breaking rocker arms?

[NKau]

I've been having problems with my '65 breaking rocker arms. I've owned the car for 4 years, and driven it pretty sporadically due to wiring problems. Just got done installing a new painless kit to eliminate all the gremlins. Got it running 'good', but noticed a definitive miss/stumble off idle; same problem it had after breakinga rocker arm 2 years ago. Pulled the valve cover, and low and behold, another one basically just split. Our prevailing theory is that the previous owner who built the engine may have the wrong valve springs in (has a 'mild' cam according to the PO), causing binding, thereby breaking rockers. Pushrods aren't bent, which kind of leads me to believe there isn't any kind of p/v clearance problems (think I would hear that anyway).

What do you guys think? I'm really miffed by this.

 

[Max Power]

If it is a mild cam, you may not be binding, as the lift on mild cams usually isn't enough to cause a problem. I would find out how strong the springs are. They may be way too stiff for your rockers.

 

[rbohm]

if the rockers are stock, and the cam has more than .465 lift, the rockers are binding against the rocker studs. you either need a lower lift cam, or longer slot in the rockers, or replace the rockers with some good roller rockers. any of the three options will solve your problem, but #3 is best.

 

[65up2d8]

Rbohm is most likely all over the problem, and he gave very good advice. The only other possibility that popped into my mind is that you've accidentally mismatched components from different years, and your pushrods are too long. I still think Rbohm's analysis of the problem is much more likely, however, as I doubt that a pushrod would break a rocker without bending the pushrod. Just simply trying to think of all the possibilities.

 

[302 coupe]

I've run the stock rockers with .512 lift and had no problems.

 

[rbohm]

I've run the stock rockers with .512 lift and had no problems.

yea, but that depends on what stock rockers you have. the hipo 289 rockers allowed more lift than the other 289 rockers, but even then you were very close to having problems with rocker arm breakage. stock chevy rockers are even worse than the ford rockers though.

 

[302 coupe]

they were stock rail rockers, and still had some room to spare before the slot bottomed out on the stud.

At any rate, I think the dinky 5/16 pressed in studs would pull out ( or break), or the pushrod would bend, long before you break a rocker arm. Maybe they're just defective, made from a bad batch of metal or something.

 

[NKau]

Thanks for the replies guys. My engine components are fairly mismatched......'67 289 with 302 4V heads of unknown vintage. The thought that the rockers themselves could be a problem never crossed my mind.....I know the stock 5.0 rockers really don't become an issue unless running a real radical cam. Thanks again for the insight.

In response to the last poster, even with the other broken rocker arms, I haven't had issues with studs or pushrods being damaged. Also, what rocker arms would be a failsafe addition without breaking the bank? It's a mild motor, and I'd just like to pick up some factory style (i.e. cheap) rockers to replace the current batch.

 

[brianj5600]

If your push rods are a little long it will bottom the slot with less lift. I would think if you are running out of slot there would be a mark on the stud.

 

[Edbert]

What does a set of cheap roller rockers cost these day...$125?

 

[Dark Knight]

I had the same prob with rockers breaking against the stud, roller rockers fixed it... you might also check to see if the valve spring retainer is hitting the top of the guide..


Also, do you have the heads with narrow slots for the pushrods, or do they have a big hole? If you have the ones with the big hole, you'll either need guide plates, or I think someone like comp cams makes a roller rocker with rails.. not sure though