So the BS GS has experienced a rocker arm blowout on cylinder #6 Springs are single Manley springs right at 300lbs I don't rev past 5500rpm most times No valve float that I can feel at hi rpm (doesn't nose over at all) TA 9.325" pushrods are spotless The rockers were a little noisy, especially on cyl 6. I am thinking of possibilities... poor oiling from cyl 6 lifters too much lash on cyl 6 rockers - valve stem height? old steel rockers reached the end of their service life any other ideas? It bears mentioning that the same cylinder did break the tip off a TA adjustable pushrod a year ago or so, set at 9.325" at about 3500 rpm. ZERO lash has repeatedly measured 9.310". The drivers side is near silent running 9.325" pushrods. clicking can be heard on the passenger side running the same length. here is the latest pic:
What is the lift? Generally anything over 0.520” ish is hard on those rockers. 69 430 rockers hold up much better. If you run the steel arms, debur the oil hole. That hole looks like it might be pierced and has a sharp edge on it/some.
Steel arms just don't hd up, 400/430 with correct pushrods or bite the bullet and get some rollers. It is possible depending on heads deck heights etc to need a different rod side to side
I kept having that problem years ago. New rockers solved it in that engine. They were just old and worn out.
300 psi sounds high to me for factory rockers ! If I was to chance running that much open pressure I would send the rockers out to get Cryo treated! Also a kind of repeated failure on that same valve would cause me to think that dispite having 300 psi of open pressure that valve spring is not controlling the valve action as it should and your hammering that push rod into the rocker at certain rev's.
It is suspicious that trouble repeated on the #6 cylinder. I hadn't thought to suspect the valve springs, thanks.
I just found a damaged rocker on the driver side, cyl #1. Same failure mode as cyl 6 which failed previously. This is good in that the failure is no longer isolated to one cylinder. This leads me to believe that the old steel rockers are indeed just tired out. So i've installed a new set of steel rockers. And I am sticking with the 9.325" pushrods. We had measured carefully, several times, to determine the correct pushrod length, so I am trusting those numbers.
70-71 alum 455 rockers would be the best choice here.. plenty durable for any most all flat tappet cams, and they don't require the hybred pushrod the 67/9 stuff does, I save those for mild roller cams. I have had that pushrod break thru on those rockers on brand new ones. JW