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Old 12-15-2012, 01:10 AM
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pushrods lenght on Mopar SB stroker

Hi guys,
a buddy of mine just did a stroker on a 318 Magnum and he's having hard times with pushrods lenght.

Engine is running fairly smooth but there's a minor valvetrain noise that gest louder as you increase RPMm we think this may be cause by the lash between hydraulic lifter and pushrod itself or lack of preload, comp cam says preload should be .030ish , on the web we found .060 or .050...

He put a Comp Cam with about 480 ex 480 int lift on it but kept stock pushrod lenght, springs are harder and put as well new performance keepers and retainers.
We are wondering if the noise is caused by short pushrods, i tryed yesterday to figure out the correct lenght by using a tool i made, problem is that lifters comes up while doing this (cannot understand why) so that is messing up the whole thing.
So, i called Comp Cams and asked them if the base cirlce of the new cam is smaller compared to the stock one, the guy told me that is possible but he doesn't know for sure.

Anybody know the right pushrod lenght?
Any help would be greatly apprecciated, i can give you more specs if needed, thank you.

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Old 12-15-2012, 06:37 AM
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Is this motor an earlier LA style small block or a Magnum?

Hard to believe but Magnums require 2 full turns of preload where as others are less than a turn.
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Old 12-15-2012, 10:22 AM
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Even if the base circle is a little smaller than stock, on a 0.480" lift cam I wouldn't think it would be smaller enough to cause problems with pushrod length. This is one of those things that a builder checks in the mock-up before final assembly.

Viewed from the front of the motor, where is the rocker engaging the valve stem tip? Is it right in the middle of the tip or more toward the lifter valley or more toward the headers?

Back off the preload until the rocker clatters, then give the nut 1/2 turn. Go to the next rocker.
The studs are likely 3/8"-16, meaning that there are 16 threads per inch. If you divide 1 by 16, you get 0.0625". That equals one full turn of the rocker nut. If you turn the nut 1/2 turn, you get 0.03125", right where Comp told you to put the preload.
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Old 12-16-2012, 03:37 AM
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Thank you for the answer, they're so much apprecciated.

This is the valvetrain we are talking about:

Chrysler 318 Engine Rocker Arms Photo 14

As you can see on the picture they are different from chevy's wich have a locknut with a taper underneath that matches the rocker so you set up the preload just by add one extra turn or so, Chrysler ones have a simple bolt on top to tight at 22 lbs ft, what we probably can do is to put a spacer on the stud so the rocker will seat higher if needed or machine it on the lathe in the case longer pushrods are needed but i think get longer pushrods is easier.

What is hard to believe is that when you buy a specific camshaft to put on a stock engine the company doesn't tell you pushrod lenght.

Thank you
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Old 12-16-2012, 04:35 AM
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That's a LA small block. You really don't want to cut the stands or do anything to the shafts themselves. Have you isolated the noisy rocker or is it all of them?

A couple of things to look out for. Depending on the mileage those rockers wear quite a bit where they rub against the shaft. If you're able to isolate the noisy rocker observe it while you're tightening the shaft to see if you're getting any preload at all while that lobe is on its base circle.

Also there are left and right offset rockers. Make sure you have them in the right position. If not the pushrod will act like it's short because it will be at an angle and not straight.
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Old 12-16-2012, 10:08 AM
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Quote:
Originally Posted by jeepers creepers View Post
Thank you for the answer, they're so much apprecciated.

This is the valvetrain we are talking about:

Chrysler 318 Engine Rocker Arms Photo 14

As you can see on the picture they are different from chevy's wich have a locknut with a taper underneath that matches the rocker so you set up the preload just by add one extra turn or so, Chrysler ones have a simple bolt on top to tight at 22 lbs ft, what we probably can do is to put a spacer on the stud so the rocker will seat higher if needed or machine it on the lathe in the case longer pushrods are needed but i think get longer pushrods is easier.

What is hard to believe is that when you buy a specific camshaft to put on a stock engine the company doesn't tell you pushrod lenght.

Thank you
You'd be miles ahead of the game w/an adjustable valve train.

If that's not happening, you might find you need several lengths of p-rods to get the exact same preload- this is because of differing wear and differing seat heights if the heads were rebuilt and the seats were not done all the same. Fortunately the preload need not all be the exact same.

Make an adjustable push rod and use it to determine the p-rod length you need. You need to check ALL the valves then hopefully there'll be a single length that'll put the preload somewhere within the range of preload available from the lifters you're using.

You will need to make a solid lifter by stacking a hydraulic lifter full of washers or filling it w/grease so it will not compress while you do the checking. If you use a lifter from the engine be sure to not mix the lifters up- the lifters HAVE to go back onto the same lobes they came from. If you use a solid lifter, be sure the p-rod seat height is the same as the hydraulic lifters you are using (or you account for the difference in your measurements), else the p-rod lengths will be off.

Click on image for details on making an adjustable push rod:

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Old 12-17-2012, 03:19 AM
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Thank you for your time guys, well, the picture i posted is not the engine my buddy is working on wich is a '96 Magnum, i already made a tool to measure up pushrod lenght, i will post a picture of it but is very similar to the Cobalt's one except i'm using two nuts on each rod side to get them solid and prevent the two parts from moving.
We tried to measure the lenght but as i told you in the first post we had difficult because of the lifters were extending and we actually got a shorter measure wich is about the stock pushrod lenght minus the preload of about .060.
Using a solid lifter would be great but i guess we have to take apart the intake manifold and i guess he doesn't want to of course but we will if there's no other way to do that.

About the noise; that was coming out from all of them, honestly it wasn't to bad, i would say that if you have a loud exhaust that is quite hard to notice but noise increases proportionally with the engine RPM.
My friend has been through lot of issue with that engine, the builder mad a lot of mistakes and they probably machined the heads may be more than once so i'm thinking about too much preload on the lifters due to the shorter height of the heads and may be as well the block, i have to ask him.
Talk soon.
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Old 12-17-2012, 05:09 AM
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Quote:
Originally Posted by techinspector1 View Post
The studs are likely 3/8"-16, meaning that there are 16 threads per inch. If you divide 1 by 16, you get 0.0625". That equals one full turn of the rocker nut. If you turn the nut 1/2 turn, you get 0.03125", right where Comp told you to put the preload.
TI, a whole ago I posted basically the same thing regarding using the stud's TPI to figure how much preload was being applied to a hydraulic lifter (in my case it was a 3/8-24 stud, not 3/8-16).

In any event, someone said the rocker ratio had to be accounted for. So using your example above, it would then look like:

1/2 turn = .03125" x 1.5 (or whatever the rocker ratio is) = 0.047" (rounded off).

Just wanted to get your thoughts on this.
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Old 12-17-2012, 05:50 AM
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Like I said in an earlier post the equivalent of 3/4 of a turn is not enough on a Magnum Mopar.

I had a 360 Magnum in the shop this past summer for the same symptoms. In his case the heads were already converted to an adjustable rocker. I set them up at 2 full turns. On a Chevy I generally go a half turn or less but for some reason Magnums require more.

Read through this post, specifically page 2

small block mopar issues • Speed Talk
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Old 01-22-2013, 10:47 AM
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Hello guys, are the friend of jeepers creepers,finally I managed to make the measurement:
6.8140 intake
6.8170 exhaust
I enclose a photo

pushrod which do you recommend?

Thanks
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Old 01-22-2013, 11:55 AM
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Quote:
Originally Posted by FabioV8 View Post
Hello guys, are the friend of jeepers creepers,finally I managed to make the measurement:
6.8140 intake
6.8170 exhaust
I enclose a photo

pushrod which do you recommend?

Thanks
If you're asking what brand, there are several very good pushrods available (Manton, Smith, Trend), but if you're asking what length, both if that's what it takes to get the right geometry.
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Old 01-22-2013, 12:59 PM
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the average is 6.81 they told me to add .060 ,so I should take 6.87
these might be okay?

Summit Racing® Pushrods SUM-G6413 - SummitRacing.com
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Old 01-22-2013, 01:25 PM
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Quote:
Originally Posted by FabioV8 View Post
the average is 6.81 they told me to add .060 ,so I should take 6.87
these might be okay?

Summit Racing® Pushrods SUM-G6413 - SummitRacing.com
I wasn't paying close enough attention to the decimal places, the difference between the two is negligible.

I'm guessing they say to add 0.060" to make up for the oil holes. If that's the case I agree that the pushrod length you linked to will be almost perfect. The only thing is if the cam requires a stiff valve spring, these economy p-rods might not have the wall thickness you need. But for a street engine, no prob.
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Old 01-22-2013, 01:45 PM
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I use a 390 stroker kit
original head
rocker arms original
cam
COMP Cams Xtreme Energy Camshafts 20-745-9 - SummitRacing.com
valve spring
Mopar Performance Valve Springs P5249464 - SummitRacing.com
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Old 01-22-2013, 09:22 PM
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You should be good to go, but I cannot find the wall thickness of them. I thought they were at least 0.065", but they might not be. Keep your eye on them, if you have unexplained valve float it could be from them flexing and making a pole vault effect.

Last edited by cobalt327; 01-22-2013 at 09:31 PM.
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