stud boss crack .. Joe Lucia

[John G.]

Joe ..
I read with interest your replies on how to fix the lifter bore crack on John Randolph's '67 BB. In my case, one of my heads (SB) has a crack in one of the rocker arm stud mounting bosses. The crack runs parallel to the stud, itself. This crack measures about a 1/4 inch in length.
The stock rocker arm stud bosses were tapped and threaded for straight shank screw-in type studs (non hex nut style). One of them ended up with a crack at some later point in time .. Can the repair technique you described for the BB lifter bore fix be used to repair a stud boss - 1/16th inch drill bit and JB weld to fill the hole .. ? ..

John

[Harold #43147]

The Boss

John were the tops of the stud boss machined flat. I have seen home drill & Tap jobs do that and also seen this happen if the drilled & tapped hole is not deep enough and the stud is bottoming out. I have repaired this crack type a few times I drill a hole at each end of the crack take die grinder or dremel and v out the crack from drilled hole to drilled hole then I pre heat the area the area and then TIG Weld it with Nickel Weld Rod then just let cool and I have never had a problem with it. I read the artical on the cracked lifter bore and Joe's input that,s a tuff spot to repair I don,t know if I would or would not weld it pinning is a way never have done it in a engine block have used Bronze pins in cast iron bases on machinery and it held up but there was no heat to effect it. Any good welding shop could weld it for you cast iron is welded ever day.

[Joe L.]

Re: stud boss crack .. Joe Lucia

John-----

I don't think that the same sort of repair would work for this type of situation. However, you do have an excellent option available to you, as I understand your situation. You can have the rocker stud bosses machined down for hex base style screw-in studs. This way you should completely eliminate the cracked area and you will end up with a much better end product. The hex base style rocker studs are the best type, hands down.

Of course, the hex base style rocker studs were never originally used on any pre-1970 Corvette small block (neither were the type of screw-in studs you currently have). However, no one will really be able to discern the difference (except for 69+ small blocks where someone, theoretically, could peer into the oil filler opening).

Also, it will be necessary to remove the heads from the engine to effect this machine work and conversion.

[John G.]

Re: stud boss crack .. Joe Lucia

Well, therein lies the dilemma - fix the crack or completely pull the heads and have the stud bosses milled down to accept the hex style rocker arm studs, as Joe suggests. Harold, no the stud bosses weren't milled down. I probably should have gone that route. At the time these straight shank style studs were installed in the heads over the hex type studs I didn't think it made much difference between the two types. The crack seems so minor I'm tempted to go the fix route over pulling the heads and doing it the right way. Gonna have to sleep this one over . .! . .
Thanks Harold and Joe ..

John

[Craig S.]

Re: stud boss crack .. Joe Lucia

John/Joe - while I agree that removing the heads to install the hex style studs it can be done on the heads, with the right tools. I just completed doing this with Dave Barclay on his 66. There are some pilot based facing tools at Goodson with two carbide cutters in the head that will work if done CAREFULLY with a solid hand drill with a side handle. We had minor chatter which would not have been there if done on a bridgeport or drill press with fixture, but it was fairly insignificant and a few light strokes with a flat file made the bosses smooth. We also used a special bridge between adjacent bosses to insure even material had been removed from the bosses, and it also served to insure the tapping process was true to the stud bore as it provides a tap guide. We used this after starting the tapped holes with a custom tap with pilot. Judicious plugging of all oil drainback and pushrod holes, plus using "toilet paper" tubes and a shop vac during the machining were key in controlling shavings to avoid and contamination. It can be done......but the tool investment is not cheap...Craig

[Craig S.]

Re: stud boss crack .. Joe Lucia

My first sentence was worded very poorly, what I meant to say was the process can be performed with the heads installed on the engine, but for sure with them off is the easiset and best way from a machine work perspective.

[Joe L.]

Re: stud boss crack .. Joe Lucia

John------

One thing that you could do is this: first, check to see how much of the thread length in the cylinder head stud boss that the crack overlies. Next, see how much effective thread length that the stud engages BELOW the lower terminus of the crack as it exists now. If there is at least 3/8", or so, of thread engagement below the lower terminus of the crack, then I'd say that drilling a hole at the lower end of the crack to prevent further propagation of the crack will represent and adequate repair.

If the crack overlies most of the thread depth in the cylinder head boss, then this sort of repair is not going to do you any good, at all. While you can prevent propagation of the crack, the crack has already compromised the strength of the boss to an extent that renders this sort of repair ineffective.

The type of studs that you used have pros and cons. On the "pro" side, they do maintain the configuration of the cylinder head very much like the original press-in studs---most folks wouldn't be able to tell the difference looking at the "naked" head. In addition, they are much more easily removed and replaced than press-in studs, which is especially useful in a "field" replacement sort of situation.

On the "con" side, they are not as strong as available hex-base type studs and they are not as easily replaced as hex base type studs. In addition, if there are any cracks in the original stud bosses created as a result of the original press-in stud installation, those cracks remain a problem for the screw in studs. My bet is that the crack that you have now has been there, to one degree or another, for a LONG time and was created when the original press-in studs were factory-installed (or, more likely, when someone tried to replace a press-in stud). The crack may have propagated since you installed the screw-in studs that you currently have, though, and that may be why it went unnoticed at that time.

[John G.]

Re: stud boss crack .. Joe Lucia

Craig ..
I had forgotten about that special fly cutter tool that can be used to cut down the stud bosses with the heads installed. Sure beats having to completely pull the top half of the engine apart in order to do this kind of operation. The big drawback are the metal particles flying around, of course, but it sounds like you guys had this problem under control.

Joe ..
The crack extends from the very top of the stud boss and down about 1/4 inch, fairly parallel with the installed rocker arm stud. There's a good chance the crack is actually enough above the total length of threads so that there's easily more than 3/8th's inch of thread material below the terminus of the crack. I'll have to eyeball it over much more closely than I did before. Since only one stud boss is affected I'm tempted to go with the 'easy' fix and repair the crack if it looks to be reasonably fixable.
I think you are right to say this stud boss crack may have been there for some time. These rocker arm studs were installed in these heads back in........geez?........the 70's .. ! ..

Thanks for the follow-up replies.

John