Cracks revisited

[Robyn]

Well Im off on another build and as usual the issue of a craked main bolt hole comes right in my face as soon as I get the engine apart.

The Lock and Stitch company markets an insert that has a reverse hook thread that screws into the hole after slightly drilling it out and tapping it.
The insert is solid and when the torque is applied the threads actually pull the material together instead of trying to wedge it apart.

The spreading forces on the 12mm main bolts is terrific and its no wonder that the cracks just continue to spread over time.

I spent a fair amount of time this morning chatting with the folks at Lock and Stitch corp and have decided to purchase the tooling to do the 6.2/6.5 main bolts holes.

With all considered I should be able to offer a repaired hole for about $30 each.

Now this is figured on a clean block that I can get around without getting filthy and also one that I can get my Mag drill onto without needing to scrape off a foot of silicone and dirt

There is one shop in PDX that does this but only on their rebuilt engines and not as a service out the door.

I have already put the word out of the upcoming service and have several 6.5 blocks waiting for a date with me.

One fellow wants all 6 outers done as a precautionary measure.

This system is being used on some pretty large equipment and I have spoken with a tech at the local CAT shop and they have used this on large engines with cracks in castings and are very pleased with the results.

WE shall see.

The tooling is available with inserts and such specifically for the 6.2/6.5 mainline 12MM and 10MM holes

best
Robyn

[BigGun J]

Robyn,
Good news for me! I live in Seattle so a drive to Oregon with some wine tasting thrown in for the wife makes for a pleasant trip. I will most likely be meeting you come spring. Post some success stories.

Jim

[Robyn]

Sounds good to me.

I am assuming you have a block that needs a crack or two fixed??

Robyn

[Kennedy]

Mark Bajus from B.C. had a cracked block in his 1993. He went with this repair and installed my splayed main caps. I was a bit concerned about the crack spreading (building on an unsound foundation) but it has worked flawlessly so far.

[Robyn]

John
Thanks for the input.

I have been nervous about any usage of a cracked 6.2 or 6.5 block up until I found out about these inserts.
The special length insert is 1.125" long so it fills almost the entire length of the outer bolt hole. This translates to a lot of holding power instead of the wedging action of the standard thread trying to split the block more.

After consulting with a local builder that has been using this system on the 6.2/6.5 engines now for quite some time and with zero failures it seemed like a positive step to save many of the dwindling band of otherwise good used blocks.

Yesterday I had occasion to speak with a local who as a matter of boredom I think decided to rebuild his 97 6.5 with only 90K on it.

3 cracks found. He was ready to toss the block on the heap but after our conversation he decided to let me install the inserts.

I personally would be very nervous about a block that has seen the cracks progress beyond the bottom of the bolt holes or one that has the cracks originating from the corner of the register fit area.

I am optimistic but yet guarded about this.

My current project block (Red 6.2) is going to get the inserts (One small crack) but also I am going to stud the outer mains and run them at slightly less torque.

WE shall see.
If the trend that some others have seen prevails, this will be a good thing.

Best

Robyn

[trbankii]

I'm a little far to drop by with a block...

But you mention doing this work as a precautionary measure. I'd like to keep my 6.5 around for the long haul, but don't have the budget for one of the AMG blocks or anything that extravagant.

Not that I'd necessarily be set up to do this work myself. But is it just a matter of drilling out the bolt holes (you mention a mag drill), threading them, installing the Lock and Stitch, and then putting things back together?

[Hubert]

As a discussion...

So what does this say about the block rigidity theory vs just a poor choice of material???

If you drill out the holes and put in inserts of really tough? or strong? material to allieviate the stress concentration and all is well seems to me points to the material specification or quality from GM supplier was wrong. Wonder how much the price difference in material was for that selection?

[Robyn]

There are several things that are or could be Wrong with the block on the 6.2/6.5 family.

The RED block (Real early) 6.2 is reported to have had a higher nickel content and is considered by many to be the "Golden Goose" of blocks.

The issue in the lower end of these blocks is many fold. The high concentration of stress in the outer bolt holes due to the action of the threads alone is staggering.

Just consider for a moment, driving a wedge into the end of a large log.
It takes really very little work with a hammer on that wedge to "POP" that log open.

The same action is happening with the outer bolts in these engine.

Now we add in some very serious dynamic conditions that only some serious stress analysis could possibly pinpoint and all this adds up to what we see happening.

The Lock N Stitch insert is not a new idea but is a good one.
The insert is solid and of a hard material and not a simple coil like a Helicoil.

The threads on the inserts outer diameter are hooked up and out instead of like regular threads. They do not spread the material but instead as the bolt is torqued try to pull out of the hole but the barbed threads resist and actually pull any crack back together instead of like driving the wedge further into the log and causing the problem to worsen.

The issue with the 6.2/6.5 block is a very complicated one and I am sure that if we were privi to all the engineering data from the gitgo we could ferret out what the cause likely is.

My guess is cost, plain and simple cost. Lets make it as cheap as we can and try to get it to last until its out of warranty.

This mentality is that of big corporate bean counters not engineers.

The 6.2/6.5 block that is now being made by AMG/GEP is lightyears ahead of what most of us are running.
Unfortunately so many of us can't afford to drop Mega $$$$ into an engine for an older truck.

The reports I am getting are that if done correctly the inserts will stop the cracks from becoming a fatal flaw.

If the cracks are beyond the ends of the bolt holes and out into the lower reaches of the web I would not use the block.
With short cracks that are within the confines of the bolt holes depth the 1.125" long insert seems to do a fine job of fixing the issue.

To answer your ??? I dont think the supplier had anything to do with this issue as far as any mistakes.

As I mentioned, the RED blocks were the best ones and far less prone to cracks.
I have heard that the cost factor and possibly machining issues or ???? had something to do with the choice to change materials.

The worst blocks are the early 506 blocks with the large outer bolt holes and the oil squirt holes.

The 599 blocks were fairly good.

I have seen blocks with less than 100K cracked at every outer bolt hole and I have seen blocks with 250K that were perfect.

Its a crap shoot as to what you will find.

These blocks dont have any real safety built in as far as extra material to handle the stress.

AMG designed the new 6500 blocks with a huge one piece cap and stud girdle plus better materials and a little more of it.
Plus they are using a forged steel crank.

The issue is one that we will never see (Most likely) all the dirty laundry.

My goal is to use a product that will help the issue without major remachining of the block.

The inserts can be installed in a short time with some fairly simple tools and requires zero rework on the mainline.

Unfortunately it does require the engine to be apart and clean.

Best

Robyn

[Robyn]

Yesterday saw my order confirmed on the Lock N Stitch tooling to do the "Full Torque inserts.

I suspect that the materials will be here some time next week.
In the interim I will be working on making a fixture for my large drill press to hold the engine block so that the main bolt holes can be repaired.

Make no mistakes here folks. I am excited about this repair technique but in no way do I consider it anything magical.
Further investigation locally has turned up the fact that to date many of the 6.2/6.5 blocks have been repaired via this method by a particular rebuilder with excellent results (Zero failures to date)

This rebuilder however does not offer this service on an individual or "retail" basis.

This fact is what has spurred me on and influenced my decision to buy the tooling.

The bottom line is this, if we can effectively repair blocks that have cracks that are still small in length,and have not progressed we have in effect greatly increased the number of useable blocks in the pool.

This is a good thing

Here in the greater Portland (Oregon ) area the 6.2/6.5 blocks are becoming more and more scarce and anything that is crack free goes for a premium.

We shall see where this goes. My hunch is that we can repair and return to service a lot of material that would otherwise be sent to the scrap heap

Best

Robyn

[Hubert]

Robyn I hope you don't mind me discussing it for the sake of how and why. I like to fully understand things and hopefully remember lessons learned for other applications.
Keep us posted.

In essence its like putting a bigger bolt in. But better than that due to thread profile pulling the material together. And distributes the pulling power the length of the insert. Which is better than a stud again because of the thread profile.

I wonder if the original threads were cut or rolled and if that would have made a difference?

For the "bolt thread wedge crack" Looks like a combination -weak material with probable residual stress from casting then maybe quickly drilled ie fast metal removal rate which further imparts more residual stress then add a bolt which stretches the threads what a diameter and half to 2 diameters in depth and you have this tremendous "bolt thread wedge" crack potential for instigating a crack at the top of a bolt hole.

Part of the scatter of data points of blocks with cracks vs no cracks might could be corelated to condition of tooling for putting in the original holes (tap drill size/wear and sharpness and tap sharpness) and the consistency of bolt torque and bolt quality.

I read recently someone likes to use a stud with slightly less torque I think they said to reduce cracking. Makes sense if the the above is why. I bet with better thread locking compounds and better tensile strenght qualities a stud would benefit over a bolt for this application for this wedge effect.

[Robyn]

Having to enlarge the hole to install the insert is definately not a plus because it removes valuable metal from the web. Unfortunately it can't be avoided.

The bottom of these engines have some serious No No's as in very sharp edges on the main webs at the part lines of the web and the cap.
Any sharp edge should be removed and smoothed to remove the stress riser.
All bolt holes should be lightly chamfered.
None of this is done in the 6.2/6.5 block. The holes are sharp enough to cut you as is the part lines.

All bad practice and something you would never see in a performance engine that was to run set on KILL.

There is just too many things wrong here to finger any one thing as being the smoking gun, but a combination of poor finishing, inadequate material, questionable metalurgy and a very suspicious dynamic that may also be responsible for twisting the block in ways nobody had planned.

I have stated and have heard from other diesel techs that having poor injectors as the engine gets upwards of 75K can cause inconsistencies in the power pulses from cylinder to cylinder and agravate an already precarious situation to the point that the dynamic loading of the crank and block fall far outside what the original engineering calc's showed there would be under operating conditions.

So take your pick of reasons as to why this happens.
The best we can do now is to try a fix that seems to work and to extend the lifespan of these poor little creatures.

Another thought that comes to mind is this, "If it ain't Movin, somthins a breakin"

My Dad was fond of this saying during our race days.

Now just for aguments sake, lets suppose that these engines need to move around a little due to whatever dynamic forces that are present.
The block is stressed and it cracks to relieve itself and relax a bit. Now with the outer bolts wedging with a metric buttload of force the crack gets bigger and bigger over time until we see a catastrophic failure.

With the inserts in the block the wedging action is gone but the block can move a little bit if it feels the need to.

The other day I was working on an older 6.2 and had the main caps off. I discovered the usual and much dreaded cracks. I replaced the main cap on one that had a cracked outer hole, as I tightened the inner bolts down in steps the crack in the outer hole could be seen ooooozing oil and there was not a bolt in the hole.

The block was moving some just by tightening the inner bolts.

Another scenario is that these engine blocks are coming out as what we used to call GREEN castings. Years ago castings were run through an oven and stress relieved under some fair heat then allowed to sit outside and rust for some time before machining.

This was said to cure or season the casting.

The 6.2/6.5 castings are not done this way. A new casting can and will do all sorts of wierd stuff during machining and if there are internal stresses in that casting, as soon as you heat cycle it there is going to be more stuff going on.

My bet is that if the blocks were rough machined (Bores and mainline/cam) then the caps installed and the blocks heated up to a fairly high temp to allow things to adjust and settle in the issues we see would not happen.

Unfortunately this would be very costly in the original production process.

Castings just do a lot of strange stuff once you lay cutting tools on them.

I remember years ago that we took our race block and had them heated in an oven to around 900F and held there for 3 hours and then let slow cool overnight.

If there is internal stress and you take a cut on the deck or bore the mainline the thing is going to move around and or allow things to get hinky the next time the block is heated up to operating temp.

Too much stuff is possible, just too much to say, Ah Ha this is it !

Best

Robyn

[Robyn]

Tooling arrived on Weds of this week.
I also got the good fortune of attending a seminar on this tech.

Had a great time and learned a lot about the product and the ways in which it can be used.

I am still working on things though. I have to machine a nice plate that will bolt to the bottom of the block so I can mount the mag drill and drill out and tap the bolt holes.

I have a piece of steel plate and just need to lay it out and drill it.
I will use countersunk bolts to hold the plate to the block and drill some fairly large holes to access the outer main bolt holes

Hope to get at that project tomorrow and then it will be time to get into the meat and potatoes of things.

My plan is to do all the outer holes in a 6.2 block I am using for my project Burb.

Once this block is done I have some other blocks that a local shop wants done.

The seminar really opened my eyes up as to what can be done.

Caterpillar is using this technology even at the OEM level as a preemptive step on some of there huge equipment.

One place that was mentioned was the wheel studs on the 797 Pit truck.
Cat is also allowing it to be used on head bolt/stud hole repair and other places too.

The speaker from Lock N Stitch was very very good to make sure all questions were answered fully.

Keep ya posted and as soon as possible will post pix

best

Robyn

[Robyn]

Update on the Lock N Stitch Inserts

Today I got busy and machined a piece of 1/2" steel plate that bolts onto the bottom of the 6.2/6.5 block using the pan rail bolts (8) 4 on each side to fasten it solid to the block.
I have located 6 holes (7/8"m dia) to allow drill access to the outer main bolt holes.

The plate serves as a base for the Mag drill press to lock onto.

I cleaned up my 6.2 block well and bolted the plate on with 8 countersunk cap screws.

I drilled the 6 outer bolt holes out with the drill provided in the tool kit and then using the mag drill as a guide tapped the holes with the special tap.

The insert required the holes to be deepened about 3/16" more than the stock holes were originally.

A little bit of a learning curve on this little beast but aside from installing the locking pins between the insert and the block, its done.

On the main webs it is necessary to use a flat file and make sure that the insert is flush with the parent material all the way across the contact surface.

Having any material protruding above the mateing surface would spell disaster when the mains were torqued up.

Once I had the surface nice with a bastard file I used a flat oil stone to finish the surface off so the part line with the block and the main caps are nice and smooth.

Here are some pix of things so far.
First pix is the plate for mounting the mag drill
Second and third are the special tools
Fourth is my most humble little machine shop.

Next post I will get some pix of the Block after the repairs were made.

The project block had one very short crack on the outer hole on number 4 main on the LH side and only in the rear part of the web.

The crack was fairly well centered in the bolt hole and had progressed about 3/8" to 1/2" down the hole.

The insert fills the entire hole and actually I had to deepen the hole about 3/16" over stock to get enough depth to tap the threads fully.

Hope this is interesting.

Oh and for those who like machine tools.

The Mill is a Max Mill (Bridgport clone) 9X42 with a DRO on 2 axis.
The Lathe is a Takisawa TSL 800 14X32

I bought the mill off ebay for $400 and a quick trip to LA in the pickemup to get it.
Very fine shape, was used for making soapbox derby car parts.
The Lathe came from Seattle, also off ebay.

Definately makes these little projects easier.

Best

Robyn

[trbankii]

Most definitely interesting!

Thanks for sharing!

[Robyn]

I do hope that it is as good as it looks in theory and is as good as I am being told by the shops that are using it.

The local guys that are using it are not offering it to walk in customers though, only using it on their own rebuilt engines.

Doing my block yesterday was definately the "learning curve"
As is with most instructions "Tuck flap A into slot B and smooth with a large Hammer"

Well the procedure is a simple drill and tap exercise and then thread in the insert but still not without a few little spots that took some thinking.

The install tool is supposed to drive the insert flush with the parent metal but in actual practice left things slightly above the parent metal ( just a few Thousand's, BUTTTTTTT)

I am going to look into a small spotfacer to do a final trim on the top surface of the insert so I dont have to do it by hand with a file.

Just all in a days work I guess.

The proof will be in the pudding as they say.

Later

Robyn

[Robyn]

Got the job done now and its time to move on to the cleanup and reassemble.

Here are some more Piccy's of the block and the equipment.

A view of the block with all 6 outer holes done
A view of the block with the plate sitting on the lower surface
A closeup of a finished hole.
A shot of the block and the Mag drill
Close up of a spotfacer tool I assembled ( and modified)

After getting all the inserts into the block I began to worry some about the fact that this surface has to be perfect and mate metal to metal with the main caps.

The inserts were in as per instructions but were not perfect.
An insert that is sticking up even a couple thousands of an inch is an issue that cant be tollerated.

I decided to purchase a 13/16" counter bore tool (spot facer) and then designed a custom pilot that screws into the 12mm insert and leaves a 1/4 inch pilot shank sticking up.

Normally the pilot is fastened into the counter bore with a set screw.
My concern was running the pilot on the new threads in the insert and possibly causing damage.

The other issue was the fact that the tool supplier did not have any pilots even close to the size I needed and they were not available.

Push came to shove and a bought a hardened 12mm bolt and tossed it in the lathe and turned the head off and then reduced the shank to .250" (1/4") Now I knocked the top off the threaded end so it did not fit quite as tight in the threads.

The piloit screws easily into the insert and allows the cutting tool to spin happily on the smaller pilot shank.

Just before drilling and installing the lock pins in the inserts I used the counterbore and lightly touch the surface of the main saddle and dropped the area of the insert about .030" below the surface.

Now no matter what, the caps will seat well and not have any issue with an improper contact.

During this facet of the procedure I took time to carefully examine the main caps and the block.

What I found was disturbing, the main caps and the block had some very strange contact patterns.
The caps were hard down on the area around the center bolt and had little to no contact through the area between the bolts and then hard down in the area of the register fit at the outside.

Looking over a couple other blocks reveals this to be a normal pattern.

Anyway, with the spotfaced area around each outer hole I am confident that this repair is as good as it can be and that no stone was left unturned, and that it's not going to jump up and bite me in the A$$ later on.

My present thought is to reduce the torque somewhat on the outer bolts and use Blue Locktite there too.

As I do more of these now the process will definately get easier and faster.
The learning curve is fairly well over, and now I can just get in and do it.

Hope this is useful

Robyn

[JohnC]

Nice job!

Out of curiosity, what is it about the insertion process that keeps the insert from going flush with or below the surface?

Re: reducing the torque, as I'm sure you already know, one purpose of torque is to preload the bolt. Reducing the torque will reduce the preload, allowing the bolt to strech under a lower load than originally intended. Seems like you've eliminated the udesireable forces, so why take the chance?

[Robyn]

John
The hole needs to be tapped absolutely straight right to the .001" so the insert can pull down flush.

Unfortunately the use of a mag drill is not the perfect solution and the holes can be slightly off allowing the insert to ride high on one side or another by a few thousands maybe .003-004"

Far too much to allow.
My biggest worry is to be sure that there is no interference issues when the bolt is torqued down.

If I could have gotten this chunk of iron on the mill table this may have been different.

The inserts are installed in the hole with a square headed bolt with a heavy hard washer and a jam nut,
A loctite type solution is applied to the threads as its being inserted.

The install tool takes the insert down untill the hard washer bottoms on the block surface.

The spot face trick got it below the surface to be sure and a very clean job of it.

best

Robyn

[JohnC]

...The install tool takes the insert down untill the hard washer bottoms on the block surface...

Ah-ha!

How about a shim smaller in OD than the insert, so you set them a few thou. deeper?

Save a step...

[Robyn]

Good point John

The issue I have with getting the inserts deeper is that the block already has to be drilled about 3/16" deeper than stock and the new Oversize tap drill does break out of the web a little on the flycut side of the web.

More depth to the insert requires even more drilling and more tapping.

I wish that the tap setup came with two taps, a tapered starting tap and a bottom tap so the hole could stay at less depth.

But, the folks at Lock N Stitch have done their homework so I am not going to go any further at this point.

Best

Robyn