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-   -   measure valve lift at retainer (http://www.hotrodders.com/forum/measure-valve-lift-retainer-139290.html)

GMR 05-25-2008 08:48 AM

measure valve lift at retainer
 
I'm measuring for pushrod length and have a dial indicator set up on the valve spring retainer. I'm using a solid lifter, adjustable pushrod, Proform full roller rockers, the real valve springs I will be using.

When doing the pushrod length checking the most valve lift I'm seeing is .448 and that's with a pushrod that's way too long. I've tried 3 different rocker arms from the package and got .444, .446, .448.

When using a pushrod length closer to what I'll need (roller rocker tip pattern located in middle of valve tip), I'm getting only about .439 lift.

Cam card states .311 lobe lift (.467 with 1.5 rocker). I've previously checked this by placing the dial indicator on the edge of the lifter and it's ok (.311).

I'm thinking I'm not placing the dial indicator properly on the retainer.

Is this lower lift I'm seeing to be expected or do I have a problem?

68NovaSS 05-25-2008 09:13 AM

I don't understand why you have a dial indicator on the spring, but the lift measured there should match what you see at the lifter, with solid lifters. It sounds like your pushrod maybe flexing/bending slightly? Regardless, I'd do the checking with lightweight checking springs, or remove the inner damper spring.

tdkkart 05-25-2008 10:09 AM

Pushrod lenghth should have no affect whatsoever on the lift at the valve, except on extreme examples where pushrod flex is a problem.

What I would suspect is that your rocker ratio is not exactly 1.5, woldn't be unusual at all, especially with "off-brand" rockers. Rocker flex is also a possiblity if your springs are really heavy.

Set up a test stand to check your rockers with very little spring pressure, I'll bet the ratio is actually closer to 1.44 as indicated by your measurements.

techinspector1 05-25-2008 03:04 PM

Quote:

Originally Posted by tdkkart
Pushrod lenghth should have no affect whatsoever on the lift at the valve, except on extreme examples where pushrod flex is a problem.

What I would suspect is that your rocker ratio is not exactly 1.5, woldn't be unusual at all, especially with "off-brand" rockers. Rocker flex is also a possiblity if your springs are really heavy.

Set up a test stand to check your rockers with very little spring pressure, I'll bet the ratio is actually closer to 1.44 as indicated by your measurements.

Bingo, we have the correct answer :thumbup:
I've known guys to make friends with the parts counterman at the local Chevy dealer so they could take a set of rockers home, check the ratio and return for another load of rockers until they find the highest ratio for a complete set.

Stroke 05-25-2008 07:08 PM

There is more to this along with what has been stated already. IMO, subtle changes in VT geometry will cause the things you are seeing here. Not always will max lift occur when the pattern is centered, nor will a centered pattern be the absolute correct geometry. Flex in the valvetrain components along with tolerance stacking play into this deal, as well as parts used. Checking springs do not load the components as do actual springs and their pressures and will net a different number, most always. I have tons of data in regards to this matter, and have sought to compile data for different rocker mfrs, as well as map (graph) lift at the retainer in 5* increments for 720* crank rotation for each, with up to three different pushrod lengths as well as varying valve lengths . They all net different results and give much to look at. On the geometry end of it, things are not as simple as most believe, and the only way to see these things is to actually check. Seeing is believing (read - actual measurements). My PC suffered a major meltdown though, and all the data from my notes etc. are still in that PC. I could redo all of the noted material, but that took a looong time to enter and all of that, and I've not had the chance to recover the entered data from the toasted PC, but I'll get to it - looks like in my extra spare time. This topic is a good source for debate and is much like the 'more than one way to skin a cat' deal. That being said, you may never see the advertised lift for your app, and if you do, I'd hazard a guess your geometry is wabi sabi, or, imperfect, impermanent, and incomplete. JMO

GMR 05-25-2008 07:18 PM

Thanks for the responses fellas.

I hope the pushrod isn't flexing. The spring is 115 lbs seat and 300 lbs open and the pushrod is Trickflow 5/16 chromemoly .080 thickness. I get identical results with the adjustable pushrod as I do with the Trickflow one piece unit.
But if you still think I should change the springs I'll try it.

I'm missing how I'm going to check the rocker arm ratio. I kind of thought I was doing that with the dial indicator on the retainer. Is there an easier/better way?

carsavvycook 05-25-2008 08:25 PM

I would say you are checking it real close to as accurate as you can get. Your problem is most likely the Proform rockers. I understand they are made in China and would not be surprised if they are junk.

techinspector1 05-25-2008 08:30 PM

Stroke, I see you have zero wiki edits. When you recover the information, you could do us all a good turn by posting it on the wiki for all to see :thumbup: When a certain question keeps coming up, I research what I don't know about it, then compile it into a (hopefully) comprehensive, intelligent format and post it on the wiki. The thread titled "intake manifold gasket" that can currently be viewed on the engine board is a good example. I read the poster's problem, went to the wiki and copied the URL to an article I had posted earlier, then went back to the thread and pasted the link. Quick, easy and correct. :thumbup:

Stroke 05-26-2008 06:41 AM

Good call techinspector1. I decided to look into that stuff originally because of arguments etc. Let me say this, until I did the data/measuring etc, I thought things were good to go the way I'd done it for years. However, upon digging into things a bit deeper, comparing, measuring and so forth, I have a little different view of this than before. I spent a whole lot of time doing this stuff, looking at over arcing under arcing comparing max lift and geometry etc etc etc. Some have said it's a waste of time, but having gone through the trouble, I hardly find it a waste of time. Like I said, seeing is believing. When I toasted the old PC with about 25+GB of stuff on it I was quite disturbed. Going through everything is going to take a bit but I know it won't be as tedious as when I did it the first time. It's just a matter of slaving that HDD, learning this new OS and it's 'ways' along with the time thing. Your Wiki suggestion is a good one, who'da thunk?

GMR 05-26-2008 08:13 AM

Seems you fellas are pretty much in agreement I made a mistake with the Proform rockers. They were recommended to me by the tech at Competition Products.

Anyway, good information, very helpful, thankyou.

Stroke, I might take a shot at graphing the lift vs. crank degrees and then combine those results with the pattern/witness mark I see at the valve tip to determine pushrod length. Sounds like fun. Any particular reason you chose to use an increment of crank degrees and then write down the lift, instead of an increment of lift and then write down the crank degrees?

I know the results will be the same but wondering if looking at it from the different perspectives presented by the two methods - if one makes it easier to interpret the results. Just wondering why you chose one method over the other.


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