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(I hope I'm posting this in the right area). I'm in need of advice in repairing a stripped thread. I'm working on a '65 Coupe with '65 heads, There was a small oil leak on the left bank valve cover towards the rear. In preparation for changing the gasket, I read a lot of the posts on the forum about types of gaskets and gasket sealants. However, when I started, the first indication that I knew something was wrong was the rear bolt turned out to be not a bolt at all, but an oversized stud. The stud wasn't really tight at all and more or less came out by hand.
When I removed the valve cover, I could see a hogged out hole where someone had made an attempt to drill out the original bolt and cram in a bigger one. I'm assuming the original bolt snapped off because the depth of the hole drilled isn't as deep as the other bolt holes. It could probably be drilled down another 1/8 to 3/16".
The drilled hole was not tapped with new threads and it looks like the "repairer" just tried to force the bigger bolt in. The challenge became even bigger when I cleaned up the hole and discovered three cracks in the sidewall of the bolt hole. No missing metal chunks so I don't think anything is contaminated.
This is an original '65 head and I don't want to toss it in the scrap heap. Nor do I want to remove the head at this point. It would be great if there were an easy permanent solution that didn't involve head removal. If I remove the brake power booster, there's ample access. I've got plenty of mechanical aptitude, helicoils, JB Weld, and determination, but would like to hear from others who may have experience in fixing a hole like this. I've learned over the years that it works out much better to have wise counsel before making a bad situation worse.
Thanks!
John
The red arrow point to the thread that's been stripped/drilled..
A close up of the hole, after cleaning it out a bit. Upon further cleaning, I discovered three cracks in the side of the thread wall. Another angle of the cracks. The top bolt is the one that normally fits. The bigger bottom bolt was crammed, not threaded, into the drilled out hole.
I don't have a repair solution for you but..... I have to ask. Looking at your pics it appears that the cast iron around the offended bolt hole is cracked? Are those lines that appear to be pointing to the 10 and 3 o'clock directions flaws in the pic or are they stress lines or cracks in the cast iron? They don't look good.
Bummer. I was thinking a helicoil might be the solution but now with those stress cracks - I am not sure that will work. Granted, there is not a lot of force applied with a bolt to hold the valve cover on but if those cracks are longer than maybe a 1/4 inch it may just not hold. I suspect that if the head was removed a welder could beef up that area so it holds - you wouldn't be able to see it - then a helicoil could be inserted into the hole after you run a tap down it. Others may have a better solution. Good luck.
I would think it's definitely going to need more than just JB Weld. But I don't think I would remove the head to do so.
A competent welder would be able to repair that in its place. Obviously, you will want to clean and isolate the surrounding area in preparation for the weld.
Bummer, the good news is that valve cover bolts only need approx. 30”lbs. (inch lbs.) to seal soooooo you could epoxy a 1/4” threaded stud in that hole then use one of the valve cover wing style fasteners with a spreader bar style underneath it..
or, Drill out hole for a helicoil or other type hole repair option I’m sure there are some machinist on this site that can probably lend some other info on this, good luck..
As you probably know but its vital you want to keep debris at a minimum cover/wrap all other areas so metal shavings debris don’t collect on in that cylinder head use a shop vac or vacuum cleaner as you drill repair etc..
Agreed those cracks don't look promising. They may not propagate all the way into the bolt hole, though. It would be worth trying to drill the broken bolt and get an extractor on it. There may still be enough depth for a heli coil once the broken bolt is removed. Some of that depth is below the valve cover rail and won't be cracked.
Someone on here will know if you can safely drill that hole deeper.
It would be problematic to weld those cracks even with the head out of the car. The high carbon content of cast iron (2-4%) creeps into the weld, and the result is often brittle/hard metal. I think I'd JB Weld the cracks, drill and insert helicoil because...
The torque spec for SBC valve cover bolts is only 3 foot pounds (it's surprising a bolt snapped there). As long as the new threads/helicoil and bolt run a few threads deeper than the cracks/JB Weld, then the 3 foot pounds should hold without problems. Other opinions may vary.
Charlie M's suggestion of spreader bars is a good one, and the tall wing nuts look great under the hood. The spreaders and a few minutes with a body hammer and small drift on the valve cover edge around the bolt holes eliminated a pesky leak on my 327/300 after trying many different gaskets and sealants. Then I installed chrome valve covers (I believe they are made of chineseum) and one cover is leaking again, but very slightly, and clean up is easy so I live with it.
JB Weld is powerful stuff. If you go that route be sure to get the slow curing (24 hour) - it is harder and stronger than the quick cure stuff. Hell, you could probably fill the hole with JB Weld, drill it and then run a tap into it - skip the helicoil - or use JB Weld to secure the helicoil in the hole. IF you have an old piece of cast iron laying around - an exhaust manifold or water pump or something like that, I would do some experimenting before your first attempt on the head.
I've used Time-Sert inserts before with great success. However, not for the exact repair here, the insert is one piece, not like a Heli coil, might do the job. https://time-sert.com/
I don't think you can weld it. The cast iron has absorbed oil over the years and will be difficult to burn it out before welding. Also you must use preheat and post weld heat treatment on cast iron unless there is a new weld process I don't know about. Both preheat and post weld heat treatment require uniform heating of the entire piece, thus the head would have to be removed.
Your first problem is drilling the old bolt out. Unless you have a Mag Drill, you will need to guide the bit by drilling through an old valve cover or a fixture to assure you are going in straight and remain centered.
A left hand drill bit may help remove the old bolt or might not if the PO filled it with crap. Check the depth of the other holes and use that as a guide. I checked a 66 head and the holes are 5/8" =/- deep. I think you might try drilling it for an extractor first to see if it works. If not, drill it for the 1/4"-20 tpi original bolt tap size and see if you can remove the remaining treads of the old bolt. Hopefully you have remaining good treads below the BUBBA repair attempt. You only need 3/16" of good (unmolested) thread to hold the torque on the valve cover bolts. IF you can find good threads, use a 1/4"-20 tpi stud instead of a bolt for that hole, unless you are chasing NCRS of course. I like to use studs on all 4 bolts as it guides the valve cover in place.
I would do everything possible to try to find the old bolt and remove it find salvageable threads. Even 2 or 3 threads will be stronger than epoxy. You might consider using a stud set in epoxy for that hole.
I am not sure you will not lose the integrity of the cracked iron around the hole, especially if you try to tap the hole and exert pressure on the sides. If you have to tap it, I would save the pieces anyway to determine if you need to epoxy them back to create the hole.
One might consider cleaning the hole as well as possible, then filling it and and cracks with the original 24 hour drying JB Weld or better epoxy. Then, drill and tap the hole for 1/4"-20 tpi. The cure time and temperature of the epoxy is critical. The quick dry is almost worthless for this type of repair. This would be my last resort other than removing the head and having it welded.
Make sure to have plenty of your favorite beverage for waiting the the epoxy to dry and celebrating.
A lot of experienced technicians are expending good mental energy trying to give you options that will work. Compliments to all. One more CRITICAL issue you have to consider is, is there a possibility that after a repair, regardless how you do it, is there even a remote chance that pressure resulting from the repair will force a small piece or corner of the already cracked area break off.... and work its way into the engine where it will do a whole lot of damage. If you attempt a repair by one of the good suggestions offered - the last thing you might consider doing is attempting to deliberately break off a piece of the cracked area - give it a good stress test. If it moves - it is junk. Your call - there is some risk involved here. Please do let us know what you decided on and how it worked.
A lot of experienced technicians are expending good mental energy trying to give you options that will work. Compliments to all. One more CRITICAL issue you have to consider is, is there a possibility that after a repair, regardless how you do it, is there even a remote chance that pressure resulting from the repair will force a small piece or corner of the already cracked area break off.... and work its way into the engine where it will do a whole lot of damage. If you attempt a repair by one of the good suggestions offered - the last thing you might consider doing is attempting to deliberately break off a piece of the cracked area - give it a good stress test. If it moves - it is junk. Your call - there is some risk involved here. Please do let us know what you decided on and how it worked.
Good advice from 64L76. If you have 3/16" of good threads left, you don't need those cracked pieces anyway unless it is on the exterior side of the hole and will leak oil. You may either encase them in epoxy or break them off and trash them.
Wow, thanks for all the great ideas. I didn't think of all these options. Nor was I aware of Time-Serts, I'll look closer at them. The bottom line is I appreciate all the suggestions and I am grateful there is such a wealth of experience on this forum. I don't feel so doomed after all!
I think I will start by trying to drill out the remains of the old bolt to find good threads. I'll have to be careful because I'm assuming the remainder of the hole is filled with a broken bolt. But it could be the original bolt was stripped and the repairer was drilling it out but snapped a drill bit off in it. I won't know until I actually start to drill.
I wonder how deep I could actually drill down to? R66: I wish I had 5/8", but these bolt holes only go down just shy of 1/2", more like 7/16". If I could drill a little deeper, maybe I could get some more metal to tap threads into?
The other question I have about taps is, wouldn't I need a type of tap that can be used for a hole that is bottomed instead of one that goes all the way through the work piece? I vaguely remember reading something about taps like that.
The cautions about metal chips is well taken. Right now, all the cracked pieces are intact and accounted for. Thankfully, I'm not missing any pieces and wondering where they might be. I'll also ensure the area is well masked off for any stray shards that might come off.
Regarding the spreader bar style fasteners that Charlie M mentions, I actually think I may have one in an old parts box from a previous car. I'll check them out.
Thanks again for all the ideas and confidence builders. I'm off to see about moving the power brake booster a little to the side so I can get straight-on access. I will definitely post an update.
There are many good suggestions here. A couple of things I would add. First, you are correct about different types of taps. Ideally you should use a three tap set, starting with a taper tap, second a plug tap and third a bottoming tap. You can usually skip the plug tap step if you are careful starting the bottoming tap. And, do yourself a big favor and get good high speed steel taps. The typical carbon steel taps from the local hardware store are usually weak and you have a fair chance that you could be trying to extract a broken tap.
I am a big fan and user of JB Weld, but for this application I would use one of the metal bearing epoxies. Devcon and Belzona make good ones. Also, it is critical that the area is cleaned well. I would use lacquer thinner to remove as much oil contamination from the repair area as possible before using the epoxy. I recommend the epoxy repair because I agree with others here about how difficult it is to clean and prepare oil contaminated cast iron for a proper weld.
Ted,
You just saved me a ton of hours looking up taps. I just called MSC and placed an order for the 1/4-20 taps as well as a couple of fresh #7 (.201) drill bits. MSC was very helpful and they even got their metal technician on the line when I had a question about size of drill bits. A very pleasant-to-deal-with company. I should get the taps in tomorrow.
You also mentioned an epoxy with metal added, DEVCON and Belzona. I'm starting to investigate them. When I was in Autozone the other day, I looked at their highest temp epoxy, which was 500 degree C. They also had the same temp epoxy but with metal added to it. I'll take a look at all three and pick one out. (and make sure it's not the quick set type as 64L and R66 pointed out).
I don't have a spare set of heads, am I dreaming to think I could drill virgin holes into a cast iron cylinder head? The thought was to drill the existing hole a little deeper to try and get some a couple more threads. I'm probably overthinking this.
Ted,
I don't have a spare set of heads, am I dreaming to think I could drill virgin holes into a cast iron cylinder head? The thought was to drill the existing hole a little deeper to try and get some a couple more threads. I'm probably overthinking this.
Thanks,
John
John, You are running too fast, stop, grab a breath and look at the top of the valve cover rail on the head and measure down to the inside surface of the head. All three sets I measured 66, 68, & 69 were more than 3/4" down. Therefore, I would not be afraid to drill the hole to 3/4" deep if I had to, and get new threads with a drill and tap. If I am looking at it right, the hole will be between the cylinders and worst case would be drilling into the water jacket of the head. Then a 1/4"-20 tpi stud becomes mandatory with pipe dope on it to prevent coolant leakage. Once again, the toughest part is maintaining a straight hole to assure the valve cover fits. Hope you don't have a broken tap in the hole.
10-16-2022, 09:32 PM
Valve Cover Bolt Thread Repair
