defresh

Putting together a new L31 350, new fast burn heads, .026 mls head gasket, scorpion 1.6 rollers with an LT4 hotcam. Using a checker i set it to 7.2. Turned rocker nut finger tight plus a half turn. Spun cam over a few times and rocker left a mark towards the outside on top of valve. Set it to 7.05 and it is near center. Can this be right? I don't even see pushrods that size. Will the 7.195's not work?

vetteoz

iTrader: (13)

http://www.summitracing.com/int/sear...yword=pushrods

AlkyIROC

Proper geometry will produce the smallest witness mark across the top of the valve tip as the rocker sweeps across it. The smallest mark will not always be directly in the center of the valve tip.

defresh

Thanks for the link and the info about the mark needing to be the smallest. I had not read or seen that. The mark was smaller at the 7.2ish mark. Just a bit off center. The 7.00 setting had it dead on but did make a bigger mark. Two questions arise. Are the 7.05 pushrods or any pushrods for that matter universal between makes? I don't think I've seen the 7.05 because I've been searching with "sbc" in there. The second question is, do you think the 7.195 would work if the mark is smaller but a little off center? I have a fairly common setup and seems everybody has used 7.195 that is pretty much the standard for factory roller cam applications.

sofakingdom

iTrader: (1)

Doesn't matter where on the stem the mark lands; what's important is that it be AS NARROW AS POSSIBLE.

Given that, then YES ABSOLUTELY, 7.195" will work better than 7.05" (.150" short) SINCE THE MARK IS NARROWER.

The narrowest mark means that the arc that the rocker tip swings through during the course of its travel (since it obviously doesn't move in a straight line) is CENTERED on the valve. That means that it's "scrubbing" across the valve stem the least amount possible, which in turn means that (a) the greatest possible amount of its motion is parallel to the valve stem (greatest possible lift), AND (b) the side force on the stem in the guide is at a minimum, meaning, the LEAST guide wear.

Since we're all really smart people here, (except me of course) I'll introduce you to a technique used by someone almost as smart, Albert Einstein. He called it the "thought experiment". The one we're going to do is this:

Lay a pencil on your desk. Push it on the eraser end, right in the center of the eraser, perfectly in line with the pencil. Put the tip up against some object that it can slide; a small book for example. Which way does the pencil go? Right straight along its length, right?

Now push on the eraser somewhere besides on its center; off to one side somewhere. Right out at the edge even. But, still push exactly in line with the length of the pencil. Which way did the pencil go this time?

Now... push on the pencil right in the center, but NOT directly in line with its length. That is, push just slightly sideways. Which way did the pencil go this time?

THAT'S why you want the mark to be the NARROWEST, but it doesn't matter if it's centered or not.

Usually, with an aggressive cam, the push rod will end up being LONGER than stock, because in order to make a cam "bigger", they don't make the tip of the lobe "taller"; it's already always (except for small base circle setups)as big as it can be and still be installed; rather, they make the back side SMALLER, which lets the lifter sink farther into the block at zero lift. To keep the mark NARROW i.e. re-center the arc, the push rod usually has to be about .050" longer for ever .100" of lift above .500" or so, in a small block. Not hard-&-fast law, just a rule of thumb. But since you've got such a little tiny cam so near stock anyway, don't expect a huge difference.

That said, you can get push rods in any imaginable length, and probably a few lengths you can't even imagine.

http://www.summitracing.com/search/d...s?PageSize=100

AlkyIROC

If you really want to get picky, you would be checking the pushrod length for every single valve. You would find that 16 pushrods are not going to be all the same length. Pick a length that's the closest to the length required to get the smallest sweep across the valve tip.

Looking at that link, I can see 7.200 length pushrods and if you say that leaves the smallest mark, that's what you should use. Don't get hung up on it not being in the center of the valve tip. That's not what you're looking for. Smallest sweep is the best setup.

If the perfect sweep is too far off the tip then you need to correct the geometry with different length valves as well as the pushrods.

skinny z

What's the most effective marking medium to use? Layout ink? Magic marker?

sofakingdom

iTrader: (1)

Either of those works good. Gear marking compound also works, as does plain old white lithium.

It's important to use "check" springs, or to create a solid lifter identical in height to your own. Regular hyd lifters, whether roller or flat, will be compressed internally, which makes your "measurement" come out too long.

AlkyIROC

I use a sharpie

skinny z

I've used all of the above and although the marker method seems to be the most popular

http://www.lunatipower.com/Tech/Valv...nGeometry.aspx

I've had marginal results. My latest go round was using dark lipstick which made for a wonderful transfer however after reading about the width requirement being as important as the location, I'm thinking the grease of the lipstick is too thick to make for a mark that can be interpreted correctly.
The reason I'm asking is that I'm going through another round a valvetrain set up now that my heads have come back from the shop (pushrod hole enlarging and valve deshrouding to gain a couple of cc's). While the guides measure out to be within spec, I think there's too much wear associated with the amount of run time this engine has seen and I need to revisit my checking procedure.