Custom pushrods, how much stock lifter preload?

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MopaR&D

MopaR&D

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I'm running a 5.9L Magnum short block with Edelbrock RPM heads for an LA engine with a custom-grind Racer Brown hydraulic roller cam. I'm using the stock roller lifters which the cam grinder (Jim) gave the OK. Initially I'll be using factory stamped LA shaft rockers but with .548" max lift on a fairly steep roller profile I'll be giving them close attention until I can afford adjustable roller rockers. Anyway, mocking things up with the heads torqued down on their gaskets the stock Magnum pushrods are way too long, holding the valves open to where they're touching the pistons... After I figure out length with a pushrod-checking tool with no compression of the hydraulic lifter, how much preload should I add to that figure?
 
If you are not making a high RPM race only motor. you don't have to have roller rockers. In my opinion you are taking a shortcut. A shortcut is the quickest way to somewhere you didn't want to go. Get the adjustable rockers. It is almost impossible to make the pushrods the right length for proper preload on all 16 lifters
 
Ted Carlson said:
If you are not making a high RPM race only motor. you don't have to have roller rockers. In my opinion you are taking a shortcut. A shortcut is the quickest way to somewhere you didn't want to go. Get the adjustable rockers. It is almost impossible to make the pushrods the right length for proper preload on all 16 lifters
Click to expand...

Ideally that's what I would do but school is starting back up so I can't work as many hours at my part-time job; if I waited until I had money for adjustable rockers it would take another 2+ months to get this thing running especially since there aren't many decent budget-minded choices when it comes to LA shaft rockers besides the factory 273 ductile iron pieces; still need to do some more research on that to find ones I like.

Anyway I've decided to go with .080-.090" preload; people running less report a noisy valvetrain and according to Hughes Engines and a couple other places it seems like the Magnums like a lot of preload.
 
Keep in mind that IF the lifters were to pump up, those valves are moving closer to the pistons. Don't let them use up all your PV clearance,lol.
I used to run 1/4 turn, but had to increase it a little, cuz it doesn't take much and things get noisy. So I went to 1/2 turn or so on the rockers. At 28 threads per inch, 1 turn is .036 ..... so I run ~.020 with Hd circlip lifters. This makes them run almost like solids and I don't worry about pump-up.
If you are running .548 lift,then you must be using some HD springs. Some guys here on FABO, have had the unfortunate experience of seeing a pushrod or two punch thru the stamped rocker(s).
Jus saying.
 
Although mine is a 440 .525 lift cam it happened today. Hopefully it was just a weak rocker.

67D5AD63-63CD-4E48-8881-7084BEBBFE26.jpeg
 
AJ/FormS said:
Keep in mind that IF the lifters were to pump up, those valves are moving closer to the pistons. Don't let them use up all your PV clearance,lol.
I used to run 1/4 turn, but had to increase it a little, cuz it doesn't take much and things get noisy. So I went to 1/2 turn or so on the rockers. At 28 threads per inch, 1 turn is .036 ..... so I run ~.020 with Hd circlip lifters. This makes them run almost like solids and I don't worry about pump-up.
If you are running .548 lift,then you must be using some HD springs. Some guys here on FABO, have had the unfortunate experience of seeing a pushrod or two punch thru the stamped rocker(s).
Jus saying.
Click to expand...

Sounds about right however you're running a flat-tappet cam, hydraulic roller lifters need different preload to work correctly. I know the stock rockers are borderline but I'm hoping the oil feed through the hollow pushrods will help keep them from punching through; with the stock LA oiling setup it's really difficult for oil to make its way up to the pushrod seat and I have a feeling that has something to do with them failing. More lift = more motion = more need for lubrication...

In my mind if I ran less preload to where the lifters made noise that would be lost motion transferred to the pushrods and rockers; my understanding is the noise comes from the initial ramp of the cam lobe taking up slack in the lifter plunger (and thus the rest of the valvetrain), meaning that much less lift at the valve as some of the lift is being "eaten away" by the lifter plunger. I've found some references where people had better performance AND less noise after increasing the preload on their roller lifters to .060" or more, and running very little preload (like is sometimes done on hydraulic FT cams) made them excessively noisy and reduced the RPM limit.
 
AJ/FormS said:
Keep in mind that IF the lifters were to pump up, those valves are moving closer to the pistons. Don't let them use up all your PV clearance,lol.
I used to run 1/4 turn, but had to increase it a little, cuz it doesn't take much and things get noisy. So I went to 1/2 turn or so on the rockers. At 28 threads per inch, 1 turn is .036 ..... so I run ~.020 with Hd circlip lifters. This makes them run almost like solids and I don't worry about pump-up.
If you are running .548 lift,then you must be using some HD springs. Some guys here on FABO, have had the unfortunate experience of seeing a pushrod or two punch thru the stamped rocker(s).
Jus saying.
Click to expand...
Heck... that happens all of the time on stock engines.
 
No. That's a super bad idea to run hollow pushrods. But it's your motor do whatever you G Damn want. :)
 
You have enough oil on the top end. Don't be pumping more up thru pushrod holes.
 
72Dart6pack said:
You have enough oil on the top end. Don't be pumping more up thru pushrod holes.
Click to expand...

I'm running external oil feed for the shaft rockers which I will be testing different restrictor sizes so there isn't too much oil up top. I actually grabbed some stock LA valve covers I'm going to cut the tops off of so I can watch the rockers while I prime the oil pump and turn the engine over by hand, then later watch again while the engine is running.

Here's a thread of my build for some background, it's definitely not your typical SBM "pick the parts and put it together" deal: Junkyard 5.9L Magnum + Edelbrock LA heads build
 
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