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Old 09-16-2002, 03:18 PM
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Post Longer push rods

OKAY, so Mrfixmaster doesn't know it all!! There I said It!! NOW somebody please tell me why I see .100 over length push rods?? Doesn't make mush sense to me.Tell me, Tell me PLEASE!!! <img src="confused.gif" border="0">

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Old 09-16-2002, 03:52 PM
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what are you talking about?
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Old 09-16-2002, 06:25 PM
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i think the longer rods are for solid cams.

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Old 09-16-2002, 06:45 PM
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The only reasons I've known longer pushrods to exist is for large or aftermaket cams that have smaller than stock base circles, or if the heads were angle milled. This is done to keep the rocker geometry correct ( otherwise you can kiss your guides good-bye among other things) I'm sure there are other reasons too but these I know.
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Old 09-16-2002, 06:55 PM
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different length pushrods are used just to keep the valvetrain geometry correct. You want to keep your rocker arm back and forth motion as little as possible and in the center of the valve as much as possible, this keeps side loading, or "scrubbing" force off the side of the valve, which does wear out the valve guides/stems rather quickly. Excessive head/block milling, small base circle cams, heads with different length valves, taller block decks, all sorts of things like this affect the valvetrain geometry and different length pushrods are the quickest and easiest remedy for this.
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Old 09-17-2002, 05:58 AM
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You will also notice that some manufacturers offer valves with longer stems. This allows you to use longer valve springs, therefore more lift before encountering spring bind (or stack). With the longer stems you would need longer pushrods to compensate for the longer stems, keeping the rocker geometry correct. However, when these types of mods are completed the best bet is to check the geometry very closely as .100" longer pushrods may be in the ballpark, but you need to be exact on this in order to do it right. In other words you may need a pushrod that is .078" or .106" longer. Proper rocker geometry is extremely important to make an engine run correctly and is often overlooked when changing heads, milling, angle-milling, etc., etc. Custom made pushrods are necessary, I think a recent Crane magazine ad stated that they can produce special length pushrods to order in 2 days or so.

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Old 09-17-2002, 06:16 AM
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Thanks for the info. So if I change cams, to a smaller base circle for instance, how do I determine if I need longer push rods?? Is there a formula to use or a specific angle I am looking for at valve closed/open? Or do I just rely on the manugacturer to tell me that I need them??
M.F. <img src="confused.gif" border="0">
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Old 09-17-2002, 07:08 AM
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As NAIRB stated in his post, you want the rocker to stay in the center of the valve stem tip as the valve opens and closes. Best way to check is to turn the engine over by hand (this should be done while still on the engine stand) until the valve is at 50% of total lift. Look at the rocker arm very carefully and it should be at right angle (90 degrees) to the pushrod. If the rocker is not at 90 degrees at half lift, then you will need longer (or shorter) pushrods. As I recall Moroso and Manley make pushrod checking tools that install in place of the rocker for checking pushrod length. I haven't personally used these tools, but assume that they do work. Another check it to put some machinist's blue on the valve stem tip and turn the engine through several revolutions. Look at the marks left by the rocker arm. This pattern should be centered on the stem, if not then you will need custom length pushrods.

[ September 17, 2002: Message edited by: engineguy ]</p>
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Old 09-17-2002, 07:27 AM
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[quote]Originally posted by Mrfixmaster:


Is there a formula to use or a specific angle I am looking for at valve closed/open? <hr></blockquote>

-Here- is how you go about making your own pushrod length checking tool. Sometimes you may also need a shorter rod. It is best to check all the rocker arms for proper stem contact.

This tool is also available from your larger cam manufacturers along with instructions (CompCams) on how to check for proper stem contact.
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