Hi anastasie
Based on my approximately 50 hours of experience with the 85 cm Berta flail mower powered by a BCS 740, I think you are pushing your tractor and mower to the limits and perhaps expecting a little too much of both of them
Mowing tall, dense - and perhaps also wet grass, is a tough job for any flail mower, as it does not only cut the grass, but also has to cut it into small pieces. This is a very power consuming process, compared to simply mowing the grass with for instance a sickle bar mower.
The fact that your flail mower and tractor wheels both stop rotating, indicate that your clutch is torque overloaded and therefore slipping, as the PTO and the wheels are powered through the same clutch. If only the mower stopped rotating, while the tractor kept on moving, I would expect the 2 V-belts on the Berta to be slipping. The high pitch sound that you hear, is the clutch crying out loud for mercy
My feeling is that there is nothing wrong with your Grillo or your Berta - you are only pushing both of them pretty hard
When mowing with a flail mower in tough conditions like yours, it is important to run the engine at full open trottle and at maximum speed (3600 rpm), in order to get the rated power output (11.7 hp). The Grillo company has designed the clutch to cope with the torque produced under these conditions I’m sure. If you overload your tractor though, engine speed and power output will drop - but engine torque will rise! If you allow engine speed to drop to 2500 rpm - still with full open trottle - the engine will reach its peak torque value, which might be more than the clutch is build for. By allowing the clutch to slip, the entire powertrain is protected against overload and possible failure. If engine speed drops below 2500 rpm, both power and torque will drop, and if the load isn’t reduced, the engine will finally stall. For a more detailed explanation, you might want to read this thread:
Gasoline versus diesel
A high engine speed is also important in order to keep the hinged knives in their mowing position. If engine speed - and thereby the speed of the rotor - is allowed to drop, the centrifugal force on the knives will drop, reducing their ability to cut the grass and keep themselves clean. You end up in a vicious circle, where the risk that the grass will wrap around the rotor increases, because the knives will have less power to cut it and to keep themselves clean.
In order to reduce the load on your tractor, you could adjust the support roller to the lowest position, giving you the highest cutting hight for the first cut. If needed, you can reduce the cutting hight in subsequent cuts, until you have reached your desired cutting hight.
As your Grillo G110D is equipped with the 5x12x22’’ wheels, I would definitely adjusting the Berta to better fit your wheel size! But please note, that you should
raise the PTO-flange on the mower - not
lower it! (Page 21 in the Berta
User and Maintenance Manual)
My recommendations:
- In tough conditions always run the engine at or close to full throttle in order to get peak power
- Do not allow engine speed to drop too much - reduce load
- Begin mowing in 1st gear and where the grass is shortest and less dense
- Consider mowing tough spots with a lot of overlap
- Adjust the roller for the highest possible cutting hight
- Mow only when the grass is dry
- Remove the rear deflector/baffle, if you have it in place
I hope this helps a little, and that you will have a lot of pleasure with your Berta
Best regards
Jens