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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Ronno6 on February 01, 2019, 01:58:05 pm
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355 SBC 880 roller block.
LT4 Hot Roller Cam
GM Hyd. roller lifters
Scorpion Race Series Roller rocker arms
Comp Cams high energy pushrods 5/16 X 7.205" (7808-16)
aftermarket aluminum heads
7/16" rocker studs
Erson guide plates
In my initial attempts to check pushrod lengths, I have tested 2 cylinders.
So far, I have seen 1 pushrod a tad too short,
1 pushrod a tad too long, and
2 pushrods that appear to be right where they should be.
I understand that the desired roller to valve stem contact patch is dead center across the valve stem.
Is there an acceptable tolerance for that?
I am using hydraulic roller lifters. I have read that those will tend to minimize minor
deviances of contact patch locations (pushrod lengths.)
Is it conceivable that there will ultimately be several different pushrod lengths in 1 engine?
At this time I am not satisfied with the alignment of the rocker arms.
I am awaiting delivery of self aligning roller rocker arms before doing this test in earnest.
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Do you have them out on a table and comparing the length side by side?
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Do you have them out on a table and comparing the length side by side?
Not currently, but I will.
As an update, I checked all 8 on the same head; 6 dead center, 1 high, 1 low by less than half the width of the contact patch.
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Flat cam or collapsed lifter could cause the perceived difference. I bet they are all the same length or at least they should be.
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Lay a straightedge along the valve stem tips to see whether they are all the same height.
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Lay a straightedge along the valve stem tips to see whether they are all the same height.
I'll do it!
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If the valve stem heights with the valves closed are equal, the pushrods are shown to be equal length, the lifters have uniform dimensions and piston heights, and the rocker arms have uniform ratios and dimensions, then you have an error in your method of determining correct pushrod length. While checking, bear in mind that hydraulic lifters collapse under valve spring pressure. This introduces a wild card while attempting to determine pushrod length. To compensate for this, temporarily swap the stiff single or dual valve springs installed in the heads for low pressure "valve checking springs."
Upon re-reading your initial post, do you realize that pushrod guide plates are adjustable? Have you attempted to adjust them? If you proceed to use self-aligning rockers, be sure to remove the guide plates to prevent valvetrain binding.
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I had adjusted the guide plates to get the best rocker to valve alignment possible, but I was not able to align things to my satisfaction on every valve.
I am considering guide plates which allow for c to c spacing adjustment between each pair of pushrods/rocker arms, but I have optet to purchase self-aligning rocker arms.
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Do you have them out on a table and comparing the length side by side?
Laid out pushrods on a table and put straight edge across both ends.
They are about as dead nuts equal li length as that method can measure.
Also placed a straight edge across the valve stems and they too are even.
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Do you have them out on a table and comparing the length side by side?
Laid out pushrods on a table and put straight edge across both ends.
They are about as dead nuts equal li length as that method can measure.
Also placed a straight edge across the valve stems and they too are even.
as they should be. Lifters collapsed would be the likely cause
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A new wrinkle, possible cause of some of my problems: eccentric rocker arm studs.
The machine shop supplied me with PBM 5183 studs.
I noticed a pretty pronounced wobble as I screwed them in and out.
Roughly measured the runout on these to be .012" or greater.......
Put a high one nest to a low one and .024" difference can be realized.
I have read that some studs are out by as much as .030"...!!!!
That can really "screw" things up.........
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So a 'wobble' would indicate the stud is bent, yes?
And you said the machine shop supplied them?
Take them out and place against a straight edge and replace as needed.
But how did they get bent??? ???
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So a 'wobble' would indicate the stud is bent, yes?
And you said the machine shop supplied them?
Take them out and place against a straight edge and replace as needed.
But how did they get bent??? ???
No...not bent.
Place a straight edge across studs and some have gaps to the straight edge that close when the stud is turned.
The gap is parallel all the way down to the base.
The center of the top portion of the stud is not concentric to the bottom thread..nit on the same center.
Kind of like a cam......
ARP centerless grinds theirs so that the top and bottom sections are concentric within .005"
Got some comin...........
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OK. I ordered and received the Proform 66790 pushrod length checker.
Using that gauge I determined my 7.205" pushrods were .045" too short.
I lucked into a set of Comp Cams 5/16 x 7.250" pushrods for a great price.
Those should be perfect !!