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Author Topic: broken rocker arm  (Read 3154 times)
68rsssrag
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« on: October 26, 2006, 11:44:38 PM »

When I started my L35 after a full rebuild it ran fine for 30 minutes with lots of oil pressure. Just as i kicked it down to slow idle after bedding in the cam, there was a loud noiseand one exhaust valve stopped opening. Upon investigation the rocker arm on #6 exhaust was broken in half. The fracture was clean and through the pivot hole.

I have seen this only once before on a SB where the pivot hole was punched out. The nature of the fracture looks like metal fatique.

I repalced the rocker arm and everything seems fine. Anyone have any experience with this?

Arno
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RAfbody
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« Reply #1 on: October 27, 2006, 09:40:00 AM »

If you put a cam in that has more lift, it may open the valve more than the slot in the rocker can handle and it will rip the rocker in half.  Don't ask me how I learned this.
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Russ
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« Reply #2 on: October 27, 2006, 10:25:42 PM »

From my expereince there are usually only two reasons a rocker arm breaks--coil bind on the valve spring or lack of lubrication. Is there bluing of the metal where it broke? That would suggest lack of oil on startup and you'd have a galled rocker ball. Hopefully, you just had a bad rocker arm! Congrats on your rebuilt L35 and good luck.
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HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
Butternut Yellow    black standard interior
68rsssrag
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« Reply #3 on: October 27, 2006, 11:52:56 PM »

The cam is close to stock. There is no bluing either.

A tip for new motors from post break research I did to try to figure this out, coat the rockers with a moly spray to prevent galling on run it.

Arno
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nuch_ss396
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« Reply #4 on: November 04, 2006, 06:03:54 PM »

Just a suggestion for you.  A full rebuild in my book would entail new rocker arm assemblies as well.

BTW, if the rocker arm slot was not long enough, more than just one would have broken.  Some
day, someone is going to develop a see through valve cover for engine break-in so we can watch for
things like this.

I'm toying with opening up a top window in a set of big block valve covers and placing in a cap so I
can remove it from time to time during the run-in phase every time I build a big block......... Cheesy

Steve
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69 SS 396, Hugger Orange, D/80, D/90
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Steve A.
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68rsssrag
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« Reply #5 on: December 30, 2006, 02:37:11 AM »

Nuch, you have a good idea there on the see through valve covers. I am seriously thinking of replacing all of them but the machinist and mechanic (35 years of big block time) say to leave well enough alone. I think you are correct.

Arno
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sam
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« Reply #6 on: December 30, 2006, 07:43:02 PM »

There used to be see through valve covers. (clear plastic) Drag racers had them years ago. Have not seen them in years though.
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