I was installing a new set of screw-in studs (the old ones were stressed due to improper rockers) and the head just cracked around the threads. I was torquing them to 65 ft-lbs., as my machinist said, when I suddenly felt no more tension on the bolt.

I think I already know the answer to my question, but is there anything that I can do? These L98 heads have about twenty hours of porting done (by me) and at least $300 into them. I really don't want it all to go to waste.

 

ouch


sorry, no help

 

Damn!

Okay, well you know how a friend of a friend of my sister's boyfriend, etc., etc. repaired a crack with some JB Weld? You've heard that one, right? Well, I don't know if it's true and it probably falls under the heading of urban myths and legends, but if I was desperate, I might give it a try.

 

Cut a v in it and weld it like everyone else does.

-- Joe

 

 

Pulling the head would make the job easier, but can it be done with the head still installed?

I looked at the remaining bosses and I didn't see any cracks, but is there another way to tell if this is going to happen to another stud boss?

 

Drill it out to the size of a convenient pipe plug, install said plug; grond off flat; drill & tap.

Welding may work, but is unreliable, because it's also cracked in places you can't see or weld.

 

Due to the probable reason why the metal was stressed such as it was, and the need for new studs, yes I'd say there was a chance of recurrence on other bosses as well. Depending on what happens it may be worth it to toss and start over.

 

I always thought that the studs would crack long before the cast heads even showed signs of stress, due to the hard nature of cast iron. Guess not. Or, maybe it was a machining flaw.

RB83L69, how would that method work? Since I can't torque a stud, I don't see how the pipe plug would stay in place (for long)... I'm assuming that you mean the threaded plugs, similar to the kind used in the block?

 

Yup... a tapered pipe thread plug.

You screw it in and stake it.

Cast iron is soft. Well, not "soft", but fragile. It cracks easily, especially if it has an inclusion. Stuff like that happens all the time.

The stud is probably at least twice as hard, and many times less likely to break, as the cast iron. That's why they make blots and race car chassis and lots of other things out of steel instead of cast iron. Even coat hanger wire material is stronger than cast iron.

 

Thanks for the clarification, RB. Not to be a moron, but is the crack also welded in your method of fixing the head? If the crack is left alone, I don't understand how simply "reinforcing" the threads with a pipe plug will prevent it from worsening.

 

You would drill out the damaged casting metal completely; and use a large enough plug to fill the entire area, or even to fab up a whole new boss, if that's what it takes to get to good sound casting.

 

I'd send a PM over to ede, or someone else whos a certified welder.

Usually cutting a v in it and welding it outlasts the rest of the head. It could be cracked from the underside too, but I highly doubt it.

I wouldn't weld it on the car either.

-- Joe

 

The guy who did the heads is on vacation, so I called another engine machinist that I know. He said that in a case like this, he'd coat the threads of the stud with JB Weld and install it... permanently. He claims that he's done this on race cars and it's held up. I don't really like this idea, and especially not being able to remove the stud in the future.

I do some technical work for another fellow who owns a prototype machine shop, so I called him for a favor. He's going to machine a small plate to fit over the top of the boss that will be screwed in with flush-mounted screws. We're then going to cut a V in the crack, as anesthes suggested, but use JB Weld for only the crack. The stud will be coated with thread sealant. This may elevate the stud up to 1/8" higher than the others, but I don't think that would be a problem.

I figure, it's worth a shot... and I don't have to pull the head to do it. The part will be free, too. If it breaks again or doesn't work out, I'll remove the head and get it welded or reconstructed.

 

Are you using guide plates or did you retain the self aligning rockers?

 

I don't have guide plates, but I don't have self-aligning rockers, either. The heads have narrow slots to guide the pushrods.