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..

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.

Sorry josjay, but that info won't help you, since my driven pulley is on a shaft with a sprocket and the auger is chain driven from that sprocket. I'd have to do some disassembly to get all the numbers.

ok thanks for your info ,mine is the same driven pulley on shaft with sprocket auger ischain driven.

josjay, just thought of something else. On this type of blower, the distance between the auger and the housing is critical for distance. Make sure your auger is in close. If you can adjust it, great, if not, then make up something similar to a Clarence kit for the two throwing paddles. Also, they throw a lot better when the auger is kept full, so keep up your forward speed in light snow. Now that I can see your pic, it's not a lot different than mine except for length. My driven pulley is centered on the housing (longer shaft) because it comes off of the front PTO. This pic (if you can see it) shows a 20HP driving a single stage 48" blower. http://www.mytractorforum.com/attachment.php?attachmentid=145587&d=1298832440

got a 4'' pulley today could not find a 4 1/4 will try this one soon as i get time will let know how it works. thanks alot for info i understand how a pulley system works alot better now.bill h i seen your pic it throws snow good what is a clarence kit.

Just search here for 'clarence impeller kit'. You'll only need two pieces for your paddles. If you can adjust your auger within 1/8" or 3/16" of the housing you may not have to.

ok i tried the 4' pulley today it did not work very well it would stall engine very easily.then tried a 3 1/4' but not work as good as a3 1/2. so i guess the 31/2 is the best im going to get work not bad throw snow 10 feet  would like to get further but dont know what else to do also was very wet snow chute plugging up.

Put a big Vangard V-twin on it.  The additional power will allow a lot of pulley size flexibility.

Not surprised the engine didn't have enough to drive a 4" pulley and turn a 36" blower.  That's asking a lot of a 10hp engine.  Your probably going to need something like a 16hp to really get things going.
Or as borat suggested the Vangard V-twin would certainly give you what you need.

would bigger pulley on bottom make any difference or would i be wasting my time.