To stud girdle or not?

[afgunn]

I do not want to start a war but... I have read from one end to the other on this. One person saying the stud girdle is "the thing" and another saying "girdles are only good for holding everything together AFTER it lets go". So, any real world experience? Girdles on some of the new gasers are one solid mass for the center mains. In other words, the center mains are all one piece. And the stud girdle kit is not like that. So, how say you?!

[john8662]

It's been hashed before, but not really ALL in one thread.

The general consensus (as I remember anyways) is that the girdle is a band-aide.

The true girdle will tie ALL 5 mains together, plus be tied to the pan rail to further sturdy the block itself, besides just the mains.

Yes, a girdle can be suggested to help a block that has one crack, couldn't hurt at that point. It should also be used as a preventative measure, because, what else are you going to do if you ain't gonna splay it?

Peace of mind as I've put it before...

Another member here that I'm aware of is working on a custom girdle to be tested on his higher-than-most HP 6.5.

We'll see.

I'm installing a regular stud girdle on an engine I plan on abusing on the track (and the weakest '506 block, it's crack free now).

J

[Robyn]

If you have a block that has even one small crack showing, TOSS IT ON THE BONE PILE.
If you are going to spend any money on one of these little beasties be sure the block is sound.
The girdle is not a bad way to go to help the cause.
Splayed mains has many good points. It is a major machine shop operation and is not cheap.
If I were going to spemd some serious $$$$ on a 6.5 I would look at one of two plans.
1- Dig up a 599 block (early 92-94 6.5) and magnaflux it and redo the bores and check the mainline.
2- step up and buy a new block that is produced by Navistar for AMG
I rebuilt a 599 block in my 94 Burb and it was on the backside of 200K when torn down. (Fluxed it and it had no cracks)
Block was sweet and bores were good for more so it went back together for another stint with rings, bearings, lifters, timing chain, oil pump and a new set of heads from clearwater. A high flow water pump is a nice addition too.
New set of squirts and a few hoses and your good to go.

[afgunn]

I agree with both of you. I just wanted to condense the info here up or down since, on so many threads the discussions were either on the stud girdle or splayed mains but, no discussion on one vs. the other or... neither. The Turbodiesel Project Truck did not use either and was a 599 block and Jim towed fairly heavy. I will not be towing or hauling but, I lean heavily toward the stud girdle - an extra measure of insurance at a reasonable price.

Robyn, "new set of squirts" - are you talking about the oil sprayed pistons? It was my understanding that a 599 block did not have oil spraying (same as the 141 and 929 blocks).

I am asking these questions because in the near future (~ 1 year) I hope to be building an engine similiar to the TD Project Truck and I will need to find and purchase a block or short block. I am guessing I have the weak 506 block and do not want to invest in this weak block.

Thanks for the input! Great info! Keep it coming!

[trbankii]

Guessing "new set of squirts" refers to new injectors.

[afgunn]

yea... ! That would be it! Sorry for being so ignorant!

[Robyn]

Yup
Squirts = injector nozzles for us old diesel hands.

Too many slang expressions

Robyn

[Cowracer]

I have the girdle, and this is my totally non-tested opinion. I have no data to back up this claim so I might be totally full of crap, but here goes.

To my thinking, its not lateral displacement that is killing these blocks, its a rocking action of the bearing boss. Lateral displacement (taking the bearing caps straight down) would not generate enough tensile loads to break the block. But rocking of the main caps would, at least on one side of the boss, and then the other until such time as the metal failed.

I have knocked all the inner castings out of a few SBC blocks to lighten them for use as mock-up blocks for building race cars. A suprisingly light blow with a sledge hammer, at an angle that actually knocks the bearing cap backwards or forwards, will break the main bearing boss right out of the block.

Look at it this way, if the cap is on and torqued, and if you applied a force that moved the cap backwards, the back face of the boss would be in compression, and act as a fulcrum, and the front face would be tension. The distance from the bottom of the cap to the fulcrum point would be much larger than the distance from the fulcrum point to the other side of the bearing boss (thickness of the boss). That means the forces applied to the bearing caps would be multiplied many times on the other side of the boss. You could see how these forces could easily be greater than the tensile strenght of the block metal, at least in a tiny portion of the outside edge of the bearing boss

To fail in a lateral mode, the entire width of the bearing boss must have its tensile strenght exceeded all together. I cant imagine what could happen in a running motor to cause that other than a catastrophic failure of the crank or rods. But that is not the case here, as people have driven many mile on blocks with cracks in them.

Summary:

It is my opinion that the three middle main bearing bosses on the 6.5 are too thin, and they can flutter (bottom of caps moving fore and aft) under the right conditions. This flutter builds up tensile forces in the meat of the bearing boss which fatigues the metal and caused failure. I would even hazard a guess that most engines with broken blocks have the thrust bearing worn beyond specification, allowing fore-aft displacement of the crank, causing this flutter.

A stud girdle reinforces the bearing bosses and helps contain the flutter, and thus prevents failure of the block.

I think a stud girdle is a good thing

Tim

[Big Green]

I recently added a main stud girdle to my engine. It's the off the self version that ties the middle 3 mains together. As some might remember from an earlier thread (Another cracked block), when I pulled the pan I found a single crack right where the outer bolt is threaded into the block, center main, drivers side, back side of the web. The crack was just about the same length as the bolt hole is deep. Since this engine was running just fine and I had no indication of when the crack started I made the call to install the girdle and run it until it broke.

Basically, I have no idea when it cracked. It could have been because of the catastrophic pilot bearing failure a couple of years ago, the worn out dual mass fly wheel, or maybe even the failing harmonic balancer. It even could have been caused by the changes in the stress patterns within the block after GM replaced the head gaskets at 99k. Basically, who knows...

I have to say that before the gear drive that I just installed the engine always had a significant low rpm flutter because of the slack in the timing chain. The additional stress from the scattered injection timing could have even caused it.

So, basically I've made myself the test mule. Stick around; I'll let you know when and if it fails completely.


Big Green
'95 6.5TD
Cooling mod's, gear drive, JK exhaust, intake mods and injectors
soon to come: chip and boost control

[cudaaa]

Cowracer I think you have the right idea. If you look at all the race motors out there making big HP #'s mopar ford chevy I have never seen cracks in blocks like the 6.5. I know alot of chevy guys running some form of girdle to make things ridged.

[john8662]

Interesting note about the possibility of excessive thrust or endplay on the crank. Although, I find that the blocks I've taken apart didn't really have much, and ones being put together really don't have much either...

It does seem that blocks with the manual tranny behind them seem to be cracked more (only my personal observation).

J

[Kennedy]

Most of your high HP race engines use a splayed outer bolt...

The girdle is better than nothing, but doesn't really help the twisting of the block...

[JohnC]

There really isn't much thrust force generated by one of these engines. A little from any helical cut accessory gears, and a little when you press the clutch pedal, but all in all very little.

The only way I could see any significant side forces on the bearing caps is if the crank is flexing enough to cock in the bore. Possible? got me...

If you want to talk about thrust forces, look at a piston aircraft engine. Now there's some serious force on the thrust bearings.

[Cowracer]

There really isn't much thrust force generated by one of these engines. A little from any helical cut accessory gears, and a little when you press the clutch pedal, but all in all very little.

The only way I could see any significant side forces on the bearing caps is if the crank is flexing enough to cock in the bore. Possible? got me...

If you want to talk about thrust forces, look at a piston aircraft engine. Now there's some serious force on the thrust bearings.


I dunno. Seems to me that if the crank can flex enough to crack the bosses laterally, which is the assumed method of crack development, then getting enough flex to deflect the bearing caps fore and aft would be no problem.

Tim

[afgunn]

IIRC, Jim has said somewhere that they think most of the cracked blocks come from towing or hauling heavy. This causes the entire driveline to be stressed/flexed/torqued and it would appear that the engine block is the weak link. This also seems to be proven out by the manuals having more cracked blocks than the automatics (as stated above) - the torque converter probably absorbs some of the torque/stress. Then there are the motor mounts. If the mounts are weak or broken this will add more stress to the block esp. if the trans mount is good and esp. if it is a manual trans.

It is interesting that AMG changed the "metal mix" (and a few other things) on their blocks and eliminated the problem.

I am guessing that the stud girdle kit will strengthen the block from this stress and if so, will reduce the possibility of cracks. I will not be towing or hauling but, I will probably still put the stud girdle kit in as some rather inexpensive insurance.

Thanks for all the info guys!

[JeepSJ]

There really isn't much thrust force generated by one of these engines. A little from any helical cut accessory gears, and a little when you press the clutch pedal, but all in all very little.


Idunno...

An automatic can generate A LOT of thrust force on the crank. All that nice fluid pressure wants to push the TC through the back of the block. I don't know if it is enough to contribute to the cracking problem, but it generates a lot more force than accessory gears or the clutch.

Mark

[JohnC]

All that nice fluid pressure wants to push the TC through the back of the block.

I must admit, I don't know enough about automatics to comment on this. That won't stop me, though ;) I'd think that those forces would be pretty well balanced. Still sticking to my story on the manual, though. Is it the thrust bearing boss that's failing?

[Arlie]

Anyone consider the possible role of the dual mass flywheel causing more failures in the manuals? It's notorious for breaking down due to spring fatigue (I think) with a resultant out of balance condition.
Arlie