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Broken rockers after cam

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Old 02-25-2017, 04:57 PM   #1
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Default Broken rockers after cam

Ls1 stock
799 heads with 0.40 cometic gasket
Brutespeed blower cam Dur @ .050 232 int 240 exh
Lift .595 int .608 exh LSA 115.0
PAC max life beehives .625 lift max
Patriot 7.40 pushrods
Stock rockers tq. @ 22ft/lbs

I fired it up after swapping in the cam and the oil pressure was consistently between 55-60psi, the car idled great, no smoke or misfires, but the valvetrain sounded like a sewing machine. I expected it to be loud for a few seconds on initial start but it stayed pretty loud. The car idled for a total of 2 min. and I couldn't take the sound of the valvetrain anymore so I shut it off. I pulled the valve covers off and 2 of my rockers caps had come off and the roller beads were laying just underneath.

I've read a few posts about stock rockers breaking after a cam install, but I was wondering if you all think it could be something else? I went ahead and ordered the Comp truion rebuild kit and Comp 7.425 pushrods to give those a try.
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Old 02-25-2017, 05:21 PM   #2
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Usually break from coil bind. Can you post pic of how they are now or is it tore down already. Longer pushrods will only make the problem worse.
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Old 02-25-2017, 06:00 PM   #3
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Old 02-25-2017, 07:44 PM   #4
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Time for trunnion bushings........
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Old 02-25-2017, 08:27 PM   #5
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Pretty common unfortunately. Just replace the trunions with an upgrade kit and you should be good to go.
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Old 02-25-2017, 09:17 PM   #6
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Measure for correct push rod length and lifter preload load after you fix the rockers.
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Old 02-25-2017, 10:28 PM   #7
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Yeah I just ordered a truion kit. I'm happy to hear that it's a semi common issue. I actually have a pushrod length checker I just need to figure out how to use it with hydraulic lifters. I have LS7 lifters do they have a standard preload or do I need to compresse all of the oil out and figure it out with a micrometer?
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Old 02-26-2017, 12:35 AM   #8
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Measuring pushrod length is easy.

Drop your checker in (I'd put tape on it so it doesn't move on you - but loose enough you can turn it) and put the rocker on the pedestal and hold it with your finger. Turn the motor over so you're on the base circle of the cam (usually if the exhaust begins to open, you're on the base of the intake and vice versa). Adjust the checker until you no longer have up and down clatter when you try to move the rocker. At that point, you're at zero lash.

Remove the checker and measure it with a caliper. That measurement @ zero lash + desired preload = overall pushrod length. Some pushrods are sold cup to cup for an "effective" length. So you just have to specify when you order that you are providing the overall length. I believe the Comp checker tool if you do the rotation crap gives you the effective length. Don't rely on that. Tape the checker and hold it steady and measure with a digital 8" caliper. Harbor Freight has one for $20 with a coupon.

Repeat several times. Pick an intake an exhaust valve from each side at least. And then get the average value with 2-3 measurements each. You should be within .010-.015" across all those measurements. Then you have a good figure without compression the lifter.

But the whole point is you need to find the length @ zero lash. All that means is the measurement of a pushrod with just enough length to take all the slack out of the system. And then you need to add preload since it's a hydraulic lifter. With the LS7s, .060-.080" is a good value.
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Old 02-26-2017, 07:02 AM   #9
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I would check for coil bind as well, i.e., coil clearance at open. You have springs rated for 0.625 lift and lift of 0.608 so this is something that should be carefully checked. Not sure if you checked the installed height but you will likely find is less than 1.800 so you may be closer than you think.
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Old 02-26-2017, 08:10 AM   #10
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^I second that motion
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Old 02-26-2017, 08:49 AM   #11
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Evidently Trend makes Comp's pushrod length checker tool, and the measurement taken with a caliper across the ends is the effective length. Meaning that you don't have add any additional length (such as .0085" per ball end) when ordering, what you read on the caliper is the length you want. I did all 16 holes when I was measuring my junk; there was a .022" variance - so it pays to know what you have even if you have forgiving lifters.

Cool tip on the tape to add drag to the checker. I just called upon my mad Game of Operation skills to pull the checker out undisturbed. Then I triple checked the measurements.
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Old 02-26-2017, 11:57 AM   #12
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Thanks everyone and Jakefusion the way you explained it makes it much simpler than the instructions that came with it!
I'll try to measure my coil bind also to see if that's an issue. I may need to buy a set of dual springs so I'll have a little more forgiveness and not be so close to the springs max lift.
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Old 02-26-2017, 12:17 PM   #13
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Yeah it's not hard once you figure it out. The trick is getting it right to the point where the clatter is gone.

Another thing I'd do to help hold to the pedastal is flip a bolt upside down and push down on the trunnion. That way you know it's tight against the pedastal.

Also check the coil bind. While you have the rockers off for the trunnion upgrade.
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Old 02-26-2017, 12:31 PM   #14
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Use Teflon tape on the threads of the length checker....Works great!
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Old 02-26-2017, 12:38 PM   #15
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The springs should have a min-length spec (shortest they should be compressed) On my last motor build I had to have the spring pockets machined .060 deeper to accommodate the only spring that would work with my cam/valve/head/rocker configuration.
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Old 02-27-2017, 12:25 PM   #16
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Quote:
Originally Posted by pdxmotorhead View Post
The springs should have a min-length spec (shortest they should be compressed) On my last motor build I had to have the spring pockets machined .060 deeper to accommodate the only spring that would work with my cam/valve/head/rocker configuration.
But you don't want to do that on most LS heads, especially ported ones. There isn't a whole lot of meat below the spring pad so you could risk it cracking or completely breaking apart. You would probably be better off with +.100" valves.
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Old 02-27-2017, 02:46 PM   #17
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I went ahead and ordered a set of PAC 1904 dual springs to prevent the possibility of coil bind. Hopefully by the end of the week I'll have it back together and I can give you guys an update.
Do you think I need to check for coil bind on the new springs too?
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Old 02-27-2017, 03:04 PM   #18
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I would just to be safe. Just measure your installed spring height, and get it to what PAC recommends and you'll be fine.

What does the tip of the valve look like under that rocker? It looks a little chewed up almost.
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Old 02-27-2017, 08:06 PM   #19
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Quote:
Originally Posted by PowellSixO View Post
I would just to be safe. Just measure your installed spring height, and get it to what PAC recommends and you'll be fine.

What does the tip of the valve look like under that rocker? It looks a little chewed up almost.
Awesome I will thanks! I didn't even look at the tip but now that you say that it does look chewed up. I'll have to look at it when I get home tonight. *cross fingers*
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Old 03-15-2017, 08:06 PM   #20
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Update* The issue ended up being PTV clearance! Ugh.
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