BAD-HABIT

Well went to Cumberland again last week and during a trip to the falls I just get on plane and BANG the engine starts backfiring through the carb. No flame just one hell of a pop. I took the valve covers off and noticed that one of my exhaust studs had broke in two. I am using L31 Vortec heads with ARP guideplates and studs. 7/16 bottoms and 3/8 tops. I am using stock style Crane rockers with long slots. Comp cams pushrods and roller with 218/224 duration with 495/503 lift. Also Crane springs. The stud broke off about 1/2 the way up the threads on the 3/8 side. I ended up putting a stock lockwasher on to make it home. I am using Crane polylocks on the rest of the rockers. Everyone I talked to had never heard of a stud breaking there.....Which makes me feel great. Nothing like something braking in your engine with no explantion...Crane had no idea,neither did Comp-cams. My marine mechanic said it must have had to much heat treating.......Just a note i have had problems with the stock lockwashers coming loose so thats why I went with the polylocks. The stud broke off about 1/8" inside the polylock...Any ideas would be helpfull.

"Bad-Habit"

Mbam

It could be do to overtightning of the poly lock, or it could indicate valve float.

BajaSquirt

I had a similar experience several years ago. The stock type long slot rocker and ball were not up to my new cam and valve springs. I bet your rocker ball is worn enough to let the side of the rocker slot scrape on the stud. I switched to roller rockers, not a prob since.

Gearhead99

Usually too much lift and not enough slot. Pushes against stud and pop it's broke.

I'd go to roller rockers. Get good ones too. Also, get full rollers, not just the tips.

BAD-HABIT

I was kinda thinking along the same lines about the rockers...Any suggestions? I have the centerbolt heads which I belive limits my choices. I am using Moroso valve covers which advertise room for rollers...I would hate to buy a set and have them not fit. Crane advertises a set just for centerbolts but they are the only ones Ive seen.

Bad-Habit

rws

Perhaps the pushrods are incorrect length. Did you use a pushrod rod length checking tool? Due to pushrods that were too long I once broke a rocker stud on a hydraulic flat tappet cam engine . Just a thought.
Rob

Cord

If he had a enough lift to cause a clearance issue between the rocker and the stud, then would he have seal damage?

Tinkerer

Change the studs to the larger ones and install the roller rocker arms. I broke quite a few of the 3/8 inchers with my GLASTRON before I went to the bigger ones.