A sad tale of woe

[Robyn]

Well I got the word back just a little bit ago that my prize 599 6.2 block has cracks just starting in two of the middle main webs.
One is about 1/2 inch down on one side of the outer bolt hole and the second is about 3/8 inch down on one side.

Not real bad but enough that I am nervous and will not use it.
Might be a great candidate for a splayed main cap set???

Anyone here thats done that feel free to chime in.

Robyn

[Robyn]

Talked with a local fellow hee that has 6.5m block that has some serious issues and it has a set of splayed main caps on it.
I am going to try and buy them off him and use them on this 6.2 block and then all that will be needed is a line bore job and poof good usable little beastie again.

Never a dull moment is there.

Robyn

[More Power]

I'd recommend not using a block with even small cracks. It's too much work and expense to risk, and it'll always be in the back of your mind, even if were to run a long time.

I've got a 6.2 block in the shop that ran for 200K with a Banks turbo. It has small cracks in the center main web bolt holes (that developed at some point in its life). I use it for a photo prop.

I think Kennedy and Diesel Auto Services in Canada began using splayed main caps 2002 (they were all JK's caps).

Jim

[Robyn]

I have had a couple Pm's with RJ about this issue.

My plan at the moment is to see if I can secure the used splay caps from this local fellow, if that happens I am going to go to work on the thing.

Beings the cracks are still in the very upper part of the bolt hole and have not reached the threads yet I am not really worried.

My intentions are to drill the end of the cracks to stop any further propagation and then to chamfer all the bolt holes and break all the sharp edges on the main webs to help reduce the stress risers.

I have the ability here to set up the splay caps and do the drilling and tapping myself.

The block will fit on my milling machine table just fine and should not be a real issue to get the caps very close since they have already been used.

Once they are bolted in place all nice and snug in a new register I will send the sucker off and have the main line redone to true everything up.

My other choices are to use a 506 block I have or possibly an older J block.
I dont have a crank for the J block but I know where I can put my hands on one.

The 506 block can go right back together as its in fine shape and needs only a set of rings on the original pistons.

I will sort this all aout over the next few days and then see whaqt presents itself as the best way to go.

I know little about the J block as I bought it off ebay about 3 years ago and did nothing but lift the lid off the crate and look in.
I know its fairly clean but cant tell you anything nmore at this time.
Its on the egenda to get it out and off to the machine shop for a trip through the hot tank and a walk past the magnaflux.

Really hurt to hear that the 599 block was compromised.
I really have no issue with fixing it though and if I go that way I am not going to worry a bit about the thing coming apart.

(Just stuff a small broom under the front seat) ;0)

[john8662]

IIRC, the DAS Splayed caps were totally different than that of KD's caps.

The DAS caps are a cast cap similar to the factory cap. The KD caps are steel caps.

Having both I can compare...

J

[Robyn]

I have seen the KD caps and they look great.

The set I sam trying to buy are KD caps.

Any way. Got the Old J block uncrated this morning and in the ack of the dually and after I stuff some groceries down my neck Im off to the machine shop with that oily old wretch.

later folks

Robyn

[ronniejoe]

The DAS caps are stepped so you don't have to machine the registers. The Kennedy caps are not stepped.

[john8662]

The DAS caps are stepped so you don't have to machine the registers. The Kennedy caps are not stepped.

Exactly, enables you to leave material on the block.

J

[Robyn]

Well I just got back from the machine shop and a really good look over the 599 block which had sat all night after the main webs were heated to reveal any cracks.

A careful look over the situation revealed that the cracks were far more extensive than was first believed and went about an inch down and into the area near the pan rail on the number two main.

Sadly I have relegated that block to Sanford and Son.

My 86 J block is now at the shop and we spent some time with the magnaflux and then heated the webs and found no indications whatsoever.

I have high hopes that all will be well.

The next step once the block is through the caustic tank will be another good look over, then on to deburing the main webs, bolt holes and such followed by a trip over to the boring machine.

This block will finish up real sweet with the .50mm OS pistons.

Oh well.
Now I have to scrounge up a crank for a two piece rear main engine.

I needed a different flex plate anyway as the ones I have are all for 4L80 trannies and wont work with the 700R

Looks like I will be able to use the heads that came from the 599 engine though as well as the IP and the injectors.

Such great fun trying to salvage old junk and make it like new again.

Stopped off at the local parts store and bought a couple rattle cans of CAT Yellow paint

This should make things at least look a lot different under the hood.

I just have to do something different on this one. I have always followed factory paint schemes to the letter. NOT ON THIS ONE.

Just gonna let my hair down a bit and have some fun for a change.

All for now

Robyn

[ronniejoe]

Exactly, enables you to leave material on the block.

J

The problem I see with stepped caps is this: There must be clearance at the outer lands, because you cannot precisely locate on two different surfaces no matter how good you are at machining. This means the location for the caps is determined by the inner surface that sits down against the main web. The outer part that sits over the top of the step in the block must have some clearance. If this were the locating feature, you would be pulling the center of the main webs down to contact the cap. This would be very bad to have this tensile stress in the webs.

Since they locate in the center with clearance at the outside ends, the cap is now being pulled in tension across the top. You're also pulling the pan rail into tension as I described previously.

With a flat cap and machined registers, there are no added tensile stresses in either the cap or the block. Since the cap mating surface sits squarely against the block web for the full length, both surfaces are in compression with only local tension around the threaded holes in the block. This is a much better residual stress field for the operating stresses to be applied to.

Stepped caps have been used with success in many applications, but I believe that flat caps are better for the 6.2/6.5.

[Robyn]

I agree with RJ.
The idea of basically creating two stress fields just somehow seems to me like adding more troubles to an already bad situation.

And as RJ just mentioned no matter how hard you try you are not going to align 2 register fits absolutely perfect.

If I were going to do it I would go with the KD caps.

But as I mentioned, with my block the cracks are just too far to even consider it as a fix.

Interestingly enough its really hard to say just how long that old block would last before it finally gave up the ghost.

NOT ON MY DOLLAR THOUGH.

I will admit to building some shakey things in my time but this is just not going to happen on my watch.

later troops

Robyn

[More Power]

John, you may be right about the caps... Perhaps it was the pistons I was thinking about. Here's a shot of the DAS caps.

http://www.thedieselpageforums.com/photopost/data/500/das05.jpg

[john8662]

RJ,

Yes, there is the problem with the outside section not applying force to the block and changing the way the block is stressed under fastener torque. And, the problem that the machining involved isn't easily achievable to perfection to make it even like a flat cap.

I'm still on the fence though.

As mentioned, it has worked well for other splayed caps on the market for other engines, namely Big Block Gassers and SBC racing engines.

MP,

Yep, that's the cap! It's a little different than the KD Cap.

KD Cap here:

http://www.thedieselpageforums.com/photopost/data/505/spayed.jpg

[ronniejoe]

My thinking is that those other applications aren't prone to crack problems already. The 6.5 is, so extra caution is needed.

In fact, the only small block Chevy that I've ever cracked a main web on was the result of a crank failure.

[EWC]

Anyone have any more info on the DAS mains or a website ?

[neo]

Robyn,
You mention deburring the main webs and removing stress risers, or potential risers. Can you provide more detail on this procedure? I just tore down my 83 6.2 today and will take it to the shop monday for tanking and magnafluxing, and then would like to clean up the casting, provided it passes the crack inspection! Any guidance is greatly appreciated. I also notice some flashing on the crank, can that be cleaned up? I intend on bluprinting/ballancing and would love any guidance on that too. Never done a diesel, only gassers. Not certain how different it is. I have read some cautions with regards to dynamic vs. static ballancing. Also, does it help to lighten/ clean up the con rods and pistons where possible? Again, thanks for the info!
Neo

[Robyn]

Well the deburring is an easy question to answer.
Break all the sharp edges on the main webs at the part lines with a fine file.
Now ya dont need to get crazy about this but just knock off the sharp "BUR"
thats along that edge (Boths sides) Use an electric drill with a counter sink and just touch the bolt holes in the block to break the sharp edge

Maybe to 1/32" wide on all the edges, holes too.

Sharp ragged edges can and do promote the start of a crack.

As far as the ballance issue goes I am not sure what you have been told about static or dynamic ballance.

There really is no such thing on an engine as static ballance.

The job is done as follows.

All the moving parts, rods pistons ect are weighed and adjustments are made so that all the pistons weigh exactly the same. All the rods weigh the same
(also the rods are weighed on each end and that is matched up as well as the total) ( the rod bearings are also incuded in this)
Once the reciprocating pieces are matched a set of clamp on weights are set up and placed on the crank throws and the crank is spun in the ballancing machine at the same RPMs that it will peak at in real time running.

The best way to do this is to also include the harmonic ballancer and the flex plate/flywheel that is to be used.

If the technician is real anal ( as am I ) about the job, the crank pulley will be witness marked and included too.

The whole assembly is spun and the vibrations will indicate on a meter that reads from sensors mounted to the machine that read both ends of the shaft.

Once the readings are taken metal is either added or subtracted from the crank counter weights to bring the shaft assembly to a point that it runs smooth.

Back when I was racing we usually tried to get things down to about .1 mils or less.
I have seen factory stuff that was no better than 3 mils
The better it is to start with the better its going to be when its running.



Generally on a slow speed engine like the 6.2/6.5 this is an easy task.

I have seen some very high speed engine cranks that would give us fits to get them right.

Some times you will find a particular setup that will have a fussy spot (Critical speed) and will set up a harmonic, and be a real PITA to get it right.

The little diesels run at a relatively slow speed so these types of issues are not a problem normally.

The term you spoke of "Static Ballance" taken literally this means non moving.

Dynamic means "Changing or moving"

The type of ballance we do on an internal combustion engine is refered to as "Dynamic"

Another point here, Forget that its a diesel, it's a 4 stroke internal combustion engine. Good assembly practice follows suit across the board.

Hope this helps

Robyn

[neo]

Great info Robyn. Thanks! Makes alot of sense with regards to the deburring and crack propagation-some thing I really want to address. I had always heard of static ballancing as the piece part comparison - as you described, where each piece is checked for weight against the other parts (primarilly rods and pistons, and rod ends, then dynamic ballancing as you described with the crank, flexplate, HB and pulley. Seems somewhere I had read something that indicated one of the two steps was unfavorable or somthing of the sort.
I noticed a bunch of flashing on the parting line on the crank and was curious if it advisable to remvoe that too? I am not trying to build a high hp machine, but do want to build an engine that will bring years of life since I am retrofitting it into a grand wagoneer.
The more I read, the more I have become to be a believe in the webs flexing, allowing the crank to flex and break and then take out the lower end as the most common mode of failure. I suppose I feel this way becuase of mentions (like your coveted 599 block) that have hairline cracks and no crank failure. To this end, I am planning on (proved my block comes back with a clean bill of health) to build a lower end girdle. I have contemplated the splayed mains and wonder if there have been any lower end failures (crank) with the splayed mains? If there are none reported, then that would further provide evidence the weak link may indeed be in the thin mains. To that end, a good strong girdle would probably make a big difference, or the spayed mains.
All I am really seeking is reliability. Thanks again for all the information!
Neo

[Robyn]

I have looked these things over a lot.

I have discussed this issue with many folks here and locally.
My personal opinion is that this is a very dynamic issue with many causes.

The crank is a piece of peanut butter for one. The block is less than optimal as far as it rigidity and the depth of the skirt.

The formula that is used in the cast iron has issues.

I was speaking to a fellow today that mentioned that AMG has just recently released a new steel crank, new heads and new blocks for civilian sale from a web site.
This is hear say and I have not had any time to check out the validity of this revelation.

There are many things that could have been done and that can be done to make the 6.2/6.5 engines far better.

The best fix is a better block design as well as a steel crank and beefier heads.

I have thought long and hard about a lot of what we have speculated as to why GM did what they did.
It is my opinion for what ever thats worth that GM designed the 6.2/6.5 on the cheap to get a good mileage engine out in numbers that would last fairly well.

This got them some good fuel economy numbers and saved the bread and butter engines. (350 and the 454) that were very reliable and made bucks for the company.

The diesels were a throw away and the bottom line was they won all the way around even with all the warranty stuff that went on.

They then scheduled the 6.5 for the heap and came on line with the Dmax.
They will do the same with the Max. it will run for a few years and then they will scrap it too and move on.

With AMG reworking the 6.5 it will most likley get much better.
The military does not use the DS4 IP and all the not so reliable electronics on the Humvee so once they get the bugs worked out of the iron so it does not crumble the little diesel rat will be a winner.

A good block with a good ballance job and a set of spayed mains should get you a long way though.

I will say this, and I dont want folks to take this wrong.

Many folks have done a lot of hard work and deserve a lot of credit here BUT
The spayed mains are a bandaid for a far more serious problem.

This engine does not make enough power to really have a need for such modifications.
There is a very sinister combination of events taking place that I am not quite sure of totally.

It would be very interesting to do a stress analysis on this engine in the computer and simulate what is going on while its running.

I do believe this engine is acting like taffy under certain conditions and doing a lot of moving in places it should not be.

A deep skirted block like the old Ford 427 with cross bolted mains on the center 3 would fix most of the issues with the basement going south.

The upper cylinder issues with the cracking on #8 cylinder are due to a couple of stress risers and the thickness of the cylinder wall.

The fact that many engines like the one in my 94 Burb with 250K on it and still using the original pistons, crank and such leads me to beleive that there may be other strange things happening with combinations of parts.

The fact that some run 200+K and others dont make 100K before they break in half sends up a red flag.

Sure, driving habits can hurry some failure along but this stuff does not seem to really care.

But one thing for sure, with Folks like John Kennedy and Ronnie Joe, many good folks at least have the chance to keep the 6.5 alive and get many more good usable miles from their rigs.

I would love to get my hands on a new AMG Block with the new heads and the steel crank.
Unfortunately I cant budgit that kind of $$$.

My hummer project is gonna get a good Old J block and some good used 6.2 heads that still ave miles left in them.

Any way, we just plug ahead with these things

Robyn

[mstockton]

Hooray for CAT yellow! I took a bunch of my half used cans from work and painted mine that way, looks great!! I'm always happy to see our colors on someone else's engine! Not sure if the old detroit engineers would be ;). If you have any surfaces that have problems with paint adhesion, i would strongly recommend the CAT yellow flat primer, really helps with adhesion problems.

-Martin