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Minding my P's & Q's
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Discussion Starter #1
Craftsman 917.251522 tractor. Model 842.242560 snowblower

Power transfers from a lower power shaft with a 15T sprocket on the end, via #40 chain up to the 45T sprocket on the impeller shaft.
I am replacing both sprockets.

Wanted to increase the impeller speed. See if I can throw the snow a few feet farther than is does now.
Was going to put a 42 tooth sprocket on the impeller. Ordered it from a local store, but was told 42T NLA from Wesler. So I just bought a 45T replacement sprocket from a big box store. Figured I would keep looking for a 42T sprocket and change it out if I found one. But for now I want the blower up and running.

I was thinking the 40T sprocket would be too much of a speed increase. So went with the 45T that was original.

Ordered a new 15T sprocket for the lower shaft. Order arrived in the mail.
They sent me a 17T sprocket instead of the 15T I ordered.
Could probably work it out with that company to get an exchange, but do not want to wait another week to get it in. Sprocket only cost me $6.00

So question is will that be too much of a change if I change the lower power transfer sprocket to 17T instead of the stock 15T?

I measured with a laser tach 2 years ago. Before any changes, when engine was at WOT of 3633 engine rpm, power transfer shaft was also at 3363 RPM, and impeller on snow blower was running at 1079 rpm.

I should know the math to figure this out, but it is just not coming to me. And staring at a hand written page full of numbers and ratios is not getting me there.

With the 17T sprocket in place, how much will it change the impeller speed?

Any thoughts are welcome. Should I hold off and find a 15T sprocket and work at making the upper sprocket smaller instead?
Seems to me that speed will increase with a larger lower sprocket, but will lose torque.
 

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I get 130 rpm with a lot of rounding off through calc's, so I concur with Don (nice to hear from you again); as appose to 86 rpm increase with the 42-45 mod.

I would go for it!!
 

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work out the difference between 42/15 and 45/17. The 45/17 will spin the impeller slightly faster than the original setup.

From this page: ⚡Chain and Sprocket Calculator | RPM and Chain Speeds
Using 42/15 w input speed of 3300 rpm, impeller is at 1179
Using 45/17 w input speed of 3300 rpm, impeller is at 1247

Only 70 rpm faster, so about 6%. Not a huge difference, so it likely will work just fine. It'll probably throw a bit further, and you may have to go slightly slower if you load up the blower with heavy, wet or hard, windswept snow.

You may also wish to add rubber flaps to the impeller if you haven't already "the flapper mod", if there is much of a gap between the impeller and the housing. By reducing the gap with rubber strips (once they wear in so they aren't rubbing much on the housing), the snow flies further and they typically also handle heavier, wet snow a bit better as well.
 

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Minding my P's & Q's
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Discussion Starter #6
Thanks guys!
Appreciate the work. Life has had me buzzing the last 2 weeks or so.

I had looked for that Chain and Sprocket Calculator. I knew I had been there before, but did not stumble across it. Book marked now.

When I opened the box and found a 17T sprocket instead of a 15T, I was not feeling too bad about it since I could not get the 42T upper sprocket. Figured I still might be able to increase impeller speed.

Seemed to me it would be a little more than a 10% increase in impeller speed.
Always heard/read you should stay at or under 10% rise in speed.

Was going give it another try and figure out speed difference today, but clothes dryer went kaput this morning and I spent the day working on that. Happy wife, happy life.

I'm going to go for it.

Problem was I was having to move at a crawl now. Had to run the Hydro at slowest speed. Hoping higher impeller speed would push the snow out faster and not build up so much in front of the blower.
Will see what happens. (If I get it done and back together before the next big snow. )
Maybe just getting new sprockets and bearings, and having it all lined up right will be a big improvement.

Yes added flappers a few years back. Well worth the effort. Made it throw wet snow 6 to 8 feet further. Just enough more to clear the driveway when blowing from one side to the other.
Used side walls from tires I cut out.
Noticed during my latest repair work the flappers look pretty worn down. Just bought 2 feet of 4" wide new belting on Thursday when I picked up the new 45T sprocket. $2.99 per foot. Guy cut me off closer to 3 feet, 31-1/2". Going to put it on doubled this time.

Will pop back in once I test it.

Belting 4 X 30 DSCF6208.JPG
 

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The known impeller speed at WOT with 15:45 is 1079 rpm. Going from 15 to 17 teeth on the driving sprocket is increasing the speed on the driven sprocket by 1.1333 times (17 divided by 15). And 1.1333 times 1079 is approximately 1220, so it will increase the impeller rpms from 1079 to 1220, or just over 140 rpm.
 

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Power transfers from a lower power shaft with a 15T sprocket on the end, via #40 chain up to the 45T sprocket on the impeller shaft.
. . .
Was going to put a 42 tooth sprocket on the impeller. Ordered it from a local store, but was told 42T NLA from Wesler. So I just bought a 45T replacement sprocket from a big box store.
. . .
They sent me a 17T sprocket instead of the 15T I ordered.
The sprocket combo is NOT going from 15:45 to 17:45, it is going from the original 15:42 to 17:45.
From 2.8:1 to 2.647:1, a 5.78% increase.
The original was 15:45, not 15:42
 

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The sprocket combo is NOT going from 15:45 to 17:45, it is going from the original 15:42 to 17:45.
From 2.8:1 to 2.647:1, a 5.78% increase.
Re-read the original post in this thread. He said:

Power transfers from a lower power shaft with a 15T sprocket on the end, via #40 chain up to the 45T sprocket on the impeller shaft.
I am replacing both sprockets.
 

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Thanks guys!

...I'm going to go for it.

Problem was I was having to move at a crawl now. Had to run the Hydro at slowest speed. Hoping higher impeller speed would push the snow out faster and not build up so much in front of the blower.
Will see what happens. (If I get it done and back together before the next big snow. )
Maybe just getting new sprockets and bearings, and having it all lined up right will be a big improvement...
I always thought two stage blowers on Craftsman tractors worked well. It was traction a steering I had a problem with. I like to see it working or not. Post video when your done.
 

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Minding my P's & Q's
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Discussion Starter #12
Finally got the blower all back together. Getting the power transfer shaft this sprocket is on to run true was a real bear. Frame was a little bent and a little twisted.

Hung the blower on the tractor today, and it runs smooth. Much quieter than it was.
Will be out testing snowblower tomorrow.

17T sprocket instead of 15T required adding a half link to the chain.


001 Chain DSCF6300.JPG
Chain on sprocket 17T DSCF6313.JPG

Will know better tomorrow how well it works. Should have a few drifts to cut up. Will see if it blows snow any better than before.
If it clears the auger housing out a little faster, that will be a win.
 

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Finally got the blower all back together. Getting the power transfer shaft this sprocket is on to run true was a real bear. Frame was a little bent and a little twisted.

Hung the blower on the tractor today, and it runs smooth. Much quieter than it was.
Will be out testing snowblower tomorrow.

17T sprocket instead of 15T required adding a half link to the chain.


View attachment 2444077
View attachment 2444078

Will know better tomorrow how well it works. Should have a few drifts to cut up. Will see if it blows snow any better than before.
If it clears the auger housing out a little faster, that will be a win.
Well?
 

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Minding my P's & Q's
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Discussion Starter #14
Threw the chain. Half link broke. Twice.
Story is over here:
Half link broke

Not tried the rpm meter yet. Been busy just getting it to work. Wondering how much increase I will see.
I know from the couple times I made it out in the snow the blower seems to throw better.
It does clear the auger housing out faster in 4 or 5 inch depths.

I should have it all back together tomorrow. Again.

Some time this week I should be able to get it outside, measure WOT rpm, and impeller rpm.
 

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Minding my P's & Q's
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Discussion Starter #15
Took awhile but I did get it together, and working right today, and did some clean up.

Swapping 15T out for a 17T drive sprocket does seem to make the blower throw snow better.

But when I got out the laser tach, it was not working. Only bought it 2 years ago and used it on 2 occasions. Well taken care of and now it is junk.

Has laser light when I hit the TEST button, but nothing when I hit the measure button.
So do not yet know the rpm increase of the impeller.
Will have to get another one.
2445009
 

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You might want to re-read the instructions for it? I've got a similar unit, and the button labelled "TEST" is the measure button, and the "MEM" button is the memory button... You hold down the test button, then point the laser at the path of the reflective marker to get a rpm reading.
 

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Minding my P's & Q's
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Discussion Starter #17
You are correct sir!
Just realized that this morning searching for any answers on how I might fix it. Was thinking I may have a bad solder joint I could resolder.

Came back to edit, but too late. I got caught.
So just put this one down as operator error.

Just looked at instruction sheet again. There they call the TEST button the Measure Button.
That did not sink in yesterday.
Will give it another shot today.
 

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Minding my P's & Q's
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Discussion Starter #18
Finally able to measure the rpms today.
WOT rpm has dropped. Was at 3633 Avg. last time I checked. (2 years ago when I set it that high to improve snow blowing ability.) And impeller was at 1079 Avg.

Checked it today.
Engine WOT is at 3392 avg. and impeller is 1148 avg.
Have the new 17T sprocket on the drive shaft.

Even with that drop in WOT rpm, the blower was throwing snow a few feet farther than it has been along the driveway. Easily clears the other side of driveway ditch. In the parking lot I could see snow clumps landing 50 feet away. Seemed to work pretty good.
May not have to bring rpm back up there. Running at around 3400 rpm may be better for the engine in the long run. But I may have to check rpm every Fall before I put the snow blower on.

Did not seem to lose torque. Was in some pretty heavy stuff today. Old snow banks. Seemed to just power right through it. Slow pace but pushed through it all.
 
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