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#1
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Valve stem tip height
I got my heads back from the shop and I noticed that the valve stem tips are not all exactly the same height. I laid a straight edge across the valve stem tips and found there was quiet a bit of variance. Won't this effect pre-load etc..? I have non-adjustable rockers. What is the fix? can the tips be ground down to the same height? How much variance is tolerable?
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#2
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IT will effect pre load, the tips can't be ground that much cause they are only hardened so deep into the stem. Did you install new valves or seats? Most likely the reason. If hte seats have been ground on a lot or the valves have been ground on then that causes them to sit deeper than some and it changes the stem height. New valves and seats will cure it for sure.
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#3
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I've never used them,but would valve stem lash caps on the short ones fix the problem? How much difference is there? You might have to take back to machine shop and have them fixed.
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#4
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You could use lash caps, but that's a cruch. Better to take it back and fix it the right way.
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#5
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If your valves are the same length, it means that in some chambers the valves have been ground deeper than in the others. This will also affect piston to valve vlearances, chamber sizes etc, and grinding valves deep will also usually make the heads flow worse.
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#6
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The machine shop messed them up. Have the machine shop make them right.
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#7
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In defense of the machine shop---they usually only grind the seats enough to clean them up. If you want to "equalize the seat depth", that usually requires more $$$. And that should be discussed before the work begins.
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#8
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Like Sanborn said, the seat work for a standard valve job does not equalize the depth. You will also find they sometimes use replacement valves that aren't exactly the same length or have some that have been ground and some not.
Just went through the same thing myself with over .010 difference in height. Since I needed to shim the shaft anyway, I had them shorten the long ones to match the shortest and then shimmed the shaft to get good contact patch. Be sure to do all the shimming and contact patch work before you check your pushrod length. |
#9
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How much are we talking about here? Lash caps will work fine, just make sure they dont touch or "lay" on the retainer, this would be bad.....if more than .050 you might have problems, with lifter pre-load,
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#10
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The worst one is almost .020 higher than the rest. The others are within few thounsanths of each other. I talked to the shop (I know the guy pretty good)and he said he is confident it won't be an issue with hydraulic lifters. I am going to check the preload tonight and see what the differences are there.
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#11
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Out of the box mopar performance Stage VI's had .060" difference.
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#12
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Quote:
I checked an old set of 906 heads I had lyning around and they are almost perfect, maybe .003-.005 difference. |
#13
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.020 isnt that bad, if this is a typical rebuild dont worry about it. what cam and lifters are you going to run, some of the Xtreme comp stuff requires very little preload, but they also suggest adjustable rocker gear.....
run it! |
#14
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You do need to check the contact pattern on the valve tip with the rocker. .020 is plenty enough to mess up the contact and shorten valve guide life, or even eat pushrods. The rebuilder books will give a tolerance of something like .030, but just because the lifter can handle it, doesn't make it a good idea.
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#15
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It is a MP .509 cam. I am replacing the lifters with new CompCam lifters.
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#16
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I would try to get them closer than that! Trying to make up the diff. with lash caps doesn't work too well. I've tried that before and it's more trouble than it's worth.
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#17
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If the valves are all the same length the problem is with the seats or the area on the valve head that seats on the head. You could try grinding all the valves to match the shortest one and then use lash caps to get the height back. A lot depends on how much power you want to make. If it's a high output engine better fix it right and use lash caps for added valve tip life. If it's just gotta run pretty well then patching it as I suggested here will likely work just fine.......djs
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