Detroit Diesel 6v92 crank shaft failures 12

[MarkAlert]

I have a Detroit Diesel 6v92 crank shaft that keeps failing (break). This is on a well drilling machine. The crank shaft runs 2 hydraulic pumps. The shaft breaks where the harmonic balancer fit to the shaft.We have an omega 60 coupling to couple the pumps. We had 3 coupling failures and 2 crank shaft failure in the last 6 years. The last failure where the crank shaft broke (again) only ran for 45 hours. When the coupling failures happens only half the coupling fails.

Concerns questions

These omega couplings are big and heavy and are only statically balanced.

There is not much shaft material where the shaft breaks.

Is the harmonic balancer doing its job ? (why only half the coupling failing ?

Thanks in advance

Mark Alert

 

[MarkAlert]

more pics

Thanks

 

[Tmoose]

how much power does it take to drive the pumps?

It looks to me like the keyway is wallowed out, and the crank diameter is fretting, implying the hub was loose on the shaft.

Do all the components on the crank snout butt together, so tightening the crank bolt clamps their face together.

Dan T

 

[MarkAlert]

Not sure how much power it takes to drive the pumps but the pumps are vickers 200 psi and a Vickers 4400 psi pump . Te pump shaft is 1 1/4 inch shaft so I would assume its ok. The crank shaft where the harmonic balancer is fastend to is a 2 inch shaft.

Yes I see some fretting also - The fretting seems worse in the pictures thou.

There might be alittle wear on keyway but it was not noticable.

The harmonic balancer, belt pulley, and coupling are bolted to each other then the unit is bolted to the shaft. I don't think it shoulderd the the shaft step thou.

Mark

 

[IceStationZebra]

Was this the original engine or a repower? Curious because if it is original it should have been approved by Detroit Diesel or a distributor.

The crank failure originated at the keyway. It looks like a combination of bending and torsion fatigue. So it is either seeing excessive side loading or too much power transfer. There could also be a crank defect, but I would be surprised to see this twice in a row.

Have the system pressures or flows been raised above the original values? Do you know what the volume of the pumps are? If so we could calculate the power. Then the trick would be knowing what the engine was rated for on the front end.

As far as side loading goes it could be unbalance, excessive engine movement, or excessive misalignment. Have you changed to a different stiffness coupler than the original? Have the engine mounts been changed or are they worn out?

ISZ

 

[MarkAlert]

This is the orignal engine,
The pump volums have not changed - the 1st pump is 20 gpm and the 2nd is 35 gpm.
Attached is the motor specs.

I think something needs to be done with with coupling. The coupling fails first, the coupling seems large and heavy for this.

The engine mounts seem fine.

Thanks Mark

 

[MikeHalloran]

The crank nose on a similar size Deere engine is only rated for 70HP at 1800 rpm, or equivalent torque, plus limits on belt pull.
You need to check the DD crank nose rating for your speed.

This is the sort of application where press fits and/or Loctite are critical to longevity. Evidence of fretting suggests the components may have been too loose after repeated disassembly.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

MarkAlert,

Check the installation alignment between the matings shafts. I believe those Omega couplings are only good for about 2deg angular and .063" offset.

Also, as MikeHalloran suggests, check your horsepower/torque ratings for the crank nose. If I read your posts correctly, the 4400psi pump at 35gpm would require over 110hp (3851 in-lbs @ 1800rpm) alone. The size 60 Omega coupling is good for 12,500 in-lbs.

http://www.delzer.com/v5fmsnet/LinkPosting/link.asp?offerseq=3382&LinkType=1&OrdobyId=0&PmSess1=115

Hope that helps.
Terry

 

[rmw]

Are you pulling anything with the flywheel end of the engine and if not, why aren't you pulling these pumps with that end?

The Detroit 6V92TA's that were in my life for a long time pulled ~50-75 HP worth of A/C compressor, condenser fan and radiator fan through a gear box.

Never a problem with that end of the shaft.

rmw

 

[rob768]

by the looks of the picture, this is a torsional fatigue fracture. Change elastic coupling or better yet, perform a torsional vibration calculation.

 

[MarkAlert]

What type of coupling do you recommend?

Mark Alert

 

[rob768]

i don't know what the torsional stiffness of the omega's is. Personally, i would make a calculation first. That way you confirm torsional resonance with the exsiting coupling, and get a feel of the effect of a modification.

 

[dicer]

Other than a belt driven accessory, anything else will detune the damper. Besides most accessories on a detroit are driven by the cam pulleys. Its time to figure out another method to drive the pumps. Most normally off the flywheel end. The stress against the keyway by the pumps and detuned damper don't help. I think your asking too much of that end of the crankshaft. I have a question, was the damper replaced each time the crankshaft was? If not its mostlikely junk.

 

[MarkAlert]

There was no damper installed on this crankshaft.

Mark

 

[MarkAlert]

Does anyone know how much H.P the crank nose can handle ?
Its a 6VF198920 8067-3B21 type swvs.

Thanks

 

[mechanic6]

it is unusual to break the front of any crank,especially on a Detroit 6v-92.
i would think if the crank and the couplings have been breaking,maybe you have too much of a load there.
this may be a hydraulic load that is an on/off kind of application.
so a high load that cycles like that would be the most likely cause of crank breakage.
i agree that there are lots of mounts on the timing cover at the rear to mount pumps,should be easy enough to do.
i think that taking 100hp or more from the crank nose is asking too much.
that being said i have seen lots of stuff driven from front,usually using simple ujointed drive shafts.
best thing would be to get the nice guys at the nearest DDA dealer
on this.
let us know how you make out.

M6

 

[rogzog]

I am just guessing here but are you having to drive the loads off the nose of the crank because of rotational direction for the pumps? If so, maybe you should consider some type of transmission or drive to change the rotation off of the tail of the crank where the motor was designed to take the load.

If you are thinking cost, think how much it is costing to replace the crank over and over.

And as mentioned by others, check the alignment of the equipment in all axis and confirm that the alignment is within tolerance of your coupling.

Just a thought.
ROGZOG

 

[Tmoose]

Is the hub attachment a "factory approved" design, at least in regards to HP?

Regardless, Looking at the shaft fretting and damage originating from the key I'd start by questioning the attachment of the various hubs to the crank.

I think the assembly of new hub and various auxiliary stuff and OEM gears, sprockets, whatever needs to be a sandwich, all clamped axially HARD against a large diameter face of the crank main bearing. That makes the keys' job of transmitting torque/power minimal, and protects them from torque reversals and variations. It make the larger diameter of the hubs, etc responsible for the handling of bending loads (that should really be minimal anyhow).

 

[bcs5274]

I also believe it to be an alignment issue, had similar situation with a gas compressor, if alignment isn't with .040" or less overall, i prefer .010" or less. It might be a situation were the alignment is lost after the unit is moved from one location to another.

 

[dicer]

No matter what, you are asking too much of that keyway, with adding extra torsional load via the pumps, combined with torsional vibration. What is driven at the flywheel end? What is the load at the flywheel end? Is the load constant? And what percent of rated HP is the load at the flywheel end?