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Broken Rocker Arms

This is a discussion on Broken Rocker Arms within the Internal Engine forums, part of the LSx Technical Help Section category; I have an 01 TA. TQv2 cam, hardend pushrods 7.4, Stage 2.5 heads. I broke two rocker arms in the ...

  1. #1
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    Broken Rocker Arms

    I have an 01 TA. TQv2 cam, hardend pushrods 7.4, Stage 2.5 heads.

    I broke two rocker arms in the past week. I went a bit cheap and bought the Jegs brand Alum. Rollers. I wasnt over reving when they broke. I was thinking that they are not strong enough for the double spring tention. Does this sound right? I was thinking about upgrading to Comp Pro Mags. They are breaking on the pushrod side.
    When I replaced the first one the engine ran great for two days then another one broke. Im getting tired of pulling off the valve cover and replacing these. Someone please give me a for sure answer to this problem. Thanks.

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    Veteran Hi-Po's Avatar
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    A for sure answer would be to put the stockers back on there. There light, and very strong. Then to go a step further, get the Harlan or COMP trunnion upgrade. Do your heads have bronze valve guides? Assuming stock valve angle?
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    Member marksls1ta's Avatar
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    have you checked the pushrod length to make sure the 7.4 are the correct length for you?

    also what rpm range have you gotten the car to before they broke?

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    Which 2.5 heads do you have? I have the 5.3 stage 2.5 with a 228r cam and the Jegs lifters as well. The rocker wipe pattern looked good on the valve, but zero lash seems to be way off with a 7.4 inch pushrod. It's like the pushrods need to be much shorter. Even so, I wouldn't think it would matter unless you hit coil bind. I hope not or I'm going to be buying new rockers as well. I couldn't find any info on those rockers so I thought I would take a chance.

    The LS7 lifters I am running have a lot of travel past where you first find spring tension on the lifters. You wont notice it if you presoak your lifters in oil.

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    I ran a pushrod checker on those Jeg's roller rockers and came out with 7.25 for zero lash. Depending on how much preload you want to run that puts your pushrods at about 7.3 to 7.35. 7.4's are too long. I still don't think they should have broke the rocker. We'll see. I have the PRC double springs as well.

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    Veteran Hi-Po's Avatar
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    One of the most common causes of a broken rocker is improper push rod length.

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    Quote Originally Posted by Hi-Po View Post
    One of the most common causes of a broken rocker is improper push rod length.
    I wouldn't think that it would be a problem unless you were bottoming out the coil. Which may be exactly what is happening because .1 is pretty big to be off on the rocker side which translates to .17 on the valve side. I'm going to run the Jeg's rockers and see what they can do. It's good to know cheaper alternatives.

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    also you said your not over reving but if your going off a stock tach they tend to be a bit lazy...May want to go with a shift light or aftermarket tach. i know far fetched but was happening to me on my old stroker motor

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    I found out that the JEGS rockers max spring load is about 20lb less than the double springs on the PRC 5.3 stage 2.5 heads when fully open. I cant remember what the exact numbers are but im going to run my stock rockers which were recomended by Texas-speed. I wouldnt run the JEGS rockers, go the extra mile and spend a few $ more for like harland sharp or comps rockers if your hell bent on getting aftermarkets. The horsepower gain isnt going to be noticed on the track or the street.

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    You should check the rockers you still have in there to see if your coil binding the spring. this will snapp a rocker in a heart beat.
    Last edited by JaycenK; 03-05-2010 at 02:03 PM.

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    Quote Originally Posted by 2001TransAm View Post
    I found out that the JEGS rockers max spring load is about 20lb less than the double springs on the PRC 5.3 stage 2.5 heads when fully open. I cant remember what the exact numbers are but im going to run my stock rockers which were recomended by Texas-speed. I wouldnt run the JEGS rockers, go the extra mile and spend a few $ more for like harland sharp or comps rockers if your hell bent on getting aftermarkets. The horsepower gain isnt going to be noticed on the track or the street.
    Where did you get that info from? BTW what is the spring pressure? I guess I'll be installing the factory rockers.

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    I called Jeg's and the guy didn't have a spec on the spring force but only the length. I believe he said it was 1 5/8 and usually a triple spring. I don't know that much about springs so I'll have to research it myself.

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    I wasnt coil bind, I had more than .06 clearance easy which is what the comp website suggests for safety. The Double springs can handle .650 lift anyway and im well under that.
    Some of the Tech guys at Jegs are better than others. But id put my trust in the whole valve train strength to Texas-Speed. They have been building ls engines for awhile and have done just about every combination there is.

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    Moderator Firebirdjones's Avatar
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    I've seen aluminum rockers break before, but usually on solid roller setups after alot of use in an extreme environment racing environment with 300 lbs seat pressure springs. Aluminum after time gets work hardened, and can get brittle.

    On a street motor such as yours, with such a mild cam, and mild spring pressures, I highly doubt that is what happened here. They were either a defective part, or you have some sort of binding going on.

    I run aluminum rockers on 3 engines of 3 different brands, and Crower chrome molly rockers on another engine.

    Never had a failure with any of them, after thousands of street miles and countless drag strip passes.

    As far as aluminum rockers go, I have Harland Sharps on my 70 bird, Crane Energizers on a 406 I built, and my wifes 4th gen LS1 has Crane adjustable rockers with screw in stud/guide plate conversion.
    All of which have worked flawless.

    I do tend to stay away from the cheaper brands, as the roller tip pins on some are simply a press fit, and work themselves loose. Anymore I lean towards Crower or Comp chrome molly setups.

    The LS stockers are okay, but not something I would want to run with a high lift camshaft.

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    Moderator Firebirdjones's Avatar
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    Here is a shot of my wifes car. As you can see, those are double springs with titanium retainers. Although the spring pressures escape me at the moment, they are similar to other double spring setups accross the board. For mild hydraulic rollers that usually consists of 120-150 lbs. seat pressure or so.
    Those are aluminum Crane variable ratio rockers, or what ever they were called. Not sure if these are still made or not, since Crane filed bankruptcy and reorganized.
    In any event, these were installed along with the cam at 40,000 miles, car now has 72,000 miles with plenty of spirited driving and several drag strip runs. No issues.


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    IIRC those Jegs RR's are rebranded Scorpions that are pretty prone to breakage. Seen a lot of guys on different forums have problems with them......

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    Quote Originally Posted by SOMbitch View Post
    IIRC those Jegs RR's are rebranded Scorpions that are pretty prone to breakage. Seen a lot of guys on different forums have problems with them......
    yea but you still have to ask why they broke. most say, ah these POS rockers broke. and then they go on about how everything is or was right and 2 weeks later there is a small post about how the engine blew, or they post nothing at all. There is always a reason to breakage. the question as to why can vary alot. most don't check if thier springs are coil binding with thier rocker ratio and cam selections and what not. Always ask why first and when there is no logical answer then call the manufacture and get your money back because if you have truely looked at everything that you controll that can break them, the manufacture will not have a leg to stand on.

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    I wasn't implying that aluminum rockers were a bad way to go. I guess what I was trying to say was that the JEGS brand and Scorpion brand are some what cheap. Im not doubting Comps or Crane RR. would break like mine. I admit I went a bit cheap on the final assembly of my engine (rockers) and learned from my mistake.
    Simply that I checked for coil bind and investigated every other possibility of why my rockers were breaking after 3000 miles and concluded that it had to be the rockers, either for them being bad parts from stock or that they couldnt handle max spring pressure.

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    To the OP. Did they break in the pushrod cup? That seems to be the weak point of these RR's. I believe they redesigned them at some point but not sure....

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    Quote Originally Posted by 2001TransAm View Post
    I wasnt coil bind, I had more than .06 clearance easy which is what the comp website suggests for safety. The Double springs can handle .650 lift anyway and im well under that.
    Some of the Tech guys at Jegs are better than others. But id put my trust in the whole valve train strength to Texas-Speed. They have been building ls engines for awhile and have done just about every combination there is.
    How are you measurring .06 clearance? Did you run the little bar that ties the two rockers together? Without the bar the rockers sit lower and an even shorter pushrod length is required. Even budget rockers shouldn't break so easily.

    I had to run 7.3 rods and it gave me a preload of about .9 after tightening down the rocker. Assuming my measurements are correct (and that isn't a given). It gives you and error of .1 which translates into .17 at the valve end. Add .17 to .595 (lower value of lift spec on your cam) and you get .765. If the springs are rated to .650. You are already past the limit of the spring, but take into account the lifter will compress some when you hit coil bind.

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