Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Starting a thread for gearboxes.

Catt,  There have been many discussions regarding cast iron versus aluminum gearbox cases.  What have you seen over the years regarding the two?  I can see how cast iron would be very strong, but to be honest I've seen gearboxes torn up inside but the case castings were fine.  

 Me to.  4-5 aluminum with broken cases but never saw a cast iron case broken.

 

That I know of there are no white papers, studies or other specific info I could ever find related to snowblower gearboxes.  My base has been formed by reading lots of net postings from posters who seem knowledgeable and working on quite a few. 

   

Point 1. Strength.

   The impression I get is cast versus aluminum is mainly for strength when taking a hit.  Cast is one added feature in making a machine more robust boosting it into the category of heavy duty, industrial or commercial. 

 

Point 2. Long term wear.

   It’s possible that the added rigidity may have a miniscule effect on wear over 20-30 years but from my estimate if both a cast and aluminum with the same internals were used in the same service over 30 years the wear would be the same or the difference insignificant. 

 

Point 3. Robust build.

   Cast gearboxes often used to come with two roller bearings or heavy flanges.  Ariens use to used two roller bearings up to about 2004.  I think they are now all bearings in Ariens cast and aluminum.  There are generally more support parts in a cast.  The trust washers and collars may be more robust than used in an aluminum.  An MTD is low end and collars often break in those with an unusual but solid hit.  So casts, depending on the make, my have more and better internal parts even if the gears are similarly sized to an aluminum.   Generally though, aluminum gearboxes are simpler with less robust parts.  There are worm differences also with smaller diameter one piece shafts with a milled worm versus a separate replaceable larger diameter worm on a larger shaft. 

 

Point 4, Utility.

   A cast would be good for commercial and industrial use.  A small company would have one for their lot where the operator may not be so caring about use so a beefier box good.  Operators may nor be familiar with the lot they are clearing so chances of picking up debris higher or hitting hidden obstructions greater. 

 

  A homeowner would be more caring of a machine and knows his area but there are lots of “I got’cha’s” around a house, newspapers, doormats, and kids toys but for the savvy homeowner there is no reason to get a cast over an aluminum.  A low end aluminum (Murray or worse MTD)  in average home service will outlast the other parts of the machine.  For home use with an average driveway any gearbox is fine.  For bigger areas with big drives MTD is not so good but passable.  A better bet would be aluminum by Murray(low end ok), Toro, or Ariens ((XS), the compacts Ariens is now the size of MTD.  The old Ariens gear with a collar was ok).

 

Point 5, Other.

   Yamaha and Honda use aluminum and I don’t know of any complaints about these.  They both use 4 roller bearings in the gearbox.  Yamaha may have gone to two.  There are two Honda dealers in the area I’m fairly friendly with and they have zero problems with the gearbox. 

 

   For the average machine in homeowner service I don’t see any need for cast over aluminum unless there is a specific need.  Any of the gearboxes on the machines at Lowes or HD seem fine to me for use around eastern Massachusetts.  For areas with more snow ok to a point but better aluminums would be good.  If someone had a long drive with trees on both sides and old branches fell all the time that get buried then big aluminum or even cast.  No benifit to cast without a need.

Trouts2,

What do you know about 'Shock Protection' system that Yamaha is using?

They have done away with shear pins. I am assuming some type of presured bearing plate in the trasmision that can pop out when the auger jams, then pop back in when back in operation.

I would be curious on any information about this. The thought of no shear pins is attractive. I can change them, but if I am out of town, my Wife can not.

rubinew wrote:

My Toro has something like this as it only has shear pins on the auger blade itself not on the gearbox. Toro says they don't need shear pins on the gearbox.

   I have not been able to find drawings for the new Yamahas.  If you know of any online please let me know.  I'm aware of the shearpin stuff and given it's Yamaha would think it ok but do not have any specifics.  

Heard of the first broken Honda gearbox ever today.  An HS624TA hit something and "broke the axle and gearbox" so I may pick it up for parts.  Does not indicate anything unless frequency counts.

Excerpt from Yamaha's ad:

Shock Protector is a shock-absorbing device fitted inside the auger designed to prevent mechanical breakage in the event the auger comes into contact with a hard object.

I'm not familiar with Yamaha's snow throwers but many outboard motors use hard rubber splines on their props that match the stainless steel splines on the prop shaft.  When the prop hits an object, the rubber splines slip over the steel splines then immediately re-engage with the next set of splines to continue power to the prop once the obstacle is cleared. 

I'm wondering if Yamaha is using something similar on their snow throwers.  It works very well on outboard motors and would likely be very effective/reliable on a snow thrower.    

I don't know how they do it either, but I remember quite a few years ago I had one of those small radio controlled backhoes and the gear boxes that controlled the digging bucket had a built in torque limiting gear.  I am not sure what they are called and have been drawing blanks looking for pictures.  They basically took the gear and split it in 2 pieces with a kind of half circle wave connecting the 2.  There was a spring that held the 2 pieces together, but if the torque got too high the wave design would overcome the pressure of the spring and the gear would slip.

EDIT:
Found this link that is similar in theory to what I was referring to, but a different design.
http://technicbricks.blogspot.com/2008/02/tbs-technugets-01-inside-technic-clutch.html

Shryp wrote:

Hey thanks for the info! 

If Yamaha is using a similar principle in their gear boxes, I real hope it isn't stamped 'LEGO'  :-)

trouts2 wrote:
I haven't found anything specific yet but Yamaha's Japan site might turn up something.  At least the PDF manuals for their Japanese models are there.

http://babelfish.yahoo.com/translate_url?doit=done&tt=url&intl=1&fr=bf-home&trurl=http%3A%2F%2Fwww.yamaha-motor.jp%2Fsnowthrower%2F&lp=ja_en&btnTrUrl=Translate

Here are some gearboxes for comparison:

Ariens aluminum in smaller models.  This may not be the most current.  This gear has a collar which is dropped in some of the newer models but I'm not sure if it's all.  The newer gear without the collar is about the same diameter as the old gear.  The old style was probably stronger.

Ariens XS aluminum which comes in bigger machines in loose terms mid frame to large frame.

Ariens cast iron approx 2004 and earlier.  Used roller bearings.

Ariens cast iron post 2004 version.

Toro aluminum.  I don't think Toro offers a cast iron gearbox.

Snapper cast iron, used as far as I know in all Snappers except their small models >7hp, so all mid frame and large frame regardless of heavy or medium duty.   Came standard in the 8265 models (available in the mid-late 90's) which was one of the best snowblowers in that class ever made by any maker.  It came with a great top dash chute control, electric start, night light, excellent bucket paint, top notch gearbox, slightly wide good diameter tires, a zerk mounted in the auger support flange, easy to lub enclosed chain case. and a great chute with a remote hood control (that did not freeze up).  Many of these models are still around, look great and are a great bargin as a used machine with most I've seen capable of 20 more years of service. 

MTD aluminum, the winkie of the lot but good enough for most people.

Jacobson, a cast robust gearbox

I don't get it!  My ariens is 15 years old and it has  a aluminum gear box.  Yes I ate my share of sheer pins , but I never had a gear box failure.   If the purpose of sheer pins is to fail to save your gear box, why does anyone need a cast box? If your snowblower eats something , the pins will sheer in any case. My little 8 hp does a fine job. Even the big bad 13 hp  high dollar Honda blowers have aluminum boxes

Look again at all the various aluminum types above.  They are not equal.   The older style Areins has no relationship of quality to the Honda.

Pins don't always break.  Sometimes the forces involved bypass the auger pins and even the key or dowel in the gear.   It can happen that the forces go to the gearbox.