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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
After reading more on the subject - including the PDF linked above - I conclude that the Proform tool is correct and is positioning the rocker such that it will be at 90 degrees to the valve axis at half the total valve lift. Which will yield correct geometry. So I do need 7.050" pushrods. The Comp pushrods are .150" too long.
And this is why everything gets triple checked. Using multiple techniques.
GD
Last edited by GeneralDisorder; Oct 19, 2018 at 10:35 AM.
How does this look? That Proform plastic rocker tool is useless. Did not yield anything close to a reasonable geometry. This is actually the pattern from the stock length 7.200 pushrods. Seems centered and relatively narrow. Looks like a win to me.
Originally Posted by GeneralDisorder
After reading more on the subject - including the PDF linked above - I conclude that the Proform tool is correct and is positioning the rocker such that it will be at 90 degrees to the valve axis at half the total valve lift. Which will yield correct geometry. So I do need 7.050" pushrods. The Comp pushrods are .150" too long.
And this is why everything gets triple checked. Using multiple techniques.
GD
So now I'm confused. What was wrong with the ProForm tool measurement yesterday that is better today?
The Proform tool actually puts the rockers to a position such that at half total valve lift the rocker is at 90 degree's to the valve axis. You can read the PDF linked through the post link above, or you can just visualize that the rocker tip swings in an arc (portion of a circle) and since the valve has to move linearly along it's axis, you want the portion of the rocker's arc that is the most linear for best efficiency and lowest side load. That portion is the one where halfway through the total valve lift the rocker makes a 90 degree angle between the line's containing the valve's axis, and the line through the rocker trunion axis and the roller tip axis.
So regardless of contact location, you want the most linear motion with respect to the valve stem axis. This should also result in the smallest contact patch - but measuring that by guessing and checking is not the efficient way to go about setting it up.
I've read the PDF before and agree with what that man explains. It's just i don't know what you didn't like about the ProForm checker tool in the earlier post #50 saying it was worthless. Not trying to flame you but thought I had missed some kinda flaw with using the checker tool. My self I a advocate of using checker tools for moderate/modest lift cam. I own 2, one from MOROSO and one from ProForm and FYI they will measure a little different but close is good enough I have learned. My personal opinion is the checker tools are well engineered to make engine building a street motor much easier. To bad they create so much contriversey. Having tried to use the adjustable p-rod method with the block in the car i would only recommend that method for those that enjoy pain.
My experience is you can only buy p-rods in like 0.050" increments unless you are willing to spend for custom made. I measured my TrickFlow p-rods and found them a few/several thousand off the ordered size which was also lazer etched into the p-rod.
The checker tool put the pushrod at the location that makes sense from the engineering aspect. I had initially got all youtube certified and tried running a pattern test like virtually every youtube video (even Summit's own video on pushrod length), and got what looked to be a great centered pattern using the 7.200" stock length pushrods included in the cam kit.
Then after reading more on the subject, and taking the approach of measuring the tip to trunion distance and aiming for half the valve lift, I also discovered that the Proform tool was aiming for that same point.
I ran the pattern test again and realized that with the hydraulic lifter you actually want the pattern to be slightly toward the intake side of the valve stem as there is a delay in the valve motion while the lifter compresses.....
Ultimately there are a TON of videos and articles full of the wrong method. Turns out you just buy a $7 plastic tool and it takes care of it. Not that it's so hard to measure half the valve lift and use a straightedge to put the trunion that far below the valve tip.....
I ordered the TrickFlow 7.050" pushrods. I'm not too worried about a couple thou. Hell the lifter pre-load differences will likely be more than that..... But 150 thou isn't going to do it for me.
So regardless of contact location, you want the most linear motion with respect to the valve stem axis. This should also result in the smallest contact patch - but measuring that by guessing and checking is not the efficient way to go about setting it up.
The mid-lift method (as you're describing) is the only way to determine correct valve train geometry. That fact is lost on so many trying to establish the contact on the centre of the valve tip and thinking that's the best result. Good bye valve guides.
That said, there's more than one way to establish that. Measurements, using the roller tip axis and rocker fulcrum axis as compared to the lift at the valve is the most precise. No specialized checking tool required. Just the basic machinist/millwrighting tools like calipers, dial indicator and a ruler.
As you've already observed GD, with the valve in the closed position, the roller tip centreline should be exactly half of the valve lift "higher" than the rocker trunnion centreline. This can be done with the running springs used in the build. The rocker doesn't need to tightened down either. Resting on the stud is sufficient.
Last edited by skinny z; Oct 20, 2018 at 03:19 PM.
Yep that's the PDF that was in another thread linked above. Long winded for what amounts to a pretty simple (and obvious, once you look at the physics and the geometry) rule of rocker placement. Which yields pushrod length as a consequence.
I'm still mad at Comp. It's the cup in their lifters that's causing the stock length rods to be too long. And the lifters/rods came in the same K-kit. As if there's a universe where those will work together (there isn't). It's just careless and greedy of them to package all that together. I suspect next time I may look at other manufacturers. Lunati maybe? Don't see much complaints about their products.
Yep that's the PDF that was in another thread linked above. Long winded for what amounts to a pretty simple (and obvious, once you look at the physics and the geometry) rule of rocker placement. Which yields pushrod length as a consequence.
I'm still mad at Comp. It's the cup in their lifters that's causing the stock length rods to be too long. And the lifters/rods came in the same K-kit. As if there's a universe where those will work together (there isn't). It's just careless and greedy of them to package all that together. I suspect next time I may look at other manufacturers. Lunati maybe? Don't see much complaints about their products.
GD
For what it's worth, all methods of measuring pushrod length are not created equal.
For a variety of reasons, I started with Comp and have stayed there for several builds. Using their pushrod measuring criteria, their adjustable pushrod and their lifters, I've managed to get some consistency with VGT. This isn't to say that I didn't suffer from poorly executed or misguided technique but sticking with one brand, or fully understanding the differences between them, at least eliminates that variable between brands.
Yeah but we aren't talking about a 17 thou difference here.
The cam seems nice, but I paid over $700 for a complete kit, of which I used only the camshaft. The rest was not fit for purpose. The springs may have been ok, but don't fit the Vortec heads so I had to get proper Vortec diameter springs from Alex's Parts. Who I'm quite happy with and will buy from again BTW.
Live and learn. But Comp needs to up their game just a little. As a performance shop owner I have multiple opportunities on a daily basis to reccomend parts to my customers and all these experiences play a major role in what I will or will not reccomend. Their kits I will not be recommending. Individual parts may be ok. We shall see how this cam performs and lasts. I'll be putting this on my dyno once it's broken in.
WOW, that Cloyes Hex-A-Just timing set really looks like a quality piece.
The quality is excellent and it dialed in nicely without requiring any changes to the crank keyway. The IWIS chain is finshed very nicely. One thing I noticed - the crank sprockets for the Comp kit and the Cloyes kit are not just identical - they appear to have been made on the same machine. I'm betting Comp rebrands some of the Cloyes products. It did not have an IWIS chain and the poorly finished chain it had was looser than the Cloyes IWIS chain.
I have the Hex-A-Just as well and have buried it behind the Cloyes 2-piece timing cover.
While I've never exploited the advantage of having the two piece cover, it is something I might investigate as I get into what's ailing this particular engine.
