Stripped bolt in valve cover. Best way to fix?

[Freddo]

Hi everyone! Got a quick question on the best way to deal with a stripped bolt in my valve cover. It's a 1967 283 with Mickey Thompson valve covers which appear to be aluminum. These were on the truck when I bought it 1 1/2 years ago. The bolt holes on the valve covers are raised and it appears that some slightly longer bolts than stock were used and even though they are longer, these longer bolts don't appear to get a lot of threads into the hole. These valve covers have been leaking since I bought the truck and after reading the threads, put on a felpro neoprene gasket with the steel which sounded like the best bet for stopping leaks. I got everything changed and as I was tightening down the lower front bolt on the passenger side, I stripped it. It wasn't very tight, so it might have been already stripped. I pulled the bolt out and the threads look thicker on the bolt about half way down it, but it doesn't appear to be cross threaded.
Bolt length is about 1 1/4 inches & it has a 7/16 inch head. I was planning to go down to parts store & buy a slightly longer bolt to try to get it past the bunged up threads in the head. I don't have a tap or other tools to clean up messed up threads & haven't used one before but would be willing to buy one (if not too painful) and learn. What would be the least expensive and/or most effective way to fix this so that it holds the bolt? All help appreciated!

[SS Tim]

So its the head that has the thread issue and the bolt is the holdown bolt going through the valve cover, correct?

Cleaning up the threads might work with a set of studs. If you are unsure how get some help. Worse case you can put a keensert in the head.

[supercheyenne]

Originally Posted by Freddo

I was planning to go down to parts store & buy a slightly longer bolt to try to get it past the bunged up threads in the head.

This will be the cheapest and easiest "if it works". You can test the threads in the hole by removing the cover and gasket.

Here's what I'd try (for free!).

1) Remove cover and gasket.
2) Place a bolt in hole without turning. Measure how much it sticks up.
3) Now cautiously turn the bolt into the existing threads and measure when it bottoms out.
4) If the depth ends up being 1.5 times the diameter of the threads then you will be fine using a longer replacement bolt.

BTW, these are 1/4-20 bolts/threads. So you'd like to see the depth at 3/8".

[SIXTY9]

I have used Helicoil Kits at local parts stores. You can buy the kit with the correct drillbit and tap to install the helicoil, all you need is a drill and tap handle. like Supercheyenne said 1/4-20 threads.

[SIXTY9]

Originally Posted by SIXTY9

I have used Helicoil Kits at local parts stores. You can buy the kit with the correct drillbit and tap to install the helicoil, all you need is a drill and tap handle. like Supercheyenne said 1/4-20 threads.

looked online at parts store I guess you have to buy the drillbit now. Been few year sence I bought one.

[BLT gmc]

Definately recommend the Helicoil. Bruce

[Freddo]

Thanks to each of you for your replies!
Tim: Yes, It's the head that has the bad threads and the bolt is the hold down bolt for the valve cover.
SuperCheyenne: Thanks for the suggestions. I'm going to remove the valve cover and try what you suggest. (Couldn't get either bolt to thread with the valve cover on)...
I went to the local parts store this morning. You were correct: This was a 1/4 inch by #20. Bolt length was 1 inch. The next size up the store had was 1 1/2 inch. I brought it home to try it. I also was able to clean up the bolt that came off the valve cover. (Once the threads were cleaned up, it looked great.) , But couldn't get the danged bolt to start.
I haven't had any experience with taps. I'm assuming that a decent parts store. (The fellow at the one I went to this morning had no experience with helicoils) could give some guidance? Can I buy a helicoil with 1/4 inch by #20 thread? From what I've seen, the outside thread on the helicoil is a specific size. Would I buy a tap with that specific size? Some mentioned a drill bit and I've seen some threads on epoxying in a helicoil. What is the best way to get this fixed so that it will hold?
My plan is to remove the valve cover again and do what is needed.
I know these are very basic questions and to some of you with more experience, probably a dumb question, but I appreciate your help and replies.

[brown7373]

Before I got into a helicoil, I would try buying a 1/4 20 tap and run it into the hole. Heads are pretty tough, and can probably be fixed. Using a tap just involves screwing it into the head a little at a time, keeping it straight into the hole. You may have to screw it in some, then back out a little. You should also be able to find 1 1/4 length bolts at any good hardware store, like ACE, if 1 1/2 is too long and 1 is too short.

[SS Tim]

Problem is Helicoils don't work as well as a Keensert. Either is going to be a problem due to it being a shallow blind hole. They both install by drilling oversize then restoring threads. The helicoil uses a wound diamond shaped steel coil to creat a thread within a thread. The keensert is a threaded sleeve that isn't prone to unwinding like a coil is or have the bothersome driving tang. But most inexpensive "kits" are not intended for blind holes. This probably isn't the project for you to be learning how to install thread inserts on.

If you are going to try and chase the stock threads you will need a bottoming tap. Probably two so you can grind one to a short semi-starter nose. If you can clean them, then a full set of valve cover studs and locktite will keep you from cycling the threads again.

[70CHEVYBB]

I would try a bottom tap first and then a stud

[67 cst swb]

Originally Posted by 70CHEVYBB

I would try a bottom tap first and then a stud

Agreed...
I put studs in all my engines for the valve covers... it is so much easier to just place the gasket (I always use cork) onto the studs, then the valve cover, then put on the nuts with the flanged washer built-in.
Plus once you fix the threads (however you decide to do that) you thread a stud in once with some thread-locker on it and your done with that thread issue.

[swamp rat]

Another vote to run a bottoming tap first, hopefully it will fix the buggerd thread.

I also run studs cause it makes gasket changes easyer. fully agree with 67 cst swb.

Keenserts are better, but i havent had a problem with helecoils comming unravled so both will work ok as long as the Keensert does not require too large of a hole for the raised wall on the head.

[67 chevelle]

Originally Posted by SS Tim

Problem is Helicoils don't work as well as a Keensert. Either is going to be a problem due to it being a shallow blind hole. They both install by drilling oversize then restoring threads. The helicoil uses a wound diamond shaped steel coil to creat a thread within a thread. The keensert is a threaded sleeve that isn't prone to unwinding like a coil is or have the bothersome driving tang. But most inexpensive "kits" are not intended for blind holes. This probably isn't the project for you to be learning how to install thread inserts on.

If you are going to try and chase the stock threads you will need a bottoming tap. Probably two so you can grind one to a short semi-starter nose. If you can clean them, then a full set of valve cover studs and locktite will keep you from cycling the threads again.

I am a certified machinist ,,,, I will reiterate this """This probably isn't the project for you to be learning how to install thread inserts on.""" cylinder heads and in particular the 4 small threaded holes for the valve covers are a real pain to mess with , the metal is super hard after thousnds of heat cycles and it does things that surprise even old machinist/mechanics ,, get someone who is well acquainted to resolve this for you ,, this is been there, done that , had it bite me in the ass advise