Threaded insert for head bolts

[Joe L.]

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.

Patrick------


If Heli-Coils were used and if the internal thread size is 7/16-14, then the drill size should have been 0.453". Of course, after tapping, they might be a little larger.

I'm not surprised, at all, that you found the holes/tappings to be "crooked"; that's EXACTLY what I expected you'd find. This job was done by a "crude-dude KLUTZ" using a hand drill while the engine was installed in the car. If they had all come out straight, it would have been a total accident.

Personally, I don't think you'll be able to correct this. If the oversize holes/tappings had all been straight, you MIGHT have been able to do it with different type inserts, as you suggest. Add in the complexity posed by the "crooked" holes and I say it's hopeless in any practical sense.

[Richard M.]

Re: Threaded insert for head bolts

Patrick,

I also suspected the "driller" didn't keep the alignment to spec either. Just like candles on a birthday cake right? Amazing.

It's too bad your friend also modified the holes in the intake. Ouch! Now things got worse.

It makes sense to cut the losses and get replacement parts. At this point I agree with Joe. Since I experienced the identical issue with those 427 heads I understand, but in my case, I already had the heads rebuilt so I was locked in to get the holes repaired myself. Rock and a Hard Place.

Rich

[Richard G.]

Re: Threaded insert for head bolts

Time to rethink the effort required to repair this fiasco.
Sounds like it is going from bad to worse.
I would attempt to find the correct heads and a replacement manifold and move on.
Even if correctly dated is important to the owner I think it might be easier than you think.
I would only attempt to repair thees if I was out of options.
As a retired professional I always hated to see amateur work.
Always took more effort and dollars than if it was done correctly the first time.
Also noted; That sometimes the amateur work was completed by professionals.
Rick

[Patrick H.]

Re: Threaded insert for head bolts

Oh, I agree. Then again, I never would have enlarged the manifold holes, but another "professional" suggested he do it.

I found him a set of heads and we will see if they get purchased. I've also encouraged him to buy another manifold and let this one go.
Hopefully over the winter the new heads can be refurbished and they are ready for him in the spring when he returns from FL.

[Patrick B.]

Re: Threaded insert for head bolts

Oh, I agree. Then again, I never would have enlarged the manifold holes, but another "professional" suggested he do it.

I found him a set of heads and we will see if they get purchased. I've also encouraged him to buy another manifold and let this one go.
Hopefully over the winter the new heads can be refurbished and they are ready for him in the spring when he returns from FL.

I think that the GM manifold bolts with built in washers would work just fine on this manifold even if the holes are opened up 1/16". They are used on big blocks but I don't remember if they came on small blocks. Even if they are not absolutely original on small blocks, they could be preferable to trashing a fairly rare 71 LT-1 manifold. Also, if the heads you acquire have had any milling done on them, the manifold with the enlarged holes may fit better than a new manifold.

[Patrick H.]

Re: Threaded insert for head bolts

Patrick, good thought on trying those bolts.

The owner wants to be a bit frugal and think about at least trying the original manifold before buying a replacement. Those bolts are likely a bit larger than using AN washers under normal sized bolts, and could work better.

[Gary J.]

Re: Threaded insert for head bolts

In case the washers don't work Jerry McNeish can save the original intake manifold if he is dead set on on saving the original. It won't be cheap so forget being frugal. I would just replace the heads and intake with the correct dates and move on.

[Joe L.]

Re: Threaded insert for head bolts

Patrick, good thought on trying those bolts.

The owner wants to be a bit frugal and think about at least trying the original manifold before buying a replacement. Those bolts are likely a bit larger than using AN washers under normal sized bolts, and could work better.

Patrick-----


One way the manifold might be saved would be to install bushings in the oversized holes. If you could find some bushings with 9/16" OD and 3/8" ID (actually, I think the original holes are 25/64") they could be installed with green Locktite. A piece of tubing of the aforementioned dimensions could be cut to the proper length and installed as bushings.

[Patrick H.]

Re: Threaded insert for head bolts

Patrick-----


One way the manifold might be saved would be to install bushings in the oversized holes. If you could find some bushings with 9/16" OD and 3/8" ID (actually, I think the original holes are 25/64") they could be installed with green Locktite. A piece of tubing of the aforementioned dimensions could be cut to the proper length and installed as bushings.

I thought about that too. However, being very particular, you would think that the new holes should first be machined to be centered on the original hole locations. After all, opening them up was a Bubba move to follow the previous owner's crooked Helicoil Bubba move.

I also thought about Jerry MacNeish, and did tell the owner to at least call him to discuss it.

[Patrick B.]

Re: Threaded insert for head bolts

You guys are way too concerned over the enlarged holes in this manifold. As I understand, the holes are only enlarged about 1/16" so there is no threat that the flanges are weakened and may crack. The holes do not locate the manifold; the head surfaces do that. Unless the block and the heads have never been milled and the head gasket is of the original thickness, you would probably have to either enlarge the manifold holes or mill the mating surfaces of the manifold for it to fit anyway.

Worry about the heads instead. Real LT-1 heads would be hard to find when looking for a small date range. Loose heads have probably been worked over a few times in 40+ years, and if they have been milled, a perfect manifold is unlikely to fit without modification. Finding ordinary heads with the right casting number in your date range is easier, but they will need a lot of machine work to turn them into LT-1 configuration. The rocker studs will have to be pulled, drilled and tapped, and machined for guide plates and screw in studs. The valve seats will have to be machined for 2.02 and 1.60 valves. As mentioned here before, do not let the machine shop install hardened seats. The pushrod holes may need to be enlarged also. Use your old heads as a model.

[Richard G.]

Re: Threaded insert for head bolts

The rocker studs will have to be pulled, drilled and tapped, and machined for guide plates and screw in studs. The valve seats will have to be machined for 2.02 and 1.60 valves. As mentioned here before, do not let the machine shop install hardened seats. The pushrod holes may need to be enlarged also.

You forgot to add machining the side of the chamber next to the intake valve.