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#1 |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Why are my Rocker Arms Breaking?
About 2 weeks ago I had a backfire (through the carb) problem that was the result of a broken rocker arm. My mechanic replaced the rocker arm and told me that he rarely sees this and thought that the rocker must have been defective. The truck ran great home from the shop and then sat for a week. 20 minutes into my next drive the same backfire noise started happening again. This time it turns out to be another broken rocker arm on a different cylinder. Both broken rocker arms happened on the same side of the engine. What could be causing this? THANKS FOR YOUR HELP!
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#2 |
Registered User
Join Date: Mar 2008
Location: Salt Lake City UT
Posts: 441
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Re: Why are my Rocker Arms Breaking?
Is this a recently rebuilt engine?
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#3 |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Re: Why are my Rocker Arms Breaking?
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#4 |
Account Suspended
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
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Re: Why are my Rocker Arms Breaking?
Do you have a picture of the broken arms? Seeing the failure mode will help a bunch in determining where the issues are.
Are there any marks on the stud? Unless it's just a mechanical failure from the rocker ball galling, these almost always occur due to bad valvetrain geometry in some way. No other changes to the engine...? |
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#5 | |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Re: Why are my Rocker Arms Breaking?
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#6 | |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Re: Why are my Rocker Arms Breaking?
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#7 |
Registered User
Join Date: Jun 2002
Location: central pa
Posts: 1,525
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Re: Why are my Rocker Arms Breaking?
I would check the timing. If it were an older engine I would say the timing chain jumped on you.
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72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne |
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#8 | ||
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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Re: Why are my Rocker Arms Breaking?
Quote:
Like ticker said, Are there marks on the studs? It is possible that the cam lift is more than the rockers can handle, but that usually bends pushrods... How about the rocker balls? Galling? Certainly the ball was replaced on the broken rocker arm?
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#9 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Why are my Rocker Arms Breaking?
are the heads vortecs? stock they're very limited in lift and r usually machined and speings changged for higher lifts
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#10 |
Registered User
Join Date: Nov 2006
Location: Sutherlin Oregon
Posts: 495
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Re: Why are my Rocker Arms Breaking?
They might be a cheep brand. I had the same problem, I had 2 brake. After the second one, I bought a whole new set and have not broken any more. It may have taken a few miles, and a few heat cycles for them to start braking. I would still check everything else also.
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#11 |
gets board easy.......
Join Date: Mar 2009
Location: Colorado Springs
Posts: 717
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Re: Why are my Rocker Arms Breaking?
I had some speedway rocker arms do the same thing........but only at high RPM, but have never had a stock one break like that,
Were the rockers replaced at rebuild? What oil are you running? possibly the fulcrum balls got mixed up during rebuld??? even though i have ran many that way, maybe some of your had wear |
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#12 |
Account Suspended
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
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Re: Why are my Rocker Arms Breaking?
I should have said this, but the area where the rocker ball goes is the most interesting
![]() But, if f there are no marks on the stud...then I call junk rockers. I have *never* seen a fracture like that ![]() You definitely need to check the valvetrain geometery before doing anything, though. I don't like the device below much...but it will tell you if things are way off, which they'd have to be to break a good rocker. http://www.summitracing.com/parts/PRO-66789/ These are the rocker arms I'd replace 'em with. http://www.summitracing.com/parts/CCA-1212-16/ You're sure to hear you should go with roller tips, full rollers, 1.6 ratio, etc. Don't. Just replace the stock rockers and get back on the road. |
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#13 |
Registered User
Join Date: Mar 2010
Location: ELGIN,TEXAS
Posts: 79
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Re: Why are my Rocker Arms Breaking?
Replace all of them i f one broke their all going to brake sooner or later the mech should have done this when the first one broke
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#14 | |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Re: Why are my Rocker Arms Breaking?
Quote:
The mechanic said if it were his truck, he would pull out the cam to see what size it is and then replace all the rods and rockers match up. What do you think? He said, "It's not looking good." ![]() |
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#15 |
Account Suspended
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
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Re: Why are my Rocker Arms Breaking?
Um....no. There is no reason in the world to remove the cam, and in fact it's not possible to find the correct pushrod length that way.
If there are no witness marks on the rocker studs, then you just need to measure what length pushrods you need and order them along with a new set of rockers. Everything you need is in my post above, linked below. http://67-72chevytrucks.com/vboard/s...8&postcount=12 You also need to check very carefully for coil bind; I suspect in the end this is what caused the failure more than the wrong length pushrod. If you look at the valve stem, is the rocker contacting it in the middle? Valvetrain checking springs: http://www.summitracing.com/parts/CCA-4758-2/ Air hold fitting http://www.summitracing.com/parts/WMR-W84005/ Valve spring compressor, on car http://www.summitracing.com/parts/PRO-66784/ Last edited by Ticker; 03-17-2010 at 06:18 PM. |
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#16 |
60-66 Nut
![]() ![]() Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,247
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Re: Why are my Rocker Arms Breaking?
I would suggest also checking spring retainer to seal/guide clearence
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#17 | |
Account Suspended
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
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Re: Why are my Rocker Arms Breaking?
Quote:
![]() Last edited by Ticker; 03-17-2010 at 11:50 PM. |
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#18 | |
Registered User
Join Date: Oct 2006
Location: California
Posts: 28
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Re: Why are my Rocker Arms Breaking?
Quote:
I really appreciate everyones input!! |
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#19 | |
Account Suspended
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
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Re: Why are my Rocker Arms Breaking?
Quote:
![]() ![]() For the rocker breaking, you're going to check everything...so at least on the valvetrain geometry you'll be sure that it's right and you won't break anything else there. If it was me, I would probably roll the dice on the shortblock and square away the rockers. Do not use this to kick my a$$ later if the thing goes up ![]() ![]() |
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