Snow Blower Drive - Roll Pin Question

[Redrum]

Hi,

experienced back yard mechanic but a novice when it comes to roll pins, so I could use some thought from someone who is.

I have a NH TZ25DA tractor with a NH 50CS front mount snow blower attachment. For the second time I have somehow damaged/lost a roll pin in the drive path. Starting from the auger back toward the mid PTO drive, here is what I have:

The two augers are on horizontal shafts that are driven my a gearbox. The augers are attached with shear bolts. From the gearbox, another shaft runs back toward the tractor, and the secondary thrower (fan) is attached to this shaft with a shear bolt. This shaft drives a gear on the back side of the blower, which is connected to another gear/driveshaft** with a chain. This driveshaft connects to the quickhitch to be driven by the mid pto driveshaft. So it goes driveshaft from blower->gear->chain->gear**->driveshaft**->quickhitch (to POT driveshaft)

The gear/driveshaft** is a part that is offered by NH as only an assembly (H40C12). However, the gear is/was connected to the shaft with a roll pin. The first time it broke it looks like the pin sheared. I found a roll pin that seemed to fit, but my dim memort tells me it might have fit looser than I wanted (SAE vs metric?). Since they are not separate parts there is no spec on the roll pin size. The second time (a couple years later and a couple days ago) when the snow stopped blowing, I took a look and the pin is gone.

I am almost 100% positive this pin was never meant to shear, as there are shear bolts on the augers and the fan. Right? I also am betting I put a pin in that eventually worked itself out. I imagine since these tractors were built overseas, the roll pin must be metric, right? Also, are their different hardness/ratings on these pins?

I spoke with one of the local NH dealers and they couldn't offer any help, they would only replace the assembly (must not be farmers). Not only do I not want to replace the assembly, the pin hole is accessible to repair without disassembly

Any thought?
Thank you, Jim

 

[seville009]

Not sure exactly what the roll pin is, but Messicks has parts diagrams. You probably have already looked at it, but if not, hopefully it will help

New Holland (5CS) - SNOW BLOWER (1/3-1/15) Parts Diagrams

 

[zzvyb6]

On some equippment I have ( Kuhn tedder/rake for example ), there is a second roll pin driven inside the first to expand it. An all weekend project to remove them if they break.

 

[s219]

If the first pin sheared, I would check the actual shear pins to make sure they are the proper grade bolt. If for some reason they are stronger than they are supposed to be, they probably transferred the load up to your roll pin.

For not too much money, you can order a variety pack of roll pins and have a bunch of sizes at your disposal to play with. Better yet, put a caliper inside the hole and measure it exactly, then look up the proper pin for that hole size. The pins should take a little effort to get started, but not too much once you tap them in -- about like driving a framing nail into framing lumber.

 

[wheelbuilder]

I'd check if the parts protected by shear pins have seized to what they ride on. That would push the failure point back to the next weakest link.

 

[Redrum]

thanks for the replies. Regarding the parts diagram, yea, I checked that, unfortunately, the part itself (shaft and gear) is not serviceable, and about $150. I could just buy the part and do the diassemble/reassemble, but the pin hole is just looking right at me . The original roll pin failed about 4 years ago, and it was sheared (and a bear to get out). All of the shear bolts were OEM, so who knows why the roll pin sheared (I know when, snow stopped blowing, so that was the stressor). Like I said, the second one that failed/fell out wasn't OEM because NH doesn't sell it.

I guess it's time to buy a kit and or measure. I had one (momentary) thought to replace it with a bolt, but visualized the damage that any play would cause, and thought otherwise .

Regarding metric vs sae, anyone have any idea/experience on what it would be? That would help if I was to buy a kit that is one or the other....

Jim

 

[Captain Dirty]

The original roll pin failed about 4 years ago, and it was sheared (and a bear to get out).
I guess it's time to buy a kit and or measure. I had one (momentary) thought to replace it with a bolt, but visualized the damage that any play would cause, and thought otherwise .
Regarding metric vs sae, anyone have any idea/experience on what it would be? That would help if I was to buy a kit that is one or the other....Jim

Speculative opinion: The 4 year old replacement pin may have been the wrong size (the original pin was a bear to get out; the second one apparently fell out); the pin may have corroded to where it was weaker than the shear pins.

"One measurement is worth a thousand expert opinions"

McMaster-Carr has a vast array of roll pins in varying design, material, and sizes to confound you even with accurate measurement.

 

[LouNY]

Roll pins are a royal pain when they act up.
They are not designed to be shear pins, though they will shear occasionally.
What we have seen on many times is that the use subjecting them to vibration or
load unloading cycles will cause them to loss the original spring tension and they will start to
walk out of the holes once they travel past one shear point they will shear or compress and fall out.
One remedy is to pass a heavy wire thru the roll pin then wrap it around half of the shaft and twist the ends together.
This helps to keep it in the proper location. Also as has been mentioned many times a second roll pin is placed inside the first.
The function of a roll pin is simply to maintain the proper position of parts.
Also they make special punches to remove and install roll pins, they have a dimple in the center and a recessed groove in the outer portion.

 

[WranglerX]

Roll Pins are by nature interference fit, they need to be drive in and should never "fall out' if it falls out it is wrong size (too small) .... As some famous carpenter says "measure twice cut once"...

IF I don't know size of hole, I use a drill bit as size gauge and go from there...

Dale

 

[ruffdog]

I'd check if the parts protected by shear pins have seized to what they ride on. That would push the failure point back to the next weakest link.

^^^correct...the OP should remove the shear pins and make sure the slip pieces are not rusted solid.