Listening to my neighbor engage the deck on his new JD (big box model-but I have heard this on dealer versions also) got me to thinking about this-the engine must have lost at least 1/2 the rpms as the deck was first engaged, then it quickly came back up to operating speed, my Exmark Quest small deck also lost alot of rpms-my new Cub with a 20 hp Kohler and 42" deck by contrast loses very very little speed when I engage the deck AND the Kubota diesel mowers I have tried didn't even flinch when the deck-regardless of size- was engaged; whats up with this??-not enough engine, not enough torque, too much deck???
What makes an engine slow down ALOT when the deck is engaged?
- Thread starter robert
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My guess is the amount of torque available to do the job. Smaller engines, less torque and smaller flywheels; larger engines, the oppposite is true. Just a guess.:smile:
JDgreen
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What RPM's do you think your neighbor was running his JD when he engaged the deck? The big box store JD's don't have all that much hp, and his being a new machine possibly meant the belt and spindles, etc. were very tight and there was more initial friction to overcome. My Deere idles at about 1,000 rpm, I can engage the deck at idle speed and the tach barely registers an RPM drop.
I think you are right when you say torque is the reason. Your thread also leads to another interesting point, I have never been sure exactly what RPM I am supposed to engage the mower at. My manual says "put throttle at one-third position" which is about 1400 rpm, but what is the point of speeding up the engine when engagement at idle speed (950 RPM) barely drops the RPM?
Yep its a torque thing. My 15hp JD rider does the same thing. My owners manual says you're supposed to engage the mower with the engine running at full speed. If I tried to engage the blades with the engine just idleing I'm sure it would die, though I've never tried it. Cubic inch for cubic inch, diesels have considerably more torque than gas engines, and a 2 cylinder 20hp gas engine should also have substantially more torque than a 15hp single piston one.
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wjjones
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I have heard the new ones have to get the clutch/ pto burnt in good first before they will engage smooth.. Kinda like a break in period i worked for TSC some years ago, and the older guy there did this to every new Cub cadet there before they delivered them.. He would engage, and dis-engage the pto 15, or 20 times because he said Cub recommended they be burnt in before use.. I wouldnt know why the older mowers would do this except for maybe loss of engine hp from wear, and hrs of use..
wjjones
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Yep my Craftsman has to be engaged at full rpm, or it will throw the belt. I have never actually put it to the test but sears informed me it would.. Mine has the 24hp twin Briggs with the 54" deck, and it doesnt really bother it much.. maybe it is one of those adjustment things?? I know my manual has a section for adjusting the pto clutch to keep it in spec tolerance..
It sounds as though the neighbor is at full throttle when he engages the deck, I know the deck is larger than my 42", probably a 48" which would mean three blades on the Deere?, but man alive the thing sounds as though it runs at a 50% reduction in rpms for about 3 seconds or so.
After JD mentioned the recommended point for engaging his deck I went and got the manual for the Cub and it does say to engage at full throttle.
Maybe its the fact that I have a small deck with two blades, or maybe its the design of the Command 20hp or perhaps both, but the Cub drops very few rpms when the deck is starting and none really when compared to the Deere next door.
After JD mentioned the recommended point for engaging his deck I went and got the manual for the Cub and it does say to engage at full throttle.
Maybe its the fact that I have a small deck with two blades, or maybe its the design of the Command 20hp or perhaps both, but the Cub drops very few rpms when the deck is starting and none really when compared to the Deere next door.