Berta flail mower

   / Berta flail mower #71  
This may explain your issue. I recalled something with the PTO but went to Earthtools sites and found this:

One of the reasons the Grillo machines are significantly less expensive than the BCS models of the same size/capability is because Grillo has elected to stick with a slightly “older-fashioned” transmission design. This results in the advantage of a easier-to-service tranny design that requires no special tools or procedures if it needs to be worked on… but this simpler design can be a disadvantage in that with a Grillo tractor, the PTO direction actually reverses when the tractor is put into reverse. This is not an issue with any soil-working implement, as the tractor has a safety lockout mechanism that prevents engagement of the PTO drive when the tractor is in reverse anyway…the implements you may notice an issue with are rotary mowers, hay-rakes and the hay-baler; they will simply not operate while the tractor is in reverse. (If you engage reverse while mowing, the mower is protected from damage by a one-way ratchet inside the mower gearbox.) To some folks, this is not an issue, because they are either A. Not using a the above-mentioned implements, or B. Have a property layout that doesn’t require much reversing while using these implements. However, if brush-mowing , lawn-mowing, or hay-baling is high on the list of what you want to do with your walk-behind tractor, AND you have a lot of forward-reverse maneuvering to do in tight spots, the BCS may be a better choice for the sake of operator convenience.
   / Berta flail mower
  • Thread Starter
Hi ;)

Recently I reached the first 50 hours on my Berta flail mower, and decided to do the first proper maintenance. I always check the blades and the rotor thoroughly after each job to make sure that everything is in good and safe working order and ready for the next job, but I hadn’t done any formal maintenance until now :cry:

The original „user and maintenance manual“ from Berta tells you to grease the 2 grease fittings behind the belt pulleys on the right hand side of the mower, and the 1 at the support end of the rotor on the left hand side, after the first 5 hours of work, and then after each subsequent 10 hours of work. This is also an obvious chance to check the tension of the 2 V-belts transmitting power to the rotor. The level of the transmission oil is easily checked also with the dipstick. What isn’t mentioned in the manual is that the dipstick has a magnetic tip, which of course is a clever way to collect small metal debris suspended in the transmission oil. The dipstick on my Berta looked like this after the first 50 hours:


The support roller at the rear of the mower is greased and sealed from the factory, and doesn’t need any further greasing or maintenance.

Like most other users of the Berta flail mower, I have been pretty impressed by the performance of this implement. For most of my jobs I have the cutting height set to its maximum of 5 cm (2’’), and I usually drive in 1st gear with the 23’’ wheels. As much of my mowing is in tall eagle fern, dense blackberry and brush, the Honda GX 390 engine often has to deliver all its 11.7 hp to stay on top of the 85 cm (33’’) flail mower. I always try to begin the job in the least dense part of the plot, as the first cut has to be full working width of course. Subsequent cuts I usually make with between 1/2 - 2/3 working width, depending on how dense and tough the material is. The left photo below shows the first cut through dense, and up to 6’ tall vegetation:

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The right photo above shows up to 2 m (6 1/2’) tall eagle fern at the edge of a meadow. The main reason for mowing the eagle fern, is to help small orchids that would otherwise have no chance to compete against the much taller fern. The main species here in my area, is the heath spotted-orchid (Dactylorhiza maculata), which grows to about 50 cm (20’’):


Even the Berta has its limitations though, and the toughest seems to be the most woody and fibrous material. One member, Maine Hills, has mentioned that he tries to avoid mature burdock. Another member, wstr75, has mentioned vine stuff like kudzu as a problem. Finally, Joel Dufour from Earth Tools has a note on his homepage, telling that mature sunn hemp might cause problems for most flail mowers.

I have had similar problems mowing hedge bindweed in autumn and early winter, when the vine has withered and has gotten so tough, that I can hardly tear it apart by hand. It seems, that in stead of mowing the stuff, there is a risk that the blades will simply catch the vine, and within a split second, more square feet has tangled to a solid mess around the rotor :mad:

Best regards

   / Berta flail mower
  • Thread Starter
Hi ;)

After 65 hours of heavy use - and sometimes probably even abuse - the knives on my Berta flail mower look like this:


I therefore decided to reverse the knives, in order to use the other cutting edge of them. This is a straightforward operation, that took me an hour in total to complete. For easy access, I turned the mower upside-down, and after a bit of cleaning, it was easy to remove the nuts with a ratchet with a 19 mm socket, and a 19 mm wrench on the bolts. After having reversed the knives, I first tightened the nuts by hand. Sadly the User and Maintenance Manual does not mention what tightening torque to apply to the nuts, so I sent a mail to the Berta company asking for this information. A quick reply from their support departement stated it to be 25 Nm (18.4 lbf-ft). This value is at the low end of the scale on my torque wrench, but now that everything is set and done, I look forward to a new season with sharp knives again :)

When the new edges gets dull and warn out at some point in time, the knives themselves have to be replaced of course. I therefore ordered a complete set of new knives, bolts and nuts by my dealer.

The nuts are standard self-locking M12 nuts, whereas the knives and the bolts are heavy-duty items, made of high-strength steel. The bolts are M12x45 shoulder bolts with property class 10.9, which I believe is similar to SAE grade 8 in the US. Not surprisingly, Berta recommends that the bolts are replaced with the knives. This sounds very sensible to me, as both these items are working under a lot of strain, and a failure might have serious consequences to the operator or anyone in the vicinity of the mower.

As expected for a Berta product, the knives makes a very tought and durable impression. They are 5 mm (approx. 3/16’’) thick, and weigh in at 168 g (almost 6 oz). Such quality products of course have their price. I have paid 6 Euro ($6.47) for each knife, and 2.75 Euro ($2.97) for each bolt with the nut. For the 85 cm (34’’) model with 36 knives, this adds up to: 36 x 6 + 18 x 2,75 = 265.50 Euro ($286.28). On top of that came shipping and 19 % VAT, making a total of 358.19 Euro ($386.22). Members having the 65 cm (26’’) or 75 cm (30’’) models can save a little, as these models only needs 28 knives and 14 bolts.

These spare parts certainly are expensive, but when working with a potentially very dangerous implement like a flail mower, safety should be our first priority, I think. I don’t like to image what could happen if a nut comes loose, or a bolt or knife fails and are hitting someone at great speed :cry:

Best regards

   / Berta flail mower
  • Thread Starter
Hi ;)

As I often do, I recently scrolled through some of Earth Tools pages, and noticed something new to me on the page concerning flail mowers:

Flail Mowers - Berta, BCS, Bellon, Green Technik - Earth Tools

The Berta company now offers „Anti-Scalp Skids“ for their flail mowers, and as Joel rightly says in the video, you might experience „scalping“ when working on undulating and uneven terrain. As the mower rests on its rear roller, the knives might hit the ground before the roller has a chance to raise the mower, when approaching rising terrain. The first parts of the flail mower to hit rising terrain are the side panels, and they don’t offer much help in raising the mower, as they are only 3 mm (1/8’’) thick.

Most of us have probably experienced this, but I haven’t seen it as a big problem myself. In order to be a bit more gentle to my knives though, I decided to purchase a pair of skids and give them a try. As they arrived and I was unpacking them, I couldn’t help having a smile on my face all the time. Although they basically are 2 simple curved pieces of metal bent 90 degrees and painted black, they felt so nice to have in my hand, that I found it difficult to let go of them, and to put them on my Berta flail mower ;)

Perhaps it sounds silly, but in some rare moments in life, one might come across a product so well designed and made, that it is a pleasure to see and to hold. I had the same experience in the late 1990s, as I treated myself with a Leatherman Wave. It was much too expensive for my budget at the time, but every time ever since, I get a smile on my face when I hold the original leather sheath in my hands, opens it, and hold the Leatherman in my hand. Both are so well made, and they really pleases the eye and the hand at the same time. I use my Leatherman regularly, and when I think of all the smiles it has brought to my face, it has been worth every cent! (y)

The skids for the Berta perhaps didn’t quite make it to that level, but they came close! The photo below is a close-up of my left-hand side panel after slightly more than 70 hours of hard work. Clearly the side panels have dug into the ground more than once, as part of the paint has been worn off.


This is how the right-hand side panel looks, after the skid has been fastened:


The skids are around 24 cm (9 1/2’’) long, 30 mm wide (1 3/16’’) and made of 5 mm (13/64’’) thick metal. I have used them for around 4 hours on 3 different jobs, and had very little scalping. It is of course very difficult to say how these jobs would otherwise have been, but I have the impression that the skids works like intended.

As with anything coming from the Berta company, these skids doesn’t come cheap. My bill for 2 skids, 4 carriage bolts with washers, and 4 self-locking nuts began at 124.50 € ($139.89). With 11.00 € ($12.36) for shipping, and 19 % sales tax on top of all of it, my bill reached 161.25 € ($181.19) in total.

Best regards

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   / Berta flail mower #75  
it still amazes me


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   / Berta flail mower
  • Thread Starter
Hi again ppea ;)

Thank you for sharing your photos with us (y)

You are absolutely right! In a few month I have had my Berta for 4 years, and I am still impressed by the performance of this implement 💪

As an owner and operator, one is getting used to this powerful mower of course, but I always get a smile on my face when I work with it for new costumers or friends, who haven’t seen it in action before. They are always very impressed by the performance, and can hardly believe that such a small tractor and implement can mow that efficiently.

Almost 2 years ago we had the question of whether to sharpen the knives on the Berta or not in another thread. I haven’t sharpened the knives on mine ever, but I would like to ask if you have?

Best regards

   / Berta flail mower #77  
yes,i sharpened repeatedly and i turn to other side.I make more pictures to knives tomorow.


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   / Berta flail mower #78  
Almost 2 years ago we had the question of whether to sharpen the knives on the Berta or not in another thread. I haven’t sharpened the knives on mine ever, but I would like to ask if you have?

I live in northern New England USA and encountering rocks is just a normal part of mowing. I've replaced my blades many times but I've never sharpened them. The idea of the dual sided blades seems nice, but I find that when a rock or other hard object gets kicked up, it bounces around quite a bit under the deck before being ejected out the front. By the time the front cutting edge is worn out, the rear edge is smashed up quite a bit as well, so I don't bother reversing them, only replace.

I recall the manual suggests not sharpening, due to potential balance issues. I find it hard to believe a few grams here and there would make that much of a difference compared to the normal "heavy use" (not abuse) the blades encounter. Has anyone noticed any problems from sharpening? I still have all my old flails and it would be nice to sharpen and put them back in the maintenance rotation.

Generally I don't think of my flails as "cutting" so much as "smashing" and/or "pulverizing". They have enough mass and rotation to do a nice job seemingly without regard to the condition of the cutting edge...
   / Berta flail mower #79  
i sharp many times,and no balance issues.
   / Berta flail mower
  • Thread Starter
Hi again ppea, hi again jeepcoma ;)

Thank you very much for your replies (y)

Another good example on how different conditions can result in different answers to the same question :unsure:

I rarely encounters rocks, stones or the like when mowing, and I think ppea doesn’t either. As I often work along old fences, Berta pick up a piece of wire now and then. This usually doesn’t damage the blades, but it gives me a lot of work on my knees getting it out :mad:

I can imagine that rocks bouncing around under the deck can make a lot of damage to the blades, but simply just replacing them, sounds very expensive in the long run. How long do you typically use your blades before replacing them? As I wrote in post #73, I have paid the equivalent of $386 for a complete set of blades with bolts and nuts. In my budget that is quite a lot of money, and that’s why I try to get the most out of my old blades. I reversed the original blades after 65 hours of use, and have added 20 hours on the reversed side since. The new set of blades that I have, will hopefully stay in the box for a while more.

My version of the manual (01/2010) doesn’t mention sharpening at all, it only mention replacing the blades when they become dull (page 31).

I also have the feeling that the condition of the blades are less important on a flail mower, compared to my 2 Zanon mowers for instance. I do feel though, that new/sharp blades are less power-hungry, which makes sense, I guess. The cutting edge of a sharpened blade is of course thinner than on a blunt blade, and therefore more vulnerable to damage when hitting a rock for instance. On one of the photos in post #77, one can clearly see that parts of the cutting edge has been chipped off.

Best regards