Threaded insert for head bolts

[Patrick H.]

A friend has just removed the L-98 Tuned Port system from the 1971 LT-1 he recently purchased, and is installing the original intake and carb. A previous owner enlarged the intake bolts from 3/8-16 to 7/16-14, and there is a threaded insert inside the holes as well.

Can we likely remove the threaded inserts and install ones that will bring the holes to the 3/8-16 thread? From what I can find online there may be inserts to do this, but we need to check what the external thread of the insert is before proceeding.

Does that sound correct?

And any tips on removing the inserts?

Patrick

[Joe L.]

Re: Threaded insert for head bolts

A friend has just removed the L-98 Tuned Port system from the 1971 LT-1 he recently purchased, and is installing the original intake and carb. A previous owner enlarged the intake bolts from 3/8-16 to 7/16-14, and there is a threaded insert inside the holes as well.

Can we likely remove the threaded inserts and install ones that will bring the holes to the 3/8-16 thread? From what I can find online there may be inserts to do this, but we need to check what the external thread of the insert is before proceeding.

Does that sound correct?

And any tips on removing the inserts?

Patrick

Patrick-------


I don't know how it could be done with the available inserts. The original tappings would have been enlarged to accept the 7/16" inserts. I don't know of any 3/8" inserts that could be installed in tappings this large. If such inserts existed, accomplishing what you suggest would be simple----just remove the existing inserts and install the 3/8" inserts.

It's possible that he might get lucky, though. If he were to switch the type of insert (e.g. from Heli-Coil to Threadsert) he MIGHT be able to find a 3/8" insert of a different type that would work with the existing tappings (or, even, a slightly larger tapping).

[Richard M.]

Re: Threaded insert for head bolts

Oh Boy this brings back bad memories....

Yes measure the OD of the existing insert. You may be able to use a 9/16" OD diameter insert with 3/8 ID threads like I did on this set of 427 heads.

The process to do this may be tough if the prior "insert" installer wasn't careful in ensuring alignment.

More gorey details, and some Threadsert info here.....

https://www.forums.ncrs.org/showthre...-Thread-Repair

Rich

edit.....You can get up to 5/8" OD inserts, but be very careful to ensure that there is enough head material along the OD of the insert and ensure you won't pierce through into the water jacket or valve ports.

[Patrick H.]

Re: Threaded insert for head bolts

Thanks Rich. I will also have to see how keen the owner is on removing the heads. If they weren't off the car previous to this, then the odds of the holes being straight is not that high...

Patrick

[Gary R.]

Re: Threaded insert for head bolts

Patrick
That might be tricky finding the OD thread for a 3/8-16 insert that is the same as the 7/16-14 insert- I don't know off hand. You should check the wall clearance and thickness in that area too to make sure it will support it. I usually put a drop of Loctite on the inserts when I use them and depending on the location and application may stake the OD thread. If you decide to remove one hit it with a propane for a minute to get it hot enough to break loose any Loctite on the threads, that should be about 350-400*F.

You might be able to make up some once you know the actual size of the tapped hole as there would be more "meat" to tap in the 3/8-16 vs the 7/16-14. Whether it's worth the time, effort, and money I can't say.

[Patrick H.]

Re: Threaded insert for head bolts

Yes, time, money and effort would be the issue. They are the original heads. We have no idea why this was done, but the owner does not want to "hog out" the bolt holes on the original intake just so he can use the larger replacement bolts. His preference is to use the original size bolts with original heads - if possible.

[Joe L.]

Re: Threaded insert for head bolts

Yes, time, money and effort would be the issue. They are the original heads. We have no idea why this was done, but the owner does not want to "hog out" the bolt holes on the original intake just so he can use the larger replacement bolts. His preference is to use the original size bolts with original heads - if possible.

Patrick-------


The only reason I can think of that the bolt size would have been changed is because there were one or more tappings with stripped threads and whatever klutz worked on the engine did not know they could be repaired with thread inserts. The L98 manifold used the same 3/8-16 bolts as all other small blocks.

In order to do this, if it can be done, at all, the heads are going to have to be removed from the engine. Trying to do it with the heads on the engine will likely result in the same sort of problem that Rich M had with the L-71 heads. I also caution that if he takes these heads to a machine shop to have the work done, assuming he can find any willing to take it on, it's going to be very expensive due to the time and effort involved.

[Richard M.]

Re: Threaded insert for head bolts

Patrick, Yes heads MUST be removed to do this task, no question.

What's hard for me to understand...... is why they used "inserts" for such a oversized 7/16" diameter bolt. I have a feeling a very inexperienced person did this. If they did it using a hand drill they are likely not done right.

Are they Helicoils? If so, those have a thin wall thickness and you may be able to use a adequate insert in their place. Regardless, it will be quite a effort for a machine shop to do this properly.

As you mentioned, you will have to take some measurements to see if a larger insert will work. The machine shop will need a Bridgeport, along with special fixturing to hold the head in the correct plane. After drilling out the old inserts, a special mill will be needed to accurately create the new widths and depths of each hole. Then the appropriate tap for the chosen insert.

Timewise, for my attempt at repair, the machine shop set me up on the Bridgeport and after a short training session, I did all of this work myself. I probably had about 5 or 6 hours of my own time at the shop, physically working the heads to prep them. The machine shop charged me some rental time but it was pretty reasonable. I was lucky to have them on my side to help. Then I took the heads back to my own shop to install all of the inserts. Overall, total wall clock time was about 3 days, back and forth north to Grainger for inserts, then south to the shop a few times, my shop, etc.

In my case it was important to salvage the original properly dated heads, even though unseen, and I understand how the owner wants to keep them. If so he needs to expect it to be not only costly, but there also may be risk of failure if the chosen machine shop isn't proficient in this type of repair.

It would help to post some example photos of a few locations on those heads, along with some OD measurements of the existing inserts. It would also be a good idea to thread all of the pre-repair locations with long bolts to see what the angular alignment is. I don't know what the spec is for small block, but the big block heads were not 90*.

After some anxious moments, the results were successful. I was able to salvage both heads.

Rich

[Gene M.]

Re: Threaded insert for head bolts

Manchine shop time can be costly for custom work. Would it not be more prudent to get another pair of heads. I would think heads for a 71 would not be difficult to locate. Standard valve grind, guides, & surface is fairly reasonable since most shops are set up for that. One doing own thear down and assembly avoids cost too.

[John D.]

Re: Threaded insert for head bolts

There are inserts called Big Serts for use in threaded holes previously repaired. They saved many a Northstar engine from the scrap yard.

http://www.timesert.com/html/bigsert.html

[Patrick H.]

Re: Threaded insert for head bolts

Even at my (low) shop rate, it's probably going to be less expensive to get new heads, unless I can talk a patient into machining them in his spare time. He's done some work for me in the past. To have a normal machine shop do them may cost a lot more than new cores.

Sometime this month I will try and get out there and look at the heads myself, then report back.

[Joe L.]

Re: Threaded insert for head bolts

Even at my (low) shop rate, it's probably going to be less expensive to get new heads, unless I can talk a patient into machining them in his spare time. He's done some work for me in the past. To have a normal machine shop do them may cost a lot more than new cores.

Sometime this month I will try and get out there and look at the heads myself, then report back.

Patrick------


I somewhat blew it in part of my previous response. Somehow, I lost sight of the fact that these heads had been fitted with 7/16-14 inserts. I responded as if they were just drilled and tapped for 7/16-14 bolts. I recognized the inserts in my earlier response but seem to have forgotten that fact in my most recent.

In any event, with the inserts it's actually worse than if the heads were just drilled and tapped for 7/16-14. Even if Heli-Coils were the type of inserts used, it would require drilling out to 0.453". Other types of inserts might require an even larger drilling. Even at 0.453" I'd be worried about "break-out".

I really think these heads have been ruined by someone's foolish decision to install these inserts for 7/16-14 bolts.

[Patrick H.]

Re: Threaded insert for head bolts

Patrick------


I somewhat blew it in part of my previous response. Somehow, I lost sight of the fact that these heads had been fitted with 9/16-14 inserts. I responded as if they were just drilled and tapped for 9/16-14 bolts. I recognized the inserts in my earlier response but seem to have forgotten that fact in my most recent.

In any event, with the inserts it's actually worse than if the heads were just drilled and tapped for 9/16-14. Even if Heli-Coils were the type of inserts used, it would require drilling out to 0.453". Other types of inserts might require an even larger drilling. Even at 0.453" I'd be worried about "break-out".

I really think these heads have been ruined by someone's foolish decision to install these inserts for 9/16-14 bolts.

Joe,

7/16-14, not 9/16-14.
Not much better.

Patrick

[Joe L.]

Re: Threaded insert for head bolts

Joe,

7/16-14, not 9/16-14.
Not much better.

Patrick

Patrick-------


This thread must be a jinx for me. I made two crazy mistakes in a row. Anyway, I corrected the foolish mistake.

[Patrick H.]

Re: Threaded insert for head bolts

I went and examined the car today.

As recommended, I had the owner purchase some long bolts in 7/16-14. It was then relatively easily seen that the Helicoil inserts had not been installed straight, as the bolts were not quite parallel to each other. Some tipped in or out, some forward or back. See photo below which shows one hole closer to the lower edge than the other. After doing a lot of calling and finding that no one had Helicoil removal tools available to purchase or borrow, I did some Google searching and found that a large easy-out will remove the inserts. And, it did with little fuss, and only one nice laceration to one of my fingers.

It appears (?) that the external thread might be 1/2-13 with the internal 7/16-14. I need to do some more precision measuring but have not had time tonight.

Unfortunately, since my original post, the owner thought he'd change over to the larger 7/16-14 bolts, and opened up the bolt holes of the LT-1 intake. Of course, it doesn't fit because the misaligned bolts won't align with the holes and they bind.

Our thoughts -
Can we purchase EZ-LOK thin wall inserts with 1/2-13 external and 3/8-16 internal threads? We would then use these to repair the heads using the current tapped holes. Since the intake now has large bolt hole openings, slight misalignment of the bolts will not result in them interfering with the edges of the holes. We would have to use AN-style washers with each bolt, as 3/8 size bolts are really too small for 7/16 holes.

https://www.ezlok.com/cds_categories.php?cid=aaa-carbon-steel&filter=thread_type%3A2%3AUNIFIED%20COARSE%3Binternal_thread%3A2%3A3%2F8-16

To have them machined properly may cost more than they are worth, but that of course is another option. However, there is not a lot of extra metal to machine them any larger for a different sized insert. This is especially true for the end bolts with their blind openings.

Or, do we purchase different heads and (now) a different intake with normal sized holes, and get it all back to correct?

Thanks for your thoughts.