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Broken rocker arms , Why ?

I was doing a late night run. when i lost power, I had her towed to the shop , i removed the valve covers rocker arms on cylinder 2 up and lower were broken, this happen to me at LasVegas speedway on the banking at 150 mph back in 2001 on the fresh build , but that time it was number 5 cylinder. when the shop was doing a valve adjustment the wrench said that all the valves were way to tight and found number 6 set were cracked and about ready to let go also,
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Old 03-01-2014, 11:53 AM
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Valve piston contact?
Old 03-01-2014, 01:03 PM
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Sometimes the rocker can break when you have piston to valve strike and
the valve will be fine.

Cheaper to swap a rocker -- than do a complete valve replacement.

m
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Old 03-01-2014, 01:19 PM
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Here are a few things that cause rocker arm failures: a closed throttle over-rev (such as if you downshift from third to second, when you meant to upshift from third to 4th), valve springs with the wrong tension (far too stiff), and valve springs with improper pre-load (too long and/or not shimmed properly).
Old 03-01-2014, 01:39 PM
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I suspect valve-piston contact also.
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Old 03-01-2014, 01:40 PM
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Valve float with pistons/exhaust valves making contact.
Old 03-01-2014, 03:09 PM
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and if you have after market rocker arms you only rent them.. for a little while.
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As far i know the rockers are factory 930 rockers, the springs are ASSCO racing high RPM with titanium retainers , I have 45000 miles on this build, with many track, autocross events and drag racing, i put 18000 last year alone ,
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1986 944 turbo -first car
1997 993 Cab 6 speed-sold
1992 964 C2 turbo
SOLD, 911GT ,CIS, 428 fwhp 450 trq, Carrillo rods, 964 cams, TT retainers,7.5 comp 1.1 bar boost 320 ml black fuel head 009 injectors, 044 pumps, 60-1 T4/T3 dual scroll turbo
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I would check the AASCO spring installed height (no less than 34mm), and also verify that the cam lift is less than 13mm. Finally, turn the engine by hand and measure the space between the valve spring coils and max lift. If there isn't any, that might be the problem.
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Sorry, meant to say measure the space between the coils at max lift. That will tell you if the coils are going solid, which could be the result of the installed height, or improper valve adjustment, or both.
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Was this after your turbo ate itself? I wonder if any pieces could have made it into the chamber and sandwiched between the valves and piston? Bizarre things happen when metal bits are flying around an engine where they don't belong.
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Old 03-02-2014, 07:19 PM
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Quote:
Originally Posted by PrimeMvr View Post
Was this after your turbo ate itself? I wonder if any pieces could have made it into the chamber and sandwiched between the valves and piston? Bizarre things happen when metal bits are flying around an engine where they don't belong.
Good point, and if it happened before, maybe a piece of a valve is what went through the turbo, given all of the broken/cracked rocker arms. Not likely, I suppose, but a leakdown test following the rocker arm replacement would be interesting.
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Are rockers busted on both sides? If you pull the motor to replace the rockers, pulling the heads off as a unit is only a little more effort. Than you can see how the valves look in person. I assume you will check cam timing to make sure your chain didn't jump. Therefore, pulling the heads is only a little bit more if you split the exhaust and pull the whole side off without dropping the exhaust. No biggie and piece of mind.
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Ok ... The rockers were replaced and the valves adjusted, fresh mobile 1 , and put the inter cooler back on.... But wait ... Half the O ring is missing . I think my turbo ate it, That' s what I think chewed up the turbo , that had posted about earlier , she started up great, leak down test done, and all is great . Hmmmmm I'll take ,
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1986 944 turbo -first car
1997 993 Cab 6 speed-sold
1992 964 C2 turbo
SOLD, 911GT ,CIS, 428 fwhp 450 trq, Carrillo rods, 964 cams, TT retainers,7.5 comp 1.1 bar boost 320 ml black fuel head 009 injectors, 044 pumps, 60-1 T4/T3 dual scroll turbo

Last edited by heliolps2; 03-05-2014 at 04:27 PM..
Old 03-03-2014, 08:38 PM
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