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

 

[rmw]

dicer,

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

rmw

 

[rmw]

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

 

[MarkAlert]

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

 

[Tmoose]

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

 

[rmw]

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

 

[bcs5274]

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.

 

[dicer]

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.

 

[macquari]

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

 

[cityguy]

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.