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

what size pulley should iput on 305cc engine there is a 51/2'' pulley on blower .it is a 36' cut blower for a lawn mower but i am modifying to go on atv .its a single stage so i want to get most power i can out of it.any help would be appreciated thanks..

Yes, changing any of the sprockets or pulley diameters will effect how the blower performs.  And how the engine responds when you fill the blower with snow.

I'm trying to figure out how many pulley's and or chain sprockets you have (I'm thinking probably 4).  Does the engine crankshaft have a belt pulley on it, or a chain sprocket?  Does that belt or chain go around another pulley or sprocket that is on a shaft that goes into a right angle gear box?  Is there then another longer shaft that comes out of the gear box that has a chain sprocket on the end of  it. And a chain that goes around another sprocket that is mounted on the end of the auger shaft?  Need to know the diameter of all the sprockets and or pulley's. What's coming off the engine shaft a belt or chain?  The is no way to figure out anything without knowing how the auger is being driven.

If it's any help, my single stage runs at 900 RPM when engine is at 3600. So a stepdown of 4:1 at 10 ft lbs of torque for each 1' of auger. If you have more torque per ft you can go faster thus throwing further.

ok this is what i got a 31/2' pulley on engine with a belt to a 51/2' pulley on shaft. at end of shaft there is a 2' sprocket and a 6' sprocket on auger driven by chain there is no gear box  . it seems to throw not bad but only about 4 feet would like to throw farther.any help is appreciated thanks.

josjay,

Do you have some pictures of your setup so we can get better understanding of your equipment?

There are a lot of factors and number calculations that go into getting things like this correct.  Finding out what brand blower you have and what it was made to go on would be a big help to you.  Knowing what speed the auger was designed to spin at is an important number. If you know what brand blower you have and or what the model is. It would be to hard to get some information on it.

If you use the 900 RPM speed that Bill H posted and the pulley and sprocket size you posted.  It could go something like this
2700 RPM shaft speed X 2 (sprocket size) = 5400 / 6 (auger pulley size) = 900 RPM
(Engine crank speed) 3600 RPM X 3.5 (engine pulley size) = 12600 / 5.5 ( pulley size) = 2290 RPM
That 2290 RPM speed is to slow you need 2700 to have an auger speed of 900 RPM
So if you decrease the "driven" pulley size from 5.5" down to 4.5" you get.
12600 / 4.5 = 2800RPM
If you then recalculate that would work out to an auger speed of 933 RPM.
But all this depends on the 900 RPM auger speed being what you need.

What you're trying to do, is do able. But you have to know where you're trying to get to, before you can figure out how to get there.

I think you may need more information to get things right.

Don't know what make of blower it is, I think it was for a lawnmower but not sure, I want to increase throwing distance the engine pulley is easy to change but auger pulley is welded on shaft and would have to change shaft and all... I am goin to continue to import some pics I took.... Thanks.

Not havin much luck uploading pics can't understand the directions... will keep trying..

To BillH , what size of pulleys do you have on your engine and auger, and does it throw snow far? Thanks

http://www.facebook.com/photo.php?pid=17742599&l=7a643f213d&id=821330296

You may be able to view the photos on this site... let me know... Tks..

The photo does help. To make things a little easier. The pulley on the engine crankshaft is usually called the "drive" pulley.  The belt goes around that pulley then around the other larger pulley.  Called the "driven" pulley.  Same thing with the sprockets.  "Drive" sprocket (the 2"one) "Driven" sprocket (the 6" one)
Messing with the chain sprockets size probably isn't needed. At least the 6" one
Can you somewhat easily remove the (5.5") "driven" pulley from the shaft that it is mounted on?
For every 1/4" change that you make in the diameter of the "drive" pulley up or down.  You get a + or - change of 900 RPM.  That is with an engine RPM of 3600. 
By my calculation if you use a 4 1/4" "drive Pulley on the engine you should end up with an auger speed right around 900 RPM.
4.25" drive pulley 5.5" driven pulley  2" drive sprocket 6" driven sprocket. Auger shaft RPM around 900

Maybe someone else could check these numbers.  I'm not exactly sure about the sprockets.  I'm making an assumption that you can use the same formulas as are used for pulley's but not sure about that.
We don't know for sure if the 900 RPM auger speed is what it was designed to be run at.
 You are I believe using a 10HP engine.  Which may or may not be large enough.  If the tractor that the blower was meant to be used on was running a 12, 14 or 16hp engine then you may have a problem.
There is a point where the engine drive pulley that is needed to reach a certain RPM will be to large for the engine to maintain it's RPM when put under a snow load. When you get to that point or have that problem all you can do is bolt on a larger engine.
The blower should, for sure be able to throw snow further than 4 to 5'.  Single stage blowers don't usually throw as far as 2 stages.  But you should be able to get at least 12 to 15' or more if things work out.