Run it til it breaks

[dstrbdxp-AK]

A few weeks ago I started getting some very loud noise in the top end, well tonight I was able to figure out why.

You can see the issue from the pic. When I popped the valve cover off I found the rocker laying on it's side against the base of the head clean and out of the way. Tip of rocker stud broke off inside the posi-lock and the bottom end of posi-lock broke off.

Rocker looks fine other than a few scuff marks, pushrod looks good as well.

Any ideas as to why this happened? I ran through the top-end a few months ago and haven't had any issues since.

 

[scouthead]

What motor? what heads? Cam? how hard do you flog this thing?
What brand Stud/polylock?

 

[dstrbdxp-AK]

'69 396, 781 heads, all crane gear from the cam to the poly locks. I didnt build the motor. Studs appear to be factory, I'd say

I do a tad bit of hot rodding with it on the streets, keep the rpm's on the somewhat mild end

 

[Greg72]

Same exact thing happened to me on the way back from BlazerBash 2002.... also in a 396 motor. Left me stranded in Barstow....what a lonely hell hole that place is.

It's not that easy to find a BBC rocker stud at a parts store, or junkyard either. I think we had to go to about 4 different places before we got one used from a salvage yard.

My solution was to replace all the factory rocker studs with quality ARP ones... that solved it for me.

 

[dstrbdxp-AK]

Ok well, maybe I have my foot it in more often than not, LOL.

I found another cracked polylock. I had only touched a few of the rockers not long ago, and from the looks of it those that broke had only 1/3 of the poly lock even engaged into the stud.

We've got some really good motor shops here, I can surely scrounge up a stud and I know they have a set of polylocks on the shelf.

I will say whomever built the motor put a lot of high dollar parts into the valvetrain.

 

[76zimmer]

I'd say using the posi-lock nuts, on stock length studs is a no-no. I don't think there is enough thread engagement on the nuts.

 

[sweetk30]

x2 on the arp studs for the perfect fix.

 

[dstrbdxp-AK]

rocker side thread length is 1", stud length 1.75 OAL 2.75, polylocks are 1"

Hafta go with some 1.9's and new locks

These will allow for a guide shank under the guideplates

Rocker Nuts

Better recommendations?