Stock Crank Strength and Stability

[SmokeShow]

Ok, so some crank failures have been seen in high output efforts.... To help combat this, as far as I know, the most common thing done is to use main studs. Every once in a while, while digging on the interwebby, I read about main girdles on our trucks. What I don't know is if anyone is using one yet. It sure seems like they would help add strength and stability to the crank, no??

Some things that I've read along with the use of girdles is that, while they do add strength and rigidity to the lower end of the engine, the lack of the same rigidity in the top end can introduce new problems up top. IF this is the case, what, if anything, do you then do to the top end to add strength and stability up top as well? Is there something up top to girdle or brace?? Sorry if that's an elimentary question.

Just digging for more information just for the sake of my own curiosity and knowledge.


C-ya

 

[McRat]

Fill the block with concrete. (grout)

 

[MAXLLY]

The only cranks i heard broke were in a max effort twin set up. The claim was that even though they reduced compression considerbly that the twins could shovel enough air to actually "lock" the piston/rod assembly, subsequently breaking the crank Odd not the piston or the rod but all the way down to the crank! I guess it would be tough to tell post event but that was what i heard. Broken cranks, not bolt failure or cap failure.

I don't want to start rumor, just share an event from a reliable source.

IMHO If we start breaking cranks, prior to that ever happening, we would have spent 20K+ in the motor (rods/pistons/heads/machining/chargers/N2O/trans) we should expect it. That is a massive amount of power.

Stuff is gonna break no matter what.

 

[SmokeShow]

now I am starting to see the light in the new stroker kit from SoCal. It would add cubes thereby making it easier to make power doing what you always have because of it taking less work to do achieve the same results OR it can provide a stronger platform to further raise the bar also because of more cubes and stronger parts.


So, if a person were still wanting to rev in order to stay away from the higher cyl. pressures and the resultant torque, but became worried about the bottom end being the weak link... Shall we talk about DESTROKED engines? It could rev higher and get there faster and would introduce a stronger and hopefully lighter crank for strength and revs. Only hurt is the loss of cubes. Can someone tell me if the loss in power potential due to loss in cubes be outweighed by the increase in revs and the benefits introduced by being able to rev??? Basicly, has anyone sacrificed cubes for revs in a forced induction application and come out on top???


Yeah, I'm a little bored and like the tech. banter. So spill your guts. These are age old thoughts that have been gone over many a time by the gassers but I'm interested in how they apply to the modern day diesel.

 

[MAXLLY]

I think this may be a Johnboy gig/question. Purdy sure Johnboy is a machinist and is into this sorta stuff. Mike is scientific and could answer as well. These are the guys i would hope to answer. Maybe Pat has tossed it around.

I think this... torque will go down, HP should go up and subsequently move up in the RPM range. Member the BOSS 302? muddy puddle of water from idle to 3,000 then it took off, heads played a big part. It loved to roll around at 4500 RPM, but it was naturally aspirated.

Finally our blasted trucks are 7000 lb pigs +/-, we need the bottom end torque to get them into the sweet spot.

 

[JOHNBOY]

IMHO the cranks where hurt for different reasons. Kyle hurt his because or bent rods. The others that have hurt rods or pushed bearing I consider failures because of lack of understanding of torque and or poor tuning.

Just because you can make big torque does not mean you should. There is a lot ot it. Think about rattle. What is it. It is knock or premature ignition IMHO. Watch the vids of some of these big power trucks that use sealed tunes. If the camera is 30'+ feet away and you can hear the rattle as they spool it is very bad! One of the bent crank guys has several vids on youtube. When he sarts to spool you can hear that engine rattle hard. That is way hard on parts. The peak cylinder pressure comes way to early. That kills parts plain and simple. I knew it was a matter of time for him. Sucks but that is the way it is. Some of these sealed tunes I have been around had nasty rattle. This is why I peffer the idea of tuning on a loadcell in person. When you change cams, injectors, pistons, turbos, fuel pumps you need a custom tune just like gassers. Diesels are far more forgiving. But you can still hurt them with poor tuning or poor tuning ideals.


A girdle for a Dmax is not hard to make. Because the main bearing caps sit in the block like a Buick 3.8 V6. Here is an example of a Buick 3.8 girdle. http://www.rjcracing.com/RJC_Buick_Products/RJC_Engine_Girdle/231c-1/231c-1.html

Just a flat ground peice of steel really. You need longer mainstuds and oilpan studs. You also need to worry about the oil pickup. But it is not hard to do. This a Max effort thing just like a stroker kit. I am still on the fence about stroker kits. While more cubes is good I would rather make more cubes with overbore. As you have figured out these engines are more than capable of hurting hardparts and wallets with just 403 cubes.

 

[Mike]

I feel there are so many variables that it's hard to pinpoint an exact cause for crankshaft failure. Flex is a big issue and so is harmonics. I believe a crankshaft lives longer when flex ( constant +torsion to -torsion ) and noise are kept to a minimum. I wish I knew exactly what caused each and every crankshaft failure I've seen as well as pictures and stories from others that have had failures. Heck, I remember seeing Olds 350 diesel cranks break, most were said to be caused by torque. Later some discovered that retarding the timing a bit and adding a little fuel would help keep torsional damage at bay. I'm not sure, but I can say the engine didn't last long no matter what was done.

Seems to me cranks, damaged by dynamic compression, would show signs of fatigue ( show cracks ) or twisting. Maybe check each cylinders crank journal for tdc with a degree wheel to verify each as having a perfect degree in relation to the 360 degree circle.

As far as a lower block girdle, If we could make the block so stiff as to not cause other stress related issues, A billet reinforced oil sump would be too cool. Normally, rotating assemblies show signs of bearing damage when a girdle should be implemented. But heck, it's hard to pull an engine and check the bearings after every run to see if one is required.

As far as what is right and wrong tuning wise, I believe the engine build should follow the the tune. If all D-Max engines have the same tune, we would know exactly what parts are required to live in the "Tuned" environment. Lots of fuel and air early require a very stable and sturdy bottom end.

 

[SmokeShow]

anyone care to touch the notion of destroking more so for discussion rather than necessarily as an aide in bottom end strength? Is it completely ridiculous? Plausible? Would work but not be worth the effort? Anything else you smart people want to say about it?


At the risk of this being placed elsewhere, I'll ask anyways... As for proper tuning, what is the general philosophy for safe, yet power producing tuning? As low a timing as you can get away with while still being able to get enough of fuel in? How do you stoichometric efficiency? By that, I mean, how do you know when you have? Is that just a numbers on paper thing or is it real physics/science that can be seen, tested for and optimized in our application?



Shoo, I realize this last post of mine is asking a lot, but I think some good conversation can come from it. It probably should be two threads I guess. Would be really cool to see some of the more experienced and well versed tuners on here discuss (notice I didn't say argue) their approach and WHY.

I expect my morning read to be a good one.


C-ya

 

[Bluemax]

Seems to me that de-stroking wouldn't be very feasible for a truck that was going to be used for anything other than racing, I would think that the bottom end loss due to the lower compression would make it a pain to try to drive on the street. It seems to me it would be harder to keep the heat in the cylinders at low rpms which would lead to white smoke at idle and maybe wash the cyl walls with the unburned fuel? I suppose maybe you could fix some of that with the tune but you'd probably have to raise the timing back up to compensate for the loss of heat and compression. Seems like you gain some of the stress back on the crank. I don't know maybe I don't know what I'm talking about but sounded right to me...

 

[LBZ]

My 2 cents:Allign bore to make sure everything is straight. And check that you have the right amount of crankshaft endplay. Also using viscous fluid dampner instead of the stock rubber one will also help eliminate torsional harmonic vibrations. A balanced flywheel probably would also help.

These things alone and I believe we should not have to worry about breaking cranks. As far as destroking, IF we can get the rpm's up high enough, we can start to use rotational mass to make up for CI losses. But the bottom end would really suck as previously mentioned.

 

[02freighttrain]

One of the trucks featured in the springfest video, broke a crank about a month after the event. This was a 650 hp, built motor/DD truck with minimal time.

The motor had an aftermarket balancer. I have been told the stock balancer is the way to go. Several motors, that have had crankshaft issues, have had one common componet. An aftermarket balance. fwiw

 

[LBZ]

Interesting.....Any word on what kind of balancer they were using??

 

[SmokeShow]

Interesting.....Any word on what kind of balancer they were using??

Fluidamper

 

[Bluemax]

Can someone help explain to me how the fluid based dampers work? It seems to me that if something is out of balance and you put fluid in it while spinning wouldn't the fluid run to the spot that was already out of balance and throw it further out? And if the crank failures are from the crank flexing, how does the fluid or solid balancer come into play? Any chance of driving habits having any effect on the life of the crank on some of those trucks Steve, like warm up and cool down times or anything like that? Maybe i'm thinking all wrong, but I don't get it. Please forgive my stupidity.

 

[LarryJewell]

They are pricey too.

 

[02freighttrain]

According to some builders, The Duramax need's to have the reciprocating components balanced with the balancer that will be used in the running engine. Fluiddampnr say's their product can be added to the motor at any time after a build and work fine, as it is built to factory specs. This look's good on paper, but does not work in practice. Not bashing their product in any way. They have a long history of manufacturing great products. I need to ask Guy what balancer he will recommend with the 7.1 kit.

 

[LBZ]

In my experience, ALL the bigger engines use a fluid style dampner and I'm talking 1200HP to 2200HP engines that I work with every day.

But the smaller engines use the rubber ones. Maybe it's a cost related thing, I don't know. But I do know if you run without the dampner or if the rubber one is bad, you will notice the engine vibration a lot more. Maybe it was and install thing with those fluid dampner's. I don't know how the would cause damage or be worse that rubber.

 

[SmokeShow]

....I need to ask Guy what balancer he will recommend with the 7.1 kit.

kit comes with his own design damper IIRC.

 

[Mike]

In my experience, ALL the bigger engines use a fluid style dampner and I'm talking 1200HP to 2200HP engines that I work with every day.

But the smaller engines use the rubber ones. Maybe it's a cost related thing, I don't know. But I do know if you run without the dampner or if the rubber one is bad, you will notice the engine vibration a lot more. Maybe it was and install thing with those fluid dampner's. I don't know how the would cause damage or be worse that rubber.

I'm with you in respect to the fluid damper thing. I believe in fluid dampers and all high performance gas engines I've built received one. Can't believe fuel typed engines make a difference. But, I don't have all the experience and have not been able to have a company explain the difference. I have not had a company say they are not recommended for a diesel engine.

 

[LarryJewell]

I'm with you in respect to the fluid damper thing. I believe in fluid dampers and all high performance gas engines I've built received one. Can't believe fuel typed engines make a difference. But, I don't have all the experience and have not been able to have a company explain the difference. I have not had a company say they are not recommended for a diesel engine.

They do advertise a lot in several of the Diesel magazines though