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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!
I just wanted to run this past everyone to make sure I'm not barking up the wrong tree before ordering my pushrods.
Using Chris Straub's video as a reference to obtaining proper geometry, I've found the following.
Camshaft: XR276HR-10
Intake Gross Lift using 1.6 ratio rockers: .535
Half of the gross valve lift: .2675
3/8 studs = 24 threads per inch or .042 per turn
.2675/.042=6.36 turns
After establishing that the center of the rocker trunions were 90 degrees to the valve, I spun the nut down approximately 6.36 turns, and then expanded the adjustable pushrod out. After taking everything apart and measuring the pushrod length, I get 7.4376".
I repeated the process and was able to reproduce the length within about 1/10th of a turn of the adjustment nut.
That all being said, I decided to crank the motor over a couple of times to check the pattern. Knowing that these are hydraulic lifters, and not pumped up at all, I knew it wouldn't be right. However, I was concerned that the tip of the rocker was too far forward on the stem. I also stumbled across another thing - the roller doesn't make an even mark across the valve stem. It clearly removes my marking from the right side, but doesn't do much on the left side. Observing the witness mark, the pattern seems chubby and farther forward than the examples I see online.
So, the questions I have.
1) How concerned with the pattern should I be?
2) Do you feel I should round the pushrod length down, or up?
3) I assume that I use the same pushrod for exhaust since lift is only .009" higher?
0) Since the lifter was allowed to compress during testing, whatever pattern, length, or anything else you got, is meaningless.
1)
2)
See 0)
3) Push rods usually come in .050" increments. If your exh and int are .009" apart, odds are, they're both within the same .050" "band". Kinda like speedo gears... if you've got a T-5 and a 7-tooth (3-series) drive gear, then the steps are 19, 20, 21, & 22. Doesn't matter if your "ideal" gear is "calculated" at 20.76 teeth; you're stuck with 19, 20, 21, & 22. Take your pick. Same deal here. I would not classify that as "assume"; rather, a concession to an unfortunate reality.
If you crank the engine over a couple of times with some lightweight checking springs like you're suppose to use then the lifter won't collapse.
I'm with Sofa. What kind of pattern you have on the valve tip is meaningless. You've already determined the proper length pushrod from a half lift measurement. If the length you determine isn't exactly correct, buy the length that's closest. If a longer 7.450 pushrod is used, you are 0.0124" off your measurement of 7.4376. If a shorter 7.400 pushrod is used, you will be 0.0376 off so the longer pushrod is more desirable.
Don't forget, the hydraulic lifter works with a preload so that slight variation in length won't make a big difference.
I guess I should have asked the real question: Do I trust my half-lift measurement, or do I go buy checking springs and a retainer removal tool so I can verify it?
The half-lift and the pattern will generally produce similar results, within some level of uncertainty. Neither is 100% "perfect" in all ways and all cases. Doing both gives you the best of both worlds but either one is better than slapping it together without checking anything.
A slightly short push rod is better than too long. THINK: what you're trying to do is, minimize side loading on the guide. This load is inherently highest at high spring pressure, and of course is higher the more the rocker is moving across the tip instead of perfectly in line with the stem (which can only occur at the center of its arc more or less, depending on some of the other angles of the parts). With a slightly shorter push rod than "optimum", the sliding action is reduced at high lift when spring pressure is highest, at the minor compromise of slightly poorer geometry at low lift when pressure is lower and therefore it's not as critical. I prefer to find "optimum" then install one increment shorter for that reason.
Doesn't matter where on the valve stem the pattern lands. With 1.6 rockers especially it will almost always be offset toward the exh side.
So, just for kicks, I decided to do the operation again on the other head and found it to be longer, at 7.49". Which means I either did something wrong on one side or the other, or the passenger side head is sitting taller for some reason. That's almost a sixteenth of an inch difference.
I'm going to go recheck a couple of times to make sure I'm not doing something stupid.
Edit: After checking 4 more times on various valves, I found I was right initially and that I must've not been 90 degrees to the valve on this particular check.
So I may be late to the party, and I'm not familiar with the video you referenced, but I just bought an adjustable pushrod and some checking springs. Sharpied up the valve tip and looked at the wear pattern. Painfully easy. Countless videos and posts on this, as well as several guys I know locally who've successfully built far more engines than me recommended doing this.
Is this an old school hack method, or an accepted procedure?
This is the video mentioned. It shows you how to accurately find half lift for a perfect geometry. Using a sharpie on the valve tip isn't close to 100% as most people are overly concerned about getting the mark as close to the center of the tip as possible but it's the smallest mark made by the tip as it goes through it's sweep that's the most desirable. Only the half lift method will give you the smallest sweep.
I prefer the Half-Lift method as proposed by Jim Miller.
No checking springs.
No screwing down of an adjuster nut.
Just measurements that are going to be as close to 100% accurate as you care to measure.
Full running springs are used.
Lifter on base circle of cam with valve in closed position.Valve and spring installed.
Rocker sitting on stud, No adjusting nut.
Using the top of the retainer (or the bottom it doesn't matter) as a reference plane, measure from this plane to the centre of the trunnion axis. Then measure from this same plane to the centre of the roller tip. The difference in the roller tip measurement from the trunnion axis measurement should equal exactly half lift of the cam plus rocker ratio.
Done.
It's easy enough to check visually to see if the roller tip is close to running off the edge of the valve. Checking springs could be used here however the measurements may not be very precise as the lightweight springs don't load the valve as do the running springs. Still for the purposes of gauging where the sweep is on the valve tip, not for pushrod rod length, the light springs will do the job.
Red dot to red line equals roller tip reference. Green dot to green line equals trunnion reference. Red minus green equals half lift.
So it looks like I can get pushrods in either 7.425 or 7.45 for the same cost. I have a measured height of 7.4376. At this height, with these rocker arms (Scorpion SCP1002 1.6s) the roller tip sure is close to the edge of the valve stem (towards the exhaust port or away from the intake), especially on the exhaust valves. It has me a little concerned.
In my own most recent setup, I made a reference jig using a pair of old calipers. (They were handy and fit perfectly).
A suitable straight edge (a wooden caliper is used here) wedged under retainer. This ensures a surface that's 90 degrees to the valve stem to measure from.
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Measure from the caliper top side to the trunnion axis using a piece of bar stock (hex key working here).
Measure from the reference plane to the centre of the trunnion. A hex key worked perfectly in this case.
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Measure from the caliper top side to the roller tip axis via Verniers.
Adjust the pushrod to get my half lift measurement.
Done.
Measure from the same reference plane to the centre of the roller axle.<br/>
This was done initially with checking springs. The true running springs can and should be used.
This looks a bit easier than balancing something across the retainer(s) to use as a guide for eyeballing it. I don't think I have anything suitable, though. Hmmm... I might need to make something.
So it looks like I can get pushrods in either 7.425 or 7.45 for the same cost. I have a measured height of 7.4376. At this height, with these rocker arms (Scorpion SCP1002 1.6s) the roller tip sure is close to the edge of the valve stem (towards the exhaust port or away from the intake), especially on the exhaust valves. It has me a little concerned.
How close is close? Is there still full roller contact on the valve tip? If yes, then I'd say you're good to go. If the roller is starting to run off the side then that's something you'll have to address.
My heads came with .100" longer than stock valves. As such, my contact was already compromised towards the exhaust side. I went with a backset trunnion rocker to bring it back in line.
This looks a bit easier than balancing something across the retainer(s) to use as a guide for eyeballing it. I don't think I have anything suitable, though. Hmmm... I might need to make something.
Yeah, the balancing act with a straight edge across the top of the retainer is a little awkward. In my case, it's impossible as my retainer have a curved top side and nothing flat to lay against. If the retainer is flat across the top though, a magnet can be used to hold a ruler in place. This frees up the hands to measure accurately.
This approach, once you get past the hows of measuring, is practically fool proof.
How close is close? Is there still full roller contact on the valve tip? If yes, then I'd say you're good to go. If the roller is starting to run off the side then that's something you'll have to address.
My heads came with .100" longer than stock valves. As such, my contact was already compromised towards the exhaust side. I went with a backset trunnion rocker to bring it back in line.
I'll try and get some pictures when I get home from work to make it easier to explain.
So 1 thing that has been brought up once, is the compression of the lifter. Even the video doesn't address this. Am I correct in assuming that a modified hydraulic lifter is needed in making these measurements? Modified to be a solid roller lifter that is.
The video doesn't need to worry about compressing the lifter because they have lightweight checking springs holding the valves up. These springs are light enough to hold the valve against the seat and weak enough that they won't compress the hydraulic lifter.
You don't need expensive brand name testing springs. Something from Home Depot etc will still do the job.
The video doesn't need to worry about compressing the lifter because they have lightweight checking springs holding the valves up. These springs are light enough to hold the valve against the seat and weak enough that they won't compress the hydraulic lifter.
You don't need expensive brand name testing springs. Something from Home Depot etc will still do the job.
The article skinnyz references says that measurements could be off by as much as .040" using those 'weak check springs'. Recommends using the intended springs for the build. But also there, no mention of a solid lifter or not.
Following that article also has the lifter on the base circle. In that case it doesn't matter if it's a solid or a hydraulic lifter. It isn't being preloaded. Just the weight of the adjustable pushrod wedged against the rocker arm.
The potentially .040" difference makes you think how much light springs might make a difference. They certainly make it easy to see where the rocker sits on the tip with the marker method but it's a compromise when measuring mid lift. So in reality, it's the running springs for the actual geometry measurements and then a swap out to the light weights to verify the contact patch.
I suppose the question you have to ask is how close do you want to be? That and how much are you prepared to spend if you don't get it right?
Here's a few shots of what it looks like with the adjustable pushrod in, and adding a half turn of preload. The witness mark is just from pivoting the rocker gently on the stud.
Solidify a lifter so that its guts don't affect the push rod length measurement (since if the lifter internals become some amount shorter during your test than they will be when you set to zero lash and then add your desired preload, then your flawed "measurement" will automatically end up calling for a push rod that's that same amount too long), or use a pair of checking springs, and see what happens to the width of the mark over the entire cycle of motion.
Narrowest sweep is best. Ignore where on the stem it falls, within reason. Which the mark in the pic is definitely within reason.
That retainer looks to have a reasonably flat surface to work from.
Perhaps a machinists ruler laid across the top so you can measure to the centres of the trunnion and roller tip axis' (with the lifter on the base circle) ?
So I started over again and decided to try and get the smallest width witness mark possible. Turns out I was pretty close. I tore apart one of my lifters and made it solid to test with. The thinnest witness mark I could get was .046 (which still looks kind of fat compared to some of the pictures I see posted around the net, but oh well), and I was able to achieve this at a length of 7.468. I was originally going to go with a push rod length of 7.45, which I think I'm still going to run with.
I guess I should have asked the real question: Do I trust my half-lift measurement, or do I go buy checking springs and a retainer removal tool so I can verify it?
Well this confirms what I have been saying for years now- that Chris struab/Stupid Technologies method is just a set up for failure to the new enthusiast!
To get an accurate measurement with the adjustable p-rod the lifter has to be at 50% lift. Stupid technologies doesn't even mention that let alone show you how! You need a solid lifter/follower with a flat surface for a dial indicator to measure this. I have send vendors selling these as tools but I make my own from gutted hyd lifters.
Once the rocker is at 90 degrees to the stud for 50% lobe lift and the lobe verified at 50% lift then you swap in the real lifter and adjust the adj p-rod to fit.
If you think you are having problems with the lifter cup staying up or depressing you should check it first by holding it securely on the bench and try and push it in with a p-rod. More than likely you will be surprised and the cup doesn't move as mine only put dents in the block of wood I used to push with. But if it should be found week then yes you can try the weak spring trick and the local home depot/ HW store sells'm cheap.
Hope this can help and please give us feedback with what you find.
Well, using the method demonstrated by Straub got me within 1/32 of an inch. As far as I can tell, that's well within the margin of error for measuring push rod length.
To get an accurate measurement with the adjustable p-rod the lifter has to be at 50% lift.
No it doesn't.
Use full running springs and measure with the lifter on the base circle.
Done.
The witness mark thing can be used to verify location (although that can be done visually) but then you run into problems with hydraulic lifters (not all can be converted into solids).
Well, using the method demonstrated by Straub got me within 1/32 of an inch. As far as I can tell, that's well within the margin of error for measuring push rod length.
Well now I'm confused here as I read you are still trying to get it right. And that picture of the witness mark in post #20 is way off. Is that still the case?? Are you not using an adjustable p-rod? What happened? Did I miss something?
Not trying to flame you here but it reads to me like your still struggling. Though I think you understand what to do now.
"So I started over again and decided to try and get the smallest width witness mark possible. Turns out I was pretty close. I tore apart one of my lifters and made it solid to test with. The thinnest witness mark I could get was .046 (which still looks kind of fat compared to some of the pictures I see posted around the net, but oh well), and I was able to achieve this at a length of 7.468. I was originally going to go with a push rod length of 7.45, which I think I'm still going to run with."
"So I started over again and decided to try and get the smallest width witness mark possible. Turns out I was pretty close. I tore apart one of my lifters and made it solid to test with. The thinnest witness mark I could get was .046 (which still looks kind of fat compared to some of the pictures I see posted around the net, but oh well), and I was able to achieve this at a length of 7.468. I was originally going to go with a push rod length of 7.45, which I think I'm still going to run with."
Yes, why did you not get an adequate witness mark and "start over"? It reads like you thought it was inadequate but looking back with hind sight you think now it was OK?
Regardless its apparent in your own thread here you had to devise your own method for determining/setting up 50% lobe lift. You did reveal this in your efforts here and I don't understand why you are defensive about it.
What I want to show/reveal is this is not a simple operation and for those with little or no experience it becomes an error trap. I read one guy that used that Stupid Technologies video and somehow determined to set his 90 degree rocker angle at TDC! I can provide you with the link of that one if you request.
Well i've said what i can say about this. Take it or leave it but i am glad you got it figured out and shared your experience here - it helps us all.
10-13-2016, 01:52 PM
I can provide you with the link of that one if you request.