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You don't want to deflate them. If you do, and use that as your dimension, you will bend pushrods or valves when the engine is running.

Do you have stock rockers, or are they adjustable ??

If they are stock, you need to get or borrow an adjustable pushrod (preferably one with a 7.375" - 7.875" range). Rotate the engine until the cylinder you are checking is @ TDC (lifter is on the base circle). You need to do this for both the intake and exhaust valves to be sure they aren't different. Put it in and adjust it until you can't spin it with you fingers. Now, remove the rockers shaft and remove the pushrod without changing the adjustment. measure it, and get the next size LONGER pushrod. They are made in .050" increments.

Let's say you got a length of 7.670"...if you get the next size up, which would be 7.700", you will have roughly .030" of preload on the lifter, which is about what you want (.020" - .050" lifter preload is good). If all you did was change cams, then all 16 shoudl be the same length, but if you have any head work done like new valves or such, you may need 8 of one length and 8 of another.

If they are adjustable, chances are you can adjust them to compensate for the extra needed length. BUT, you need to make sure you meet the adjustment specs for the rocekrs. Some are quite tight, and if you are outside of them, the rockers' adjusters won't get lubed like that are supposed to.
 

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Thanks, that's what I wanted to know, and it also answered a few questions that I forgot to ask. lol.
Thanks RCC Master ;D

What I was getting at, was right now they are rock hard because of having the engine running and the oil pressure pumping them up. So now, I can't push them down by hand. But, come to think of it, the amount of pressure from the valve spring times the rocker ratio should calapse the lifter for the preload :-\

I found adjustable pushrods on hughesengines.com
http://www.hughesengines.com/general/valvetrain/pushrods.asp
I think that they wound be my best bet for now.
 

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Well, I shy away from adjustable pushrods personally...I just can't see how they can be as strong as non adjustable ones.

For that price, I'd take an old one, cut it in half, and thread it for a rod to make your own adjustable pushrod, check the length, and then buy a set of 5/16" chevy pushrods in the correct length (should be around half the cost of the hughes adjustable ones).

I went with the comp cams magnum adjustable roller rockers on mine...

Actually, they won't 'collapse' the lifter, but may prevent it from fully 'pumping up'. it all depends on oil pressure and spring pressure.

Check maciniracing.com for their price on pushrods. You can get cut to fit race strength pushrods for less than 125 a set.


OK...new thoughts......if you can measure how short they are...summit has 7.550" 4130 chromemoly 1 piece pushrods for a SB chrysler for 89.95 a set. These will be .050" longer than the stock ones (assuming you have a hydraulic cam/Lifters). They should be all you need, and a bit cheaper yet than the other two.

Just trying to save ya some money, but if you can't figure out a way to measure how long they need to be within .025" or so, you may be better off buying the expensive adjustable ones.
 

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I checked some of the local parts stores and I can get a set of pushrods for about $70 or so. I found a pushrod length tool for about $15, but your idea to cut one and thread is alot cheaper. ;D So, I do as you were saying and use the tool to get the length and then buy a set of pushrods a little longer than what the tool says the length is.
 

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yes, but not more than .050 longer.....030 longer would be better.

the 70 buck pushrods are probably stock length, which wont help you.

I just ordered the 7.550 ones for my engine from summit.
 
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