# If you need IMPELLER shear pins - the machine is flaky



## unknown1 (Dec 13, 2015)

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! 

STOP DON'T READ ANY FURTHER!!!
DON'T WASTE YOUR TIME!!!

However... if you want to watch me speculate myself right up my own colonoscopy-access-panel... go ahead.
I've got rabbits, cheshire cats and mad hatters up there!

A lot of this thread contains truths but it all falls apart when I switch from ASSERTIONS to GUESSES (flagged as "best-guess-13 and 14" in the verbiage)
I knew I didn't want any best guesses... but I gave in and went down that route anyway!
Even that erroneous best-guess contained my own self-doubts related to belt-friction that should have sent me in the correct direction (not the wrong one)
If it feels wrong... it usually is.

I won't delete everything because it's a good reminder for me to go with DATA every time. Only go with guesses as a last resort.*
*I knew that! I even SAY that in the thread... But I didn't follow my own instinct to avoid the guesses.

Read on if you must
;-)

-------------------------------------------------------------------------------------------------------------------------------------------------------*







This is going to be quite a controversial hypothesis... I will try to be clear in my thought process.

Please pay attention to whether I am saying IMPELLER or AUGER in the following. Otherwise you will get the wrong end of the stick.
PLEASE DON'T GUESS THE ANSWERS... I WANT TO HEAR FROM THE MANUFACTURERS OR PEOPLE WHO KNOW FOR CERTAIN.

Assertion 1: Whenever you see a shear pin anywhere on a machine, this is an admission by the manufacturer that some part of the machine is vulnerable to damage when blowing or throwing snow.

Assertion 2: It is important that the shear pin must be WEAKER than the vulnerable component otherwise it won't protect the component

Assertion 3: If a particular shear pin is designed to be intentionally VERY WEAK it possibly implies that the component it is protecting is also VERY WEAK

Assertion 4: An example that most of us are familiar with is the AUGER shear pin.... This is designed to protect the AUGER gearbox which sometimes/often has a vulnerable brass gear inside it.

----- so far I don't think I've said anything controversial ----- It's the next bit that is controversial 

Assertion 5: In the past, it was pretty much unheard of for an IMPELLER to have a shear pin. They used to have "permanent" roll pins. (I have been informed that Honda and Yamaha may be exceptions to this rule).

Assertion 6: These days, more and more machines seem to have IMPELLER shear pins.

Assertion 7: Therefore, these IMPELLER shear pins are trying to protect some part of the machine that is now considered to be vulnerable to damage 

So this begs the question... what is it about these recent machines that is now vulnerable to damage that was not historically thought to be so vulnerable to damage in the past? Why is that?

------- and now for the controversial statement --------

Assertion 8: Any machine that has shear pins on the IMPELLER (not the auger!) is an admission by the manufacturer that the Engine or maybe the transmission is now vulnerable to damage

Assertion 9: One of the following must therefore be true...
(a) Either....The potential for damage to the engine or transmission was ALWAYS high (in the past) but many designers "forgot"(?) to put shear pins in the IMPELLER(s) for many decades.
(b) Or..... Some engines and/or Transmissions are now more vulnerable than they used to be in the past and the IMPELLER shear-pin is an admission of that fact

I am particularly interested in hearing from an employee of Toro, Craftsman or any other 2-stage or 3-stage manufacturer that currently has IMPELLER shear pins.
Please identify who you work for and which manufacturer/models you are talking about in any response. Please also disclose any vested interests. It would also be very useful to hear the source of your knowledge. - Thanks. 

If anyone else knows FOR CERTAIN please speak up.... but please don't guess the answer.

Here is my question to them...

What part of your engine or transmission is now so weak that it needs to be protected by an IMPELLER shear-pin?
a) The engine and parts inside it? Which part(s) in particular?
b) The transmission and parts inside it? Which part(s) in particular?
c) All the above!
d) Some other part of the machine... please be SPECIFIC... Which part(s) in particular?

---------- and now for the most controversial part...... I'm using hyperbole here to make the point...

Assertion 10: Any machine that has recently introduced IMPELLER shear-bolt(s) designed into it is .... by admission from the designer... vulnerable to damage like never before in the past .....and therefore may be a machine to be avoided. On the other hand, maybe they finally got wise and added the shear pins that should have been there decades ago but were "forgotten".

Assertion 11: If you find you are using many shear bolts/pins in a typical season then either..
a) You are being unfair to the machine by running over newspapers, rocks, gravel, welcome mats, tree stumps or crashing into obstacles like wood-piles etc.
b) or.. You are being quite reasonable to the machine and the shear bolts are intentionally designed super-weak to protect something that is super-weak with your machine
c) or.. This is an attempt to sell shear bolts by the hundreds of thousands for no good reason and maybe those shear bolts are overly-sensitive. Maybe.

-------------------------------------------------------------------------------------------------

BTW: This thought process came about after posting a slightly humorous and slightly satirical rant over on the Craftsman thread bemoaning the junk being manufactured these days.
I spotted that the impeller shear-bolts were something I had never seen before and thought to myself...... wait a minute!! WHY?

That rant is here... some of it is specific to the downfall of Craftsman as I perceive it....other bits are generally applicable to the industry as a whole.
http://www.snowblowerforum.com/forum/1265098-post6.html

Full Disclosure: I am just a hobbyist and do not, have not and currently have no intention to ever work for any designer, manufacturer, wholesaler or retailer of snowblower equipment.
I am however deeply concerned by the current "race to the bottom" when it comes to quality and reliability of machines. 
I believe I see this across most if not ALL manufacturers to a greater or lesser degree.... even those we've loved in the past... whichever company that might be.
By the way... the PowerTiger stuff I am claiming to sell on my home page is intended as a joke... if you saw it... surely you knew that?!?!


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## orangputeh (Nov 24, 2016)

wow!


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## unknown1 (Dec 13, 2015)

orangputeh said:


> wow! you may be onto to something....


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *

Thanks but please don't guess  I want to hear from the MANUFACTURERS or people who KNOW FOR CERTAIN
THEY are the ones who added the shear-pins.... THEY are the ones who should know why.


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## sscotsman (Dec 8, 2010)

stuart80112 said:


> Thanks but please don't guess  I want to hear from the MANUFACTURERS or people who KNOW FOR CERTAIN
> THEY are the ones who added the shear-pins.... THEY are the ones who should know why.


Unfortunately you arent likely to find those people here..as far as I know, this groups membership contains *one* person who is an employee of a manfacturer..Honda. he can probably give some insight, but he will likely be the only one.

And because of that, I can tell you now that you will need to give up on saying " I want to hear from the MANUFACTURERS or people who KNOW FOR CERTAIN"  because 99 out of 100 posts in this thread are going to be speculation from people who are not manufactures and who dont know for certain! 

Because this group simply doesnt contain the people you hope to hear from..but others are going to chime in, which is fine..thats what this forum is for, to talk about snowblowers.

Scot


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## orangputeh (Nov 24, 2016)

stuart80112 said:


> Thanks but please don't guess  I want to hear from the MANUFACTURERS or people who KNOW FOR CERTAIN
> THEY are the ones who added the shear-pins.... THEY are the ones who should know why.


I deleted my stupid comment.


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## YSHSfan (Jun 25, 2014)

I am no expert nor have I worked for any snowblower manufacturer, but one thing I can say is that the statement_* "*_*Any machine that has IMPELLER shear-bolt(s) designed into it is .... by admission from the designer... vulnerable to damage like never before in the past .....and therefore is a machine to be avoided."* is wrong IMHO*.

*Honda and Yamaha which are in my opinion the two top snowblower manuafactures (followed by Ariens and Toro) use impeller shearpins and I believe they use them from their very first models. 
If the previous statement implies that one should avoid buying a Honda or a Yamaha snowblower because they have impeller shear pins, I'd say this is wrong (but this is my opinion alone).
:blowerhug:


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## unknown1 (Dec 13, 2015)

sscotsman said:


> Unfortunately you arent likely to find those people here..
> Scot


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


I hope you are wrong.

If I was the CEO of a snowblower company, I would want my back-room people participating (or at least lurking) to take the pulse of what's being said about my products and competitors' products.
It's a great way to get competitor intelligence and a great way to win brand loyalty by helping your best customers. 
Even if some of the manufacturers are not here, there should be people with inside contacts who can obtain DEFINITIVE answers from them. (licensed repair outfits etc)

KUDOS goes to HONDA for being here. 

BTW I already made my speculations clear concerning the engine and/or transmission to get people thinking. 

Let's try to keep the thread clear for the manufacturers for a week or so to give them a chance to do their internal research and get back to us. 
Make sense? <rhetorical question>
Thanks for caring!!


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## unknown1 (Dec 13, 2015)

YSHSfan said:


> I am no expert ...


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


I get your point...as I explained...That was intentional use of hyperbole to make the controversial point.
. 
Since HONDA is represented here.. I look forwarding to hearing the answer to my question from him/her concerning the specific part(s) that need to be protected by the shear-pins.
What is the second weakest link in the chain after the shear-bolt itself in the case of Honda? Maybe he/she knows (or can find out) the breaking-forces needed for that shear-bolt which also tells us by implication the strength (or weakness) of the protected part(s). (see Assertions 1,2,3)

Assertion 9a and 9b covers the case where shear-bolts might have been necessary from day one for certain weak components. There's potential KUDOS for Honda and Yamaha there.

I modified assertion 5 to mention Honda and Yamaha as possible exceptions to the roll-pin rule. 
I also softened the hyperbole in Assertion 10
Thanks for caring!!


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## unknown1 (Dec 13, 2015)

orangputeh said:


> I deleted my stupid comment.


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *

Certainly NOT stupid... just a bit premature.. I'm hoping to hear the FACTS first and the speculations later.  Thanks for caring!!!


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## YSHSfan (Jun 25, 2014)

On you first assertion you may want to change the word "plowing" to blowing.


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## unknown1 (Dec 13, 2015)

YSHSfan said:


> On you first assertion you may want to change the word "plowing" to blowing.


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *

Done! Thanks!


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## sscotsman (Dec 8, 2010)

Honda the company isnt officially here, but an employee of Honda is a member here..Robert has good insights, but he usually makes it clear he is speaking for himself, not for his employer. Honda has no official presence here.

But..I forgot.,Ariens, the company, has been here! Someone did join this forum in an official capacity representing Ariens. Her name is Mary Lyn, and the username is "Ariens Company"

Scot


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## unknown1 (Dec 13, 2015)

sscotsman said:


> Honda the company isnt officially here, but an employee of Honda is a member here..Robert has good insights, but he usually makes it clear he is speaking for himself, not for his employer. Honda has no official presence here.
> 
> But..I forgot.,Ariens, the company, has been here! Someone did join this forum in an official capacity representing Ariens. Her name is Mary Lyn, and the username is "Ariens Company"
> 
> Scot


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! 


* Awesome! Thanks! That's good to hear and is really what I hoped and half-expected to be hearing.
KUDOS to Ariens for that! A few dollars spent on tech support on this forum can buy a lot of brand loyalty.
Folks on this forum have the passion to steer our family, friends and neighbors in certain directions.. when asked.
It will be interesting to hear from their perspective why they do (or do not) feel that the impeller shear-bolts are (or are not) needed on their machines.
I'm sure she'll know or know who to ask.


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## unknown1 (Dec 13, 2015)

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *

Having slept on this, it is highly unlikely that any representative of a company would say anything that could possibly be translated into "We've added low-strength shearbolts to protect our low-strength engine components".
Although that would be honorable, it would also be financial suicide. I was overly optimistic and probably totally naive to think that might be even remotely probable. So I am backing off on waiting for manufacturers to comment..

So if anyone is interested in giving their speculations.. feel free to jump in whenever you want... what was I thinking?

I've thought this through a little further and will continue with my personal speculations if anyone cares... I'll keep the "assertion #xx" format to make it easy to refer back to any logic errors I've made along the way. 
----------------------------------------------------------

Assertion 12: The "shear strength" of a shear-bolt tells us when that shear-bolt is designed to fail. It therefore gives a good indication of the resilience (strength) of the component that it is trying to protect. The bolt needs to be a tad weaker than the component. If it is substantially weaker.... the bolt will fail too often for no good reason. If it is stronger... it won't fail at all and the component will break.

Best-gusss 13:The impeller shear-bolts are there to protect the ENGINE and not the transmission. If the impeller shaft suddenly stops, the transmission is not at risk because it can happily move the machine forward whether the impeller is spinning or not. On the other hand, if the impeller suddenly stops (and if the belt frictions are sufficiently strong) this will suddenly stop the engine's drive shaft. This in turn will either stall the engine (if the connecting rod is super-strong) or snap the connecting rod (if the connecting rod is "weak"). Another possibility for strong connecting rods is that the belts will simply slide on the pulleys to relieve the situation and maybe even "melt" the belts causing them to snap.

*--------------------------------------------------------------------------------
EDIT: This next guess #14 is wrong... the belts typically cannot pass the shock into the engine....they will slip and slide or burn out.......so everything below here is therefore bogus or irrelevant
--------------------------------------------------------------------------------
*
Best-guess 14rotecting a belt from melting is not a high priority because they are inexpensive. Protecting a connecting rod makes a lot more sense. So I conclude that impeller shear-bolts are there to protect the CONNECTING ROD and that the shear-strength of the shear-bolt gives us a good indication of the strength of the connecting rod (see #12)

So.. if you buy everything I've said so far... the presence of a shear-bolt on the impeller(s) does not imply anything suspicious per-se. however...

Best-guess 15: If the shear-strength of the impeller shear-bolt(s) is HIGH... this implies that the connecting rod is STRONG If the shear-strength of the shear-bolt is LOW.... this implies that the connecting rod is WEAK

Best-guess 16: So the question I should ask myself when I look at a machine with shear-bolts on the impeller is... "What is the design strength of those bolts and what does that tell me about the "quality" of the connecting-rod?"

Assertion 17: The title of this thread should have been "If you need WEAK shear bolts on an impeller.. this suggests that the engine (and specifically the connecting-rod) is correspondingly "WEAK". Perhaps the word "flaky" is too emotive.

Assertion 18: If the impeller shear-bolts keep breaking on you for NO APPARENT REASON.... this is either because the shear-bolts are designed way too weak (mentioned in 11c) and these bolts are not really "fit for purpose" ..or.. the shear-bolt strength is actually appropriate for the connecting rod and (if they keep breaking on you for no apparent reason) it's because they are trying to protect the engine which apparently has a weak connecting rod and therefore the engine is not really "fit for purpose"... (aka flaky).

Assertion 19: On the other hand, if the impeller shear-bolts are failing when an immovable object (such as a rock) gets trapped.. they are doing the right thing and working as designed to protect the engine and its connecting rod. 

So all that remains (in my mind at least) is to answer the question .. why did impellers not have shear-bolts from day one on all machines? ( I am told that Honda and Yamaha machines possibly DID have them).

I can only think of two possibilities.
a) Either.. Connecting rods used to be a lot stronger than they are today.... there was no need for a shear-bolt.... the engine would simply stall (or the belts would simply slip and slide and eventually burn out). No big deal either way in the grand scheme of things.
b) or.. The connecting rods were just as weak in the past as they are today and a heck of a lot of designers over several decades simply "forgot" and missed the opportunity to protect the engine by adding impeller shear-bolts. If this is the case, I'm told that Honda and Yamaha did not miss that opportunity.


MY CONCLUSION: If impeller shear bolts are WEAK.. question the suitability of the engine. If impeller shear bolts are STRONG... no big deal. Trouble is, I don't know how to assess the strength of a shear bolt when standing in the store unless the manufacturer clearly states it on the box or on the machine itself or in their owner manual. The link I'm about to give you DOES let you figure this out by seeing the markings on the bolt.. I don't think it helps you with shear pins which serve a similar purpose but are not actually shear bolts.

Please feel free to correct my assumptions, fix any logic errors or give alternate explanations.
Phew..sorry to be so verbose but I've tried to make my thought processes as clear as I could (at least to myself)

If you have the interest, check this out...
Everything you need to know about shear bolts
http://www.orangetractortalks.com/forums/showthread.php?t=23019


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## guyl (Jun 12, 2016)

Thing is, people tend to assume (often quite rightfully) that any design changes are made in an attempt to lower the cost and to otherwise cheapen a product, but there are times where it actually is an improvement. Protecting an engine sounds like a laudable goal. Maybe there is also a safety factor involved. Isn't that what most changes are about, like the auger brake? What if the impeller is designed to stop immediately by shearing a pin for safety reasons if something that really shouldn't be in there gets in?


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## sscotsman (Dec 8, 2010)

guyl said:


> Thing is, people tend to assume (often quite rightfully) that any design changes are made in an attempt to lower the cost and to otherwise cheapen a product, but there are times where it actually is an improvement. Protecting an engine sounds like a laudable goal. Maybe there is also a safety factor involved. Isn't that what most changes are about, like the auger brake? What if the impeller is designed to stop immediately by shearing a pin for safety reasons if something that really shouldn't be in there gets in?


Thats a good point..

Without an impeller shear pin, if something gets stuck in there, and the operator removes it (even with the engine off) the impeller can then move under belt tension when the obstruction is removed..a potential safety hazard.

But if the impeller shear pin breaks, the impeller is then loose and "free-wheeling", not pinned to the shaft, and it wont move when the obstruction is removed.

Scot


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## unknown1 (Dec 13, 2015)

sscotsman said:


> Thats a good point..
> 
> Without an impeller shear pin, if something gets stuck in there, and the operator removes it (even with the engine off) the impeller can then move under belt tension when the obstruction is removed..a potential safety hazard.
> 
> ...


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *



The additional safety aspect (that comes into play to protect your hand against belt tension after a blockage has been removed)... is a valid observation.

However, I don't think for one minute that was the PRIMARY reason for introducing a shear bolt and probably not even on the designer's radar at the time.
I believe it's just an unintended consequence that just happens to be marginally favorable as a side-effect in this case.
I've now convinced myself that I am 99.99% certain that impeller shear bolts are to protect a vulnerable engine and that it's the connecting rod that is vulnerable.

EDIT: that 99.99% becomes 0% in the next couple of messages so everything here is either bogus or irrelevant





As an extreme example, if an engine was made to be infinitely strong and therefore subject to zero possibility of damage... I don't think you'd ever see impeller shear bolts.... you would see a rollpin or similar.

I'm guessing it's for that reason that rollpins were used for decades on most machines.... the connecting rods were probably stronger.
However, unless I get the necessary bench equipment to test this hypothesis for certain (by intentionally breaking a bunch of old and new connecting rods) I won't ever have the DATA to prove that. 

This is similar in some ways to some Toro machines...
I've heard that some Toro auger gearboxes are "so strong that they do not need an auger shear bolt".
If that's true, I bet they didn't put a shear bolt in there anyway "just for grins" to cover the case where some obstacle jams up the auger, puts it under tension and then springs back at your hand when you remove the obstacle. I may be wrong but I doubt it.

In any case...I'm not going to be removing obstacles by hand from either location... in the words of Monty Python.... I will poke at them with a pointed stick. ;-)

The main question I will be asking myself from this point forward is..
Does this machine have a STRONG shear bolt to protect a STRONG connecting rod? ..or..
Does this machine have a WEAK shear bolt to protect a WEAK connecting rod? (aka flaky)

I would be really interested to know the shear force needed to break a Honda or Yamaha impeller shear bolt versus the shear force needed to break the shear bolts found in BigBox model XYZ
I have my suspicions but I have no DATA to back that up.

Who knows.. maybe connecting rods are so inexpensive to produce by the hundreds of thousands that everyone uses the SAME strength anyway.
Without data I will just be conjecturing until the cows come home. That's why I was hoping to get info and data from the manufacturers instead of guesses.
I don't expect to get that anytime soon for the obvious reasons... it's not because they aren't on the forum.... it's because no one is willing to say "Hey... buy our machines... they're the weakest connecting rods on the planet". The only ones who may speak up are the ones who believe they have the best.


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## unknown1 (Dec 13, 2015)

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


OK some of the FACTS and DATA are rolling in. ( I was off on other threads trying to find them)

KUDOS to [email protected] and KUDOS to Honda if they are actually PAYING him for all his efforts.. they should!! If I was CEO blah blah blah 
From the horse's mouth (and I don't mean Mr. Ed)

Okay, here are a few Honda facts...

• The impeller shear bolts are all the same on all HSS-series 2-stage machines.
• There is not a published spec for the torque required to break a shear bolt.
• The shear bolts are specially designed 6x18mm carriage bolt with a metric class 10.9 strength rating. This strength rating is 940 MPa min yield strength (136,000 psi) and 1040 Mpa min tensile strength (151,000 psi).
• Honda does recommend you use only Honda shear bolts; there is a risk a non-Honda shear bolt may not 'shear' when it is supposed to.

Now... if I can just get similar answers for BigBox machine XYZ. 

If I do a little introspection to figure out WHY this subject has me hooked.. I think I am looking for an externally-visible way of revealing the internal hidden details about a machine/engine.
That way I'd have a quantifiable verifiable way of making quality assessments when I'm looking at one machine or another.


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## jtclays (Sep 24, 2010)

Thes


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## jtclays (Sep 24, 2010)

Sorry


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## unknown1 (Dec 13, 2015)

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


Interesting... it's good to know MINIMUM strengths for bolts (especially if you are trying to keep the rotors attached to a helicopter)
It's also useful to make sure that a shear bolt does not break too early.

But in the case of a bolt used as a "shear bolt" ... we also need to know the MAXIMUM strength.. that's the only way we can guarantee it will fail when it needs to.
Maybe I'm nit-picking.. I don't think so.

Anyway, it seems that the data for that is simply not available so I will move on.


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## unknown1 (Dec 13, 2015)

jtclays said:


> These are belt driven , not gear driven impellers. The belt is not going to transfer enough energy/friction, by simply stopping, to overcome 6-16 gross torque from the engine sheave and break a connecting rod, IMHO. On a properly running, correct compression engine the belt will stop, and the sheave will burn a nice half moon into the top. Low compression engine with a farty running carb, it may stall out from a momentary lap in it's marginal running sequence. I think they put the shear pins in there mostly for ease of removal of the auger assembly without having to remove the belt cover, belt, the bucket, drive pulley and impeller bearing assembly. There's lots of people, myself included, that would have loved to see just a couple impeller shear pins to pull and remove an old Ariens impeller fan from the shaft. Some have spent days and weeks with hammers, spray and hydraulic presses trying to get the fan off the shaft:grin:


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *



I worried about that possibility in "Best-guess-13" and "14" (but I only mentioned it obliquely).
If you are right... I'm not going to ever get the externally-visible quality-at-a-glance data that I was hoping for. Dang it!!

<<speculation removed here>>

I should have asked robert the questions I had already proposed in between Assertion#9 and #10.... 
They were....

What part of your engine or transmission is now so weak that it needs to be protected by an IMPELLER shear-pin?
a) The engine and parts inside it? Which part(s) in particular?
b) The transmission and parts inside it? Which part(s) in particular?
c) All the above!
d) Some other part of the machine... please be SPECIFIC... Which part(s) in particular?

......but I didn't....I went straight to the specs for those bolts. I'll get back with the answers soon.
In fact I'll try to pull him onto this thread so I can get out of the way as middle-man.
It's all a bit verbose so I'll focus him onto your post 19 and this response on this thread.

Note to self.... stop mixing terminology shear-pin versus shear-bolt


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## sscotsman (Dec 8, 2010)

jtclays said:


> Sorry on the pics not showing up.
> I don't know what's going on with photobucket, may need to just scrap that whole account.
> I'll try to upload them here directly.


Photobucket imploded a few weeks ago:

https://petapixel.com/2017/07/01/photobucket-just-broke-billions-photos-embedded-web/

Scot


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## unknown1 (Dec 13, 2015)

jtclays said:


> Sorry on the pics not showing up.
> I don't know what's going on with photobucket, may need to just scrap that whole account.
> I'll try to upload them here directly.


*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


Google photos works well for me. That way you don't hit your "max upload space" on this forum
Simply put a link to your specific publicly-shared album(s) in google-photos in your post.


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## jtclays (Sep 24, 2010)

Afte


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## unknown1 (Dec 13, 2015)

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! 

So I think I just speculated myself up my own colonoscopy-access-panel
I put a clear edit at the top of the original post warning people away from the rabbit hole.*

Here's [email protected]'s reply to my questions asking WHICH parts are being protected....
Again from the horse's mouth

------------ robert starts here
The engineer tells me the shear bolt on the impeller is there for general protection from damage due to a clogged impeller. Any number of things connected to the impeller could be damaged otherwise. On HSS models, the impeller is driven off a belt, which connects to the crankshaft. Generally speaking, damage usually happens to the impeller, the shaft driving it, and the belt/pulley that powers it. It is rare for a locked-up impeller to cause much damage beyond that, but not impossible. To my knowledge, all Honda 2-stage machines have used shear bolts on their impellers. I'm not privy to the testing data the design team used for evaluating the shear bolt spec/design, sorry.
------------robert ends here

*
My house of cards collapsed on best-guess-13 and 14 when I refused to listen to my own advice to not guess. Go figure!*
The correct answer was hidden in best-guess-13 but so was the wrong answer.
I mentioned the belt-friction as being critical
If those frictions can translate shock into the engine... we can safely go down the rabbit hole towards connecting rods
If they can't (and in most cases they can't) the susceptible part must still be back towards the auger bucket and the belts themselves (I already mentioned the belts burning out)

So the "impeller shear bolt" is there to protect......... drum roll here........ "the impeller" (more or less)
Duh!

I've spent so long looking at 30 year old impellers (that I can barely lift) that I missed the obvious observation that I had already made over on the Craftsman rant.
Those accelerators (front propellers) on the Craftsman 3-stage look flimsy to me. So it's no wonder they have shear bolts on them. (I'm not talking Honda here)

mea culpa
--------------------------------

I'm still left with one nagging question though..... I already mentioned it in message #21 on this thread
I will repeat it here.... 

It's good to know MINIMUM strengths for bolts (especially if you are trying to keep the rotors attached to a helicopter)
It's also useful to make sure that a shear bolt does not break too early.

But in the case of a bolt used as a "shear bolt" ... we also need to know the MAXIMUM strength.. that's the only way we can guarantee it will fail when it needs to.
Maybe I'm nit-picking.. I don't think so.

can anyone help with that one? 

Why do the specs talk about minimum strength when they also need to talk about maximum strength (for shear-bolt applications)?
Is it all just based on knowing (or believing you know) the metallurgy and therefore the "Shear Capability" and plugging it into the following equation.

SF = SC in KSI * SA

SF = Shear Force needed to cause failure
SC = Shear Capability of bolt 
SA = Surface area

Wouldn't it just be easier (and safer) to specify the MAXIMUM strength in the specs instead of hoping that the metallurgy grade is correct in production?


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## guyl (Jun 12, 2016)

Ah, but that's the dumbed down, simplified, laymans way to figure it out. For those of use really into this, try the more accurate calculation:


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## unknown1 (Dec 13, 2015)

guyl said:


> Ah, but that's the dumbed down, simplified, laymans way to figure it out. For those of use really into this, try the more accurate calculation:


Wait.... on that nested summation ( I mean the one summing from s=0 to s=m)... on the denominator where you say (m-s) factorial times 2 to the power (m-2s)... shouldn't that be (m-3s) ??
I may be wrong but I don't think so
Boy ... if I had a dollar for every time I made THAT newbie mistake.

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


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## guyl (Jun 12, 2016)

stuart80112 said:


> Wait.... on that nested summation ( I mean the one summing from s=0 to s=m)... on the denominator where you say (m-s) factorial times 2 to the power (m-2s)... shouldn't that be (m-3s) ??
> I may be wrong but I don't think so


I also saw that. I concluded that (m-2s) would be right for MTD machines, and (m-3s) for Honda. Thanks for pointing it out...


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## Tom Burns (Apr 26, 2017)

guyl said:


> Ah, but that's the dumbed down, simplified, laymans way to figure it out. For those of use really into this, try the more accurate calculation:


My wife and I were talking about that, this morning. Nothing was resolved. I went to the dump and she did laundry. Very productive day, anyway.


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## unknown1 (Dec 13, 2015)

guyl said:


> I also saw that. I concluded that (m-2s) would be right for MTD machines, and (m-3s) for Honda. Thanks for pointing it out...


PERFECT! I agree with that conclusion!
That's the externally-visible thing on a machine that gives me the definitive insight into the quality of the engine after all!!
I'll keep that equation in my back pocket for the next time I'm at BigBox Depot.
Boy... sometimes I miss the totally obvious!!! 
It's just like forgetting to turn the gas shutoff valve to the "run" position or forgetting to reconnect the spark-plug.
Thanks again for pointing that out!!
Forever in your debt.

*** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! *


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## unknown1 (Dec 13, 2015)

Tom Burns said:


> My wife and I were talking about that, this morning. Nothing was resolved. I went to the dump and she did laundry. Very productive day, anyway.


Yep... sometimes I wish I'd just done laundry instead!! ;-)

*
** Warning to anyone stumbling into this thread 
** Don't waste your time 
** I'm totally wrong 
** Just go to another thread instead !! 
*


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