Gonna post this here ans see if anyone has come across this: Was investigating a top end noise on my 71 455, and went to pull the rocker shaft and coolant came gushing out.. Investigated further and the casting at the bottom of the blind hole for the rocker bolt is just gone. The threads are there, and strangely it seems to hold pressure with the bolt seated. Here's a video where I ran a scope down the hole: I have never used anything other than the factory hold down bolt, and it could have been this way for quite a while? There was no coolant in the oil and I suppose it doesnt pose any more of a problem than a frt cover bolt that goes into the water jacket if the side of the boss isnt cracked too. I'm wracking my brain on how it could be fixed - drill the hole larger, run a set screw in and follow that with a helicoil? Does anyone make blind thread inserts? Thansk, Rhett
First I've seen that happen. My vote is stick with your idea of treating it like a front cover bolt on a through hole. Good thread sealer and call it done. Devon
Just casting that protrudes down into the water passage of the head. you can feel it in an undamaged head through the intake passage, it's kinda like a cast iron dome. I assume that piece is somewhere in my head if it was ever there at all...
Possibly at some point in its life, a longer-than-stock bolt bay have been tried, and when torqued it blew out the bottom. Devon
Thats the best possible guess, or at least weakened it to the point of recent failure. I'd had that shaft off recently when the system wasnt under pressure and noticed no leaks. I was very surprised that it hadnt been sending water or at least vapor up into the shaft, but there was no wear on the rockers of shaft, and no "soup" anywhere. You can see from the video, sending the bolt down in shuts off the water flow like a spigot.
Thanks to everybody - given that I cant tell the condition of the remaining casting, and I've still got all threads intact I decided to order a stud kit from TA and epoxy that one in place. that ought to add some strength to the casting, and I dont have to worry about side stress breaking off a larger piece or potential failure from drilling and tapping, or repeated torquing. . I'm glad I can salvage the head cause I just got it the way I like it! I dont know why I didnt think of that in the first place.
If you rely on epoxy vs thread sealant, the stud will have to be installed hand tight only, then you'll need to immediately put that stud under torque before the epoxy cures. You don't want epoxy between the top of a stud thread and bottom of a head thread. The epoxy must cure with the stud in it's as installed circumstances. Personally I wouldn't do it...I'd sleep well with thread sealant. Heck, you did fine without even having that before. If it makes you feel better, studs plus thread sealant is just fine. Same hand-tight install recommended, typical for studs. A good time to not overthink things, lest you invent a new problem. There are millions of engines out there that do just fine with bolts into through-holes into a water jacket. Devon
Well, I can def start out that way and see how it goes, right? The reason I figured epoxy (Metalset A4 is what I generally use ) was for stud stabilty is the sidewall of the thread boss was comprimised as well. I dont know whats cracked and where, or how far. But I sure wasnt in love with the permanent install of the stud, in case that would get in the way of future machine work, etc.. and honestly I'm not sure there's anything left to torque against. I could see being able to thread that stud in until it's flush. I could install it and torque down the shaft, I guess that would pull it into place but to your point, I cant see the harm in trying it with just plain thread sealer first.
I agree with Devon. When using a NPT thread. A tapper thread has several mechanical features working for you. (1) A tapper thread has a very good locking effect being a tapper thread. (2) Using a thread sealer adds more protecting against possible coolant leaks. (3) A tapper thread plus a thread sealer ensures the threat will not come lose under engine vibration. I really think you are in good shape.
