sickle bar speed

[erik hergert]

Hi, I am adapting and old Simplicity sickle bar to a current lawn tractor. The bar speed is rated at 720 strokes per minute. Can anyone tell me if a stroke is "one" revolution of the driving pully or is that "two" strokes because the blade went forward and back. I need this info to select my pullys.
Thanks

 

[LenND]

That should be a complete run --all the way extended and then all the way back. If I'm wrong somebody can correct me.

 

[erik hergert]

OK, thanks

 

[Anonymous-0]

Eric,
Good question, I don't know but on the basis of engine mechanics a stroke is the lenght of travel in ONE direction. So I will GUESS that one revolution gives 2 strokes.

 

[erik hergert]

oh oh, two different answers, anyone else want to take a stab at it? thanks again.

Erik

 

[James Howell]

One revolution should be a 360^o turn for the drive pulley.

One revolution, one complete stroke, should take the knife out and back.

 

[RodinNS]

I don't know how strokes apply to pitman drives for certain, but in relation to an engine.... one revolution of the crank requires TWO strokes. Up and down.
I'd reason that a mower would be no different. Two strokes; one out, one back.
As far as I know, that's how they're rated... though 720 strokes per minute seems slow to me, so that might well be revolutions.
You might have to look back and see what the PTO drive speed was on your old tractor and then follow the ratios out from there to figure out what speed it should be turning.

Rod

 

[Anonymous-0]

Rod,
Actually first time I've ever heard this question and don't know the answer. But the stroke of an engine is the distance the piston travels in ONE HALF of a revolution; TDC to BDC. After a little looking in the JD #5 manual(they have 3 sprokets for speed adjustment) I agree that it probably is a complete revolution (in and out) and 720 is a bit slow; The JD would be 1.6 or more times the 540PTO speed on the pitman driver.

 

[RacerX]

You too? I'm rebuilding/modifiying a Simplicity sickle mower for one of my tractors this winter also! Are you going to use the original sickle with the 2" sections? I'm building a new 54" cutter bar with Ford guards on it and a new sickle with 3" sections. I've already lengthened the pitman arm so it will have a 3" stroke.
Pretty much I'm copying the modifications shown on the Simple Tractors website. I figured I wanted it to use easily available sections so I could replace them when they get dull.
I decided that one stroke was in and out, or one turn of the drive pulley. I've got mine geared down with a right angle gearbox and pulleys to give 1000 strokes per minute at full throttle. I figure I can always run the engine at 3/4 throttle or so if that turns out to be too fast.
But I don't have mine running yet either, I could be all wrong!

 

[RodinNS]

Yes... two strokes per rev.
A manual would be a good suggestion on the mower tho.

Rod

 

[erik hergert]

Sounds like I will go with the one stroke = one rev of the bell crank pulley theory. Racer X, I am also running the 90 deg gear box and will try to add an electric pto to engage it. I will stick with the stock Simplicity set-up for now just to save time. The Ford mod will have to wait. Just curious, but what did it cost for the conversion parts? The welding and machining I can handle here. Also, the manual shows the 3rd mount as a chain hooked from the frame to the bell crank pulley guard. Is this correct? It looks like the bar would not raise and lower correctly like this. Any ideas?
Thanks, Erik

 

[RacerX]

The conversion parts cost about $350. That includes guards, sections, hold downs, wear plates and plow bolts. It also includes the aluminum stock for a new cutting bar and the tool steel for a new knife back.
The lift chain on the pulley guard is to raise the inboard shoe off the ground a couple inches. All versions of the sickle mower have this feature.
How the cutter bar is raised depends on which version mower you are starting with. The earliest models had a long lever mounted to the pulley guard, you simply pulled on the lever to raise the bar. Later models have a cable attached to the mower head and the tractor rock shaft. When the mower lift is activated, the rock shaft pulls on the cable and raises the cutter bar. These versions also have a big helper spring hooked on the mower head across to the mower hitch to reduce the effort required to raise the cutter bar. I"ve got one of these, but I"m also cheating a little because I"m mounting the mower on a tractor with power lift.

 

[Billpa]

Racer
are you sure a longer pitman arm will give you a longer stroke? think about it.

 

[erik hergert]

I may need to send you a picture of the chain part I don't understand. My concern was that if the chain hooks to the cutter head and not the hitch, they will bind up because they are pivoting on different axis. It seems the chain should hook to the back of the hitch so that it won't interfere with the raising and lowering of the bar. BTW, mine does have the helper spring you mentioned. My unit was severely butchered when I purchased it, so I'm guessing at how it all went together originally. My plan is to also purchase a $60 12volt winch from Harbor Freight to raise and lower it.

 

[RacerX]

If you haven't already, you might go to Simplicity's website, www.simplicitymfg.com, and click on manuals. Then input your mower's mfg number, (either 990XXX or 169XXXX) and look at the operators manual for your mower.
The operators manual will show how the mower hooks up, gives operation tips and even has part breakdowns and part numbers. (Not that the part information helps a whole lot, almost none of the parts are available from Simplicity anymore. The exploded views are nice to see how things are supposed to be assembled.)
If you can't find your mfg number, try 1690030. That's the newest version mower and while the drive is different, it shows the best pictures of how to hook it up. You could also look at 990687, which is likely the same as your mower.