Snowblower shear pin mystery

[07wingnut]

I have a 2750D front mounted snowblower mounted to a BX23 tractor, that has performed well for the last couple of years. The only shear pins that have let go, did so because of encountering obstructions of some kind, the kind that does the pin in from physical shock. Lately, that has changed, and pins are shearing during normal blowing.
The shear pins are grooved grade 8 for the fan and grooved grade 5 for the augers. During the last snowfall, 20 inches of wet heavy snow, the snowblower went thru a dozen shear bolts for the fan only, and none for the augers. The sound of the blower changed as well, not a smooth sound, but more cyclic. Some of the bolts sheared when there was very little loading on the fan. My take on this was that there must be some vibration in the snowblower drive train that was causing fatigue in the shear bolts. So, the snowblower was partially dismantled in the garage for a bearing check, but they all were tight and smooth. The drive chain was not too loose, but on closer inspection, it was obvious that it was stretched or worn at the pins. The chain could be lifted from the top of the sprocket, even though it was tight. So, not seating properly on the sprocket teeth. I put on a new chain which did sit correctly on the sprockets, buttoned everything up, and spent 3 hours blowing snow with not a single breakage.
This apparently was the cause of all the shear bolt breaks. A worn chain causing repeated shocks to the drive train and inducing fatigue in the fan shear bolt. Who knew.
Hopefully this will help somebody from killing numerous shear bolts that were innocent of any crime.

 

[GreensvilleJay]

I did.
When you replaced the chain you 'should' have replaced the sprockets as well though. Anyone old enough to have replace timing chain AND gears in a car will know why. Those into motocross always replace chain AND sprockets....

Also after a few hours, be sure to inspect and retighten the chain ! I'll bet 99% of owners never do.....

And, inspect the holes where the shearpin goes. It should be a 'silky smooth' fit NO slop, NO 'eggshape'.

 

[200mph]

Something else to keep in mind, especially when auger shear pins break...

The left and right augers have to be timed or oriented to provide smooth delivery of snow to the fan. If an auger is out 180 degrees the delivery of snow to the fan will be cyclic and the sound will be different.

Most blowers have a sticker inside the housing showing the auger orientation. After use though it may not be in a readable condition.

 

[07wingnut]

I did inspect the sprockets and they look like new. Forgot to mention that the chain used is conventional roller chain, not Oring chain, and these wear out pretty quickly and should probably be replaced every year. It's easy to just cut a section off the roll in the shop and replace the old chain. Likewise, the auger timing is correct, 180 degree out of phase. The shear pin holes are not deformed and the fit is snug. I believe this is because grooved pins snap cleanly, and don't tend to smear like some of the softer bolts that are sometimes used.

 

[DustyRusty]

Chains stretch and fatigue, but the sprockets are hardened steel, and wear very slowly. I change the chains every year, and for the past 15 years, I have never needed to change a sprocket. You can tell when the sprocket is worn, because the teeth will come to a sharp point from wear. As long as the teeth are still good, no need to replace them. Timing gears on cars travel 3000 - 5000 RPM for 60 or 70 thousand miles before they need to be replaced, and your snow blower will not travel that many revolutions in its lifetime. Lubrication is key to keeping your chain and sprockets in good condition. The manual recommends lubing with chain bar oil every 4 hours of operation, but most never do this, which causes the chain wear. The bearings in the machine are factory lubed, and that lubrication needs to be replenished every couple of years, by removing the bearing seal, and repacking. Some bearings you cannot do this with, so replacement is the only way. I always check the lubrication on new bearings, because I have found that many manufacturers skimp on the grease.

 

[07wingnut]

The chain in question had 2 seasons of use and if I recall, probably was not lubed often enough because you need to remove the cover. Not a big deal, but inconvenient in the winter. This mod makes it a lot easier and such, will be used more often.
Simply remove the plug, squirt in some chain oil, and let it trickle down the drop tube, directly onto the chain. The fly in the ointment is that the snowblower should be operating slowly, so the oil is distributed on the chain. My BX has a safety disable switch, which allows the pto to run while the operator is off the seat. Other options to do this may exist, depending on the tractor.

 

[twomany]

A new chain went on the B series blower this morning. The original broke a link!
I couldn't find a #40 o-ring chain local, so common #40 roller chain was used.
Cheap enough not to fret over. I'll keep my eye out for #40H

I left the cover off. Easy enough to lubricate and check on tension etc. that way.