318 speed up deck

P I Pete

Member
I have a 318 w/ a 50 inch deck, not satisfied with mowing job. Recently found out a speed up pulley is available to increase tip speed by 10%, is it worth it. Does it do a better job of mowing? Pete
 
Hey Pete. Don't know about the pulley but one of my neighbors did something today. He brought over his Cub cadet twin blade walk behind mower. "It is not cutting!" He had a set of brand new blades for it in his hand. Well I grab the air gun and am ready to change his blades. Not only were they dull, the ends were rounded almost the size of a quarter! I changed them and he went on his merry way to mow his little lawn. Took me about fifteen minutes each with an angle grinder to get them back to a nice straight edge. Took them over and told him to let me change them a bit more often. The last inch or so of the blade is what does the cutting. It must be nice and straight, a 90* angle. If your blades are straight all of the way then hope that speed up pulley will do the trick. Here is another thought. If you don't have a bagger try a set of "sand blades". They are a blade with almost no lift to them. Keeps the deck from getting chewed to shreds. Also lets a lot more power and speed go to cutting grass and not blowing it out. Give a pair a try. Hope I helped.
 
I have had many JD lawn mowers, both new and used. One was a used 318 with 50 inch deck. Mower had 99 hours on it when I got it. Looked new. It mowed terrible, always leaving a very small strip, no more than 1/2 to 1 inch wide. Did not seem to mow even. I have worked on many mowers of varies brands. Worked on the 318 doing everything I new how to, even followed the steps for setting up the deck that the service manual provided. Took it back to the John Deere dealer where I purchased it and said, fix it or get me something else. Two days later they called me and said it was fixed. They had put new blades on it and they were wrong. The box that the blades came in had the correct part number, however, the blades did not match that part number. They found other misidentified boxes in there inventory. If your mower is leaving a small strip or mowing uneven you may want to check this out.
 
I had a 318 with the 50 inch deck. I liked the tractor, but had similar problems, particularly after the blades had some wear to them and/or lost their edge. I don't know if speeding them up 10 percent will cause much improvement. When the tractor had around 1400 hours, the engine was getting rather tired and I traded for a 425 All Wheel Steer. I DO believe the blades spin much faster on the 54 inch deck on my 425, and the blade and spindle placement might provide a bit more overlap where the front blade cuts in relation to the two rear blades. The 425 does a much better job of cutting compared to my old 318, even when the blades are dull or worn, and even compared to new blades on the old 318. As an aside, I was going to re-power the 318. When I tried out a used 425 and saw how that machine cut, I became a convert to the newer style tractor and mower, and the all wheel steer is really nice, too. I am not trying to sell you on a different machine. I am only sharing what my own personal experience was, and it was a world of difference in what I discovered.
 
I too have a 318.

Two thoughts:

1. Its been really dry here in NC where I live and my newer Toro has a hard time with the 'tails' that run up to seed as well as my 318. They just lay over and stand tall the next day.

2. What rpm is your 318 turning? I am thinking that max rpm for the Onan is about 3400. If its not getting close to that you are losing your blade rpm there.
 
The Onan B43G engine is rated to 3500 RPM Max.

If I am thinking correctly. The outside pulleys on a 318 deck (and many other JD decks) measures approx 4 3/4" dia and use a 1/4" key.
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Try to follow this little example if you can...lol

Engine PRM = 3500
Engine Pulley = 3 3/4"
Deck Pulley = 4 3/4"
Deck Pulley RPM = 2763

Now change the deck pulleys to 4 1/2" Dia.

Engine = 3500
Deck pulley RPM = 2916

Change again to 4" dia.
The deck pulley rpm jumps to 3281.

All is fine and well. But you must remember each time that you increase the deck pulley speeds you are robbing power from the engine in order to turn them..
 
Pete, I was having problems with a 48" mowing deck on a brand X garden tractor not cutting completely through thick or tough grass area, even with sharp blades. I installed a smaller pulley on the deck, increasing the deck RPM'S by several hundred. It made all the difference on that tractor, and could completely cut through any rough or thick grass and small weeds at normal mowing speed without leaving anything standing.
 

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