Lock and stitch inserts revisited

[Robyn]

As many of you know, I am a proponent of the Lock and stitch inserts on the center mains in the 6.2/6.5 outer bolts.

The early blocks used 12mm outer bolts and the later engines use 10mm bolts.

I am of the opinion that on any cracked webs that have the 12mm Bolts that the 10mm L&S Insert should be installed in place of the 12mm ones.

The block must be drilled oversize anyway and using the 10mm insert will reduce the size of the hole and in effect keep more material in the block.

The only things is that it will be necessary to buy 6 10mm main bolts.

The holes in the cap are the same on both so that's not an issue.

If you are going to buy the tools, I would get the 10mm tooling.

Missy

[jggiedeman]

Hi Robyn,

Trying to find machine shops that willingly perform this is proving to be difficult. What do you use besides the tooling that you purchase with their kits? Is this also "Full Torque" under lock & stitches website?

thanks
Jerry

[john8662]

So, if you have a 12mm hole that's cracked, wouldn't you want to use the 12mm insert to fix the hole and pull the cracked material back together?

Here is my concern with the logic.

Use the 10mm insert?

If you use the 10mm insert you are indeed drilling the hole smaller to tap for the 10mm hole insert fix.

But?

Part of this fix is to repair the crack as well as give the block good threads for the main caps. I'm not confident that using a smaller insert would fix a hole that started a crack from a 12mm fastener. Would the smaller insert stabilize the crack? Dunno. Ask Lock N Stitch...

Just my thoughts on the matter.

Let's hear yours.

[JohnC]

The outside of a 10 mm insert is much bigger than 10mm, probably bigger than 12mm. Using a 12mm insert would remove an awful lot of material and might not leave enough to be stable after the repair. All you need is enough to remove the 12mm threads and allow a fresh surface for the insert's tap.

JMO...

[Robyn]

Back when I bought the tooling to do the inserts, I had blocks with 12mm outer holes that needed fixing.

Aftr doing a few of these blocks and installing the 12mm inserts I began to think about this whole thing.

Since GM uses the 10mm outer bolts on the newer blocks and the holes in the caps are still plenty large, it seemed that installing the 10mm inserts would be a far better idea.

The 10mm lock/stitch insert can be installed after the 12mm standard hole has been drilled and tapped with the LS tooling.

This (As mentioned) will keep more parent material in the main web.

I have done the procedure both ways now for blocks that I worked on for others and it seems to be fine either way, just makes better sense to keep the most material in the web as possible.

The cracks on these (if the block is still useable) are normally right through one side (some times both) near the center of the outer bolt hole.

The actual outside diamter of the L/S Insert is not all that much different between the 10 and 12mm inserts.

The holding power is in the reverse threads on the outside of the insert that grabs the casting and literally pulls the sides back towards each other.

The insert is solid and as such does not allow the tightening of the main bolt to cause a spreading action in the threads.

Using the 10mm inserts will simply keep more parent material in the web, nothing more.

The repair should be good either way.

The acual difference in diameters are in the range of 1/8th inch.

When GM reduced the diamter of the outer bolt, IMHO they were grasping at straws, trying to bandaid these until they could be shed of the problem.

The small reduction in bolt/hole size did not stop the cracking.
The issue was in metalurgy, internal stress and tortional issues.

If you just take a good look at the P400 and the hefty solid girdle that AMG designed into that thing, it becomes really clear that a 1/8th inch reduction in the diameter of the outer main bolts was a joke.

The fact that some blocks run 250K miles and are just fine says volumes too.


Missy

[john8662]

Thanks for humoring my curiousity.

For total confirmation I'd like to hear what Lock N Stitch has to say.

[Robyn]

I spoke with them and they pretty much agreed with using the 10mm inserts.

The Kits they sell are specific for the 6.2/6.5 mainline.

Just for arguments sake, lets say you have a 506 block with 10mm outer main bolt holes and one of these has a crack that runs down the inside of the web right at the centerline of the hole (most common place)

Now are you going to drill this out and install the 12mm insert and 12mm bolt ??

The outside diameter of the 10mm insert is only about 1/8th inch smaller in diameter than the 12mm insert

OK while I was typing this post I went to L/S web site. The 10mm insert uses a 33/64 tap drill and the 12mm uses a 21/32 tap drill. So I was off a tad, the difference is .140" (approx)

I still maintain that keeping that parent material is a good idea.

From actual experience in installing these inserts, the drill must go through the exixting hole and out the bottom and into the lower portion of the web about 1/4" more than the original hole in order to be able to tap the hole deep enough to get the insert to go flush with the main web surface.

I bought a spot facer and mae up a pilot to "kiss" the insert and make damned sure it was not sticking up AT ALL.

I mentioned this to L/S once and they now offer spot facers.

Just a light "Kiss" to make the insert a couple thou below the part line is perfect. This assures that you will not have issues when the cap is torqued down..

Again my feeling is to keep the parent material in the block if you can.
The only reason they offer the 10 and 12 mm inserts for these is that the original blocks had 12mm then came the 10mm mods from GM, so they offer that one too.

Once you have drilled one of these out and see just how much materials come out of the area, you will agree that smaller is better.

This area of the block is sadly lacking in iron anyway, so anything that can be kept there will not hurt at all.

Please call L/S and chat with one of their tech dudes, and ask them straight away.

Missy

[akmcruiser]

Hi,
Just recently I got a 1993 1 ton drive-train
It has the L65 engine, no emissions, no cats....
I was told it has 82k orig. miles
I took the heads off to find they are not the same heads
The turbo side has the #567 head, and it is cracked at the second and eighth cylinder where the valves meet
The other side has a head with a casting # L275 and has no cracks
The block is a 599 casting and was made on August 6th 1992 according to the code
Everything looks great inside the block, Pistons, cylinders, bearings, cam.....etc.
This leads me to believe it really does have 82k orig. miles
I acquired this engine to do a long awaited custom engine swap
I have the block to bare bones and am about to bring it to the machine shop for some new cam bearings and a cleaning
After extensive reading on this forum about the engine and a few other forums I became well acquainted with the popular main web cracks
Today I did some detective work and discovered some small cracks on this block
I have read extensively on the lock & stitch full torque insert fix
I'm asking for some professional feedback on whether or not to push forward on this build and do the inserts to remedy the cracks
I have read about checking the deck situation of the block to determine if it has been machined or not
Tomorrow I am going to throw the crank back in and a few pistons to check for sure if it has been machined or not
Thanks for the support
-Ben
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[Robyn]

Looking over the pics

Looks like there is a crack in the root of the register where the cap seats ???

The lock n stitch will do nothing for a crack there.

Most times the cracks are in the center of the outer bolt hole running vertical.

A register fit crack is pretty much a no go thing.

If that is indeed where the crack is I would not spend any $$$ on that iron

Sorry to spread bad news.