5.9 Magnum pushrod measuring questions

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MechNerd

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I am admittedly unfamiliar with Magnum engines and their pushrod/rocker arm setup. I had my original 5.9 roller cam reground, reusing the roller lifters and installed a Fel Pro 9898 head gasket . Only thing changed from stock was the regrind. Installed lifters and torqued the heads down. Using a checking pushrod, I've held the rear of a few rockers up to remove any slop, then adjusted the pushrod until it's tight enough to prevent rotation. Took it out and measured it at 7.075. The other rockers measured within .005 of that too. I read many times on this and other sites that Magnums like a lot of preload, so I figure I'll add .075 for a total length of 7.150. Is this a reliable method for figuring pushrod length? Is there something I have missed to accomodate for the lifters not being "pumped up"? Any answers would be appreciated. If I'm way off please point me in the right direction.
For the record, this isn't the best design I've ever seen for rockers and pushrods. Even Chevy's have SOME adjustment. These? You're good...until one dimension changes in the valve train, then you're SOL and buying parts again.
 
This obviously depends on your particular cam but that measurement seems pretty long. Sounds like you may be measuring with collapsed lifters. You might try shimming them on the inside to make a false solid lifter to get a better measurement.
 
remytherat said:
This obviously depends on your particular cam but that measurement seems pretty long. Sounds like you may be measuring with collapsed lifters. You might try shimming them on the inside to make a false solid lifter to get a better measurement.
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I went back and measured again when you pointed out the math ain't mathing. Measured 5 different valves, averaged out around 6.950. If I order 7.00 pushrods, think .050 is enough preload?
 
Is your motor assembled to the point to where you can spin the oil pump with a drill while rotating the crank with a ratchet and socket? If it is, try that to pump up the lifters. You can manually pump them by putting a little pressure against them to simulate down pressure that a push rod would provide. Do that to a few random lifters and check the measurements with the checker pushrod to see if there is consistency of the lengths.
 
You need to measure the pushrod length at ZERO lash (plunger in the lifter at the top) and be fairly accurate, and then add your preload. .050 preload is right in the middle of the range and they’ll take as much as .090. If you adjusted the pushrod, collapsing the lifter, then added preload you’ll hold the valves open.
 
TT5.9mag said:
You need to measure the pushrod length at ZERO lash (plunger in the lifter at the top) and be fairly accurate, and then add your preload. .050 preload is right in the middle of the range and they’ll take as much as .090. If you adjusted the pushrod, collapsing the lifter, then added preload you’ll hold the valves open.
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I thought about that. It looks like all the plungers are right up against the retaining clip at the top of the lifter. Hope that means they're at the top of their travel. I don't think I put enough pressure on them to push them down any.
 
MechNerd said:
I thought about that. It looks like all the plungers are right up against the retaining clip at the top of the lifter. Hope that means they're at the top of their travel. I don't think I put enough pressure on them to push them down any.
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Correct, the plunger when at the top is touching the retaining clip. Sounds like you done did it correct. But remember you’re dealing with very small measurements that are hard to see by eye.
 
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