why are there 47 diff. length push rods

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j.d.duggan

j.d.duggan

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I'm woundering why there are so many different push rods for small block mopars.does every different head,i.e.915,587,302, 308,x,j,use a different length pushrod?inlighten me please.:mob: I'm the one on the fare left,dazzed and confused.
 
It's not really different pushrods "for" the SBM it's just whatever is the right diameter and length for the application... so many variables can change required pushrod length and every engine is different. For my 5.9 Mag build I needed shorter pushrods and it turned out some COMP Magnum pushrods meant for Small Block Fords were just right. After all they are just a simple tube/rod with ends on it there isn't really a "Chevy pushrod" or "Mopar pushrod".

Ideally when putting together an engine you check the pushrod length with an adjustable pushrod to determine how long they need to be, oftentimes the stock ones are close but sometimes not close enough.

Then there's the upgrade stuff; thicker walls, harder metals, etc. to handle higher spring pressures and RPM.
 
same pushrods used in other motors?
only difference I can think of is motors using the obsolete small tip lifter and obsolete lifter- loose that combo it did not live well
if you are picky about your rocker pre load with stock rockers you might want to carefully select your pushrods- AFTER you do the mid lift drill and set your shaft height/ shim your shafts to compensate for that higher lift than stock cam and any adjustment to the base circle
 
Pushrods are the last measurement you take when setting up a valvetrain. You go through all the motions of getting the maximum amount of valve lift by adjusting the rocker while simultaneously making sure the sweep pattern over the valve is satisfactory. Once the max lift is found, the adjustable pushrod you’re using is measured and ordered, while taking into account the lifter preload. Every engine is different.
 
overthinking it...... under 500 lift run stock rockers and pushrods, im sure many will dissagree but ive had no issues
 
.....obsolete....

Once you start messing with the valve train you will of course need a specific length... as T56 explained...
 
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I can understand if you do some radical milling on heads, or decking on block, or both. you would be moving the center line of the camshaft in essence.but the low side of the cam lobe would remain the same regardless of lift of cam,Is this not correct? or am I off in that assumption?the pre-load of the lifter is set on the low side of the lobe.correct?And is rigger3006 correct in his statement about the .500 lift cam?:realcrazy:
 
j.d.duggan said:
And is rigger3006 correct in his statement about the .500 lift cam?:realcrazy:
Click to expand...

This would depend if your seriously racing your car or if your just enjoying the car in the street.

Is there a performance difference? Yes
Will I feel a power difference? Highly doubtful!
Will I see an ET difference? Yes
Will I destroy my valve train? No
Will it last? Yes

The thing rigger is stating is there is no issues with a Hydraulic camshaft running a pushrod right in the general area of length. The Hyd. lifter has a lot of play. While the length can not be to long or short, it is t as critical as a mechanical cam set up.

Yes yes yes, you can fuss with it and find power and longevity. But I agree. I have simply set the cam on its base circle, measured the depth of the pushrod while depressing the lifter to where I wanted it, measured the rod, done.

I have run them like that for years and thousands of miles. No issues, no worries, no worn out parts, no leaking seals. 17,000 miles a year on an everyday driver that have seen years of rush hour creepy crawling traffic, interstate vacation trips twice yearly traveling half the country.
 
Now on a mechanical camshaft with mechanical or roller rocker arms, the length has to be determined carefully. As well with the rest of the valve train. Everything has to be looked at. Measured. Adjusted. Corrected. And since your building your engine, be it a everyday low powered street engine or a monster racer, it should be corrected to perfection or as close as possible.
 
but the low side of the cam lobe would remain the same regardless of lift of cam,Is this not correct?
Click to expand...

This is not correct.
For most part, the peak of the cam is the same regardless of lift.
Extra lift is created by reducing the base circle, not increasing the height of the nose.

All else being equal, if you changed from a .290 lobe lift cam to a .330 lobe lift cam, and wanted to retain the same lifter preload, you’d need .040 longer pushrods.
The added .040 lobe lift was achieved by reducing the base circle diameter, so the lifter is now .040 farther from the rocker arm when the lifter is sitting on the heel of the cam.
 
using a new billet all is more likely to go well and what PHR says will not apply till you get to a much higher lift cam
measure your base circle compared to a stock cam and if you have not cut the block and heads too much you can calculate your pushrod but doing an after a trial assembly measurement with an adjustable pushrod is always better- If you have cut the head and block a lot then do the whole half lift drill i f you want to live a long time with rpm
if using a regrind than what PHR says will always bee the case
recall that if you do go to a higher lift cam (and more spring pressure) your old pushrods and especially rockers are worn in and when you increase the lift you force the pushrod to go over the lift at the edge of the old wear
this does not usually end well except maybe with worn out stock springs
and remember no oil through the pushrods stock to help, inspect your rocker cups closely- same with the rocker tips- any little cups pitch em
 
I never knew that the lift was determined by the low side of the lobe,this is the first mopar I've messed with.first motor with stationary rockers.sbc valve adjustment is so easy in comparison.I might get the hang of this if you guys keep helping me out.thanks
 
From what I’ve observed, with typical
cam in block automotive applications, the highest point of the lobe is usually dictated by the diameter of the smallest cam bearing the cam has fit through.
You can’t have the lobes sticking out past that cam journal.
Most stock cams have the nose height pretty close to that diameter.
The lift comes from reducing the base circle diameter...... because if you made the lobes taller, it wouldn’t fit in the motor.

On a SB or BB Mopar(using std size cam bearings) the diameter of the #4 cam bearing dictates how tall the lobes can be.
It’s the smallest bearing the cam needs to fit through.

I just checked two cams:
Cam A - .272 lobe lift. The lobe peak is .032 below the diameter of the #4 journal.
So, you could get a max of close to .300 lift before it wouldn’t fit in the motor without reducing the base circle.

Cam B - .378 lobe lift, with the lobe peak at .015 below the #4 journal diameter.

These are both flat tappet cams.
Cam B will have the lifters sitting .089” lower on the base circle than cam A.

Edit: I checked one more.......
.350 lobe lift, lobe peak at .015” below #4 cam journal diameter

Lifters would sit .028” higher on base circle(.028 closer to rockers)than cam B........ exactly the difference in lobe lift.
 
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I didn't see it mentioned yet but head gaskets come in different thicknesses also, slightly adding to the equation.

In my motors case it has to have 5/16 pushrods, hardened, for use with guide plates, ball/ball ends and oil through.
That's 5 specifics, and then head gasket thickness makes 6 for one pushrod part number.
 
what would be a good cam to put in a totally stock 340.4 speed car.without having to worry about valve clearance or pushrod lengths/or is there such a thing?
 
the Key is to change little from factory specs on everything.
Milling, sinking valves, high lift cams, etc all affect pushrod length.

Don’t change any one thing too much and the stock rocker components should work okay.

Something along the lines of a Comp 268H will work with stock stuff.
 
high comp or low comp 340? what other mods? headers, gears how heavy a car? dart or B body what carb
personally I would not use any comp cam shorter than the 276 HL there are too many other choices
do you have a stock 340 cam now? try advancing it 4 degrees and report what difference it made, report your cranking compression
wide LCA and very long ramps of the stock cam means there is lots of ways to make it work better without getting out of the parameters prh states
UD Harolds 268 Comp appears to work because it closes the intake earlier making the low end feel peppier
 
rigger3006 said:
overthinking it...... under 500 lift run stock rockers and pushrods, im sure many will dissagree but ive had no issues
Click to expand...
I had a .484 lift hydraulic and it worked great.............right up until the pushrod punched it's way through the shitty stamped rocker arm.
I had no idea of their life in terms of age or style of driving.
But I got a set of Harland Sharps , measured and got some Smith Bros. push rods.
End of problem.
It is the spring pressure that will bite your *** here........not the lift.
The guy I bought it from told me that he called Comp and told them he wanted 400 h.p. and that was what they sent him.
But he ended every email with God bless , and I found out later that he was using that as a punch line.
Moral of the story...........the truth is what you make of it , and spending money on parts is never a bad decision.
You really do get what you pay for.
 
How many different head gasket thicknesses are there? And that's just ONE aspect. There's head milling, block milling, different heads, different valve gear and on and on and on.
 
Is that a rhetorical question Rusty
you know you can get almost any thickness you want if you go Cometic or Copper
we ran 550 lift with the stock rockers when we had to due to some rules
the comment that it is the springs is correct
we cheated even back there by using oil through the pushrods
the heavier, hardened rockers AFIK have been gone for years
we even had some stockers re-heat treated
I posted elsewhere about the little ridge that forms on used stockrockers which is death with more lift and more spring (and on the tip side too)
 
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