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Measuring for pushrods...part deux

General engine tech -- Drag Racing to Circle Track

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travis
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Re: Measuring for pushrods...part deux

Post by travis » Wed Jan 15, 2020 6:18 pm

I need to find some lighter springs or pump up my lifters to confirm some numbers. I tried something different just now, which came up with a different number yet :roll:

I found a washer that fit perfectly on top of the snap ring and had a slightly smaller ID than the 5/16” test pushrod. This effectively made the measurement solid. The washer raised the tip of the pushrod 0.135”. I get perfect mid lift geometry with a 7.600” pushrod with this setup. So...7.600+.135+ a little lifter preload...a 7.750” pushrod should be about perfect. I get the same PR length for either the PBM rockers on a 3/8” stud, or the scorpions on a 7/16” stud.

Also...the PBM’s give .544” at the valve (exactly 1.6 ratio), and contact at the intake side of center of the valve tip. The scorpions are giving .568” at the valve (1.67 ratio) and are on the exhaust side of center of the valve tip. There appears to be no risk of either going off the valve. Is the contact point not being closer to center a concern? The sweep patterns for both look good

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Re: Measuring for pushrods...part deux

Post by Geoff2 » Thu Jan 16, 2020 4:03 am

Greater valve lift than the theoretical rocker ratio is usually caused by pushrods being too long. If you need the long-er prods to get the correct geometry, then maybe the rockers are wrong for this combo or something else is wrong in the set up [ valve length? ].

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Re: Measuring for pushrods...part deux

Post by gmrocket » Thu Jan 16, 2020 8:20 am

travis wrote:
Wed Jan 15, 2020 6:18 pm
I need to find some lighter springs or pump up my lifters to confirm some numbers. I tried something different just now, which came up with a different number yet :roll:

I found a washer that fit perfectly on top of the snap ring and had a slightly smaller ID than the 5/16” test pushrod. This effectively made the measurement solid. The washer raised the tip of the pushrod 0.135”. I get perfect mid lift geometry with a 7.600” pushrod with this setup. So...7.600+.135+ a little lifter preload...a 7.750” pushrod should be about perfect. I get the same PR length for either the PBM rockers on a 3/8” stud, or the scorpions on a 7/16” stud.

Also...the PBM’s give .544” at the valve (exactly 1.6 ratio), and contact at the intake side of center of the valve tip. The scorpions are giving .568” at the valve (1.67 ratio) and are on the exhaust side of center of the valve tip. There appears to be no risk of either going off the valve. Is the contact point not being closer to center a concern? The sweep patterns for both look good
Seems like you got it all figured out...those
Original rockers are ok.

Me personally,, I would rather error on the intake side of the sweep if it's one way or the other.

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Re: Measuring for pushrods...part deux

Post by travis » Thu Jan 16, 2020 10:16 am

Valve length has got to play into here somewhere too I would think. These aftermarket heads have shorter valves (sbc length) than stock ford heads. I think I’ll mock one of my OEM heads up with these rockers and see what happens.

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Re: Measuring for pushrods...part deux

Post by PRH » Thu Jan 16, 2020 10:31 am

It’s possible that that particular aftermarket head doesn’t really have all the placements and angles properly sorted out.


How about a pic of the new rockers on the heads, lifter on base circle, with what you feel like are the correct length pushrods.

Here’s an experiment you could try.......

Shorten the pushrod .050 at a time, and measure the lift each time..... along with the tip placement.
I would do this test using the full spring load.

See how much shorter the pushrod would have to be to get the fully loaded rocker arm closer to showing .544 valve lift.
Somewhat handy with a die grinder.

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Re: Measuring for pushrods...part deux

Post by travis » Fri Jan 17, 2020 6:53 pm

PRH wrote:
Thu Jan 16, 2020 10:31 am
It’s possible that that particular aftermarket head doesn’t really have all the placements and angles properly sorted out.
I think this pretty well sums it up. The scorpions tip is better centered on the valve tip at mid lift on my D0OE iron heads with the right pushrod length for best geometry. I don’t really like how the scorpions are on the exhaust side of valve tip center, but iiwii at this point.

I triple checked all my measurements. I can’t test with the weak stock ford springs I have because they coil bind around .510” lift. The dual springs I have will destroy my PR length tester (I guess I need to get something stronger to test with). With my light test springs, to get to .544” lift at the valve I need a much shorter pushrod which throws the geometry WAY off.

The max lift I can get at the valve is .572” (with the washer on the lifter making it solid) with a 7.650” PR length which gives excellent geometry. Going .050 longer or shorter starts losing lift...about .568”, and the lift starts falling off faster the farther longer or shorter I get away from 7.650”, and the geometry at mid lift gets worse.

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Re: Measuring for pushrods...part deux

Post by travis » Fri Jan 17, 2020 6:55 pm

Pics at 7.600” PR length...

CB20CAD3-C106-4B23-AE09-34C89FC64B7A.jpeg
6ECCF0F3-6169-4422-968A-40CA1E6D59A4.jpeg
20C84957-E68D-4C9A-B4FE-54A6CDA5CED5.jpeg
4CC86166-A0A6-4993-A51D-3176F816DA9D.jpeg
You do not have the required permissions to view the files attached to this post.

travis
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Re: Measuring for pushrods...part deux

Post by travis » Sat Jan 18, 2020 7:42 am

PRH wrote:
Wed Jan 15, 2020 12:20 pm
..... how I do it with hyd lifters is, I use very light checking springs and I fill the lifter with oil.
The springs are light enough to not compress the lifter at all.
Do you have a part number for these super light springs? I now have 3 pairs of test springs from different companies that all appear to be exactly the same...and too heavy to not compress the lifter plunger

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Re: Measuring for pushrods...part deux

Post by jed » Sat Jan 18, 2020 10:04 am

Have you tried Lowe's, Home Depo or Elliot's hardware or Ace hardware. I think the last time I got my springs
I got them from Elliot's hardware.

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Re: Measuring for pushrods...part deux

Post by PRH » Sat Jan 18, 2020 10:14 am

I bought my really light checking springs at a small hardware store about 35 years ago.

I can very easily compress them solid by squeezing them between my finger and thumb.
It might be 5lbs of load to make them solid(probably less).


In the pics........You still have the pushrods a bit longer than how I’d have them.
Somewhat handy with a die grinder.

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Re: Measuring for pushrods...part deux

Post by travis » Sat Jan 18, 2020 12:08 pm

Hmm... I’ve checked 4 local Lowe’s and Home Depot’s and found nothing remotely close. I guess I can check some of the smaller places today...

You think the setup in the pics is too long? The pic with the straight edge is at mid lift, and actually needed another .050” for the“perfect” parallel lines between the retainer and the roller/trunion centerline. But...the valve tip contact shows that the PR is too long...

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Re: Measuring for pushrods...part deux

Post by PRH » Sat Jan 18, 2020 12:10 pm

Have you tried determining the pushrod length exactly the way it’s outlined in the Straub rocker geometry video?
Somewhat handy with a die grinder.

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Re: Measuring for pushrods...part deux

Post by PRH » Sat Jan 18, 2020 12:18 pm

The “line” is from the center of the roller to the center of the trunnion.
Laying something on the retainer is used as a visual guide to get the “line” parallel to the top of the retainer.

Where the roller sits on the valve tip, after the geometry is set, is a function of where the stud is in relation to the valve...... and the length of the rocker arm.

It is not used as part of determining the correct “geometry”.

You should put the line on the rocker.

Try it like in the Straub video....... which doesn’t require turning the motor over at all.

In a nutshell......
Starting with the adjuster nut positioned so the “line” is parallel with the top of the retainer with the valve closed..... with your .544 lift cam and a 7/16” stud....... run the adjuster screw down just under 5.5 turns(5.44 turns).
(With a 20 thread pitch...... .050” per turn......., the number of turns from the point of the line being parallel to the retainer is the same as the valve lift x 10)

Then, With the lifter on the base circle, adjust your checking pushrod to achieve zero lash.
That PR length(plus whatever you want for preload) is what you should get for 1/2 lift geometry.

I believe it was mentioned by John Schmidt in the previous thread that some OEM’s prefer the trunnion/fulcrum be positioned slightly below where it would be for 1/2 lift geometry.

I would say that’s probably where I usually end up with stud mounted rockers....... with the trunnion slightly below 1/2 lift geometry.
Somewhat handy with a die grinder.

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Re: Measuring for pushrods...part deux

Post by PRH » Sat Jan 18, 2020 1:42 pm

In the first thread you wrote:
With the Scorpion rockers in place, using the Straub method mentioned earlier in this post, at .272" valve lift (1/2 max lift), I get a length of 7.750" when testing in .050" increments.
I don’t understand the “in .050” increments” part.

Valve fully closed, set adjuster nut to achieve the parallel line, lower rocker .272(5.44 turns).......from that point, adjust checking pushrod to zero lash with lifter on the base circle.
Done.

This would be with the lifter pumped up, pushrod cup up against the snap ring.

As Walter pointed out in the first thread, this will only really be “correct” if the rocker was designed to be set up for 1/2 lift geometry.

You should go re-read through that first thread...... take in all that was posted.
Lots of good info there.
Last edited by PRH on Sat Jan 18, 2020 2:20 pm, edited 1 time in total.
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Re: Measuring for pushrods...part deux

Post by travis » Sat Jan 18, 2020 2:11 pm

The “in .050 increments” comment was based on my PR length tester (comp cams 7702), which measures in .050” increments.

Let’s just add this to my recent string of WTF moments (which have been happening more and more lately). I watched the Straub video 2 or 3 times before trying it that way, and still ended up combining 2 different methods apparently. I don’t know wtf is going on with my head lately...

I’ll mock everything back up this afternoon and try again, maybe even correctly this time. I pulled the head off to start putting the valve train together, only to find the installed heights all over the place. Time to order some shims...

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