88 MACH 1

What are the chances of a rocker arm stud breaking in a 7.4 Merc? The engine had 20 hrs on it when it broke. Will the 7/16 stud break off with a roller set up or did the builder torque it down with the jamb nut installed before the proper torque was met? Thanks in advance, 88 MACH 1

formula31

After I broke my fourth one in a month many years ago, I now replace then with new arp studs evertime I do a rebuild on the heads. I think the stock ones get weak with age.

88 MACH 1

These studs are all new. They are all ARP. The general thinking of the marina mechanics is that the engine builder screwed up.

Tinkerer

Where did it break-- under the jam nut or where it threads into the head??
If it broke just under the jam nut I think you just had a bad stud. I tighten the jam nut and then recheck the lash and then tighten the nut and allen screw down to tighten the lash. I have never broken any.

88 MACH 1

It did break under the adjustment nut, right where it met the rocker arm. The top of the stud had a strange mark on it which the others did not which has me thinking that the jamb nut was in when the adjustment nut was torqued down. This mark was not on any other studs.

88 MACH 1

Well got the rocker arm stud back from ARP and a nice letter. As suspected the jamb nut was in when the builder adjusted the rocker arm. Well got to make a call tomorrow, and let him know he's FIRED.