I posted earlier about the problem I had with the timing gear on my BBC. The biggest problem that resulted is that the rocker arm stud boss for # 2 exhaust broke and the stud obviously came loose. I'd junk the heads but they are Merlin Cast iron Rectangular port heads ( 320 CC ) that I ported , CC'd etc. and really worked well. Our repair plan is to bottom top the remaining portion of the stud hole, approx. 3/8" , weld on the broken stud boss w/ a Cronatron rod which is a low nickel rod, and then install new ARP rocker stud. I called Merlin ( now Bill Mitchell ) to see if I could tap the stud hole deeper into the head w/o hitting a water jacket but they had no idea and weren't into helping . I asked for someone who knew the casting plan or blueprint and got no response. We thought if we could tap a deeper hole , use a longer reach stud from an Olds or some other manufacturer that may be a good idea.

Anybody have any experience or ideas? I really don't want to junk the heads.
:(
If we do try it and it fails am I right in assuming that the valve would close and the only damage should be to the rocker assembly and maybe the push rod?? I'm inclined to risk it if the result will only be new heads and not further damage to the motor. What do you think??

Thanks.

There would be an outside chance if things failed some loose part could get jammed in such a way to hold the valve open and then you have real problems. Also, if the rocker goes the lifter could leave it's bore and your oil presure goes.

Why not have the rocker stud boss welded back together, retap it and resinstall the stud as normal? Anything else sounds like a cobble job. Cast iron welding takes a special techinque and special rods, but if done right the piece will be as good as fresh cast. I wouldn't try to simply weld the boss back together with normal welding techinques, I'd employ someone who really knows cast iron welding of automotive heads and blocks. Part of the technique involves heating the piece to a red glow in a forge prior to the welding and this is just not something you can do at home.

If you can't find anyone local, I know a really good shop local to me (Lincoln, NE). I had a block welded (4 cracks) and pressure tested about 15 years ago. At that time it only cost about $150.

My plan is to do just that. My engine builder has experience w/ cast welding and understands the technique. I was just trying to use the deeper threaded penitration as added strength. Your right about something jambing the valve open. I'll just have to closly monitor it.
Thanks for the reply.

More importantantly, do you know what caused such breakage in the first place? Sounds like something went seriously wrong. If a valve hit a piston the push rod should have failed long before the rocker boss got broken. Perhaps you covered this in your other post but I don't think I read that one. If the stud simply pulled out of the boss I would think it would strip the threads before it would break off chunks of iron. I'd think the force applied by a failure that caused the boss to break would have to have come laterally instead of in line with the action of the rocker.

Good deal on the welding. If he indeed knows what he is doing it should be as strong as new (perhaps the casting was originally flawed in that area anyway). If tapping the hole deeper would potentially get into water jacket areas I wouldn't temp fate. Even if you go a little deeper and get close to but not into water you will have still weakened this area of the casting.

Your shop guy should probably also magnaflux the head before doing any welding to make sure there aren't other cracks or flaws that could cause further failure. If there are lots of cracks you should probably replace it.

I think he may also have to resurface the head when he is done because by heating and welding things at those temperatures things can shift slightly. Take that into consideration when doing your rebuild (use thicker head gaskets to make up the amount taken off by the surfacing unless you want to increase your compression ratio a bit).

Never had this happen so have no experience here but from an engineer's perspective, find a shop that will furnace-weld it rightb and cool it down properly to keep from cracking your head in other places!!

Then, get a longer stud and drill clean through to the water jacket or intake port or WHATEVER and thread her all the way. Seal her up with some good old Permatex, "Indianhead Shellac Gasket Cement", torque her in right AND go!!

Should work fine imho..

pdq67

TW,
If your guy can weld the stud boss, I would proceed as you have described. The ARP studs for the GM aluminum heads have threads that are almost twice as long as normal on the bottom of the exhaust studs as it is very common for them to break on the GM aluminum heads. I would not be concerned about drilling all the way through to water, there are plenty of Small Block heads that go through to water from the factory. Just use a good sealer on the threads and you should not have a problem. As far as preventing future breakage, I would definitely install a stud girdle. That will tie everything together and should prevent the problem that you had. You might want to try and find someone in your area that does cast iron spray welding. That would be the way to repair it in my opinion. Dont even try to use the broken part. Just spray weld to build up the boss, then re-drill and tap it, it will be as good as new. The other nice thing about spray welding on this type of repair is that you do not have to really heat up the entire head.

Bill,

Shouldn't he try to find a good Diesel head repair shop that should do this stuff on a daily basis??

pdq67