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Discussion Starter #1
Hey guys,

I am brand new to the forum and recently purchased an old toro 3521. The original Tecumseh was in rough shape so I swapped it with a Predator 212cc from Harbor Freight.

Unfortunately, my belts are very tight now. I used 3/8 x 29 belts for both the Auger and drive. I now realize the correct size it 29 for the drive and 29.5 for the Auger. So by my findings the drive belt should be the correct length but it is so tight, the pulley is on an upward angle, touching the side of the housing.

I feel like both belts need to be longer. What am I doing wrong here? The engine shaft is in the same location as the old motor.

Thanks!
 

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One of our members just did that swap...hopefully he'll chime in with the answer.....I've been looking at my 421 with a swap in mind.......
 

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Welcome to the forum!

If these same belts were OK with the old engine, and you're using the same pulleys, then I can only assume the new engine's crankshaft is not actually at the same position as the old engine. Or it's at the same height, but shifted left/right, thereby still requiring longer belts.
 

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Discussion Starter #5
Thanks red, that does seem logical but the after measuring the crankshaft seems to be in the same location. I must be going crazy.

I think I will just get longer belts and see how it performs. Is there a preferred method to measuring for this? Assuming I am moving away from the stock sizes?
 

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After a bit of research, it seems string or an oversized belt is the way to go for measuring. I will try this and get back to you guys.
 

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In the meantime, if anyone knows how to contact the member that successfully completed this swap, I would very much like to pick his brain.
 

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In the meantime, if anyone knows how to contact the member that successfully completed this swap, I would very much like to pick his brain.

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Looks like a member called scihi may be able to help you. He posted about adding a tall chute to his 3521. He also said that he had put a 212 predator on it. ---- John
 

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Check out V belts for less. They will give good info on how to measure and they will likely have what you need. Is the auger belt cogged?

Also another difference may be in your tensioner pulley location. When I did a Preditor swap I had to make a new longer mounting bracket for the tractor drive tensioner pulley to get it to work better and still fit under the belt cover.

If all you have to do a get a bit longer belt that may be your best option.

https://www.vbelts4less.com/message.asp?msg=49

Good Luck.
 

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If the crankshaft is 1/4" higher it doubles the difference in belt length to 1/2" which is a big difference.

You need to buy longer. It may be a guessing game, trial and error, to see what is perfect.
 

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Discussion Starter #11
I truly appreciate everyone’s help. It looks like I need a 29.5” belt for both the drive and Auger. The 29 was too tight and the 30 too loose. I did not use a cogged belt for either but it looks like my model calls for a cogged Auger belt. What is the difference?
 

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cogged is just sections removed to help it go around smaller pulleys, The lower part of the belt that is cogged just holds it centered in the pulley so not going to be any weaker as the strength is in the outer wider part of the belt.
 

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:welcome: to SBF boybadone

What I usually do for finding a belt is go to the auto parts store and pick up three. As long as you keep the receipt, the belt and it's sleeve clean you can always return them. Depending on price and if I need the machine I'm working on right then I'll keep the belt that fits or order it on line. I use an old chunk of pull start cord for measuring.
 

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Discussion Starter #14
Excellent advice, guys. So do I want to stay with a cogged belt or can I get away with a standard belt? The non cogged vbelt is obviously easier to find.
 

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Here's something that can help reduce the buy and return on unknown length belts: https://www.harborfreight.com/vibration-free-link-belt-43771.html
That's not the only source, just happened to think of it at the moment. There are some less expensive sites, maybe check out ebay if interested.


I had a couple of woodworking machines I needed belts for and used this to make belts for them. I used it first on a blower though that had some changes done to it to find what the right length of belt was. Once I had that, I was able to use it to get a regular belt of the right length for it. I've used link belts on a table saw and on a jointer and plan to on a metal lathe I have. They have worked out real well in those situations but from what I've read they can cause wear on sheet metal pulleys. In the instances I used them I have cast iron pulleys and they've worked out very well.


The thing is you can add or remove links to end up with the length of belt you need, kind of like you can do with a drive chain.


Who knows, when I try out that LCT engine on a blower, I may try it and see what happens.
 

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HCBPH, nice idea but I would bet those belts are only fractional HP rated. I did not see a rating on the HF page. Good for a 1/2 or 3/4 HP wood working tool.

The Cogged belts are made to last longer than a conventional V belt of the same width. The Cogging reduces stress as it wraps around a pulley and reduces fatigue in a reverse bending situation. The Coggs also increase the surface area to help dissipate heat. If you look on Vbelts 4 Less or Ebay you can find them. Look under a 3VX style belt for a 3/8" wide as measured at the widest point at the top. 4VX for a 1/2".

The plain conventional V belt will get you going but it will not last as long. I would order the correct OEM belt. The OEM belt is typically made better than a generic utility belt you get at the auto parts store or at Tractor Supply. Better materials ( Chords and rubber) and will not stretch as much or as quickly. Generic belts are usually ok on the tractor drive but on the Auger, where most of the power is used, you want a higher quality belt.
Good Luck.
 

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I put a HF 13 hp on my drift breaker 10 32 and the shaft was about a 1 1/4" higher than the TEC 10 hp. It took me a couple of times of trial and error to get the belt lengths right. I took one of the original belts and cut it. I then placed it on the pulleys and separated it until it looked like the right length then measured the gap. I just measured the belt and added the gap to get me close.
 

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Discussion Starter #18
Just what I was looking for. I will look for the original cogged belt. For now the machine is running great. Next on the list: studding my solid Tires and an impeller kit. I would love to motorized my chute controls operated by one 4 way joystick. But I can’t justify that right now ha.

Thanks again for all the help!
 

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Discussion Starter #20
Drm, did your 3521 have any issues with traction? I currently have to apply quite a bit of force to keep the machine moving forward. I ordered studs for my solid tires. Hopefully that will help.
 
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