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  #46 (permalink)  
Old 03-02-2012, 02:19 PM
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Mid-Lift Measuring Help

I apologize for hi-jacking this thread but I'm in the middle of assembling my 409 SBC and found Jim's mid-lift technique fascinating and I totally get it.
Since I am assembling the valve train myself and my time costs me nothing, I really want to utilize the mid-lift method for obtaining proper pushrod length.
The issue I am running into is that I am having a hard time figuring out how to measure everything properly/accurately in order to determine correct pushrod length.

My set-up is using 195cc Profiler heads with 1.6, 7/16" stud Scorpion roller rockers and a solid flat tappet Lunati cam. The heads have 'beehive' springs so the retainers are small diameter and not flat/parallel to the valve tip so I cannot use that as a point of reference.
I'm thinking I may be able to figure this out as a geometry problem but unfortunately, I don't know the exact distances between the rocker stud to valve stem or the angle of the stud in relation to the valve stem.
I also don't know the exact distance between the trunnion and the roller tip or trunnion to pushrod cup (center to center) so what are my other options?

About the only dimensions I do know are the trunnion and roller tip diameters and the rest I can 'guesstimate' but that's not close enough for my taste.

If anyone (Jim or other) can provide some insight on the best way to get this measured accurately, I would MOST appreciate it!
Thank you for your time.
Elm

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  #47 (permalink)  
Old 03-05-2012, 01:51 AM
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Mid lift rockers

It is hard to precisely check for correct geometry. I also had beehive small retainers, so I got some right angle aluminum stock and drilled a hole just big enough to go over the valve stem and sit on the top of the retainer. The other end of this right angle sat along the side of the rocker arm passing the rocker center shaft. You have to use some math here to allow for the stem tip height, the thickness of the aluminum stock etc. But the concept is to mark the exact center of the rocker trunnion and compare it's location to the center of the rocker tip axle. The tool I built allowed me to get the 90 degrees off of the retainer and project it to the center of the rocker. Using this method with the valve closed, my understanding was that you want the rocker trunnion center one half of your valve lift below the center point of the rocker tip axle. Of course, it's going to depend on correctly calculating the measurements. I did this as a second check, after first using an adjustable 1/8" wall pushrod and checking every .025" as I lengthened the pushrod for both pushrod "in and out" motion with a dial indicator as well as contact pattern using bluing at the valve stem tip. As you proceed, you'll understand as you observe the pushrod move in and out less, and hopefully the contact swipe on the stem get narrower as you approach then pass the best point. Going past optimum, you should observe the deflection increasing and the swipe widening. As I posted earlier, I could not get both ends with the first rockers I tried, but with the actual Miller rockers the deflection and the tip pattern were both good. There may now be other rockers out there that will check well at both ends, if someone has done these checks with others please post your findings. I am no expert, all I know is from reading the postings and from Jim Millers web site, then spending lots of time on the engine stand going through the tests. I did need to get a different "foot" for my dial indicator to ride on the pushrod and track the deflection. When I figured I had it pretty good, you could see the pushrod move away from the stud as you opened the valve, then after half lift it would begin moving back towards the stud as you fully opened the valve. Wow, long post with one finger...lol hope this helps....
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  #48 (permalink)  
Old 03-05-2012, 08:08 AM
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Grant4060,
Thank you for the reply!

I spent 1/2 the day yesterday measuring and re-measuring and I believe I'm as close as I'm gonna get (and probably way closer than it's ever been!).
I ended up taking a small stainless 'L' shaped ruler and was able to lay it square on the valve stem tip and supported the end going towards the intake by installing a set-screw in the valve cover bolt hole and adjusting it to be perfectly level with the valve stem tip.
From there I was able to mark the center of the trunnion on the rocker and then adjusted the length of my adjustable pushrod to get the appropriate 'mid-lift' dimension.
Even though it took a while and I double and triple checked everything, I'm glad I did the exercise as my pushrod length turned out to be WAY longer than I would have otherwise expected.
With the 1.6 7/16" Scorpion roller rockers I'm running, my pushrods measured out to be about 8.080" long. At first I had thought I missed something because I've never seen pushrods that long but the witness marks on the tips indicate about a .030 wide mark and almost perfectly centered on the tip at that length.

I didn't go as far as measuring the pushrod movement like you did as that would have taken me another whole day to figure out ;-) but I'm glad I did what I did.

Thanks again for the tip!
Elm
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  #49 (permalink)  
Old 03-05-2012, 10:57 AM
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Originally Posted by ezobens
Grant4060,
Thank you for the reply!

I spent 1/2 the day yesterday measuring and re-measuring and I believe I'm as close as I'm gonna get (and probably way closer than it's ever been!).
I ended up taking a small stainless 'L' shaped ruler and was able to lay it square on the valve stem tip and supported the end going towards the intake by installing a set-screw in the valve cover bolt hole and adjusting it to be perfectly level with the valve stem tip.
From there I was able to mark the center of the trunnion on the rocker and then adjusted the length of my adjustable pushrod to get the appropriate 'mid-lift' dimension.
Even though it took a while and I double and triple checked everything, I'm glad I did the exercise as my pushrod length turned out to be WAY longer than I would have otherwise expected.
With the 1.6 7/16" Scorpion roller rockers I'm running, my pushrods measured out to be about 8.080" long. At first I had thought I missed something because I've never seen pushrods that long but the witness marks on the tips indicate about a .030 wide mark and almost perfectly centered on the tip at that length.

I didn't go as far as measuring the pushrod movement like you did as that would have taken me another whole day to figure out ;-) but I'm glad I did what I did.

Thanks again for the tip!
Elm
OMG you guys are really stretching this. Perfect, even with Miller rockers you're never gonna get. Your stuck somewhere with minimizing lift loss and not adding a lot of guide wear.

Minimizing lift loss is a racers problem and often the trade is more wear on the stem and guides but since these engines see frequent inspections, corrections, and overhauls the wear issues with offset loads on the stem and the containment of big time spring pressure is managed by frequent service. So oil consumption down the guides will be headed off well before it occurs.

Oil down the guides is a several pronged problem.
1) Lubricating oil fosters detonation. This is also true of diesels.
2) It is baked on to the backside of the valve (coking)
a) obstructing flow
b) reducing heat transfer from the valve head and stem base,
overheating the same.
c) adds weight to the valve that the valve spring has to manage.

So while many "experts" including Smokey write that offset loading on the stem doesn't cost power of itself, it does cost power in the longer term by resulting in wear that allows oil to enter the growing clearance between the guide and stem. For a street engine, even a hot one, getting some miles up into the 10s of thousands if not 100s of thousands is of greater importance than loosing a few tenths of a percent of lift so in this case you pay more attention to keeping the contact point closer to the center of the valve stem. But for a street engine with milder rate valve springs even this worry is somewhat less. Given the desire to achieve high mileage, the valve system on street engines is not going to see service until the situation of oil consumption down the guides becomes intolerable.

Of course you don't want to run off the stem, if your testing has the contact point getting within .020 inch of the edge, I recommend lash caps to put a larger diameter contact surface under the roller tip. This of course will lead to a new set of tests to determine the proper length push rod.

The nice thing about Miller Mid Lifts is you could have both minimum loss of lift and load offset on the stem.

Bogie
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  #50 (permalink)  
Old 03-07-2012, 12:28 AM
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Mid lift rockers

Bogie, you may be right and it is quite an effort to check all this, but I'm more interested in two other factors mentioned by Jim Miller. Firstly in my mind is reducing friction and drag to turn over the engine. Miller claims there can be a substantial reduction of torque required to rotate the engine assembly with spark plugs removed if the geometry is optimized. Secondly, the transfer of camshaft profile to the valves with the least loss due to deflection. I agree that the racing engine will be torn down frequently, long before guide wear would occur. In my particular combination, I had to be about .200" long to get the geometry as I understand it should be from reading Miller's method, that is quite a major difference I feel. On the dyno the engine definitely made more power, but in fairness there were other adjustments so we'll have to test at the track to really know if we've been successful. In a perfect world, someone would do all this with no other changes and dyno before and after, but with time and money constraints we incorporated this change along with a few other things on this build. Great subjects, lots of quality debate! I would have known nothing about this if not for reading this and another thread here to get me thinking about it, thanks everyone!!
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