Deck Blade Speed?

[DavidD 0]

Can a 44 inch rear discharge blade speed be increased? I have been looking at the pulleys on the deck, looks like I could change the driven pulley and increase the blade speed. I am not trying for a major increase, maybe 25 - 35 percent? Are the blade spindles ok for that kind of increase?

[bowtiebutler956 650]

Why are you trying to increase blade speed? I find that so long as I keep my blades sharp, they cut great. You could install a smaller driven pulley on the deck, but there there would be a greater chance for belt slipping.

Matt

[Sparky-(Admin) 23,162]

If its a WH deck its actually a 42" rear discharge. Are you using the inner pulley (closest to the engine) for the mower deck drive belt? Its a bit larger and will give you maximum blade speed.

Mike.......

[DavidD 0]

Sparky, It is a 42", I just re-read my post. I have been punchin numbers all day, you'd think I could type numbers better. I did run it on the inner pulley, at the end of the summer. I also use a 54" Troybilt, and a 44" Craftsman. Both of those run higher blade speed than my 312-8. That is if my math on pulley sizes are correct. Been trying to find where I hid my sheet from last summer so i can double check. I am going to get some new blades for it first, before I do anything else. I noticed yesterday that the hickory nuts last summer kinda abused the current blades. That may have been the whole problem.

[kpinnc 14,650]

Lots of tractors user longer blades, which makes for higher TIP speed, but not necessarily faster RPMs.

Just curious- why would you want to speed up a rear discharge? Side discharge makes perfect sense, because it would spread clippings further. Not sure much difference would be noticed with the RD, unless you're using mulching blades of some kind.

[TT-(Moderator) 1,162]

The maximum recommended (safe) blade tip speed of rotary mowers is 19,000 ft./min. Anything above that could be catastrophic. (breaking blades)

The formula for calculating tip speed: shaft/spindle speed X blade length X 0.262

You'll never achieve the quality & speed of mowing with a high-vacuum deck when using an old-school Wheel Horse "rectangular box with blades on the bottom" deck.

I'm guessing that the Troy-Bilt and Craftsman decks are both high-vacuum / high-flow and designed for catchers/baggers, correct?

[DavidD 0]

Maybe I'm not looking at this right. My Craftsman is a 93 model with a 16hp engine, side discharge. That thing is a muncher, it just eats stuff up and and literaly air mails it out the side. TT, I dont think that model was set up for bagging. I will do a little research on that. I think the blades on it are maybe a little longer than the 312. I have not brought it back to the house yet. The Troybilt is 18hp (I think) side discharge, I think there was some option available for a bagger, now that you mention it. I will look in the book again. Also, thanks for the tip speed. I definitely do not want to exceed the safe zone. I have seen something similar, don't want to experience that again. It just seemed that the 312 did not cut at the rate the other ones do. It does not seem to cut as well as it did before. I probably need to check the belt for slipping, and check the spring too. I just brought the deck back here to get started on maintenance this weekend. I'll check everything and correct any slipping stuff first. Thanks everyone for your comments.

[Sparky-(Admin) 23,162]

You might also want to make sure your 312 is getting up to full RPM's. If its only hitting 3000-3100 RPM's that means your deck is running a but slower than it probably could be.

Mike..........

[Don1977 605]

Is you double pulley smaller on the top grove of the deck pulley. The 48" side discharge both pulleys are the same size as the blades are longer. I guess your talking about a Wheel Horse ,I thought the rear discharge decks were 42" and 36"

[can whlvr 994]

ya i would check the rpm,s like sparky said,as well as new blades,belt,spring and check mule drive for good bearings,i have a 312 that i thought sounded about right for rpms,it was only running at 3100 and what a huge diff the extra rpms make

[dsholler 54]

naive user question.. .how do you determine the RPMs of the deck? and what should you do if it is not right? I have no idea if this is an issue, but I have move to a house with a very large lawn, and am hoping to get the most out of the deck...

(for the record, it is an 87 414-8 with a 48 side discharge deck.. which I believe was original to the tractor. )

[Hodge71 665]

Just my opinion but I bet that even with a tractor at max rpm, all things in order, belts, bearings , mule drive, as stated above, I bet our decks still could use a smaller pulley because the blade tip speed is no way near 18,000 FPM of newer decks. I'd really like to see where this goes, but I think we have room to make our decks cut better by speeding up the blades a bit.

[kpinnc 14,650]

Like TT said, most WH decks are not truly "high lift" decks that typical lawnmowers have. Only the 37-inch SD has this feature built-in. A telltale sign of a high-lift deck is the shape of the top of it. Those decks have a smaller non-discharge side, that swells out to the maximum at the discharge chute.

Any deck with the discharge shaped like this will have better lift. The discharge for each blade grows until it reaches the chute. I just plucked this from the net, so I'm not sure what tractor it fits. It's only an example, and there are MANY different variations on the design:

By comparison, many garden tractors (not just Wheel Horse) use the flat, non-ducted design like this. There are exceptions to the rule, such as the 60-inch deck on the 520-H, but most like this just don't measure up:

I mow my lawn with traditional flat-top WH decks, and it looks fine. But NOTHING makes my lawn look as nice as the 37-inch SD model. It's just so small that it takes longer. Maybe increasing the blade speed would help the old-school decks, but only a little bit.

[can whlvr 994]

sharp blades and proper engine speed is all thats needed for my rural lawn

[tbarnhart 240]

I know this is an old thread, but I've been struggling with the same problems here in GA with the thick, long bahia grass. My pto drive pulley was worn to where the groove was a U shape instead of a V.  I put it in my small lathe and cut both pulley grooves off leaving a shoulder to bolt another pulley to. I'm going to try a 5.875 pulley which should put my blade tip speed up to about 18000.  It'll be awhile until grass grows again, but it will be interesting to see how it does. If it's too fast, I can always go smaller with the pulley.

[sgtsampay 117]

Sorry everyone for bringing up an old thread, however, I’m very curious about the conclusion for this.

 

for example: say I have a c-120 and max the kohler to the 3,600 rpms. Assuming the belts and clutch are fine of corse, what size pulley do you all think I can change the middle pulley of the 42in deck to? My goal is to be able to increase the mower deck speed so I can cut the grass in 3rd high. My thinking is the mower deck blade increase will allow for the deck to process more grass due to the increased ground. Speed of the tractor.

 

i hope I didn’t confuse you guys. Lol.thanks all. 

[rick 257]

Sounds like you need a Dixie Chopper!