 socket and ratchet. Time to mount the intake,but first I need to figure out how I'm going to mount my throttle bracket since my intake is a high rise and I'm using the stock bracket.
 
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