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

Horizontal lists don't usually post correctly so the info below.....

Make...............Engine RPM,,,,,,Auger dia........Auger RPM................Velocity out ft/min

Powerlite,  .........4000....................7........................1550..............................2840

Murray 3ph........4100..................8 1/4....................1025..............................2213

Maco 3hp...........4100..................8 1/4....................980...............................2116

Borat....................6000.................8 1/4...................1470.............................3173

Toro 350..............4200.................8 1/2.....................xxxxx..............................xxxxx

Borat,

    Your auger RPM was approximated from Maco's.  Different belts but likely both pulley diameters are the same or very close.  The estimate was 245 RPM per 1K engine RPM.

     It would be interesting to compare impeller bearings.   Murray and Maco both have roller bearings in the drive side of the auger shaft, flange on the other.  Borat your's is probably the same.  I'd have to check the Toro but I think flange on both sides. 

    The velocity out of a dual stage is 3400 to 4000 ft/min most common around 3700-3800 ft/min (that is if I am remembering those numbers right).  The better brands of machines will all be at the top of the high end.  Those numbers seem about right given what a Powerlite can do versus a dual stage in the back yard in conditions good for the Powerlite.

trouts2 wrote:
"Makers usually give a Max torque at some rpm and that is usually below max torque say 24-2800 on a 3600 engine."

You're right. However, I made no effort to use manufacturer's torque numbers (which are typically harder to find for older, hp-rated engines anyhow). If we assume that the horsepower of the engine is rated based on the operating speed (a fair assumption), then this works better. You can calculate torque if you know hp and RPM, which is what I did, for the operating speeds listed. Now, in the case of the SS322, the operating speed is 4300, not 3600. I don't know which speed the 3hp is based on. But I used the 4300, for discussion purposes. You're right that the torque is definitely a curve, so this number doesn't exactly tell the whole story. But there are so many other assumptions involved in this anyhow that it almost doesn't matter   I have come across a torque/power curve plot for at least 1 engine, I'd have to look later and see if I saved it.

" But the force figure is interesting as lb’s are sort of familiar.  Is that something like the force available would lift that amount one foot? "

Torque is commonly listed in ft-lb (well, lb-ft, really, but that's kind of semantics). A torque of 5 ft-lb can apply a force of 5 lbs (can lift 5 lbs), at a radius of 1 ft. Or 2.5 lbs at a radius of 2 ft. So, in the example of the ST824, the impeller has a 12" diameter, or 6" radius (0.5 ft). So the maximum force at the tip is torque/radius, or 38.2 ft-lb / 0.5 ft, or 76.4 lb.

So given the same torque on a 12" diameter impeller vs an 8" diameter impeller, the max tip force will be greater on the smaller-diameter, 8" impeller. It will slow down less with heavy snow. But it also won't be throwing as far.

Like you said, there are a ton of other factors too. And the impeller/paddle is doing more than just flinging snow out, it's also moving the new snow to the center. And for a 2-stage, the augers are also sucking up power, and the transmission, etc. This is just a potentially-interesting exercise in comparing similarly-designed machines, at best.

>>>You can calculate torque if you know hp and RPM

   Yes and no.  There are general formulas for doing that I’ve seen on the net but they are not accurate.  They all end up with a linear line which does not happen in reality.   If you calculated that way I think you end up with a max torque at 3600 which is not right.  Torque at 3600 on most of the snowblower engines will be 20-25% less at 3600 than max torque.  If you took the numbers from a general linear formula and sub’ed  20-25% they would be closer.

    Makers would probably be using a dynamometer or something for their curves but they probably have formulas to calculate the true non-linear curve for their engines

 

>>>So given the same torque on a 12" diameter impeller vs an 8" diameter impeller, the max tip force will be greater on the smaller-diameter, 8" impeller. It will slow down less with heavy snow. But it also won't be throwing as far.

 

   Maybe that’s way the SS’s can toss well with the lower impeller speeds compared to a 4 cycle. 

 

BTW: I picked up two types of springs this morning to replace the paper clips.  Since the cases were on and half fastened I ran them again working the rev boot with the string.  They worked pretty well so I scrapped putting in the springs.  If I do another or have to open up the cases with the ones with clips again I’ll install a spring. 

 

trouts2 wrote:
I don't mean this to sound argumentative, but *yes*, not yes and no However, the caveat is that I am calculating torque at a single RPM, based on a published hp number, and am assuming that the hp is produced at  the operating RPM of the machine. At a given RPM, there's no discussion about it; torque or hp can be calculated if you know the other one, and the RPM.

hp = (torque * RPM) / 5252

That's the only torque formula involved in my numbers. I'm making an assumption (a reasonable one, I hope) regarding the hp and RPM. If those assumptions are OK, then the torque #'s I listed should be accurate, based on that single operating condition.

You're absolutely right that this formula will show a linear hp "curve" across an RPM range, based on a constant torque. Which isn't accurate to real life. But I'm making no attempt to represent what happens at any other RPM (note that I did not attempt to show torque #'s for the higher RPM, because I have no idea what the hp & torque are when the RPM's change). I have no idea what the max torque is, which probably occurs at some lower RPM, like you said. But that wasn't what I was interested in. And, as you said, you'd need a dyno curve to really show that.

Good info on the springs! If they're not needed, that might make things simpler. Do you just tug on the string and hold it while blowing? Or do you have it going to something like a little lever?

I have my string tied off at the top of the handle.  I used a tie wrap to hold it in position.  When operating the machine, I put my left hand between the string and handle.  When I want revs, I just curl my fingers to put tension on the string.   Not much distance between string and handle so very little input is required to make things happen.  I'm very happy with the way mine operates.  Real simple, real easy and reliable.

RedOctobyr,

By a chance are you an engineer by trade?  All those charts, curves, formulas is making me dizzy.   

I can understand the principles of the "turbo encabulator", it's all based on the Heisenberg Uncertainly Principle and Nuclear Physics, but I have no idea what you're saying. 

Guilty as charged. And I love the Turbo Encabulator videos, great stuff.

This is a great site for a bunch of different Tecumseh engine info:
http://www.smallenginesuppliers.com/html/engine-specs/tecumseh-engine-specs.html

I won't insert the pics here, but they have scans of the spec sheets for a number of different engines. Including, but not limited to, the HSK600, the HSK845 (sorry, no 850), and HM80 (which seems to be a summer version of the venerable HMSK80).

These actually show charts like dnyo plots. They appear to show torque, and (I can't read it) possibly maximum horsepower in addition to what might be continuous operating horsepower. I had the most luck trying to "read" the HM80 version.

HSK600:
http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/features/hsk600.jpg

HSK845:
http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/features/hsk845.jpg

HM80:
http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/features/hm80.jpg

I found it interesting that, for the HSK600, different RPM's are spec'd for different manufacturers. 4300-4500, so my current 4600 really isn't much outside the suggested range (my service manual shows 4300). Also the HSK600 pic lists 32:1 for oil (50:1 for the HSK845), but my gas cap & service manual says 50:1.

It's a shame that these images show much interesting/useful info, but that the quality is poor enough that much of it can't be read. If anyone finds better copies somewhere else, I'd be curious to find out where.

From reading the specifications, the KSK840, 845, 850  engines are very similar but have certain components that have different part nos. 
The  power output is as follows:  840= 4h.p., 845= 4.5, 850= 5, 870= 7 h.p. 

The HSK870 is apparently very similar to the 850 although, when comparing part numbers, I see some differences.  These are the most glaring differences.

                          HSK850              HSK870                
 Crankshaft         290684               290675
 Carburetor         640313               640300
 Muffler               390318A             390343

All other relevant components share the same part numbers including the cylinder assembly, crank bearings, connecting rod kit etc. 

I also noted that the above component numbers varied between the 840 and 850.  Got to wonder what going on? 

 Are the above  parts different from each other or, is it just a numbers change?  If the actual components are different, it's not hard to understand why Tecumseh went out of business.  Way too much parts differentiation between very similar engines.  And that's just their HSK 800 series.

I guess it's possible that on the 870, the crank might have been lightened, a larger main jet and freer flowing muffler put on to allow it to rev quicker/faster.  However, there's no change in the cylinder assemblies thus no changes to porting.  I can see those changes plus additional rpm bringing up the h.p. to 7 in the 870.  I've yet to see anything with an HSK870 engine in it. 

Here are a couple links if anyone wants to check the parts numbers.   Note that the first link prices are much better than Partstree.

http://www.absolutemower.com/pages/OemParts#%2fTecumseh_Power_Company%2fHSK870-8701A%2fEngine_Parts_List%2fHSK870-8701A%2fEHSK841HSK8XX8701A-EN

http://www.partstree.com/parts/?lc=tecumseh&mn=HSK850-8317C&dn=EHSK841HSK8XX8317C-EN

Comments?

Looking in the Technician's Manual I posted in another thread, the HSK840 and 850 list the same bore (2.437") and stroke (1.812"). The HSK870 is not covered in that manual, I couldn't find much about it. But if the 840 and 850 have different crankshafts, that would seem odd, given that their power #'s are similar, and they have the same stroke. Maybe it had something to do with the ends of the crankshafts? Different output diameters or something? It seems reasonable to me that the carbs might be different (different jet sizes or something?). But why the mufflers would be different from 840 to 850 is somewhat beyond me. Unless the 850's muffler was adjusted to allow better power production at higher RPMs?

Do they say what RPM they reach those HP numbers at? It might just be an advertising thing - add a few RPMs and get more HP, but not have any more power.

RedOctobyr: “At a given RPM”

    OK, got it, reasonable and valid.  One hp & rpm getting one torque value.  No cheating….

 

The charts are hard to follow but can be zoomed in go get the values.  All you need is one and can guess the others as they just increment.

The top right is FT LBS (the solid lines across)

Lower left HP

The top right Newton Meters (the dashed lines across)

The bottom right HP in kW

The bottom RPM

 

The top line is torque.

The middle line is Maximum B.H.P & kW

The bottom line is Recommended Maximum operating B.H.P and kW

 

Red, “If anyone finds better copies somewhere else, I'd be curious to find out where.

Below for a readable PDF with many engines.  Has HSK600, HSK845 but no HSK850.

http://th.manualwebsite.com/pdf/engine_and_accessories_2001.pdf

 

   On the chart you posted. How did you that?  It looks like a jpg. It looks to clear to be a screen capture.   Did you save the XL  as a .pdf and convert it to .jpg?

 

Borat, “Way too much parts differentiation between very similar engines”.

    Not sure exactly which component numbers but…  Sears would order a cover and choke special for their machines.  That would boot those numbers and the final engine assembly.  In some cases Sears would order a lesser crank for their engines for a price break.  Ariens would require small mods at times.  MTD would have a PTO extension on the cam.  Murray used double pulleys with stepped cranks ends again causing number changes.  There might be 50-100 variations on a HSSK80 in a year.

   A few times on a rebuild the bore and piston values did not match the Tecumseh spec for that engine.  Possibly the engine was a dash model ordered on special.  ??

 

Red, “Unless the 850's muffler was adjusted to allow better power production at higher RPMs”?

   A manf requesting a muffler change is not uncommon.

 

Bill, “Do they say what RPM they reach those HP numbers at”?

    The final RPM value in the charts Red posted are all 3600.  In the manual above the spec’s use 3200 and 3600.  I think the 32’s are lawnmower engines.