Failure analysis

[MotorDoctor]

Originally Posted by toprecycler

So in the warranty papers is it spelled out that the motorcycle riders can’t do wheelies and do anything out of the ordinary other than ride a bike in a straight line otherwise it’s out of warranty?
Sent from my iPhone using Tapatalk

Well, since you asked This is what you call the "fine print". These are the rules I have to abide by, no exceptions.

WHAT IS NOT COVERED

Routine service or periodic maintenance such as tune-ups, oil changes and service checks are your responsibility to pay for and have done, and are not covered by this warranty.

Repairs to your vehicle for failures that occurred after the expiration date of the warranty period.

Damage to the vehicle that is not our fault, such as damage caused by accidents or carelessness.

Damage caused by misuse, abuse, or unreasonable or improper vehicle operation, such as intentional burning or spinning of the rear tire, shifting gears improperly, overloading of the vehicle, operating the vehicle with the front wheel aloft, or overheating the vehicle’s engine by operating the vehicle in incorrect gears for vehicle speeds.

Damage caused by negligence, such as operation of the vehicle with insufficient, incorrect, or excessive oil, fuel, coolant, or brake fluid.

Damage caused by alterations or modifications that would change the original vehicle specifications including, without limitation, modifications of any emission-related parts such as carburetor(s), fuel injection system components, the engine control module, air suction system components, the catalytic converter (if equipped), evaporative emission control system components (such as the carbon canister, fuel tank, fuel hoses, and vapor hoses), etc.

Damage to the vehicle from competition, such as racing.

Damage to the vehicle that is caused by insufficient or improperly performed maintenance or repairs, such as not performing maintenance at the intervals required in the Owner’s Manual, or the use of chemical cleaners that damage the finish of the vehicle.

Damage to the vehicle caused by improper storage, such as weathered or faded finishes, rusting, or corrosion of metal components.

Wearing or deterioration of components subject to normal wear during normal vehicle operation, such as tires, brake pads or linings, drive chains and sprockets, clutch plates, body components, spark plugs, any rubber components, with the exception of oil seals, and fuel, oil and air filters.

I could go on but it would put you to sleep. As we say, it has a warranty, not a guarantee. A warranty will pay for defects in manufacture, materials, workmanship during the warranty period. We don't guarantee that you will like it or will take it back unless certain conditions are met. If I showed you our customer service log of people calling in for the most unbelievable reasons you would be amazed. I've worked our customer service line a few times and I have nothing but respect for the people that can tolerate that kind of verbal abuse every day.

[MotorDoctor]

Originally Posted by Shade Tree Welder

Something too look at. Since both threads failed. Were they machined
correctly?

When I worked for Castrol, we had a customer complaint that our coolant was
causing thread failures on assembly. Long story short. The threads were so be
machined per the print that the thread root was to have a specified radius. The
failed parts had been machined wrong, by using a insert with almost no radius
creating a stress point when torqued in assembly. Also some variation in heat
treating did contribute. In the end we proved out coolant was not at fault.

I would look at the threads and verify they are correctly machined for the
torque and stress in use.

So looking at the fracture point, does it look like a shear load caused it or it fractured because improper machining of the threads created a stress point and when they tightened the locknut during assembly of the fork started the fracture process? All my good engineering books got destroyed by SuperStorm Sandy.

[Shade Tree Welder]

Originally Posted by MotorDoctor

So looking at the fracture point, does it look like a shear load caused it or it fractured because improper machining of the threads created a stress point and when they tightened the locknut during assembly of the fork started the fracture process? All my good engineering books got destroyed by SuperStorm Sandy.

I definitely looks like it started at the root of the thread, but what is over torqued
and started a crack or normal use caused the crack, I cannot tell by the pictures.
But since there is no other collateral damage from abuse as you stated above. I
would lean toward a defect in the parts, and that both broke... Machining, heat
treat, out of spec metal, over torqued at the factory... or just not a good design?

[toprecycler]

Originally Posted by MotorDoctor

So looking at the fracture point, does it look like a shear load caused it or it fractured because improper machining of the threads created a stress point and when they tightened the locknut during assembly of the fork started the fracture process? All my good engineering books got destroyed by SuperStorm Sandy.

I would not think shear load broke the threads. I would’ve thought you would see metal pushed/ pulled across the face of the nut.

So I think it broke being pulled apart. But, could the threaded stud have a bit of hardness in it to make it stronger, and it may have been a bit too hard, and stress cracks started forming , eventually breaking?


It kinda reminds me of some cylinder rods that’s keep breaking in some cylinders we rebuild repeatedly.

Back story of these cylinders, is they are a double ended cylinder, with the piston mounted in the center. From factory, they are 2 pieced rod, with the piston mounted in the center.

We started having problems with the rods unscrewing when cylinder in is use. The cylinder is operating a shear cutting copper tube rings, I believe the rings for pex pipe crimp rings. So this cylinder is just cycling back and forth 30-60 times a minute, and getting subject to a shock each time it shears a tube.

It just wears the seals, and rods, barrels etc out. But it is not good when the rods unscrew, before the seals wear out.

We use red locktight on most everything we put together, when it comes to pistons on rod assemblies.

Well, after several rods unscrewing, we came up with drilling a hole and welding in a pin thru the rod threads. Then we started getting rods broke at the weld area.

After several of these failures, I suggested keeping the rod one piece, and welding a steel piston in center of rod. Bosses ran with that idea.

Now we had several good ones, but now we still have the rods break at the piston welds.

I made the first one or 2 assembly’s like this, then the other machinist made them for the next 6 months. Then when I started making a couple again, I had forgotten the exact process, and didn’t cut grooves for as much weld as other machinist was doing. And the ones I did, broke a lot faster. And fingers pointed at me for not machining the weld grooves deep enough.

But I think it is deeper than that. We are still getting these cylinders regularly broke, but they may last 2-3 weeks, vs 2-3 days before they break. Customer is semi happy with that I guess.

I have asked the welder to preheat the rod and piston before welding, and to let it cool slowly. I figured the welds are cooling down too fast and hardening, causing the rods to break in the HAZ zone, but the shop welder knows more than I do, so that’s not happening. I have not quite convinced the boss yet that there might be a better weld procedure in place to prevent these failures.

I am starting to let the boss know when I get a weld back on a part that is super hard for me to machine, and I end up heating it back up with a torch to anneal it do I can machine it. Maybe someday, it will sink in about pre and post heat importance.







Sent from my iPhone using Tapatalk

[greywynd]

Originally Posted by toprecycler

I would not think shear load broke the threads. I would’ve thought you would see metal pushed/ pulled across the face of the nut.

So I think it broke being pulled apart. But, could the threaded stud have a bit of hardness in it to make it stronger, and it may have been a bit too hard, and stress cracks started forming , eventually breaking?


It kinda reminds me of some cylinder rods that’s keep breaking in some cylinders we rebuild repeatedly.

Back story of these cylinders, is they are a double ended cylinder, with the piston mounted in the center. From factory, they are 2 pieced rod, with the piston mounted in the center.

We started having problems with the rods unscrewing when cylinder in is use. The cylinder is operating a shear cutting copper tube rings, I believe the rings for pex pipe crimp rings. So this cylinder is just cycling back and forth 30-60 times a minute, and getting subject to a shock each time it shears a tube.

It just wears the seals, and rods, barrels etc out. But it is not good when the rods unscrew, before the seals wear out.

We use red locktight on most everything we put together, when it comes to pistons on rod assemblies.

Well, after several rods unscrewing, we came up with drilling a hole and welding in a pin thru the rod threads. Then we started getting rods broke at the weld area.

After several of these failures, I suggested keeping the rod one piece, and welding a steel piston in center of rod. Bosses ran with that idea.

Now we had several good ones, but now we still have the rods break at the piston welds.

I made the first one or 2 assembly’s like this, then the other machinist made them for the next 6 months. Then when I started making a couple again, I had forgotten the exact process, and didn’t cut grooves for as much weld as other machinist was doing. And the ones I did, broke a lot faster. And fingers pointed at me for not machining the weld grooves deep enough.

But I think it is deeper than that. We are still getting these cylinders regularly broke, but they may last 2-3 weeks, vs 2-3 days before they break. Customer is semi happy with that I guess.

I have asked the welder to preheat the rod and piston before welding, and to let it cool slowly. I figured the welds are cooling down too fast and hardening, causing the rods to break in the HAZ zone, but the shop welder knows more than I do, so that’s not happening. I have not quite convinced the boss yet that there might be a better weld procedure in place to prevent these failures.

I am starting to let the boss know when I get a weld back on a part that is super hard for me to machine, and I end up heating it back up with a torch to anneal it do I can machine it. Maybe someday, it will sink in about pre and post heat importance.

Attachment 169086
Attachment 169087
Attachment 169088
Attachment 169089


Sent from my iPhone using Tapatalk

We get a lot of that with the field work. We got moved today to a higher priority repair, weld procedure calls for preheat of 350F, then when welding is done, an hour of ‘bake’ time per inch of thickness (in this case 6”) then drop 50F at a time, and hold at each temperature for an hour. We’re guessing 12-18 hours from the time we finish welding until we can machine it.

These are stick bores for the pins to attach a bucket, they were cracked almost through. Bores are about 13” diameter and 18” or so long.

On your hydraulic cylinder rods, they look like IHCP, I would suggest for welding switching to straight CPO for that. I’d hazard a guess that the welding would brittle the hardened area, and allow a crack to start.

Sent from my iPhone using Tapatalk

[greywynd]

Back to the original pics, with the shock parts. Looks like there is darker areas around the outer edge of the failure, suggesting those areas cracked first. If that is what I’m seeing, I would think either torque or machining/heat treat issues.

Since it looks like stainless, I wonder if it’s as simple as someone forgot to turn the coolant on for a couple parts and caused work hardening? Or like Ron mentioned, wrong insert profile making the root too sharp?

Unless I’m looking at the drawing wrong, to ‘rip’ the piece apart would inly happen if there was an excessive upward force on the shocks, not downward load, is that correct?


Sent from my iPhone using Tapatalk

[toprecycler]

Originally Posted by greywynd

We get a lot of that with the field work. We got moved today to a higher priority repair, weld procedure calls for preheat of 350F, then when welding is done, an hour of ‘bake’ time per inch of thickness (in this case 6”) then drop 50F at a time, and hold at each temperature for an hour. We’re guessing 12-18 hours from the time we finish welding until we can machine it.

These are stick bores for the pins to attach a bucket, they were cracked almost through. Bores are about 13” diameter and 18” or so long.

On your hydraulic cylinder rods, they look like IHCP, I would suggest for welding switching to straight CPO for that. I’d hazard a guess that the welding would brittle the hardened area, and allow a crack to start.

Sent from my iPhone using Tapatalk

Good suggestion on thinking it is IHCP ( induction harden chrome plated) but it is not. Just regular chrome OD. Probably just .0005” chrome. We usually like .001” chrome, but not always getting what we like these days.

My working theory is the Haz around the weld hardens due to the cooling of the mass of the rod and piston. Since this is welded in one pass on both sides of the piston, it is not heating the rod up enough for it to cool slowly to avoid work hardening. If I machine the welds for clearance, I usually can tell if it’s harder to machine.

Our standard procedure has been in the past to move the just welded parts to our “paint area” where we can turn on a couple fans to help cool the parts. It is amazing we have not had more failures with other parts.

Appreciate the insight. I’ve been looking for a copy of the AWS section on Hydraulic Cylinders, but I don’t quite want to spend the money myself just to be a “snitch” that we are not following the best welding procedure, and argue that fact that “ we been doing this for 26 years this way, why change now” attitude.

Sorry to hijack this thread.

Sent from my iPhone using Tapatalk

[Shade Tree Welder]

Originally Posted by greywynd

Back to the original pics, with the shock parts. Looks like there is darker areas around the outer edge of the failure, suggesting those areas cracked first. If that is what I’m seeing, I would think either torque or machining/heat treat issues.

Since it looks like stainless, I wonder if it’s as simple as someone forgot to turn the coolant on for a couple parts and caused work hardening? Or like Ron mentioned, wrong insert profile making the root too sharp?

Unless I’m looking at the drawing wrong, to ‘rip’ the piece apart would inly happen if there was an excessive upward force on the shocks, not downward load, is that correct?


Sent from my iPhone using Tapatalk

Doc, does part 14-29 thread on the broken shaft above the nut?

If so why is there a nut there?

I am thinking 14-29 is unsupported on the shaft (clearance to get over the nut), you can get minor rocking of the part, crack in the thread root and then eventual failure.

[MotorDoctor]

Originally Posted by Shade Tree Welder

Doc, does part 14-29 thread on the broken shaft above the nut?

If so why is there a nut there?

I am thinking 14-29 is unsupported on the shaft (clearance to get over the nut), you can get minor rocking of the part, crack in the thread root and then eventual failure.

Sorry, working our techline today. I will put up better detailed illustrations later. Thanks for taking the time to look at this.