push rod length help

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1qwikScamp

1qwikScamp

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hey guys i could really use your help. i am building a 408 for my scamp and i am using an early 90s 360 roller block but has the oiling provisions for LA style heads. i am running a hughes hyd roller cam and mopar hyd roller lifters i have comp 1.5 roller rockers on my LA style eddy heads. i have measured my push rod length with the checker sent to me from hughes and i have it set it where i have a good contact patch for the rocker right in the center of the valve, over the entire lift of the cam. but my problem is that the push rod seems short to me. it is accually shorter than the factory magnum push rod and much shorter than a factory LA push rod does this seem right to you guys i have never used one of theese "hybrid" blocks before and just wonderring if i am in the ball park o this
 
You need to check visually for a straight line sighted from the lifter up through the adjusting screw on the rocker @55 percent of valve lift. The pushrod should be in a straight line with the lifter at that point in travel. The rocker being centered on the valve tip shows that your rocker geometry is good which has nothing to do with the push rod length on an LA motor. The adjustable pushrod is for measuring pushrods that will be the correct length to accomplish a straight line @55 percent of lift with the rocker making contact with the valve tip in the center of the valve which you already have.
 
416stroker said:
You need to check visually for a straight line sighted from the lifter up through the adjusting screw on the rocker @55 percent of valve lift. The pushrod should be in a straight line with the lifter at that point in travel. The rocker being centered on the valve tip shows that your rocker geometry is good which has nothing to do with the push rod length on an LA motor. The adjustable pushrod is for measuring pushrods that will be the correct length to accomplish a straight line @55 percent of lift with the rocker making contact with the valve tip in the center of the valve which you already have.
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I learn something new every day here on FABO. Great info. toolman
 
toolmanmike said:
I learn something new every day here on FABO. Great info. toolman
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It's horrible information and totally useless.

1. On a magnum headed engine with adjustable rockers pushrod length has everything to do with valve geometry. It no longer uses a shaft style rocker setup, it now is pretty close to a chevy small block. Once the height of the rocker is determined that gives the correct geometry and lifter pre-load, the correct pushrod length is measured.

2. Straight line from rocker to lifter? What in the world are you talking about? There will never be a straight line from lifter rocker at any lift on a Mopar small block.

3. On LA heads, the rocker shaft height sets roller to valve tip geometry. Once this is correct, pushrod length is measured so that there is about a thread to a thread and a half showing so the oiling oil in the rocker will lube the cup. It has zero to do with "a straight line at 55% lift".

Sheesh, this is why I don't hang around in the tech forums much anymore.
 
Thanks toolmanmike. I just went through this whole senario just recently with my motor. The only difference is that I was having geometry issues and had to shim up my rocker shaft which led to changing pushrods to get the proper length @55% of lift. I spoke to Dave at Hughes just to verify the procedure because I wanted to make sure I was right in my thinking and to make sure I got the correct length on my push rods. Hughes has a description of this whole procedure along with good pictures for guys like me that need the visual sometimes to go along with the verbal. It all makes sense when you can see it all in a diagram.
 
Beg the differ ramcharger! I to 2 threads showing below the rocker adjusting screw is about as accurate as zip. As I said, rocker geometry has nothing to do with pushrod length. It's all about rocker shaft height relative to the valve depending on what length valves you have in your heads. And yes you will have a straight line through the lifter to the rocker @55 percent of lift if you have the correct geometry to start with and the correct pushrod length. I did it on my motor so I know it can be done. That's why we use a solid adjustable lifter to measure lifter running length and measure with an adjustble pushrod to find the correct length needed @55 valve lift.

But hey....you're probably right and Hughes told me a line of BS and I did it just as they described it and it came out just as it was described.

Plus you might want to reread 1qikscamps thread. He said he was running "LA" Eddie heads, not magnums, which yes you're right. It would be similar to a Chevy setup. LA heads make geometry separate form the pushrod issue!
 
I've spoken to Dave at Hughes. So long as you let him tell you how everythign is, you're fine. Apparently it worked for your setup. However in terms of validity... This line is true "The rocker being centered on the valve tip shows that your rocker geometry is good which has nothing to do with the push rod length on an LA motor." That statement also makes that "straight line" theory invalid. If the geometry is good, meaning sweap is narrow and the tip of the rocker is centered at 50% of lift, then the pushrod is simply a placeholder. As a place holder, you need the minimum thread exposure, and then fill in the distance. The last hydraulic roller/LA RPM headed engine I did used the shortest pusrods I've ever used. I believe around 6.5" IIRC. There is no way you'll have a straight line "at 55%". Think about the arc the adjuster screw traces as the valve is opened and then explain how 55% becomes somehow significant.
 
The lifter angle prevents the pushrod from EVER being in a straight line to the lifter, look at the engine, not a diagram..............
 
There is no way on a SB Mopar you'll ever get the pushrod in a straight line with the lifter because the lifters are at a 59 degree angle and the head mounting surface is 48 degrees. That's an 11 degree difference. Now if you have a 48 degree race block it's a different story.

To the original poster. If your getting a good contact patch on the valve tips your fine. Remember decking the block and milling heads shortens the pushrod length needed. So does thin head gaskets. If your engine fits all or even some of that criteria that's why the pushrods are so short.
 
If what he said worked for you, that's all that really matters. But in terms of physics and design it it like when I tapp twice on a gasketed part. I know why it seals and it has nothing to do with me tapping it. But if I don't tap it it's going to leak...lol
 
If I could interdict with a question on this matter. Does the "straight line at 50%" apply when setting up a set of Hughes rockers on a BB. I ask the question because I'll be installing a set on my 383 in August and I'm using 452 heads. Personally, the first time I heard of the straight line was on the Hughes website and yes I know the importance of getting the correct contact between the rocker roller and valve stem face through the entire sweep. For that purpose and just in case I have a set of rocker shims.
 
I was told for both big block and small block "LA" to look for a straight line through the rocker adjusting nut/pushrod at half lift! But don't take my word for it:)
 
416stroker said:
I was told for both big block and small block "LA" to look for a straight line through the rocker adjusting nut/pushrod at half lift! But don't take my word for it:)
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That's totally different than the way you worded it earlier and might account for the comments. Earlier you said the pushrod would be straight in line with the lifter at 55%. Here's a direct quote from your first post.
The pushrod should be in a straight line with the lifter at that point in travel
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Now you say the pushrod should be straight in line with the rocker arm adjuster screw at 55% lift. That last statement I agree with. (well I thought it was supposed to be at 50% lift but that's close anyway, lol)

I think this clarifies things if I'm not mistaken. Funny how one accidentally mis-spoken word can change a whole statement. Feel free to correct me if I'm wrong.
 
You're right! One misposken word can put a totally different spin on things! I should of said "to" and not "with". My bad!! And yes I did say 55 which is what I was told. So yeah...50 is close/or half lift! Again, my bad!

I appreciate you clarifying my mistake!
 
Quote. That last statement I agree with. (well I thought it was supposed to be at 50% lift but that's close anyway, lol)

Fishy, Hughes engines breaks it down to 55% "valve lift" for SM's and 50% for BB's. It still remains that the straight line they're talking about is from the adjuster bolt through to the push rod which was until recently news to me.
 
The only important things in regard to the pushrod is getting the valve job right so the rocker geometry is right and don't have the adjuster so deep there's 1/4" of thread below the rocker body. Then it doesnt matter. Just connect the two points. I can make an educated guess that Hughes is more concerned with having fewer threads on the adjuster and THAT may be why he says eyeball it when it's straight. Because if the adjuster is way deep or too shallow the pushrod will be forced to lean more. If that were the case, it's simply another way to make sure you only have a max of a couple threads showing under the rocker and THAT is what affects the pushrod length. "tomato" tomahto...lol
 
ok so i set it up with a thread showing out of my rocker and turned the push rod out to make up the difrence. and rolled the cam over everything lookes good and straight through half the lift and i have a good pattern on my valve would you guys say this is probably close enough
 
demon seed said:
Quote. That last statement I agree with. (well I thought it was supposed to be at 50% lift but that's close anyway, lol)

Fishy, Hughes engines breaks it down to 55% "valve lift" for SM's and 50% for BB's. It still remains that the straight line they're talking about is from the adjuster bolt through to the push rod which was until recently news to me.
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Ok, thanks Terry. I tried to find that article on Hughes site but couldn't find it. Do you have a link?
 
one qwik... If your rocker's tip is basically dead center at 1/2 lift... and you have the right preload (if hydraulic), then your fine.
 
moper said:
If what he said worked for you, that's all that really matters. But in terms of physics and design it it like when I tapp twice on a gasketed part. I know why it seals and it has nothing to do with me tapping it. But if I don't tap it it's going to leak...lol
Click to expand...

haha!:toothy10:
 
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