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Detroit Diesel 6v92 crank shaft failures
12

Detroit Diesel 6v92 crank shaft failures

Detroit Diesel 6v92 crank shaft failures

(OP)
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

      

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

(OP)
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

RE: Detroit Diesel 6v92 crank shaft failures

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
 

RE: Detroit Diesel 6v92 crank shaft failures

(OP)
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  

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

2
by the looks of the picture, this is a torsional fatigue fracture. Change elastic coupling or better yet, perform a torsional vibration calculation.

RE: Detroit Diesel 6v92 crank shaft failures

(OP)
What type of coupling do you recommend?

Mark Alert

RE: Detroit Diesel 6v92 crank shaft failures

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.  

RE: Detroit Diesel 6v92 crank shaft failures

2
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.  

RE: Detroit Diesel 6v92 crank shaft failures

(OP)
There was no damper installed on this crankshaft.

Mark

RE: Detroit Diesel 6v92 crank shaft failures

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

Thanks  

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

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

RE: Detroit Diesel 6v92 crank shaft failures

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).
   

RE: Detroit Diesel 6v92 crank shaft failures

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.

RE: Detroit Diesel 6v92 crank shaft failures

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?  

RE: Detroit Diesel 6v92 crank shaft failures

dicer,

I think the both of us keep asking that and getting no answer.  We are getting nowhere fast.

rmw

RE: Detroit Diesel 6v92 crank shaft failures

MarkAlert,

You finally made me get out of my easy chair and go across the house and dig out my old but not very recently used Detrit Series 92 Service Manual.  Carrying that load of bricks across the house was my exercise for the day.

From it I can tell that yours is an automotive engine, starter and oil cooler on opposite sides, left turning when viewed from the front end of the engine.

I can't find the designator for the specific model (the last 21) but I doubt that is important.

It was an interesting read that brought back good and bad memories.  But, it is only a service manual and not an application guide so it did not specify rated HP's for the nose shaft.

What I did notice is that the only users of the front end of the crankshaft ever referenced in this manual were the fan, the alternator, and the A/C compressor.  (The air compressor is gear driven on the other end of the engine in automotive engines - does yours even have an air compressor?)

Accounting for the HP's involved, I estimate (without any real mental effort or research - I'll leave that to you to chase up) ~ 25-30 HP for the fan, ~ 5 HP for the alternator, and ~ 10 HP for the A/C compresor.

I would note that it would be rare for all of those loads to be maxed out at once, although the larger 2 might - the A/C compressor and the fan might be working hard on a long hill climb for a truck or bus.

That said, being conservative, I make the nose shaft good for ~50 HP.  But as I noted above, the last several Detroits I dealt with pulled 2 large fans, radiator and AC Condenser, an A/C compressor that was the size of small car engines (V-6) and an alternator as big as a WWII depth charge (well overstatement there, but it was 300 amp, however and the fan motors for the AC evaps were 80 amps each for two, so the constant electric load was significant) through a gear box that wasn't frictionless either, so I am sure those engines could have easily doubled the loads of the 3 mentioned above.  As well, all those loads are 'soft start' meaning that they aren't instant on.  Plus the coupling is rubber bushed further protecting the nose shaft from shock loads.

My gut tells me that your well drilling rig requires much more power than the designed 50 HP or even the 100 estimated HP on the coach class engines or someone would have selected some toy engine much smaller than this beast for the job.  This is not a small engine.  And, my gut also tells me that you are driving it all off the front of the engine.

I noticed something else.  If you look at the two ends of the crank, the business end is a heck of a lot beefier than the nose shaft.  That is for a reason.  The flywheel end of the crank is designed to transmit HP's in the hundreds, well a couple or three maybe and the tiny nose shaft is good for a fraction of that or about 50 - 100 HP.  The business end is also designed for someone dumping a clutch with a 80,000 lb load and the crank surviving even if it kills the engine.

If someone has applied this engine to drive a high HP load and maybe a high impact load off the nose end to keep from having to design a coupling for the flywheel end, or buy an opposite turning engine, then they have have done you a big disservice.  And I believe that is what is going on here.  Otherwise your engine code would have indicated a stationary engine designator.

If I have sized it up right, I believe you can continue to plan on broken cranks.  Sorry.

rmw

 

RE: Detroit Diesel 6v92 crank shaft failures

(OP)
I can't find out the rated HP  load at the nose end of the crank.
This was designed by a company called Schramm. Because this unit is 20 years old its hard to find info.
We are rebuilding this next week again and we really would like to get this right. The flywheel end of the motor runs an compressor.
I don't like the size of the coupling because I think it overkill and heavy. I think schramm picked this coupling beause it can easily mount to the outside of the pulley.
The pulley is supose to be  5000-7151 GM/Detroit part number 5103487. I think its a 3 groove pulley and what we had installed last time was a 4 groove pulley - which added more wieght.
Also I have a concern on how well we had this couplinged aligned so we are going to laser align this.
When the coupling failed 3 times it only failed on one half or one side and this is a concern thinking that this is also a torsional issue.
If you add all these up and the biggest concern of this having too much of a load.

Still scratching my head on this.

Mark

RE: Detroit Diesel 6v92 crank shaft failures

I think achieving the highest rating for bending loads and transmitted torque /power will REQUIRE that all the components on the crank snout butt together, so tightening the crank snout bolt clamps their faces together with a force great enough to  -
1 - directly resist the "toppling force" applied by the radial loads
2 - generate more than enough friction to transmit the required torque.

If those conditions are not met, at most the capabilities are limited to the crank diameter, initially minus a batch of stress concentration factors for keys and keyseats, and next week reduced by SCFs for ever more deeply fretted surfaces and impact loads on the keys.  The joints in the assembly will continually degrade in service.

http://www.miata.net/garage/hsue/crank/keyway4.jpg
http://www.miata.net/garage/hsue/crank/keyway2.jpg
http://www.miata.net/garage/hsue/crank/keyway3.jpg



 

RE: Detroit Diesel 6v92 crank shaft failures

Is this your setup?

http://www.schramminc.com/products/t455ws

Or something similar.  This was the only model I could find with a decent picture of the DD engine.

rmw

RE: Detroit Diesel 6v92 crank shaft failures

Also seen cranks broke from tightening big powerband belts way to tight and pulling on the crank hard enough to bow up the crank enough to break it if run any amount of time this way, checking the web deflection will show if this is the case.

RE: Detroit Diesel 6v92 crank shaft failures

The way I understand it is the pumps are not belt driven, and are driven directly through a coupling.

Compressor? Vane or reciprocating? Mr RMW is right on with the way the 2 opposing ends of the crankshaft are designed and for what load.
You really don't want to transfer power from the end opposite the flywheel, the weakest link is that snout, and it of course will be breaking on occasion from fatique, that setup is setting up extream torsional strain in that crankshaft, I'd like to know what the main bearings look like.
Wow just looked at the photos again. Look at the lack of cross sectional area because of the bolt hole in the end of the crankshaft. Again your asking too much of that end. If you have to drive the pumps from the front of the engine you are going to need either a special built crankshaft and front cover, or a much larger engine.
You asked at the very begining is the harmonic balancer doing its job? NO your setup detuned it. Any cyclic load at the flywheel end will exasperate the torsional loads at the front end, and a loose coupling wouldn't help either. Thats my opinion.

RE: Detroit Diesel 6v92 crank shaft failures

does the set up still use the taper lock balancer location and the splined oil pump drive?which tends to frett into the shoulder allowing the balancer to come loose

RE: Detroit Diesel 6v92 crank shaft failures

mark I also have several 6v and 8v 82TA engines we run in our fire service check to make sure you have the correct drive pulley. The pully has a one way roller clutch in it if it has froxen or some one put on the wrong pully this could be your problem. Your mud pump and hydraulic pumps work against each other Torsion wise. The clutch gives you a little reduction in torque when you start and stop the engine. Good luck.

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