Crankshaft issues

[jlawles2]

The company I work for has just finished changing 3 crankshafts in different cruise ship engines. One was less than a year old. They think it was a bad forging but still have not confirmed it. The strange thing is that the motor (runs one of the six generators on the cruise ship) had less than 2000 hrs on it, and it also sits with 5 others that still have not had any issues. Now these cranks see a lot, and it broke about 2 throws back from the nose.

On the Dmax, could it be a misbalanced harmonic balance that is actually fatigue cracking the cranks. Are all of the broke ones running factory balancers. Is the rubber on the balancer still in tact. Has the balancer managed to shear the rubber and "jump" time on the balance???? Could it be bad forging (or castings) on the crank itself? Until someone breaks one during a controlled run in a lab, the jury is still out on the cause.

 

[Ridin'GMC]

I've seen quite a few broken cranks on a v16 2400 hp mining truck engine, but to where I see the crank is breaking, it seems to be coming from a harmonic balancing issue. If it was from the gears, it would break at the front of #1 rod because that would be where most of the stress lies from the gear train at the front. Since it is coming from the rear of #2 rod, it is most likely a balancing issue. I would think that the factory balancer is not rated at low speeds on high HP since there is more harmonic balancing counterforce.

Another thing that seem to catch my eye is the torque overlap that you guys stated that 1&2, 5&6, 7&8, has the torque overlap but 3&4 does not. At low rpms on high torque, this may cause an unbalancing effect because #1 & 2 is trying to balance out # 3&4. That would be my opinion why it is breaking. Low rpms have less harmonic balancing than higher rpms does.

Correct me if I am wrong though. It makes sense to me this way.

 

[fishsmith]

Mine broke on the front of rod number one

 

[EDP]

I think you've been given all the information you need.

Assume all you want! :thumb:

 

[paint94979]

Assume all you want! :thumb:

why do you act like such a prick? obviously you have done something you should have not done

 

[Mike]

I don't know Nick, seems what has come around is going around. Kinda like waiting for a reply to a post in a thread. Sorta like getting more info than offering? I don't know

 

[paint94979]

Assume all you want! :thumb:

I seem to remember that Supercharger kit you had released that was apparently the "first of it's kind" yet that same Procharger F1 / GT45 setup had found its way onto Mick's truck over in Australia for almost a full year before i had ever heard of your company. So i will assume that you stole his and Mike's work, used it for profit, and it now seems you have done the same thing again:thumb:

 

[The Neens]

I don't know Nick, seems what has come around is going around. Kinda like waiting for a reply to a post in a thread. Sorta like getting more info than offering? I don't know

I just read all of this and I'll admit that I'm a bit confused...Can you elaborate?

 

[TrentNell]

Not sure i buy the harmonics being the case for broken cranks I still believe its a quality control sort of thing ( bad forging ) , but my motor wasn't balanced and so far is doing decent , I guess if it makes it this whole year it may be something of note , but 20 passes isn't too much of a test IMOP , but it should see over 1200 hp ( 1100+ so far ) by the end of the year I guess we will see how she fairs .

 

[Mike]

I just read all of this and I'll admit that I'm a bit confused...Can you elaborate?

Ok, sorry I'll be nice.

 

[Subman]

All of this is very interesting. Relative to Max'd Out, we had about 60 passes on the engine we sucked the crap through when we broke the weld on the intake pipe and munched the turbos. Heads need new valves but other than that are fine. We do need main bearings, cam, lifters all of which were shot.

None of that had anything to do with the sucking crap through the turbos, crank was moving around working the hell out of the main caps, and if we hadn't had the bad luck were probably within a pass or two of blowing up the motor. Builder said if we hadn't had the block filled the crank would have probably been on the track. All of that said, crank is fine, pistons and rods are fine. On one bank of the engine the pistons were actually touching the heads, close enough to stamp the arrow that is on top of the piston into the head so you could see it.

You would think with all of that going on and the hp we were making the crank would have let go? Rebuild is getting a girdle and when we rebuild the other engine, (not sure what's wrong with that one yet) it will get billet main caps, a girdle and filled block.

I would venture a guess, and I think its a pretty safe one, that these high HP engines will all need this type of treatment to survive for any length of time. A full season of racing and pulling will most likely necessitate a complete tear down and refresh.

 

[juddski88]

well that's discouraging

edit:

yes, Thanks Ken for sharing here. on Rick's site you said the block was reusable though correct? so it didn't hurt the mains too bad just the bearings? i was digging up some old threads on cap-walk and crank-walk on the DP and there were a few who thought that the girdle wouldn't mitigate the Crank-walk. I hope that it does help you guys, as i was really thinking about using one myself in this build. would a better balancing job ( not the normal zero-balancing) maybe be more beneficial? I know the Kuselicks were trying some new things this year with their motor and as i understood it, they had it internally balanced and not to zero (don't know if i am explaining that right). i don't know if it is feasible for a drag motor or not, as i understand this is usually common practice for pullers.

 

[SmokeShow]

They're talking 1200hp mills tho! Might get two season out of one at 800.



Nust being silly. You're right tho, that's not real incouraging, except that there's some measures at hand that are showing that they can help!

Thanks for sharing Ken!

 

[LBZ]

Thanks for sharing that info Ken. Not alot of people are willing to share that kind of teardown info!!:thumb:

 

[Subman]

The only thing that is somewhat proprietary on Max'd Out is the turbo setup's and that is for obvious reasons. That's Nathan's domain and any info there is at his discretion. As for the rest, we have had a ton of help and if we can save someone some grief or help with their build we'll do it.

In a twisted sense it was somewhat lucky the accident with the broken weld happened since it probably saves us a catastrophic failure and potential accident with the resultant oil down that would probably have happened.

 

[skintback]

Good info

When talking about balancing a motor what would you need to tell your machinist? Have it done to zero or i here some say to over do it for higher rpm's but by how much or what to what at how many rpm's? Say i want to run at 4500rpm's so i should have it balanced to 4500? What about taking weight off the crank/lighting up the rotating assembly and still have it balanced right is that good or bad?

could someone explain please

 

[kman2468]

so what everyone is saying..is having a built motor doesnt mean chit and it will still break if you push it at 1000hp? im just not clear. i figure built motor= stronger parts and less chance of breaking

 

[Mike]

No, that it still " Might " break.

 

[Kat]

No, that it still " Might " break.

:nod:

 

[paint94979]

:nod:

:hug:

Everyone knows that LB7/LLY rods bend... so us LB7/LLY guys have to address that problem. LBZ/LMM guys have to address their crack prone pistons. The reality is so many things can and do go wrong in engines that cause catastrophic failures. We will never have it all figured out, just look at the Cummins guys their engines have been out a lot longer than ours and they still have large failures.