Posted by NCWayne on February 21, 2012 at 23:19:33 from (69.40.232.132):
Not sure of over engineered is exactly the right term for what I'm talking about but it's a good start.
I've seen it before on other machines, but in this case the culprit is the bucket cylinder on a newer 120 JD excavator. Getting it taken apart this morning, with the intentions of repacking it, was a breeze since the head was simply bolted on with a handful of socket head capscrews. Unfortunately once apart my plan got brought to a screaching halt when it came time to remove the nut holding the piston on the rod.
The first thing to overcome was to get a setscrew out that was holding a ball bearing tight in a locking groove. Not only was the set screw TIGHT, they had also punched/staked the top of the hole in two places so that had to be ground out before the set screw would even move. Once that was out of the way it was time to take the nut loose. I started with my one inch drive IR impact. With my compressor putting out 75 CFM at 150 psi the impact will always perform to it's rated potentialand then some. When that didn't work I broke out my 1" drive Swench which is rated at 2000 ft lbs. I spent about 10 minutes working with that and still got nowhere. So, I placed a call to my local JD dealer. Talking to the service guy I find that the nut in that cylinder is torqued to just over 2900 ft lbs. Since the first cylinder bench I built for Dad's business is basically tied up in my parents divorce proceedings, I got to spend the evening starting on another one. When done it will be alot simpler than the other one, and I hope more user friendly as a result, while still working like I need it to.
That said, I got to ask you, WHY is there any need to torque the nut that tight in this situation. I mean they made cylinders for YEARS, with hex nuts and thread's larger than this one and didn't tighten the nut that tight. Instead they used a bit of common sense and used a lock nut, and/or a mechanical lock of some type, and often even a bit of Locktite, and the nuts have stayed on for years just fine.
Over the years I've talked to alot of other mechanics and to this day I only know of one time when a rod nut backed off in a cylinder. In that case a truck mounted crane popped the lift cylinder's rod out of the barrel, forcing the boom to knucle over backwards, tear loose at the boom pivot pins, and crush the cab of the truck. Now that was a heck of a mess, and it should not have happened, but it did....but that's another story all together.
In the end I guess what I should say is that when properly assembled, (ie not reusing certain types of lock nuts, staking threads, or using Loctite when needed, etc, etc) the thing isn't gonna come apart, so there is no need to tighten a nut to 2900 ft lbs, in a situation like this...ESPECIALLY when also using a mechnical locking device that wouldn't allow the nut to back off even it it was left loose.
I guess my point with this whole mess is the extent of over engineering put into way too many products nowdays. Granted in years past there have always been special tools needed to work on many products, and I think that will always be the case. Unfortunately, more than likely, it'll only get even worse than it is now. Thing is though, in years past, even the large Mfg's like CAT often had diagrams in the service manual telling you how to make the needed tool, or the tool was readily available at a fair price. Nowdays they add onto the whole 'special tool' mess by doing things like tightening nuts so damm tight you have to have a cylinder bench to take them apart...and then to make matters worse they come up with some off the wall design for a part (((ie the shape of the rod nut)), or do something else that's just plain odd that no "normal" tool can do anything with. Once they have you by the 'short and curlies, then the special tool is either treated like a 'trade secret', or if available for purchase winds up costing as much as the machine it's needed to work on. That just ain't right............
Like I said I know there have always been things that have been a PITA when working on equipment, but oh how I long for days gone by when the 'special tool' was nothing but a wrench with an odd shaped handle, when parts books actually contained the words, " obtain locally", and when EVERYTHING (including the headlights) didn't need a computer telling it what to do...............Now those were the days.........
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