Torque and block breakage

[Robyn]

In going over some very interesting thoughts about our venerable little diesel beasts I am starting to see some interesting things come to mind.

Engines used in light to medium service "seem" to last a long time and not break.

Engines that are used in towing and are used hard seem to fall victim to the cracked main webs.

Now these engines are used in marine applications producing some very high HP.

These engines seem to live fine.

One thing with a marine engine is the reaction torque applied to the block is minimal and the engine mounting is totally different.

I have been in the boat racing business (Drag boats)
The torque is simply a lot different with all the slippage of the prop or with a jet drive its even more so.

So we take an engine that in marine service and as they say a boat is going "uphill" all the time as there is no coast to speak of.

The engine is loaded constantly when running and there is always plenty of cushion so the block does not see any gut wrenching torque as compared to a truck that is fastened to the dirt by the tires.

The truck scene is a very dynamic atmosphere that can change rapidly depending on the driver and the task at hand.

The marine application is totally different all around.

I beleive this to be one of the big reasons that the 6.5 works so well in marine duty and of course the availability of lots of cool water to keep the heat down.

I am also thinking about another variable that we might be able to change.

The current girdles are limited and a few very creative ideas have popped up here on the page..

Just for aguement sake.

What if we were to produce an oil pan that was radically different.

Lets say we make the pan rail from 1/2" steel and then build the box from 1/4" steel and fab it up into a very ridgid box and gusett the heck out of it so it cant twist lengthwise at all.

We mill small o ring groove in the pan rail to install a piece of o ring for our side seal and this would allow us to bolt the pan metal to metal with the block with no goop to allow slippage.

Now we have created in effect a deep skirted block (Sort of)

This would not be all that hard to do.

An old used block with some cracks already would provide a great foundation to fab the little beast on.

Once the fabrication is done, the pan should be stress relieved in an oven and then the mating surfaces touched with a cutter in the mill to true everything up.

This would certainly add some very much needed stiffness to the bottom end of the block.

Just a thought for chewing on

Robyn

[john8662]

Could also be an unsuspecting surprise to any fella that's underneath a rig trying to remove the new upgraded oil pan.

Man, that's heavier than I thought!

Joking aside...

Some of the Hummer pans are said to be heavier in construction, Matt at Penn mentioned this to me once about that being another source of strength used in conjunction with the newer block.

I think the pan idea is a good one.

I'm not sure that the bolts in current use on the block are going to be large enough to support the heavier pan. Perhaps they will.

J

[moondoggie]

Good Day!

Another thought: I'd like to see an hourmeter on a marine engine, ESPECIALLY if hours at load could be determined. Why? Strictly from memory, our venerable engines seem to go 50,000 - 150,000 miles B4 they grenade when used to pull a lot; as you say, without heavy work, they might last forever. At 50 mph, that would make 1000 - 3000 hours. I wonder if any marine engines can make that claim? Maybe so, I don't know anything about this type of engine in a boat, so am simply guessing there's a small chance that none of them see the hours our trucks do.

Something to consider; data please.

Blessings!

[More Power]

Crankshaft harmonics probably have more to do with failures than anything else. You have first order harmonics, second order harmonics and so on. If your use (gearing, speed - utlimately rpm) of a diesel engine puts the rpm right on top of a harmonic, it could fail sooner - in an engine destined to fail. That failure could manifest itself as either a cracked block, or a broken crank and block...

Crankshaft loading due to the power stroke has much less effect on the crankshaft than the dynamic loading due to centrifugal force at higher rpms. If it takes 300 lb-ft of engine torque to tow a heavy load down the highway, each cylinder is only contributing a fraction of that torque. If engine torque was a major contributor to crank/block failures, it would seem logical to assume the failures would appear near the back half of the crank. In reality, crank failures appear more often at the #1/2 crank throw.

As has been written in the various diesel engine books I have that discuss the engineering principles of engine operation, literally tons of torque (twisting force) can appear momentarily in a crankshaft not properly damped - due to harmonics.

Just about anyone who has driven or towed with a diesel pickup for any length of time can tell you what engine rpm the engine seems happiest. Some of this is due to power and/or torque curves, and some is due to harmonics (or rather a lack of crank harmonics at specific rpms). For example, several years ago a longtime 6.5 owner who drove a 1994 K3500 dually with 4.10 gears and a 4L80-E auto told me 2150 rpm was the sweet spot for towing. Not 2100 or 2200, but 2150...

Jim

PS. I visited the Fluid Damper booth while at SEMA last fall. I talked at length with one of their guys about dampers. I learned that repeated engine & chassis dyno tests have proven a better damper can help produce more engine power/torque at the rear wheels. In their case, a Fluid Damper is said to add as much power/tq to the rear wheels as what a performance exhaust system does. Crankshaft harmonics....

PSS: Peninsular Diesel once told they had a 6.2L turbo marine engine operating in South America with more than 6500 hours on the clock. It had even survived a sinking in salt water.

[john8662]

Marine Verses Highway usage life...

When is a marine engine primarily operated?

When is a vehicle powered by a Gm engine on the highway operated?

For the marine engine, mainly Warmer months of the year, or summer time...

I believe that colder temperature areas where the engine is operated help contribute to cracking, which the highway usage GM diesel engine will be subjected to, not the marine engine.

J

[JohnC]

... At 50 mph, that would make 1000 - 3000 hours. I wonder if any marine engines can make that claim?...

Tru, but marine engines are typically run at very high power levels for long periods of time, so, from the standpoint of stress, they're right up there...

Forget about all this block stuff, just go with a hydraulic drive... ;)

[TurboDiverArt]

Tru, but marine engines are typically run at very high power levels for long periods of time, so, from the standpoint of stress, they're right up there...

Forget about all this block stuff, just go with a hydraulic drive... ;)
True, probably more comparable to the time our trucks are driving up a grade. I

[TAG]

I have been told by a marine engine manufacturer that all of the late 90s 6.5 turbo oil spray blocks they built cracked save one that they dont know where it is.

[Hubert]

I have been told by a marine engine manufacturer that all of the late 90s 6.5 turbo oil spray blocks they built cracked save one that they dont know where it is.

If anyone won't believe a boat is under load all the time tell them to compare taking a boat from WOT to no power and see how long it take to come to a stop then take a car/truck to the salt flats and do the same. Hull design and displacement would determine load. A big boat with deep V hull might be like a 7% grade or more??? A flat bottom light boat would be like a 1-2% grade. Depends on drive drag too.

Can you explain that data a little more. Are you saying a boat mfg had near 99% failure of late 90's 6.5's?? That seems a bit high. If it were that bad of design how could Pennisulars 400HP and + models survive with just a little more nickel in the block and 18:1? There has to be more to that story. Were all failures in big boats with big propeller or what? What were outdrives and motor mountings? What package was it?

There is not a different "marine enigne manufacturer". They all buy the same automotive engine then "marinize" it depending on the application. I don't know what they did to the 6.5. But for comparison the Mercruiser 350 magnum SBC was iirc: disassembled recranked, re bearinged, reoilpumped with stuff meant for steady hi rpm hi load operation. Then put back together with a sealed starter and alternator. Again iirc Mercruiser reaspirated it to thier design. But its still the same ole SBC "automotive" block.

[simon]

As for twisting the block under load one would say that twisting would be the greatest in the middle, but the webcracks are mainly found on # 2, at least on the ones I have seen. But maybe the stresses are the greatest there, as the front and back of the block resist twisting the most.

I was thinking of machining or casting a girdle that would include al main caps and the panrails in one solid piece . and splay the outerbolts the boot ,instead of cross bolting the girdle to the caps. That way it will be the most rigid.
And drill the panrail bolts one size bigger using grade 12 bolts.

What do you people think of that??

the cost of making it could be somewhat prohibitive though?

Is it worth the trouble?? It is probably cheaper to get a nice new China block

[ratman]

SNIP....the cost of making it could be somewhat prohibitive though?
Is it worth the trouble?? It is probably cheaper to get a nice new China block

Simon, -that's like "stirring the pot" with a 200HP outboard motor! :D

In all seriousness though, -does anyone know where that nifty picture is of that machined lower-end setup that involved the main caps and pan rails? It wasn't the AMG, -but a private operation.

I remember seeing it, -maybe on here somewhere, -looked like a one-off, -and looked really NICE (machined from aluminum).

Making something like that out of a chunk of iron would be the cat's meow (in my opinion).

For people wanting to take some serious preventive action against a broken bottom-end, I just can't see how it wouldn't at least help.

Expensive? -yeah, heavy? -umm, yeah.

[MaxPF]

Typically the cracks in 6.2's & 6.5's start at the outer bolt holes on the intermediate main bulkheads. I think when a stud girdle is installed the studs are helping a lot more than the girdle (unless the girdle is thick - I'm reffering to the thin Kennedy/DSG girdle). When you torque a bolt in a threaded hole it generates a lot of radial force as the threads in the block and those on the bolt try to force themselves away from each other. This leaves a large amount of static stress around the hole. Since studs don't rotate in the hole when torqued the friction between the threads isn't broken, and as a result there is only simple shearing stress on the threads. This is especially helpful on the outer holes since they have substantially less thread engagement than the inner holes (those closest to the crank). Has anyone wondered why the cracks don't start at the inner stud holes? After all, they should theoretically have more stress on them. I think the limited thread engagement of the outer holes makes the stress concentration extremely high there, and eventually the added stress of the engine in operation causes a crack to form.

Eliminating stress risers by chamfering (or better yet radiusing) the top of the hole and the edges of the webs at the mating surfaces would also go a long ways toward eliminating these failures. Now, the oil spray blocks may have other stress concentrations as well, and those need to be examined. I don't have such a block, so I can't really comment on that...

[TurboDiverArt]

Has anyone wondered why the cracks don't start at the inner stud holes? After all, they should theoretically have more stress on them. I think the limited thread engagement of the outer holes makes the stress concentration extremely high there, and eventually the added stress of the engine in operation causes a crack to form.

Eliminating stress risers by chamfering (or better yet radiusing) the top of the hole and the edges of the webs at the mating surfaces would also go a long ways toward eliminating these failures. Now, the oil spray blocks may have other stress concentrations as well, and those need to be examined. I don't have such a block, so I can't really comment on that...
I think you're assuming the cracking is caused by the pounding of the crank as it rotates. If the cracks are caused by the twisting of the block as power is applied through the transmission as some assume then having the cracks start at the outside and work in could makes sense. If the block being twisted and deformed causes the block failures then the greatest point of "twist" would be the outside. Now, in a block twisting theory you could have cracks form on the inside if the crank is trying to resist the twisting and deformation while the block is trying to twist. In this scenario one will win and the other lose. If the crank loses, busted crank, if the block loses then you would most likely see cracks form from the inside out. At least that's my way of thinking....

Art.

[simon]

Simon, -that's like "stirring the pot" with a 200HP outboard motor! :D

In all seriousness though, -does anyone know where that nifty picture is of that machined lower-end setup that involved the main caps and pan rails? It wasn't the AMG, -but a private operation.

I remember seeing it, -maybe on here somewhere, -looked like a one-off, -and looked really NICE (machined from aluminum).

Making something like that out of a chunk of iron would be the cat's meow (in my opinion).

For people wanting to take some serious preventive action against a broken bottom-end, I just can't see how it wouldn't at least help.

Expensive? -yeah, heavy? -umm, yeah.

I knew that if you read that" nice new china block" I would get a rise out of you rich, he he.

But I may well do the same as you though, all kidding aside.

I don't think aluminum will do the trick, and just a girdle or platesteel skirt as robyn suggested will still leave room for movement.

The trouble with cracking as I see it results from having the outer bolt holes exactly in the thinnest part of the web. If these smart engineers would have moved these bolts closer to the panrails where there is more meat I don't think you would have seen these failures.

[simon]

Typically the cracks in 6.2's & 6.5's start at the outer bolt holes on the intermediate main bulkheads. I think when a stud girdle is installed the studs are helping a lot more than the girdle (unless the girdle is thick - I'm reffering to the thin Kennedy/DSG girdle). When you torque a bolt in a threaded hole it generates a lot of radial force as the threads in the block and those on the bolt try to force themselves away from each other. This leaves a large amount of static stress around the hole. Since studs don't rotate in the hole when torqued the friction between the threads isn't broken, and as a result there is only simple shearing stress on the threads. This is especially helpful on the outer holes since they have substantially less thread engagement than the inner holes (those closest to the crank). Has anyone wondered why the cracks don't start at the inner stud holes? After all, they should theoretically have more stress on them. I think the limited thread engagement of the outer holes makes the stress concentration extremely high there, and eventually the added stress of the engine in operation causes a crack to form.

Eliminating stress risers by chamfering (or better yet radiusing) the top of the hole and the edges of the webs at the mating surfaces would also go a long ways toward eliminating these failures. Now, the oil spray blocks may have other stress concentrations as well, and those need to be examined. I don't have such a block, so I can't really comment on that...

The bottom line is ,there is frankly not enough meat in that part of the bulkheads to keep things from cracking, look at other engines especially industrial ones and compare the sizes of these webs to the 6.5 l

Example: perkins 236. 72 hp , maincap 1 1/4" wide. just 2 - 3/4" bolts, never seen a failure yet. web cracking that is.

In my opinion the main reason for studs would be that cast iron is prone to stripping the tread under high torque and studs would eliminate that problem.

[Robyn]

Has possibilities.

The grade 12 bolt idea is a moot point.
Grade 8 is more than enough to do the job.

The pan rail will go away long before the bolts will

[BoatDriver]

But for comparison the Mercruiser 350 magnum SBC was iirc: disassembled recranked, re bearinged, reoilpumped with stuff meant for steady hi rpm hi load operation. Then put back together with a sealed starter and alternator. Again iirc Mercruiser reaspirated it to thier design. But its still the same ole SBC "automotive" block.

The engines Mercruiser, Volvo and Crusader use are built by GM, to marine specs. Cam is close to pickup truck specs, water pump has stainless steel impeller, appliances (alt., starter) are shielded.
Block, heads, crank, rods and pistons are the same as production engines.
Did you think the engines were tore down and rebuilt?

[Hubert]

clipped....



Did you think the engines were tore down and rebuilt?

When GM went to the 8.1 for at least the interim of deciding what to do (I don't know what they do now maybe its different) Mercruiser was "building" up the thier 350 Magnums like mentioned.
Seen it personally with my own eyes at the Stillwater, Oklahoma Mercury Marine plant. Yes they disassembled the bottom and did that work mentioned. Don't remember exactly don't think the heads were touched. Final step was to paint it Mercury Marine black. My point is Mercury Marine did not just buy an "automotive" engine and bolt it in a boat.

Having said that. At different times and production supply and demand ebb and flow of sales etc I guess they could buy the engines more ready to drop in when GM could supply them to spec. For what its worth Mercruiser and GM have been pretty tight during some years and "Detroit" has farmed out a lot of work to production test engines at Mercury Marine facilities when GM needed more capacity or had problems. I have read and heard Mercury Marine also assembles some of GM "hotrod" crate and or Corvette engines (I would guess when capacity is needed not necessarily all the time or maybe for early production?).

I have been away from the industry for 3 +/- yrs now so if its changed post back whats current.

I can't comment on Volvo or others. For what its worth the Aspiration for that series of high HP engines was Mercruiser's design, production, and assembly.

I thought pretty positive the starter is sealed. Almost sank an inboard/ outboard a couple of times. Bilged the sump out and starter never had a problem being underwater for a few hours at a time; started right up. The Alternator could be shielded. What ever either are suppose to protect against an "open" spark/arc to keep from igniting any fumes in the engine compartment.

[Hubert]

Here is an article about MerCruiser assembling LT5 engines.

http://www.zr1netregistry.com/howlt5built.htm

Not sure about the GM "hotrod" crate engines. To be more accurate; its a little fuzzy been a while since I was there. The Mercruiser aspiration design was probably on the big block motors not the 350 magnum. Should have typed that era of high HP engines not that series. Not sure if the normal 350 SBC Mercruisers engines were upbuilt just remember it was thier "Magnum".

Anymore to the story about the failure rates in late 90's boats? What predominately was the 6.5 put in boat wise? I figure big boats and big outdrives. Be interesting to compare failures rates and modes. Same area of cracks??? Anymore or less harmonic balancer failures etc. I would think the boat accessories drive was a bit different. Any other similarities or oddities?

Any correlation: Humvee failures and boat vs civilian pickup failures.

Just wondering if the low gearing of the Humvee exposes the 6.5 to a lot of high RPM usage similar to a boat? Isn't WOT on the Humvee something fairly slow compared to a pickup (even with 4.10 or 4.11 gears?)

[TAG]

Sorry i havnt gotten a chance to post back on this. Also sorry about choice of wording in my previous post. He is not a manufacturer, but a marinizer. I did in fact quote him accurately however. All late 90s blocks cracked minus one as stated. Best of my knowledge they were in cruiser or trawler style boats as this is main market for these engines in the marine world. I was also told gm stoodbehind the blocks & replaced them but customer had to pay the labor.

[ronniejoe]

Take a look at where TAG is from. I think I can guess what "marinizer" he was talking too...

[TAG]

Good guess rj.