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Discussion Starter · #1 ·
In the middle of changing out my heads, I discovered that 9 of my pushrods are damaged... Below are pictures of a few of the pushrods and one of the rocker arms. (The one at right rear is normal-undamaged)

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Wood Metal Auto part Hardwood Steel


Has anyone ever seen this or have an idea why this would happen?
 

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What heads with what springs were on that engine before the change? Looks like either spring coil bind or maybe too many lbs of spring pressure on stock, non-hardened pushrods to me... But someone else may know more. How do your lifters look? Pull them out and put them back in one at a time or mark bores and number them all, storing them in a box numbered the same. I would just pull one then put it back in. Do you know which cylinders and exh/int valve the damaged ones go to? Start there...
 

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Could also be valve float from higher than normal rpm ranges where the spring can't catch up to the speed of the cam lobe and lifter/rod movement so it beats the snot out of the pushrods and rocker arm cup.
 

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Discussion Starter · #5 · (Edited)
Heads are re-worked truck heads from the 70's with pretty stiff springs... They were described as Z28 springs--good up to .550 lift. Not sure about spring pressure but they seem to be visibly a little thicker than the springs I am now installing. Specs on the springs I'm installing are as follows:

Installed Height = 1.7"
Open Height = 1.25"
Open Pressure = 273 lbs/in
Coil Bind Height = 1.150"
Spring Rate = 370 lbs/in.

The pushrods are Summit...least expensive stock replacements I think as are the stamped steel rockers. Rods have welded tips... I did over-rev about a year ago...shifted from 3rd to 2nd :( at speed... Maybe the pushrods were just not strong enough for the springs--especially considering the over-rev...
 

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The Z28 spring is nothing crazy, stock valvetrain components should be fine with it.

More than likely the over-rev could have been the issue

How much lift do you have?? You'll see the "Z28" springs advertised at "good up to .550" lift" but should really never be used beyond about .510" lift.

if you look at what specs you posted....if the spring is set up at 1.7" installed height and opened to .550" lift....that point is 1.150".
That would be Bad news.....1.150" is also listed as coil bind height, as in spring goes stacked solid. That would be bad.
Rule of thumb is stay .060" away from coil bind when valve is at full lift.....so even .510" lift is pushing it at only .040" coil bind clearance.
 

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Like Eric said, the Z/28 springs were only used with stamped rockers. So that in it self shouldn't be an issue. Valve float on the other hand is terrible for a valve train. I even had .080 wall Manley pushrods do that after floating the valves at 7300 in a small block. It developed a tick and I found the rocker loose, readjusted it and it would come back. Eventually pulled 2 pushrods and the one that was loose was noticeably shorter just by eye!!!!
 

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Discussion Starter · #9 · (Edited)
The Z28 spring is nothing crazy, stock valvetrain components should be fine with it.

More than likely the over-rev could have been the issue

How much lift do you have?? You'll see the "Z28" springs advertised at "good up to .550" lift" but should really never be used beyond about .510" lift.

if you look at what specs you posted....if the spring is set up at 1.7" installed height and opened to .550" lift....that point is 1.150".
That would be Bad news.....1.150" is also listed as coil bind height, as in spring goes stacked solid. That would be bad.
Rule of thumb is stay .060" away from coil bind when valve is at full lift.....so even .510" lift is pushing it at only .040" coil bind clearance.
My current cam (same as when over-rev) is .455/.465... So hopefully I'm safe on coil bind with the new springs. I don't know the actual specs on the springs ("Z28") on old heads but the spring specs above are for the springs (Comp 981) in the new heads I'm going to install .

For what it's worth, as far as thickness of the coils, the new springs (specs above) look close to identical to the old ones-maybe a little thicker (("Z28"). Old spring in middle...


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Discussion Starter · #10 · (Edited)
Like Eric said, the Z/28 springs were only used with stamped rockers. So that in it self shouldn't be an issue. Valve float on the other hand is terrible for a valve train. I even had .080 wall Manley pushrods do that after floating the valves at 7300 in a small block. It developed a tick and I found the rocker loose, readjusted it and it would come back. Eventually pulled 2 pushrods and the one that was loose was noticeably shorter just by eye!!!!
Wow--sounds similar to what happened here! Maybe springs just floated and got out of sinc with cam and lifters and beat the rods and rockers... So, Obviously I need new pushrods. I'm thinking to go with one piece pushrods and not the welded tips... Here's what I'm thinking...

JEGS Performance Products 20210: SBC Pushrods 7.800" Long - JEGS High Performance

I'm guessing I should also get new rockers (see picture above) I'm not sure if I should get stamped ones again. Also not sure if there is any advantage to get roller tip rockers like these...

JEGS Performance Products 20186: Cast Steel Roller Tip Rocker Arms for 1955-1986 Small Block Chevy [Set of 16] - JEGS High Performance

PS--- Current pushrod length is stock 7.80". I had checked with Howards Cams about pushrod length with my cam and they said 7.80" stock pushrods would be right. I wonder if I should check pushrod length anyway before I buy any...

Any thoughts?
 

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The .080 wall one piece pushrods are good. I think Summit has the trick flow brand that I have used in the past as well. As far as the roller tip rockers, I never had any use for them. I say either stamped steel or full roller. There is really minimal movement at the tip. The friction is really at the fulcrum. A good stamped steel with the grooved ball is plenty for what you are doing. Unless there is some major difference in the aftermarket head like different valve lengths I would expect the stock length pushrods will be fine.
 

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I'd get the one piece pushrods. Roller tip rockers aren't worth anything, and full rockers aren't worth much more in a mild application like yours. I'd just get a quality stamped steel rocker.

Kevin
 

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Discussion Starter · #14 ·
Thanks guys for all your help with this. Everything you all say makes sense--very helpful. One more question, What's the difference between self aligning VS non-self aligning rockers? The original heads (factory) on my engine had guideplates...Any reason I would/should have these or self aligning rockers?
 

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It depends on the lifter assembly and the head type (pushrod hole location and configuration). What heads are you putting on the motor now? The mfg should tell you what type of rockers to use, but if the new heads have guideplates, you don't need self-aligning as that's what the guideplates do :) . TBI and vortec heads used self-aligning rockers but guideplates are always better.
 

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I would use guideplates but I don't think they're set up for them yet without the screw-in studs and the stud boss being machined for them. You can likely get away without guideplates, just like all the other millions and millions of first gen SBC have for decades...

Per Summit:

Notes:
Will accommodate center bolt valve covers with minor modifications. Features ductile iron seats on exhaust ports only for use with unleaded gas. Machine work must be done to accommodate guideplates. Springs are set up to run hydraulic flat tappet cam only. Coolant temperature sensor threaded hole is 3/8 in. NPT.
 

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Discussion Starter · #19 ·
Okay..thanks. As I look at the top of the current valve stems it looks like rockers have been touching in the center but I am going to check the pushrod length anyway. If it looks good with 7.80" rods I will order the following from Jegs... Based on our discussion, these seem like they should work well... Opinions?


 

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Okay..thanks. As I look at the top of the current valve stems it looks like rockers have been touching in the center but I am going to check the pushrod length anyway. If it looks good with 7.80" rods I will order the following from Jegs... Based on our discussion, these seem like they should work well... Opinions?


regardless of whether things look okay, if you change heads, I would just be safe to measure them out to be sure. Nothing worse than spending time and $ to ruin new components because we forget something or miscalculate a measurement... here's an easier way to measure that uses your eyeballs, not math...



And then an easy way to set lifters after everything is ready to go back together:


And my favorite:

 
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