sbc 350 valve and push rod problems - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-29-2013, 05:43 AM
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sbc 350 valve and push rod problems

Hi I need some help, I resently storted doing some mode to my goodwrench 350 i have in my nova, I started by relacing the cam with the comp high energy 268h (.454 lift both in and ex) i finished that and all was good. a copple weeks later i purched a set of brand new (but second hand) RHS cast 67cc heads (2.02,1,60) I had a local engine shop accemble them, first try with installing the heads (i know this own is my mistake) i installed them using the stock push rods and aparent stamped self allining rocker with the guide plate and stotted hole that the heads cam with, so i got it together started and and lot of noise, the #2 push rod bound open and piston hit the valve and bent. so off cam the heads, i had the same engine shop replace the valve and inspect it. so now i have both heads off again, i read on rhs web site that these heads are designed to use the stock 1.5 stamped rockers with the sloted guide holes, but the rocker that came on my crate engine have the little tabs that keep it on valse, so i deside to drill out all of the guide holes round (rhs suggested with self align rockers) so then i installed the heads using metal shim gaskets , i purchased new edelbrock pushrods (they are .100 longer than stock, did not mesure rod lenth, should have) installed rocker arms using brand new power seal rocker nuts, ajusted the valve lash corectly and all looked good. i started the engine with valve covers off and herd no ticks or funy noises, so after it worms up i take it for a ride i drove about 3 miles, pulled over to listen under the hood, nothing funny, so i head home car sounds good and pleny of power, so i deside to step on it a little (that was the point) all was good . so then i down shift from 3rd to second untill about 5500 - 6000 rpm ( i did it all the time with stock 76cc mexico heads) and i herd some thing give, i get it back to garage take the valve covers off and #6 exhuast rocker is off the valve, i grab a rench to take off and it is stopy becouse the valve is stuck open (piston must have hit it) i look at the rocker and looks good, the top of valve has a small chip where it came off, and the push rod is very mildly bend (allmosy unnotisable) and it looks like there is some rub marks on the guide hole slot, I have not yet taken the head off not sure what i am going to find. hope no broke piston, I need help how to fix should i use non self aligning roler tip rockers with guide plate and properly measure for rod lenth or what. note- the valves in the heads are all stock 327 dimentions and specks the springs are liberty with dampers I am lerning all this and know enuff to get in trouble any help would be great but please dont throw me under the bus the only way for a guy like me to lern is to do it thanks for all the help

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Old 05-29-2013, 10:03 AM
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You may have a couple things going on, but the first thing I would suspect is the valve springs are not strong enough OR they're not installed to the correct installed height.

The next thing that jumps out at me is the pushrod length. You shouldn't assume the length is correct by using +0.100" p-rods- the p-rod length needs to be checked to give the proper valve train geometry. Too long or short can cause the tip of the rocker to ride off the tip of the valve.

You cannot use guide plates- even w/the p-rod slots opened up- if you are also using self aligning rockers.

There's an outside chance the valves might not have been adjusted correctly, but this is a long shot- it sounds to me like you got them right. Just the same, below is a page on adjusting the valves, along w/some other info I believe you will find useful.

Valve train geometry
Valve spring installed height
Adjusting hydraulic lifters
Cam break in
Valve train points to check
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Old 05-29-2013, 12:00 PM
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My gut tells me that with the +.100 pushrods the slot in the stock rocker arm hit the rocker stud.

If the decks or heads haven't been cut and the valves are also stock length then the stock length pushrods probably were not too far off.
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Old 05-30-2013, 04:39 PM
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thanks for the help guys, i spoke to my engine guy that install valve and springs wants me to bring him the head becouse this is the second time this has happened to me on this one head, difrent valve though. he thinks that the valve guides may be to tight from the fartory becaue this time it happened i had self aligning rockers, no guide plates and drilled round guide holes in the heads and new pushrods. he said that the valve may have slitly stayed stuck open and then all this crap happend. because it was runing fin untill i put ran up the rpms, the springs are liberty high performance and has more than enugh pressure to close the valve with my cam and the bent push rod has no markins and the guide hole has no markins, so were led to beleve that the clearances are good and the rod was good just the valve stayed open and piston bent valve and then the rocker came off the valve and the rod came up side ways and bound and bent we will see. thanks again any other info that you think may help me please fell free to tell thanks
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