[cutlas]

After cam break in, I checked my valve stem wear pattern and found this. Does this show to long or short a push rod? I am thinking to long.

[lust4speed]

Really nice tight pattern on the stem. I'd leave it alone if it were my engine. You have a nice set of pushrods, and the contact area isn't that far off center. But yes, the pushrods are just a little too long.

[steve25]

I would leave it be, looks good and the added lenght is providing a tad more valve lift than your cam is spced out for.
That push rod photo is showing, or making it look like the two top push rods are bent?

[tiacguy]

Originally Posted by steve25

I would leave it be, looks good and the added lenght is providing a tad more valve lift than your cam is spced out for.
That push rod photo is showing, or making it look like the two top push rods are bent?

Just an FWI pushrod lenght has nothing to do with lift. It only locates the rocker on the valve stem in the proper place to minimize valve and guide wear.

[cutlas]

Thanks for the responses. I will leave it be then. The push rods are strait, just an optical allusion.

[lust4speed]

Originally Posted by tiacguy

Just an FWI pushrod lenght has nothing to do with lift. It only locates the rocker on the valve stem in the proper place to minimize valve and guide wear.

I'm with Steve on this one, but I'll leave the explanation up to him. My head starts to hurt when I start thinking about arcs, tangents, and all that other math stuff.

Steve, would you also explain how there is such a tight pattern off-center on the tip. I would have expected a broader sweep. Only thing I can think of is the length between the fulcrum and the roller tip?

[screamingchief]

I never base my final decision on pushrod length/valvetrain geometry solely off the pattern you see on the tip of the valve,as that pattern is only telling you part of the story.

Normally I'd tell you a 9.350" long pushrod is waaayyy too long for any iron head pontiac,not unless you were using the "low seat" style of solid lifters (Comp et-al) and a small base circle solid cam (the higher the lobe lift on a solid cam,the smaller the base circle is).

Thing that would help to know here:
What specific cam & lifters are being used here?
What specific length are the valves in those iron heads (look like 670's to me)?
Have the heads been milled or the block decked significantly on this build?

If it's a mild hydraulic flat tappet cam and those heads have more or less stock length valves in them,then the 9.350" pushrods are waaayyy too long IMHO,and understand that situation can inturn cause other problems like running outta rocker slot travel and binding up the valvetrain leading to broken stuff like rocker studs and such.

So,you really gotta understand that there is more to proper rocker geometry than that pattern that's left on the tip of the valve.

To me,that pattern indeed suggests the pushrods are too long.

I've seen that happen a lot when a given fellow is checking the pushrod length with an adjustable PR,full valve spring pressure,and a functional hydraulic lifter,instead of using a true solid "checking" lifter that does'nt compress @ all.

Yeah it's a nice narrow pattern,but you gotta shoot for the best balance of width and centering on the tip to get the correct PR length,all while keeping an eye on other things like rocker slot clearance on the stud,and rocker to retainer clearance and such.

FWIW

Bret P.

[cutlas]

Just a little information on this.
Summit 2802 cam and lifter kit.
HS 1.5 rockers
Heads and block have not been milled or decked. .038 crush head gaskets.
Heads are 670s with longer than normal SS valves. I can't remember what the length was but longer than factory (5.1" I think). I was able to get my 1.7" installed height for my springs with only a small amount of cutting the spring seats.
I checked the pattern with a adjustable push rod and a solid lifter using only the inner spring of my comp 995 springs.
I originally checked the pattern with a XE274 cam and the pattern looked good but changed cams before start up and never rechecked the pattern.

Joe.

[screamingchief]

5.100" appx. length are the stock length valves for a 670 head.

That length typically gives an IH around 1.600" in those heads (OE/IH=1.586").

The RAIV valves are .100" taller than those (5.200" appx.).

This is the length most folks use to get to the 1.700" IH for the better valve springs.

From what you're saying,it kinda sounds like you are using the RAIV length valves here.

If so,I'd expect the optimum PR length to be somewhere between 9.200" and 9.250" or so.

The base circle on flat tappet hydraulic cams does'nt vary nearly as much as it does on the flat tappet solid cams,so that likely is'nt a major concern here.

JMO/FWIW

Bret P.

[cutlas]

Bret, the consensus I am seeing is that I can run with this pattern with no ill effects.
Do you think I will be ok with this pattern? I have no problem buying shorter push rods but don't want to throw money away either.

[screamingchief]

Originally Posted by cutlas

Bret, the consensus I am seeing is that I can run with this pattern with no ill effects.
Do you think I will be ok with this pattern? I have no problem buying shorter push rods but don't want to throw money away either.

The problem with that is it's awfully easy and mostly risk free for another guy to say that you can run it with that pattern from where they are looking at all this,as it's not their car,and it wont be them that'll have to fix it if that does'nt end up being so.

I'm just saying that there have been cases in the past of people ending up with broken parts running much the same combo of parts you are using.

Best you'll get from me is it may be OK to run it like that.

But the flip side of that is maybe it wont be OK?



Me,all I'm getting at here is this,knowing the combination of parts being used here,and looking at that pattern,I'd opt for a slightly shorter pushrod,probably somewhere around 9.250" or so.

But like I said earlier,there is far more to all this than just looking at that pattern on the tip of the valve.

That all really should've been sorted out while doing the geometry check with the adjustable PR and solid checking lifter,but you have to be sure everything was the same like the height of the pushrod cup in the checking lifter vs. the hydraulic lifters that will be used,and then you have to account for the hydraulic lifter pre-load as well,so it's easy for things to get away from you when doing this,as we're talking about very small differences in actual PR length (.100" to .200").

And not re-checking all that when you changed cams just threw another ??? variable into the whole deal as well.

And some valvetrain problems you wont even really know about till you finally run the thing hard and everything has a chance to see all the peak forces it "sees" when it's being run like that.

Bret P.

[Skip Fix]

"Just an FWI pushrod lenght has nothing to do with lift."

Pushrod length does change net valve lift. Pete McCarthy even had an article on it years ago in Pontiac Enthusiast. My simnpistic tho0ughts are it is cganging where the rocker tip hits the valve tip and actually changing the true lever length slightly, or hitting the roller(or curve of a stamped rocker) at a different point doing that. Get several different length pushrods the same rocker and a solid lifter and a dial indicator and you can see it yourself.

"That all really should've been sorted out while doing the geometry check with the adjustable PR and solid checking lifter,but you have to be sure everything was the same like the height of the pushrod cup in the checking lifter vs. the hydraulic lifters that will be used,and then you have to account for the hydraulic lifter pre-load as well,so it's easy for things to get away from you when doing this,as we're talking about very small differences in actual PR length (.100" to .200")."

So how do you guys using hydraulic rollers do this?? Get and extra and make it solid?

[stickboy]

When you put longer valves in the head, the tip gets closer to the rocker fulcrum because of the valve angle.

For minimizing the contact patch movement the pattern will be to the outside.

If you do the math and draw it out, that is the best case for side wear on the valve and nets you the most lift from the cam/rocker setup. You want to be at 90 degrees at half your valve lift.

Where the tip rides on the valve is not as important as getting the side forces minimized..........IMHO.

Now if it is falling off the edge, then you have a problem...but in most cases, it is like you have observed.....just a little offset to the exhaust side.

I would check everything else again and then run it.

Must use hyd lifter locked up to measure.

[gene simmons]

Originally Posted by stickboy

If you do the math and draw it out, that is the best case for side wear on the valve and nets you the most lift from the cam/rocker setup. You want to be at 90 degrees at half your valve lift.
Where the tip rides on the valve is not as important as getting the side forces minimized..........IMHO.

I was told this very same thing.
How does one check for 90 at mid lift without having a degree wheel or dial indicator?
This step is never expounded upon.

Also,there can be a 0.050 difference between PR lengths and available PR checkers. For instance,you measure a 9.25 on a comp cam checker,order the 9.25 PR through a vendor,and there PR could actually measure 9.20.

Will this generally cause a problem?

[cutlas]

I never checked to see how close I am to 90 degrees at mid lift. I will give this a look.
I have no binding or rubbing in my valve train so I think I will run it as is. I do agree that the push rods seem long from what I see others using but it is what it is.

Quote "but you have to be sure everything was the same like the height of the pushrod cup in the checking lifter vs. the hydraulic lifters that will be used,and then you have to account for the hydraulic lifter pre-load as well".

I did take this into account as I was using a small block chev solid lifter for checking and knew the pushrod cup location to lifter face was shorter after measuring. I also measured measured hydraulic lifter pre-load and allowed for 50% travel of the lifter cup as pre-load when adjusted.

Thought I had this pushrod length checking deal covered after lots of reading on this forum before hand.

[tiacguy]

Originally Posted by Skip Fix

"Just an FWI pushrod lenght has nothing to do with lift."

Pushrod length does change net valve lift. Pete McCarthy even had an article on it years ago in Pontiac Enthusiast. My simnpistic tho0ughts are it is cganging where the rocker tip hits the valve tip and actually changing the true lever length slightly, or hitting the roller(or curve of a stamped rocker) at a different point doing that. Get several different length pushrods the same rocker and a solid lifter and a dial indicator and you can see it yourself.

"That all really should've been sorted out while doing the geometry check with the adjustable PR and solid checking lifter,but you have to be sure everything was the same like the height of the pushrod cup in the checking lifter vs. the hydraulic lifters that will be used,and then you have to account for the hydraulic lifter pre-load as well,so it's easy for things to get away from you when doing this,as we're talking about very small differences in actual PR length (.100" to .200")."

So how do you guys using hydraulic rollers do this?? Get and extra and make it solid?

Ok so an improper length pushrod may increase lift a few thousandth the engine will never see but you will see the worn parts from the poor geometry so whats the point? Are you saying if your combo needs more lift all we need is longer pushrods? Get real here. The lift is what it is unless you change the cam or rocker ratio. Your splitting hairs. The proper geometry will yeild the valve lift the cam was desighned for and keep parts wear to a minimum. With so many length valves now availible for our Pontiacs every combo needs attention.

[llwta76]

I would never settle for that pattern.Too far to the exh side . I agree w/SC. Push rids are too long (.100-.150 @ least ) I just sold a set of PRs that had a better pattern than that for ones .100 shorter. Don't forget that even large differences in vl between int and exh. can even indicate a different PR. length. As an example my cam has .545 exh and .573 int @ the valve. The pattern on the exh valve was dead center w/ a given PR length .However the pattern on the int. valve favored the exh side . This was all due the the higher int. lift.

[dataway]

The valves don't rotate on these engines?
I'm used to building race engines for motorcycles ....OHC with rockers...the valves rotate in the guides at high rpm.
JohnnyB

[cutlas]

I will be pulling this apart again tonight. I am not comfortable with the pattern either.
Let you know what I find tomorrow.

[GR8ONE68]

Ok, I've been thinking about this and I think I have it figured out. At first glance, I would think that the push rod is too short. But thinking it through, I think it has to do with which side of center the contact point (rocker to valve stem) is on. If the contact point is less than 90 degrees (3 0'clock if the rocker stud is pointing at 12), a shorter rod will bring the wear pattern closer to center on the valve stem. If the contact point were greater than 90 degrees, a shorter rod would push the wear pattern out closer to the exhaust manifold.

Is my thinking correct or am I over complicating it? Sorry for the hijack, but this post got me thinking about it.