Blade install for balance, theory?

tom3

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Wondering if there's a certain way to install the blade to help the engine balance? Blade inline with the crank throw, 90 degrees out? Probably doesn't make any difference - but maybe it does? Have a vibrating Lawn Boy F engine, not sure if I can actually change the orientation, but still curious. Some of you folks know your stuff. Any thoughts?
 

Bob E

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Follow the keyway.
 

cpurvis

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The blade itself is symmetrical and is supposed to be balanced, so there isn't anything it can do to help balance the engine itself regardless of how it is 'clocked' on the crankshaft.

OTOH, if the blade itself isn't balanced, it can introduce vibration to the mower.
 

Teds

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Wondering if there's a certain way to install the blade to help the engine balance? Blade inline with the crank throw, 90 degrees out? Probably doesn't make any difference - but maybe it does? Have a vibrating Lawn Boy F engine, not sure if I can actually change the orientation, but still curious. Some of you folks know your stuff. Any thoughts?

It absolutely makes a difference, a huge difference in fact. Excess vibration means velocity and RPM is compromised, and how responsive or quick the governor is to changing loads. First thing is to make certain the blade is balanced, sharp, and straight, note these are three different things.

With the "C" and "D" series engines, LawnBoy recommends placing the piston at TDC, and installing the blade 90° perpendicular to that. "F" series engines they recommend in parallel. See link provided. Scribe a line on the crankshaft end once it is lined up correctly, to aid in reinstalling the blade in the future.

I first noticed this after sharpening blades during the season and reinstalling them randomly. Sometimes it was noticeably smoother, other times not so much. Didn't understand why till I got in the manual. "Aha!". The LawnBoy manual is very much recommended for describing things like this.

I even found a further vibration level improvement by flipping the same blade end for end, even though it is correctly aligned with the crankshaft. So I scribed a line on the blade for that too. It just "likes" one way better than the other, for some reason. By taking the time to do this, it will plow through thick, heavy turf much better and gives a better cut.

Make sure the engine is tuned for the correct RPM - at least 3200, that the governor components are working properly. LawnBoys shouldn't really bog down in tall grass like many of the 4 strokes do. They will "four cycle" at the end of a row, but should settle into that characteristic LawnBoy hum under load. Careful adjustment of the altitude screw on the carburetor will help with this, it is actually a very fine adjustment.

https://lookup3.toro.com/ttcgateway/acrobat/manuals/lball40.pdf
 

tom3

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Thanks for the info, now we're getting there. And I note the rpm recommendation. I have been running it quite a bit slower, governor doesn't like that slower speed either. I'll rev it up some and see how does. Any rotating part has a critical speed and I'm probably right on it.
 
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