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Tech Nerd Tractor Convert
1,388 Posts
Discussion Starter · #1 ·
I have an MTD 42" snowblower attachment (PN 190-823: diagram, manual) that I previously modified to fit up to my Cub i1050 zero turn tractor. The blower works pretty well, but when the snow is heavy and wet, the discharged snow barely makes it past the chute. Because of this, I suspected maybe it was being run too slowly. I thought perhaps the tractor it's actually made for has a larger PTO pulley or runs at a higher RPM than mine or something...

I have an ignition-cable-based TinyTach-type digital tachometer which I installed in the dash a while back, but that only indicates engine RPM. So I wanted a tachometer I could use to measure all the various rotating parts involved in the snowblower (tractor PTO, various pulleys in the blower's underframe assembly, the blower drive pulley, the impeller, and the auger) so I could get to the bottom of the speed question.

I posted on the speed question in another thread and included some diagrams of the blower pulley system and some calculations on what the blower RPM would be given the various pulley diameters involved.

I also contacted MTD multiple times to try to pry the information from them on what the required input RPM was (at the blower's drive pulley) for this blower which they manufactured. Unfortunately I was unsuccessful. Here is the exchange:
I own an MTD snowblower attachment, model 190-823, serial 1J084G10037.

What is the desired RPM at the blower's drive pulley? I would like to confirm that I am running it at the correct speed.

The pulley I'm referring to is item #60 (756-1181A Drive Pulley, 7”) as shown in the operator's manual.

We have no listing for the input RPM for the snow thrower. We recommend that the tractor the snow thrower is attached to be run at full throttle.
Thank you for the reply. I can understand how you have no listing for RPM but it must exist somewhere.. I assume the snowthrower couldn't be designed by MTD without someone having an RPM requirement established somewhere. Could you perhaps forward my question to MTD's engineering group?

My issue with simply running the tractor at max RPM as you suggest is that this snowblower was not necessarily designed to be used with my particular tractor (Cub i1050), and the input speed the blower sees is a factor of not only the tractor's RPM but also the diameter of it's PTO pulley. Also there is disagreement over even what the "max throttle" RPM should be for my tractor. A previous email response from MTD customer service indicated 3600 RPM, the Kohler service manual for my tractor's particular engine indicates 3300 RPM, and the i1050 service manual shows 3250 in a photo where max RPM is being measured).

I'm really just trying to determine if my poor snowthrower performance is due to being driven at too low of an input speed or if it's some other cause. If I could be told what RPM the snowthrower needs at it's input for proper performance that would rule in or out the issue of drive speed.

We apologize, but this snow thrower attachment has been discontinued for several years. We have no specifications available for this attachment to indicate the recommended input RPM.
You didn't ask engineering, did you? I work for an automotive manufacturer in engineering and discontinued or not, engineering always keeps records of designs and specifications. Please forward my question to MTD engineering.
We did make contact with the Engineering Department prior to responding to this inquiry. The design information is maintained, but the requested specifications has not been maintained. No information is available to indicate the recommended input RPM or the RPM of the augers while in operation.
Ok I stand corrected, sorry. You contacted engineering. But I'm flabbergasted that they don't keep all design specifications on record. That's just illogical and bizzare.
I felt a little bad for berating them after they confirmed they did contact Engineering like I asked. But then I also think MTD is equally dumb in destroying engineering records like design specifications. Sigh.

So anyway, my new Neiko laser tachometer (model 20713A) arrived a couple days ago and tonight I used it to take some readings of the engine, PTO, blower spindle, blower drive pulley, impeller, and auger.

This thing puts out a huge and bright laser "dot" (about the size of a dime) so I also used it to drive the dogs crazy chasing the humongous dot around the house and the backyard. Works way better than a laser pointer in that regard.

Below are some photos, followed by the RPM testing results.

Here's a photo of the laser tachometer in it's included box. It's one of those stiff cardboard covered in vinyl type boxes, but it's better than no box I suppose. Just above the unit you can see the adhesive reflective tape that's included. It's about 1/2" wide and there's maybe 2 feet of it. The way it works is you stick a small spot of this tape on a rotating part, aim the laser beam at the tape, and the device reads the RPM. You can get a good read supposedly even about 6 feet away. My measurements were at between 2 and 3 feet.

Here's a shot with the unit in hand so you can get an idea of it's size. It's a bit bigger than it appears in manufacturer's photos on the web. There's a "Test" button and a "Mem" button. You use "test" to fire the laser beam and get a measurement (but it doesn't appear on the display at that time). Then you release the test button and the laser turns off, then you press the "mem" button repeatedly to cycle through the "min", "max", and "last" reading. This is not the min and max of a series of readings but actually this is the min, max, and last speed it sensed during the last continuous press and hold of the test button. So if while you were holding down test the spinning part went from 2000 RPM, down to 1000, up to 3000 and then back to 2500 at the moment you released the test button, you'd get 1000, 3000, and 2500 for min, max, and last.

Here's what the spot looks like, shining on my workbench. By the way, that piece of cardboard is spinning at zero RPM.

Just for fun (since lasers are cool) I went into the kitchen and ran some steaming hot water and illuminated the steam with the tach beam. You can see that the beam is pretty well collimated (parallel rays). The spot doesn't change much in size the farther away it is. It just appears to get smaller in the photo due to perspective.

Small 1cm square of reflective tape applied to the rotating fan cover at the top of my engine. You can see how the tape doesn't have to be at the outside edge of whatever is spinning. It can be anywhere that when the part is rotating will produce an on/off visual somewhere (and that's where you then point the laser beam when measuring). I had to go almost to the center in this case because that was the only place there was sufficent smooth surface to adhere to. And it worked fine.

Here I'm taking a reading on that spot. Well, I'm simulating taking a reading.. the engine wasn't spinning for this particular shot.

Here's the tape where I applied it to the hub of the PTO pulley. This shot is at ground level looking under the tractor from the right side.

Here I applied it to one of the 6 facets of the nut attached to the spindle that is part of the snowblower's underframe assembly (the subframe and set of pulleys which reduce belt speed and turn the belts around to bring them back forward to the snowblower housing). Again, you don't have to put the tape on the face of the pulley or in the valley (and then have to find some angle where you can see it). Putting the tape on any area that does not appear stationary when the part is rotating will do. This is also a ground-level shot from the right side, just a little further toward the rear of the tractor.

This shot is showing the tape on the snowblower's drive pulley. This is an overhead shot, looking down from above where the blower attaches to the tractor frame. There was just a narrow opening to be able to see the spinning pulley but it was enough to get a reading.

Here's where I put the tape on the impeller. This is looking into the snowblower auger housing from the front, looking into the impeller cavity.

Here I'm aiming the dot at the tape (but missing it by about an inch)

Here the dot's on the tape..

And here's where I put the tape on the auger. It's a little hard to see because of the angle but it's dead center in the photo. I put the tape at the very rightmost end of the auger. This one was tricky to choose a good location because you don't want any other objects (in this case other parts of the auger spiral) to pass in front of the tape and obscure the view of it or it can produce double or triple the actual RPM value. Note that this can be useful in some cases.. for instance you can measure the speed of a fan by putting the tape on a stationary object behind the fan and point the laser through the fan allowing the fan blades to break the beam. You just have to remember to divide the displayed result by the number of blades on the fan.

So, here were my RPM measurements. Note I set the engine to 3000 RPM even though during normal snowblowing usage one should (as MTD says) set the tractor to "Max RPM", which in my case I run "max" closer to 3400 (proper Max RPM is debateable. Long story).

3010 Displayed on the digital tach on my dash (the TinyTach)
2979 Read by laser tach at the engine fan cover
2977 Read at the PTO pulley hub (so PTO is 1:1 with engine)
2397 Read at the undercarriage assembly spindle nut
(spindle's 7" pulley being driven by PTO's 6" pulley).
1223 Read at blower's drive pulley
(blower's 7" pulley driven by spindle's lower 3.75" pulley)
1224 Read at impeller (so right angle drive is also 1:1)
121 Read at auger (so auger worm gear is apparently 10:1)

So, the overall reduction ratio from my engine RPM to the blower input RPM (which is also the same speed as the impeller) is 1224/2979 or 0.41 . So when I'm doing actual snowblowing and running the engine at 3500 RPM, I should get 3400 x 0.41 = 1394 RPM at the blower input.

Now, since MTD was not forthcoming with what RPM the blower requires at input, the answer to the question of whether I'm running the blower at sufficient speed or not may have to remain a mystery.

However, do any of you out there with similar sized blower attachments have any RPM readings on your impeller that I can compare to? Are they significantly higher than 1400 RPM? I'd be interested to hear feedback on this.

Tech Nerd Tractor Convert
1,388 Posts
Discussion Starter · #7 ·
[...] One would think that MTD would retain those records for no other reason than legal recourse in the event of product failure or personal injury mitigation from law suits (?).
[...] FWIW, The thread is a great read...:
Exactly... Say one of these units flies apart in the field and injures someone and the owner sues MTD. You'd bet MTD would be interested in determining if and showing that the blower was being run "above recommended speed". But in order to do that, there would obviously have to BE a recommended speed, right? Furthermore you'd expect to see it listed in the operators manual.

Glad you enjoyed the thread. I've got another one in the cooker -- upgrading the blower to power lift/rotate using a winch for lift and cordless VSR drill for chute -- but not done with that yet. I noodling out where to mount the limit switches at the moment. I may even include some video on that one when it's done.

When i lived in the snow country(se idaho) i found my mtd walkbehind worked better w/ wet snow if i kept it traveling fast so as to keep the rotor loaded up. Mike
Thanks.. I'll have to keep that in mind. I'd heard this kind of advice for single-stage (have to keep it full) but didn't know that might help a 2-stage also.

[...]I have a mtd walk behind and a laser tach. It is only powered by a 5hp Tecumseh, but if you would like I could try to take similar measurements on my machine [no I haven't done this yet]. Please let me know.

Would it perhaps be easier to get impeller RPM through the discharge chute [wearing safety glasses of course] , or would this need to be divided by the number of blades?

Thanks, Mark
Thanks but I would say a 5hp walkbehind (with presumedly smaller auger width) may not require the same impeller speed to get the job done (or may even require higher?) so don't make a special effort since I'm not sure the results could be comparable. But if you decide to check anyway out of curiousity I'd be interested to hear the result.

Actually reading the RPM through the chute was going to be my first approach but I noticed there was just as clear of a path for the beam from the front of the auger housing. My auger only takes up the lower half of the vertical height of the auger housing so there's a pretty clear shot into the impeller cavity if you just come at it from a higher angle.

If you did take the reading through the chute you shouldn't need to do any division as long as the surface you put the reflective tape on does not get hidden and then revealed again more than once per revolution in the line of sight of the tachometer instrument. You could put it against the vertical impeller plate like I did, or on one of the vanes, either should work.

If the auger gearbox is in fact a 10:1 ratio, for those without a laser tach it might be easy enough to simply count by eye the number of auger revolutions per minute then multiply by 10.

Without doing something to defeat the seat switch, I can't watch the auger turn on my Craftsman. As soon as I get up with the PTO engaged, it kills the engine.

If I have time later today, I'll try putting a weight on the seat so I can watch the auger.
Clever idea on taking the auger speed by eye and scaling up!... assuming all auger gears are indeed 10:1 (are they?). The only other issue here is you have to be able to count quickly (or by tens) and keep track long enough to get good resolution. I would probably fumble it.

Yes, I had to get creative to keep the auger running while I was out of the seat. I won't elaborate. ;) Another easy method is to just plant a good sized mirror (or anything shiny and reflective really) out in front of the auger and you can watch it spin from the tractor seat so you can count and time it. In fact a laser tach might even work from that position if used with a mirror.

[...] I think choosing the impeller speed comes down to HP. You want it going as fast as possible without bogging down the engine. You probably have more HP than what the blower was originally designed for. In fact, to keep the input torque within design requirements (whatever they are), you must increase the speed. [...] I would start with doubling your impellar speed.
I've got a Kohler Courage 26 HP twin-cylinder engine. I always hear how modern tractor makers keep putting more HP than needed in these things for marketing reasons, so hopefully that means I do have HP to spare.

I did plan to up the impeller speed by using some different pulleys in it's drivetrain (the purpose of my original thread). My concern however is running it faster than it was designed for and putting undue stress on the components or worse. Thus the whole reason for trying (unsuccessfully) to get the desired blower RPM from MTD.

Tech Nerd Tractor Convert
1,388 Posts
Discussion Starter · #14 · (Edited)
My Honda tractor and 42" snowblower may be different from your MTD but the factory manual says to run at full throttle, 3300 RPM. The total speed reduction to the auger is 11, so it turns at 300 RPM. The second stage blower fan turns at 1500 RPM. There is a gear reduction of 5 between the fan and auger. Hope that helps.
I'd say it's probably comparable, and my impeller RPM (1400) is in the neighborhood of yours but not quite as high, and that's at 3400 RPM at the engine. So that gives me some confidence that I can boost it a little safely.

And based on TUDOR's post, I should also ask what your impeller diameter is? That way I can compare your impeller tip speed to mine and to the standard that TUDOR stated..

[...] A useful tip from my days of tracking and balancing helicopter rotors is to use a silver paint spot instead of the reflective tape. Objects like the flywheel cover are easily dabbed instead of trying to fit a tape swatch and the paint stays on permanently making subsequent services a "point and read" exercise.
Yeah I read that a few other places too so it seems to be a popular approach. Well, for now I still have a good quantity of reflective tape left but when I run out, silver paint here I come...

Great read!!

For a better answer, try impeller tip speed. There are several different diameter impellers, but the tip speeds should all be close. The tip speed and width of the impeller will determine the hp requirement.

MTD may not be forthcoming, but most smaller 3ph blower impellers run at 540 rpm and tip speeds of 2400- 3000 ft/min. ( Circumference x rpm )
Thanks, glad you enjoyed it. And thanks for the data on tip speed.. I'll have to go out and measure the impeller diameter now and report back what that results in for my impeller tip speed... stay tuned.

Hi Jack:

To not pollute this topic I'll answer over at Toolin' s Governor post.
I got a chuckle out of this because the other post you linked to where I posted about the governor wasn't my thread either.. it was someone else's post that I kinda hijacked.

Circle of life...

Tech Nerd Tractor Convert
1,388 Posts
Discussion Starter · #15 ·
[...] most smaller 3ph blower impellers run at 540 rpm and tip speeds of 2400- 3000 ft/min. ( Circumference x rpm )
Ok I went out and measured.. my impeller blades are about 6" long, so..

Circumference = 2 x pi x r
Tip speed = Circ. x RPM = 2 x 3.14 x 0.5 x 1400 = 4400 ft/min.

Hmm, certainly seems high enough. I guess what occurs to me now is all these measurements are being done at no load. Maybe when the blower is loaded down I may be getting less RPM than I'm supposed to, possibly due to belt slippage (the engine RPM is governed and doesn't change under load).

By the way, I finished (at least in the rough) my electric blower lift mod just in time to use the blower again last night.. we had a good 6" of snow on the ground. Worked great, but then again it wasn't particularly heavy snow.
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