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Thread Title:

Breaking cranks.

Created On Tuesday May 11, 2004 21:34

TomT

Posts: 3
Joined: Feb 2004

Tuesday May 11, 2004 21:34

We are running 8 John Deere Turbo 5.9 engines bolted up to 8 speed Funks.We have broken at least 4 crankshafts - just behind damper in each case. Engines have varied with between 1500 and 2500 hrs.New dampers are always fitted when engines are rebuilt. Have heard that this is a common problem with these engines ?
If breaking cranks was not bad enough we have lost 3 engines with broken piston pin / gudgen pin - in two cases we lost the block and on one the engine was shut down soon enough - any comments ?
Anyone else run these engines and have any problems with them - we run about 250 hrs a month per engine and oil change at 200 hrs.
I am at the stage of trying to talk the boss into trying a 5.9 Cummins.

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MotorCityMotorMan

Posts: 6
Joined: Apr 2004

Wednesday May 12, 2004 09:17

I'm not familiar with a 8 speed Funks- what is the application-gen set, pump,?
What type of coupling from crank to load? Is there a driveshaft in the set up? What speed/load do they run at? Steady state or varying speed/loads.

I build/run (on dynos) gas and diesel engines and have found most engines have a speed that causes "bad harmonics" to be developed in the crank. Harmonic balancers are only designed to take out a certain amount of harmonic imbalance. We've instumented pistons/rods and proven this. Give me some feedback of the application - I've been around many 5.9's in combines and tractors and in my opinion are very reliable engines.

-------------------------
John Arting
Sr. Engine/Dyno Technician
Bearing Specialist
Federal Mogul Technical Center
Plymouth, Michigan

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TomT

Posts: 3
Joined: Feb 2004

Friday May 14, 2004 03:26

All,
The engine is bolted up to a Funk 2000 series transmission by way of a flexi plate.
The engine/transmission package is fitted to off road 4x4 vehicles.
Engine RPM 2500.
No engine crank has broken at high RPM - luck? always at low RPM or after engine is shut down a oil leak is noticed or is soon noticed when the engine is started.
We had no problems when we were working machines lightly - 100 hrs a month but since working 250 + hrs a month we have seen the problem.
So far always on a different engine.
Was told that a mod crank had come out with a 1/2 inch x 4 - 1/2 inch bolt - no difference as two of these have also broken - all cranks have broken behind damper - no other damage if this is not enough damage.

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enginebob

Posts: 24
Joined: May 2004

Wednesday May 26, 2004 02:35
In your post you say new dampers are always fitted when the engines are rebuilt. So my question is; does this crank breaking happen only on the rebuilt engines, or the new or original ones also? ------------------------- With enough power anything can fly

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TomT

Posts: 3
Joined: Feb 2004

Wednesday May 26, 2004 05:47

We have been running this gear over 8 years - there is no such thing as a new motor - early on we wore a few out and had a fair bit of trouble with leaking liner seals - but as said earlier this crank problem only seemed to come through when we started to work the equipment harder - ie 250 - 300 hrs a month. We did fit a new motor - this was a JD 6.8 shipped by mistake - this turned out to be a problem motor also - but thats another story.

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enginebob

Posts: 24
Joined: May 2004

Saturday October 23, 2004 01:10
So then it is just happening to the rebuilt units? Is the rebuilder the same for all the units? So what is being changed as compaired to the manufactures original? Like the one guy says about the harmonics. ------------------------- With enough power anything can fly

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catmech

Posts: 326
Joined: Nov 2005

Sunday March 19, 2006 08:40
Are the dampers made with rubber in the assembly or are they of a gel type, and sealed. some engine work better with one or the other. check with your dealer and see if there was an update, because of this problem you discribe. maybe the problem is there.

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millertime

Posts: 4
Joined: Sep 2007

Sunday September 09, 2007 11:28
How is the balancer installed? If it is drove on with a hammer, that can break the snout of the crank. Check the press fit of the balancer, it should only be around .0025-.003 max. Even if it is pulled on, to much press fit can crack the snout. Which in turn,being cracked it will not come apart at high rpm. It is when you come down on rpm that the motor goes through tougher harmonics.

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