# Hydraulic Cylinder Repair



## RJSakowski (Mar 22, 2021)

Last Friday, I was moving some brush with the front end loader when there was a loud bang and the bucket tilt was unresponsive. I have three ft. forks on the bucket and I expect that the additional leverage caused the break, I suspended the bucket with a chain and drove back to the barn.

The next day, I started the autopsy. When I disconnected one of the tilt cylinders, the shaft fell out of the cylinder. The retaining nut had sheared, separating the shaft from the piston. With a little fiddling, I managed to pull the piston from the cylinder and the retaining nut, looking like a pretzel, fell out.


	

		
			
		

		
	
 A 5/8"-18 Nylon lock nut pretzel


The threads on the shaft were damaged but looked repairable but the piston was trashed from acting as an anvil for the nut crushing process. Fortunately, the urethane seals looked to be undamaged. An O ring for the shaft seal was also trashed from the process of removing the piston.

I found a source for cylinder parts and a new piston kit was available for $50 plus S&H and tax but hey, I have a lathe, right? I had a 6-1/2' length of 2-1/4" aluminum round for material. I reverse engineered the piston and modeled it in SolidWorks. With a drawing in hand, it was down to the shop. Because the stock was too large for my 602 bore, I decided to use my four jaw chuck as the jaws have a longer grip than my three jaw chuck. I dialed in the stock, although I really didn't have to as most of the work could be done as a first op and I center drilled so I could use the tailstock center for increased rigidity.

After a quick face of the far end. I turned the stock down to a 1.737" diameter. I used a round insert which gave me an excellent finish. The two seal grooves are .272" wide by .245" deep and a good surface finish is required to provide a good pressure seal. I elected to grind a 1/4" HSS bit as a form tool. The first groove was problematic as the is essentially a very large cutoff tool and the problems with chatter rose their ugly head. By varying the lathe speed, I was able to work around the resonance and achieve a respectable surface finish. For the second groove, I used a parting tool to rough out the feature, leaving a few thousandths for cleanup with my HSS tool.

The next step was to remove the center and drill and bore the 5/8" hole and the .844" x .109 counter bore for the O ring seal. Following that, I parted off the part leaving about .020" for face cleanup. Rather than remount in the four jaw, I elected to use my three jaw chuck as concentricity isn't a concern for the facing operation. In addition to facing, I chamfered the outside edges and broke the inner edges on the seal grooves to make seal installation easier and reduce the possibility of seal damage.


The new piston along side the damaged OEM piston.

The seals were installed on the piston and tomorrow, I will be picking up a new O ring and retaining nut. It will be my first trip to the DIY since 3/14/20. The original nut was a low profile nylon lock nut and had only about three threads of engagement. I will replace it with a grade 8 standard nut which will triple the number of threads in engagement. After that, I will flush out any remnants of the old nut from the cylinder and reassemble it, ready to put back into service.


The new piston, seals installed, awaiting the O ring shaft seal and retaining nut

 All in a day's work. Or two or three.

Note: due to a computer glitch, the original post was erroneouslky posted before completion.  The above text is the replacement.


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## markba633csi (Mar 22, 2021)

Broken clevis?


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## machPete99 (Mar 22, 2021)

pics?


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## RJSakowski (Mar 22, 2021)

See edited post


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## Cadillac (Mar 22, 2021)

On some rods Ive seen a crimped nut where the nut looks like it was smooshed from the side or dimpled nuts where they have a deformed end that conforms to the thread. Recommend red loctite and staking the thread with a punch to avoid future problems. Nice repair too!


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## machPete99 (Mar 23, 2021)

I have not seen aluminum used for hydraulic pistons, its always been steel in the few I have opened up. I wonder if the differences in thermal expansion caused it to work the nut loose?


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## Cadillac (Mar 23, 2021)

I’ve seen aluminum pistons in fact I’d say the majority I’ve disassembled were aluminum.


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## RJSakowski (Mar 23, 2021)

Cadillac said:


> On some rods Ive seen a crimped nut where the nut looks like it was smooshed from the side or dimpled nuts where they have a deformed end that conforms to the thread. Recommend red loctite and staking the thread with a punch to avoid future problems. Nice repair too!


Ideally, I would get a grade 8 lock nut with a deformed thread.  I thought about red LocTite but if I ever had to repair the cylinder again, I would have to heat it more than I would like to break the bond.  I definitely want to go with a full thread and if all I can find is standard nut, I will stake the end.


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## tq60 (Mar 23, 2021)

Nut is usually grade 8 and very very tight.

Another option is double nut

Good job on unit.

Check the other side now 

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## RJSakowski (Mar 23, 2021)

machPete99 said:


> I have not seen aluminum used for hydraulic pistons, its always been steel in the few I have opened up. I wonder if the differences in thermal expansion caused it to work the nut loose?


The nut didn't work loose.  It went with a bang.  The cylinder was bottomed out and a long lever arm was applied.  This normally wouldn't happen because the force would be applied by the hydraulics and limited to 2000.psi.  This would limit the shear force on the threads to 3200 lbs. 



tq60 said:


> Nut is usually grade 8 and very very tight.
> 
> Another option is double nut
> 
> ...


I inspected the other side, thinking it may have sustained damage as well.  It didn't appear to have any  issues.  There isn't enough thread for double nutting.

 Apparently the immovable object wasn't up to the irresistible force.


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## RJSakowski (Mar 24, 2021)

After yesterday, I probably should have moved this thread to the "Goofs and Blunders to Avoid".  I picked up a grade 2 and grade 5 nut, along with an O ring and a tube each of ted and blue LocTite.  When I got back to the shop, I thought that my best strategy was to use the grade 8 nut and the red LocTite. So I slipped the O ring on the shaft, followed by the piston, and some red LocTite.  Then I screwed the grade 8 nut on and tightened it down.  I wasn't able to get the prescribed 160 lb-ft.. of torque recommended but got fairly  close. And said to myself, "good job".

About 3 hours later, I realized my goof.  The cylinder end cap is held captive on the assembled piston and shaft.  In a panic, I started to disassemble my assembly.  LocTite starts to set in 10 minutes and fully sets in 24 hours so time was of the essence.  With a 3/4" breaker bar,, I was able to crack the nut loose and I started to unscrew it.  The nut was turning with extreme resistance and the sound ir was making was much like that when removing a nut from well rusted bolt.  

The nut did come off but I would have to agree that red LocTite is permanent.  I was able to clean up the threads in the nut with a tap and pick the hardened LocTite out of the threads on the shaft.  A brush with a fine bristled wire brush and an acetone wash and the threads were ready for reassembly.

When a gland is designed for an O ring capture, it is made to allow the O ring to deform.  O ring material is incompressible so the volume of the gland is usually about 15 -20% greater than the volume of the O ring.  In this case the actual volume of the O ring  is .038 in.^3 and the gland volume is .0275 in.^3.  The result is that some of the O ring is extruded out of the cavity when the assembly is tightened.  This extrusion was observed on both of the original cylinder assemblies as well as as my recent assembly.  Not my ideal design, but there is an old engineering guideline, "don't fix what aint broke".  The upshot though, is that the O ring on the newly disassembled shaft was totally chowdered.  I supposed that I could grease the O ring with some silicone RTV but the wiser path would be to install afresh O ring which happens to be 20 miles away.  

When I reassemble the piston and shaft, I will use the blue LocTite as I would have to disassemble it again in  the event I needed to service the seals on the end cap.  The red LocTite requires heating to 575ºF in order to break the bond and that would destroy the urethane seals as well as the temper in the aluminum piston.  I do have to say the the red LocTite is a very effective thread locker, maybe second only to welding.

Tomorrow's another day and after a trip to town for an O ring, the assembly should go smoothly.  It gives me some time to figure out a cheater bar for my torque wrench to give me enough oomph to reach the 160 lb-ft. Fortunately, there is no immediate need for the front end loader, only my onner drive to "git 'er done".


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## royesses (Mar 24, 2021)

Cadillac said:


> On some rods Ive seen a crimped nut where the nut looks like it was smooshed from the side or dimpled nuts where they have a deformed end that conforms to the thread. Recommend red loctite and staking the thread with a punch to avoid future problems. Nice repair too!


Just for info, those are called prevailing torque nuts. They are used a lot in automotive applications. Not supposed to be re used.

Roy


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## aliva (Mar 29, 2021)

RJSakowski​Might be time to invest in an O Ring kit and make your own in the future






						Amazon.com: Loctite 112 O-Ring Making Kit : Automotive
					

Buy Loctite 112 O-Ring Making Kit: Automotive - Amazon.com ✓ FREE DELIVERY possible on eligible purchases



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## tq60 (Mar 29, 2021)

If o rings and seals are 20 miles away and not open on weekends buy extra set for when the other side goes.

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