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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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Measuring for pushrods...part deux

Post by travis » Mon Jan 13, 2020 11:48 pm

After the first couple of rounds of measuring for pushrod length, I didn’t have a warm fuzzy feeling about the numbers I was coming up with, and seemed to have trouble getting any sort of consistency. So...I threw all the previous info out and started over.

I built a better base to attach to the valve cover holes for my magnetic base to start with, which makes my numbers much more repeatable now. That, and locking the garage door to keep the distractions out :lol:

For best mid-lift geometry, which also gave me max lift at the valve, I came up with 7.900” with the lifter plunger fully depressed (about 0.0875” of plunger travel). Varying.050” either way gave less lift at the valve. So I “think” that PR length is good. But...it looks like 7.900” is too long judging by the contact pattern on the valve tip...

1EC197EE-BB65-406B-BBB5-54298D4BB424.jpeg

The PBM rockers showed a contact pattern closer to the intake side, while these Scorpions are closer to the exhaust side.

Something else that is throwing me off. Lift at the valve is repeatedly measuring.572-.573” even with different rockers out of the same box. The cam is .340” lobe lift (measured), which means my rockers are measuring about a 1.685 ratio at peak lift. This seems...wrong...but I get those numbers repeatedly even after tearing my measuring setup down and putting it back together.

Am I doing something wrong???
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Re: Measuring for pushrods...part deux

Post by bobmc » Tue Jan 14, 2020 5:26 am

what engine is this? your math must take pushrod angles into account when converting lobe lift into valve lift

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Re: Measuring for pushrods...part deux

Post by travis » Tue Jan 14, 2020 6:03 am

bobmc wrote:
Tue Jan 14, 2020 5:26 am
what engine is this? your math must take pushrod angles into account when converting lobe lift into valve lift
351w, import aluminum heads, small hydraulic roller. Valve lift was measured at the retainer.

With a 1.6 ratio rocker I should have .544” lift

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Re: Measuring for pushrods...part deux

Post by bobmc » Tue Jan 14, 2020 6:35 am

I don't know anything about the 351W so no advice, I believe many chevy rocker manufacturers cheat a little bit on the listed ratio to make up for the pushrods angling away from the ports

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Re: Measuring for pushrods...part deux

Post by travis » Tue Jan 14, 2020 6:43 am

I know some rockers do give more than advertised, but this seems excessive.

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Re: Measuring for pushrods...part deux

Post by tenxal » Tue Jan 14, 2020 7:35 am

With the real spring on there, it's going to change.

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Re: Measuring for pushrods...part deux

Post by GARY C » Tue Jan 14, 2020 7:52 am

travis wrote:
Tue Jan 14, 2020 6:43 am
I know some rockers do give more than advertised, but this seems excessive.
Some rockers do show more at set up but that usually reduces with the actual spring and probably accounts for some flex when running.
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Re: Measuring for pushrods...part deux

Post by CGT » Tue Jan 14, 2020 8:44 am

Rockers can be all over the place in terms of ratio. Be happy yours off to the good. Maybe try checking the ratio at some points other than max lift....see if you find anything interesting.
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Re: Measuring for pushrods...part deux

Post by 77cruiser » Tue Jan 14, 2020 8:50 am

My Scorpion 1.65 rockers show just about 1.7, & the 1.5 were close to 1.55.
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Re: Measuring for pushrods...part deux

Post by Schurkey » Tue Jan 14, 2020 1:45 pm

travis wrote:
Mon Jan 13, 2020 11:48 pm
For best mid-lift geometry, which also gave me max lift at the valve, I came up with 7.900” with the lifter plunger fully depressed (about 0.0875” of plunger travel). Varying.050” either way gave less lift at the valve. So I “think” that PR length is good. But...it looks like 7.900” is too long judging by the contact pattern on the valve tip...
...so you'd be ordering a 7.850 pushrod, unless you want to run the lifters fully collapsed. That gets you about .0375 of static lifter preload

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Re: Measuring for pushrods...part deux

Post by gmrocket » Wed Jan 15, 2020 7:42 am

travis wrote:
Mon Jan 13, 2020 11:48 pm
After the first couple of rounds of measuring for pushrod length, I didn’t have a warm fuzzy feeling about the numbers I was coming up with, and seemed to have trouble getting any sort of consistency. So...I threw all the previous info out and started over.

I built a better base to attach to the valve cover holes for my magnetic base to start with, which makes my numbers much more repeatable now. That, and locking the garage door to keep the distractions out :lol:

For best mid-lift geometry, which also gave me max lift at the valve, I came up with 7.900” with the lifter plunger fully depressed (about 0.0875” of plunger travel). Varying.050” either way gave less lift at the valve. So I “think” that PR length is good. But...it looks like 7.900” is too long judging by the contact pattern on the valve tip...


1EC197EE-BB65-406B-BBB5-54298D4BB424.jpeg


The PBM rockers showed a contact pattern closer to the intake side, while these Scorpions are closer to the exhaust side.

Something else that is throwing me off. Lift at the valve is repeatedly measuring.572-.573” even with different rockers out of the same box. The cam is .340” lobe lift (measured), which means my rockers are measuring about a 1.685 ratio at peak lift. This seems...wrong...but I get those numbers repeatedly even after tearing my measuring setup down and putting it back together.

Am I doing something wrong???
Are you sure your full plunger travel is .0875"? That's seems like it's not enough for a typical hydro lifter

Was it at the top butting against the snap ring when you first started?

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Re: Measuring for pushrods...part deux

Post by travis » Wed Jan 15, 2020 8:30 am

Yes, it was at the top against the snap ring when I started. But...I’m not completely convinced that .0875” is right either. I think my “light” testing springs are throwing me off. I’ve got some more testing to do before I’m comfortable with my measurements being right. And possibly a call to Howard’s to see if they have an exact number on plunger travel. My gut feeling is that something still isn’t right.

Is it obvious that I haven’t messed with linked hydraulic rollers before? Maybe it’s time to switch to a solid roller, get a solid measurement, and move on with my life :lol:

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Re: Measuring for pushrods...part deux

Post by FC-Pilot » Wed Jan 15, 2020 12:06 pm

travis wrote:
Wed Jan 15, 2020 8:30 am
Yes, it was at the top against the snap ring when I started. But...I’m not completely convinced that .0875” is right either. I think my “light” testing springs are throwing me off. I’ve got some more testing to do before I’m comfortable with my measurements being right. And possibly a call to Howard’s to see if they have an exact number on plunger travel. My gut feeling is that something still isn’t right.

Is it obvious that I haven’t messed with linked hydraulic rollers before? Maybe it’s time to switch to a solid roller, get a solid measurement, and move on with my life :lol:
You may have had .0875 at the stud, but being that the pushrod cup is past the stud it was multiplying the travel to the pushrod cup. So yes there is more travel there in the lifter, but not a huge amount more. If I were in your shoes, it looks like you got a decent measurement and as long as it looks pretty decent on the pushrod cup side I would run it. It is not like you are trying to spin this thing 8500. I hate to say it, but unless it truly is a max effort build, darn close really is close enough.

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Re: Measuring for pushrods...part deux

Post by PRH » Wed Jan 15, 2020 12:20 pm

Retest with full spring load.

I wouldn’t at all be surprised to see your plunger travel end up greater than .0875.

However....... 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.

After doing the checks and adjustments to where I’m satisfied with the geometry, I measure the checking pushrod and add however much lifter preload I want to the observed length.
Somewhat handy with a die grinder.

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Re: Measuring for pushrods...part deux

Post by CGT » Wed Jan 15, 2020 12:39 pm

PRH wrote:
Wed Jan 15, 2020 12:20 pm
After doing the checks and adjustments to where I’m satisfied with the geometry, I measure the checking pushrod and add however much lifter preload I want to the observed length.
That's how I've always done it as well. If the valvetrain is adjustable, and someone is really hung up on pushrod length down to .025 or .050, that pushrod length "setting" is just a different preload amount away really.
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