the way the bx is designed plays into it too.
the bx's mount the engine separately, i.e. on rubber mounts that isolate the little engine from the rest of the chassis.
Larger ("real") tractors mount the engine directly to the tractor's transmission which IS the chassis/frame. In doing it this way, the cost to build increases (as does the price of the tractor) but it also uses the rest of the chassis (transmission/rear end/etc) as a stressed member-which significantly reduces vibration.
Yes a 4 cylinder is generally smoother running at lower speeds. Not always but usually. This applies to diesel engines specifically as gas engines don't have a 16:1-22:1 compression ratio and they don't make 500-700 psi compression, nor do they have a throttle plate that is closed at idle (which also aids in reduceing felt shaking).
Typically the more cylinders the smoother it is. Reason being, a power stroke event only lasts maybe 60 degrees of crankshaft rotation. Just before, during and slightly after TDC, the crankshaft speed is accelerated due to the expanding gases pushing the piston down the cylinder. Somewhere around 75-90 degrees past TDC, the burn is mostly over with and at that point any acceleration of the crankshaft is mostly due to inertia of the rotating and reciprocating parts. If you have a 4 cylinder, each power stroke event is 180 degrees apart from each other. 3 cyl every 240 degrees. An even firing 6 cylinder, 120 degrees. A 8 cylinder, 90 degrees.. The reason most V8 engines are so smooth is due to the fact that power strokes "overlap", so the variations in crankshaft speed are rarely if ever felt. There is also the issue of first and second order vibrations from the rotating parts, which the manufacturer addresses with "balancing". All except the 3 cylinder. The 3 cylinder always has a rocking motion from end to end, nothing you can do about it except put a counterbalancer in the engine (which adds size and expense)-but still doesn't totally solve it. 3 cyl and 90 degree V6's are the worst possible designs for this rocking couple, although a 90 deg V6 is basically two inline 3's "out of phase", so that the rocking couples more or less (but not totally) cancel each other out. In an inline 6, they totally cancel each other out which is one reason for their smoothness. The other reason is that you have 2 pistons moving in totally opposite directions at any given moment-the combination cancels vibrations out without a counterbalancer, most V6's require a counterbalancer. Also on I-6's, the engine's crankshaft is so long that it twists-which acts kind of like a shock absorber. For years they didn't have them (counterbalancers) (buick/dauntless V6, GM 4.3, Chevy 229/3.8, etc) and they were all what "I" call "shakers". Mopar 3.9's were similar for a long time too, but those were odd fire engines for years. So were the pre 1977 Buick 3.8's, etc. The odd firing order plus lack of counterbalancer led to felt shaking in the engine particularly at a low idle speed. Exactly like the Kubota inline 3's, but it wasn't near as bad as the Kubota's, the frequency of vibration was twice that of the kubota's plus the GM's were gas burners-not diesels. When you shut off an old Cummins 6BT or ISB 5.9, the entire truck shakes just before rotation stops. Always hated that about them.
Take a short sharp stick and put an apple on the end of it. Move it back and forth. There is some force in the inertia as you change directions. Now use a longer stick with the same apple and shake it the same way. There is a lot more force now as you shake it back and forth. This principle applies also to the bx (and to an extent the ZD series) mufflers, in the way that they are mounted. The muffler is a good distance away from the center of shaking, the engine flops around on rubber mounts, and when you start and/or shut it down the engine flops around even more with the heavy muffler sitting on the end of all that shaking. Add moisture and low speed running and you get some rust inside, over time the rust makes the material thinner and more crack prone.
BX1500 had a huge heavy weight on the engine which dampened vibrations. The weight was an specifically engineered mass that significantly reduced the shaking at startup and shut down. If you take it off, and let the engine idle, it shakes so bad that you can't even see the engine-it's just a blur. Same principles applied, but the 1500 was a twin cylinder and not 3 cylinder. On the 1500, the compression pressure did most of the shaking, compression is resistance to crankshaft rotation, which causes the entire engine to shake. Surprised the crankshafts last as long as they do!
On the ZD series it was an issue mostly on the bigger ones (D1105, D1305 on the 326 and 331). Had plenty of them show up at the shop with busted mufflers. Kubota addressed this by redesigning the muffler and adding a brace to the cylinder head. The BX's could have made benefit from this redesign as well, but since the muffler assembly is completely different, it would have to be a complete redesign of that system which I'm not sure would be "cheap". Not that the ZD's were cheap either, kind of pricey for that kit, but it did permanently solve the problem on those.
It's not "Just" a kubota issue either. I did kawasaki for 30 years. On the diesel Mules, you couldn't keep belt guards on them, among other things. Engine mount brackets, quite a few other issues-all from vibration, mostly from startup and shut down. Replacing said major parts (mount bracket and belt guards) required engine removal, kind of a pain to work on them. A lot of folks would weld them in place without removing the engine-and I can't blame them. Had a couple of them get burnt down, welding on them and had oil and/or diesel all over them and they didn't bother cleaning it off before hitting it with the 9000 degree arc welder.
the bx's mount the engine separately, i.e. on rubber mounts that isolate the little engine from the rest of the chassis.
Larger ("real") tractors mount the engine directly to the tractor's transmission which IS the chassis/frame. In doing it this way, the cost to build increases (as does the price of the tractor) but it also uses the rest of the chassis (transmission/rear end/etc) as a stressed member-which significantly reduces vibration.
Yes a 4 cylinder is generally smoother running at lower speeds. Not always but usually. This applies to diesel engines specifically as gas engines don't have a 16:1-22:1 compression ratio and they don't make 500-700 psi compression, nor do they have a throttle plate that is closed at idle (which also aids in reduceing felt shaking).
Typically the more cylinders the smoother it is. Reason being, a power stroke event only lasts maybe 60 degrees of crankshaft rotation. Just before, during and slightly after TDC, the crankshaft speed is accelerated due to the expanding gases pushing the piston down the cylinder. Somewhere around 75-90 degrees past TDC, the burn is mostly over with and at that point any acceleration of the crankshaft is mostly due to inertia of the rotating and reciprocating parts. If you have a 4 cylinder, each power stroke event is 180 degrees apart from each other. 3 cyl every 240 degrees. An even firing 6 cylinder, 120 degrees. A 8 cylinder, 90 degrees.. The reason most V8 engines are so smooth is due to the fact that power strokes "overlap", so the variations in crankshaft speed are rarely if ever felt. There is also the issue of first and second order vibrations from the rotating parts, which the manufacturer addresses with "balancing". All except the 3 cylinder. The 3 cylinder always has a rocking motion from end to end, nothing you can do about it except put a counterbalancer in the engine (which adds size and expense)-but still doesn't totally solve it. 3 cyl and 90 degree V6's are the worst possible designs for this rocking couple, although a 90 deg V6 is basically two inline 3's "out of phase", so that the rocking couples more or less (but not totally) cancel each other out. In an inline 6, they totally cancel each other out which is one reason for their smoothness. The other reason is that you have 2 pistons moving in totally opposite directions at any given moment-the combination cancels vibrations out without a counterbalancer, most V6's require a counterbalancer. Also on I-6's, the engine's crankshaft is so long that it twists-which acts kind of like a shock absorber. For years they didn't have them (counterbalancers) (buick/dauntless V6, GM 4.3, Chevy 229/3.8, etc) and they were all what "I" call "shakers". Mopar 3.9's were similar for a long time too, but those were odd fire engines for years. So were the pre 1977 Buick 3.8's, etc. The odd firing order plus lack of counterbalancer led to felt shaking in the engine particularly at a low idle speed. Exactly like the Kubota inline 3's, but it wasn't near as bad as the Kubota's, the frequency of vibration was twice that of the kubota's plus the GM's were gas burners-not diesels. When you shut off an old Cummins 6BT or ISB 5.9, the entire truck shakes just before rotation stops. Always hated that about them.
Take a short sharp stick and put an apple on the end of it. Move it back and forth. There is some force in the inertia as you change directions. Now use a longer stick with the same apple and shake it the same way. There is a lot more force now as you shake it back and forth. This principle applies also to the bx (and to an extent the ZD series) mufflers, in the way that they are mounted. The muffler is a good distance away from the center of shaking, the engine flops around on rubber mounts, and when you start and/or shut it down the engine flops around even more with the heavy muffler sitting on the end of all that shaking. Add moisture and low speed running and you get some rust inside, over time the rust makes the material thinner and more crack prone.
BX1500 had a huge heavy weight on the engine which dampened vibrations. The weight was an specifically engineered mass that significantly reduced the shaking at startup and shut down. If you take it off, and let the engine idle, it shakes so bad that you can't even see the engine-it's just a blur. Same principles applied, but the 1500 was a twin cylinder and not 3 cylinder. On the 1500, the compression pressure did most of the shaking, compression is resistance to crankshaft rotation, which causes the entire engine to shake. Surprised the crankshafts last as long as they do!
On the ZD series it was an issue mostly on the bigger ones (D1105, D1305 on the 326 and 331). Had plenty of them show up at the shop with busted mufflers. Kubota addressed this by redesigning the muffler and adding a brace to the cylinder head. The BX's could have made benefit from this redesign as well, but since the muffler assembly is completely different, it would have to be a complete redesign of that system which I'm not sure would be "cheap". Not that the ZD's were cheap either, kind of pricey for that kit, but it did permanently solve the problem on those.
It's not "Just" a kubota issue either. I did kawasaki for 30 years. On the diesel Mules, you couldn't keep belt guards on them, among other things. Engine mount brackets, quite a few other issues-all from vibration, mostly from startup and shut down. Replacing said major parts (mount bracket and belt guards) required engine removal, kind of a pain to work on them. A lot of folks would weld them in place without removing the engine-and I can't blame them. Had a couple of them get burnt down, welding on them and had oil and/or diesel all over them and they didn't bother cleaning it off before hitting it with the 9000 degree arc welder.
