increasing blade speed.
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=137316
Printed Date: 25 Apr 2025 at 1:06am
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Topic: increasing blade speed.
Posted By: Dans 7080
Subject: increasing blade speed.
Date Posted: 12 Apr 2017 at 11:48am
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I want to increase the blade speed on my mower. My options are going from a 5" driven pulley to either a 4.5" or a 4". The 4" would be a 20% increase and the 4.5 would be a 10%. Any opinions on which would be better? ------------- When someone tells you Nothings Impossible, Tell them to slam a revolving door |
Replies:
Posted By: Tbone95
Date Posted: 12 Apr 2017 at 11:52am
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What kind of "mower" are we talking about here? 20% is a 100% better than 10%  
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Posted By: Dans 7080
Date Posted: 12 Apr 2017 at 12:24pm
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Its a 21hp 48" cut lawn mower. My 12hp 38" will run circles around it because of the faster blade speed. ------------- When someone tells you Nothings Impossible, Tell them to slam a revolving door |
Posted By: Tbone95
Date Posted: 12 Apr 2017 at 1:28pm
| In that case, give 'er he!! and go with the 4" pulley. In any drive system, the only downfall to speeding up a driven component is a proportional loss of torque the component delivers. Can't hardly think that's going to be the limiting factor on a mower blade. |
Posted By: JoeM(GA)
Date Posted: 12 Apr 2017 at 1:40pm
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please remember many newer mowers built in the last 15 years or so are built with smaller, cheaper (fewer balls) bearings, or sealed bearing that are barely capable of dealing with the speed and load they run at now, increasing the speed may push them towards premature failure. I might push the 10, at 20 I'd have to look at pretty hard at the spindles and idlers. ------------- Allis Express North Georgia 41 WC,48 UC Cane,7-G's, Ford 345C TLB |
Posted By: BenGiBoy
Date Posted: 12 Apr 2017 at 1:47pm
If you ever go buy a new mower you want to get a commercial one, the way it was explained to me. The mowers that they sell to you (non-commercial) are limited by the government (of some form) on how many MPH the blade tip can go, the commercial ones are not, hence why a commercial rig can mow at 15 MPH and you can only go 4 or 5 MPH on a home-owner special. I would increase the blade speed all I could and make really sure I had the blades torqued on so they would not be in danger of falling off. ------------- '39 Model B Tractors are cheaper than girls, remember that! |
Dans 7080 wrote:Posted By: Dans 7080
Date Posted: 12 Apr 2017 at 1:54pm
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I'm leaning toward the 4". The mower is an 03 I think. The 38" is a late 80s before the blade tip restriction. All the spindles have grease fittings on them so I may up my maintenance on them with the faster speed. I did find new pulleys are available so if the 4" doesn't work I can always make another size and I'm just out a couple bucks. ------------- When someone tells you Nothings Impossible, Tell them to slam a revolving door |
Posted By: DiyDave
Date Posted: 12 Apr 2017 at 6:05pm
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Might have to get a shorter belt, too, if the idler won't take up enough slack...
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Posted By: Dakota Dave
Date Posted: 12 Apr 2017 at 6:05pm
| All commercial mowers are limited to 19,000 FPM blade tip speed. Most noncomercial mowers run around 17,000 FPM.Exceeding tip speed leads to greater projectile damage and greatly increases the possability of the blade disenegrating. A flying blade piece will go through the mower deck and the RV that your mowing near. the blade tip went through the inner and outer skin of the RV. I corrected Fps to Feet Per Minute. I made a pretty big error. |
Posted By: CrestonM
Date Posted: 12 Apr 2017 at 9:18pm
x2! Go commercial or go home. Residential stuff of today isn't the residential stuff of the 50s.
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Posted By: steve(ill)
Date Posted: 12 Apr 2017 at 9:39pm
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You better listen to Dave and figure out the speed of the blades.. Calculate the speed of your small mower, then calculate the speed of the present mower. I doubt they are more than 10% different.. Changing the speed of the blades can cause bearing or blade failure. Bigger diameter blades will have slower rotation speed than smaller blades... Look at why a rear chopper mower has a 540 RPM input and slower output.. DIAMETER. ------------- Like them all, but love the "B"s. |
Posted By: Brian F(IL)
Date Posted: 13 Apr 2017 at 7:52am
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Not trying to rain on your parade, but I did what you're suggesting many years ago on a mower deck of mine. I thought it was a great idea. Unfortunately, the resulting improvement didn't really make much, if any, difference at all. Good luck to you.
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Posted By: Tbone95
Date Posted: 13 Apr 2017 at 8:25am
| Yeah, all that bad stuff could happen......I'd still giver 'er and see what happens. |
Posted By: Dakota Dave
Date Posted: 13 Apr 2017 at 8:28am
| I wouldn't worry about the bearings or the blade falling off. I've seen an aircraft propeller that has been over speed . The propeller tips were shredded. Aircraft propellers are made to much higher standards than lawn mower blades. On an 84" propeller it only takes a couple hundered extra RPM to push the tip speed past the speed of sound and than they come apart. 19k FPM is about 1/3 the speed of sound. |
Posted By: DougS
Date Posted: 13 Apr 2017 at 8:39am
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The faster blade speed might help in normal grass. The loss of torque will hurt you when you're in heavier grass or when you hit a tough spot. I don't try to out-think the designer. I'd think a smaller pulley would cost a few cents less and they'd go that way in the first place if they could. |
Posted By: skipwelte
Date Posted: 13 Apr 2017 at 8:40am
| i did that once on a b210, i found that the increased blade speed loaded down the engine a lot more, it wasnt sucessfull. It must of been to large of an increase, I went back to about the same size pulley and got along ok. the tip speed increase alot as it made a lot more noise. |
Posted By: Stan R
Date Posted: 13 Apr 2017 at 10:59am
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Power required will go up by the cube of the rpm. https://en.wikipedia.org/wiki/Affinity_laws" rel="nofollow - https://en.wikipedia.org/wiki/Affinity_laws Thus, 1.2 x 1.2 x 1.2 = 1.7 or 70% hp increase. Not sure what engine hp increase it will be as some HP is serving the movement of the mower. |
Posted By: HudCo
Date Posted: 13 Apr 2017 at 11:04am
| the blade tip speed is just as fast as the 38 with shorter blades more than likley there is somthing ealse that needs to be adjusted engine rpm needs to 3400 deck needs to be slighty higher in the front than rear , i have a blade tip fps speed chart acording lenght of blade but i cannot find it now. more than likely the blades need to be replaced we have all ready had three mowers come to the shop his year that a piece of blade has went throught the deck and all push mowers . a few years ago a customer brought a push mower and when we checked it in we done the usual things while the customer was there like check the oil and air filter condition he said it did nt sound right and started it and the blade came out and punctured a riding mower tire about fifteen feet away then just spun on the ground for a few seconds sure glad no ones feet where involved |
Posted By: Brian Jasper co. Ia
Date Posted: 13 Apr 2017 at 5:31pm
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You want the front lower than the back. Having the back lower increases the power needed to do the same job. ------------- "Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford |
Posted By: FloydKS
Date Posted: 13 Apr 2017 at 9:26pm
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I have been waiting to 'chime in'... you also want the blade to be sharp, nothing slows a blade like trying to push a butter knife thru grass. Of course the ends get dull first cause they do all the cutting.
------------- Holding a grudge is like taking poison and expecting the other person to die |
Posted By: DanD
Date Posted: 13 Apr 2017 at 10:04pm
Actually the manual for Simplicity mowers says to have the front of the mower a little higher than the rear. With the blades pointing straight front to rear, it says to have the front of the center blade 1/8 to 1/4 inch higher than the rear of the two side blades. This is for a 48" three blade deck such as found on a Sovereign tractor. |
Posted By: DougS
Date Posted: 14 Apr 2017 at 5:40am
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I would think if the front were too much higher than the rear each blade of grass would be cut twice, requiring more horsepower. 1/8 inch wouldn't be noticeable. |
Posted By: Lonn
Date Posted: 14 Apr 2017 at 6:43am
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Well yeterday I just bought a new Simplicity ?????? the size bigger than the Broadmoor. I wish they'd use numbers, names just don't stick in my head. Anyhow I am going to read the manual tonight. I used to set up new AGCO Allis mowers when I worked at the dealership in the early and mid 1990's and back then the front of the deck had to be lower than the rear or it would take too much power to cut the grass. One other thought, and I'm not calling anyone an idiot because I've seen this before, but are the blades on right or are they on upside down? We had a guy trade in a brand new Homelite because he had no power and was cutting terrible. When I was going over the Homelite for resale I noticed whoever set it up had put the blades on upside down. I think he bought a 1600 series AGCO Allis from us and of course was happy with it. ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: Stan IL&TN
Date Posted: 14 Apr 2017 at 7:17am
Well you are all wrong. Now that that is out of the way, have a good Friday.  ------------- 1957 WD45 dad's first AC 1968 one-seventy 1956 F40 Ferguson |
Posted By: Tbone95
Date Posted: 14 Apr 2017 at 7:25am
??? 
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Posted By: Lonn
Date Posted: 14 Apr 2017 at 7:30am
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I've been all wrong for a very long time, just ask my wife ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: Gerald J.
Date Posted: 14 Apr 2017 at 8:37am
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Another problem with reducing the diameter of the driven pulleys on the blade shafts is that the smaller pulleys will lose torque capability and so be more prone to slipping if loaded hard. That slipping will wear the belt rapidly and the pulleys too. The reduced torque capacity comes from a shorter length of belt meeting the pulley. This will happen while the higher speed will need more torque at the blade shaft. Gerald J. |
Posted By: Stan R
Date Posted: 14 Apr 2017 at 8:45am
Assuming the current belt contact area is at design with NO over design contact area.... |
Posted By: WNYBill
Date Posted: 14 Apr 2017 at 8:57am
| Be careful increasing speed, unit was not designed for it. On a brush hog type mower, the front should be at least 1/2 inch lower or you will be cutting the grass twice . I believe our Dixie Chopper zero turn is level, to make a nicer looking finish, but those blades are only 20 inches long. When all else failes READ THE OWNERS MANUAL |
Posted By: Dans 7080
Date Posted: 14 Apr 2017 at 1:42pm
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Update. I got the 4" pulley on and it cuts way better that I ever thought it would. The blades are new and everything else is up to snuff. I will replace the belt because it was wore out before I changed the pulley, but the same size belt will work. Power is not an issue as the faster speed gets the grass out a the deck faster. Its a whole different machine. The blade tip restrictions are a joke if you ask me. I am very satisfied with the results and thank you all for your input! ------------- When someone tells you Nothings Impossible, Tell them to slam a revolving door |
Posted By: Tbone95
Date Posted: 14 Apr 2017 at 2:10pm
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Hahahaha!!! In all honesty, as I figured. Glad it worked out for you. |
Posted By: HudCo
Date Posted: 14 Apr 2017 at 4:47pm
| mtd says lower in front , tall wet heavey moister grass i think higher in the front is a little better espeicaly if the front wheels are laying it over a little |
Posted By: HudCo
Date Posted: 14 Apr 2017 at 4:53pm
| 2x that on the blades upside down or the chain saw chain backwards a few of those come threw here each year |
Posted By: fixer1958
Date Posted: 14 Apr 2017 at 5:22pm
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I had a JD 318 I repowered with a 24 HP Briggs. JD had a speed up pulley designed for that 52" deck. I got one but needed a shorter belt. Said and done when it's wound up it sounds like an airplane. Made a heck of a difference. Son uses it now. |
Posted By: DiyDave
Date Posted: 14 Apr 2017 at 6:50pm
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Dixie Chopper I have says blades a little lower on front. Logic also says that. If the front is too high, you will have a lot of short cut grass, stuck under the deck. Note: Deck height in front does not always equate to blade height. Drive to a level concrete pad, take a wooden block with you, and check the actual blade height vs the deck height. Properly tuned and adjusted, blades should always be lower in the front. OH, and synthetic oil is better, too
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Posted By: fixer1958
Date Posted: 14 Apr 2017 at 7:19pm
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I never did understand what is best as far as deck adjustment height front to rear. Too many different opinions. Never really gave 2 chits as much as getting it to cut level. Only matters to me if, when mowing, if it's sticking up, cut it down and it's all green. I'm the only one that has to look at it. Only others are friends and trespassers. UPS and the mailman now and again. |
Posted By: Lonn
Date Posted: 18 Apr 2017 at 6:37am
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Well I looked the book over on our new Conquest the other night. Yep the book says to adjust so the front of the blades higher (1/8" I think) than the rear. That's not how we did them back when I worked at the dealership. Now I got to look for the book on our old 1616. I know that it will say the opposite. Why would they change that? It makes no sense as you are going to use more power with the front adjusted higher. ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: Tbone95
Date Posted: 18 Apr 2017 at 6:46am
Maybe for mulching effect? And / or so that there's shorter clippings so they discharge easier? 1/8" wouldn't seem like it would make much difference though. Hmm.... |