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Pulled a valve cover this weekend to un-stick a lifter and found something else that kind of took me by surprise. In addition to a stuck lifter there was also a broken rocker arm on an intake valve! Have any of you ever had this happen? The car hasn't seen very hard use, but does run at about 3000 rpm on the highway. All this time I thought the acceleration lag I had was caused by carb problems. The car still ran great otherwise. I'm almost tempted to pull the other valve cover to see what's up. How common of an occurrence is this?

Nick

64.5 Coupe
289, C-4, 9 inch posi w/ 3.50's
"going fast IS looking good"
 

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I had that happen on my 68 coupe. The previous owner had a large lift cam in it and I broke studs several times. I think it needed guide plates too. I ended up changing the cam because we couldn't find the specs on the cam from any manufacture. Do you have a high lift cam in the car?

http://images.honesty.com/imagedata/h/203/00/32030034.jpg
 

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It wasn't the stud that broke, it was the actual rocker arm. It just broke in half. I don't know the exact specs on my cam, but it can't be too big as there is not much of a lope and it idles really well.

Nick

64.5 Coupe
289, C-4, 9 inch posi w/ 3.50's
"going fast IS looking good"
 
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yup, i've had this happen too. the prev owner put a high lift cam in w/o replacing the rocker arms or rods on my 289. what happened in my case is that the stock rocker arm was being lifted up so much that the edge of the slot the rod goes thru would hit the rod every time it lifted. AFter a while, it fatigued beyond it's limit and cracked in three. This actually happened three times before I had a chance to take care of it.

To rectify, I put in rocker arms w/ a large ratio (1.6) and with roller tips. these arms have a longer slot in them. I also matched it up w/ an appropriatly sized chromoly rod. Unfortunatly, I had someone else do the work, so I don't know how to figure out this stuff. Also, instead of using guide plates (because supposedly you'd need to machine down your heads to fit them in), Crane sells a rocker arm that has guides on this side of the roller tip which keeps it on the valve.

By the way, you definetly want to pop off the other valve cover and check this out. However, if you don't have a high-lift cam, this might not be the problem at all. But, if you have some weird rockers in there, you never know.

hope that helps...

Jay
1965 Pre-GT Fastback, A-code, C4 trans.
 
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I have seen a few stock chevy engines do this over the years-usually break the centers out under the pivot piece and nut.They had just stock cams, I thought of two things that might have done them-valves too tight, or defective rocker arms.

1967 S code GT Deluxe Coupe 65B
1966 Convertible 76B 289 4 speed

Descendent of Francois Seguin dit Laderoute,
Soldier Regiment d' Carignan, New France 1665-1668
 

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Yup, Used to break them all the time with a high lift cam
in my 68 in high school. Broke on the interstate in Roanoke Va
one time and all I could find was a SBC rocker. It got me back
to Richmond.

65 Coupe (The Toy)
68 Coupe (Son's)
2000 GT Conv. (Wife's)
66 Conv. (New Project)
http://www.zing.com/picture/p3228deeb98049833a72408c1fb0889a9/fec469a8.jpg
 
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