4cyl vs 3cyl

[leonz]

I have a B7800 ('03, purchased new) and I have never felt that it was too rough. Come on man, its a tractor not a Caddie! My 7800 has 400 hrs on it and has never failed to start nor had anything break (and it lives outside). I love this tractor. I agree with the others: get the tractor that can do the work you need (and then some just for "insurance").

===================================================


With the the three cylinder kubota engines in particular they are used for many other applications.


The nasty harmonics animal can create havoc at low rpm speeds if the engine isolation is poor especially with the hard( solid contact mounts on most of them.

The faster the low idle speed the greater force delivered to even the resonance between the prime mover (being the engine) and the tractor.

Using the 3 cylinder Duetz air cooled diesels as and example they are very civilized when mounted PROPERLY with the mounting feet and twin rubber pucks with steel spacers on all four corners.

When these yahoos put them in automobiles( CJ-5 jeeps) and expect to use motor mounts which are already there -thats another stupid move and the use of the rubber pucks is not possible and the normal balanced low idle which is what it was tested for at the factory and approved for with the fuel settings on the injection pump for the indirect injection engine in
which they occur with the rubber isolation mounts(been there done that (PROPERLY). The install was bad so the engine was blamed when it was the installer( outside shop that rube goldberged the entire thing.

Our boss buggies had the 3 cylinder water cooled engines in a modified kubota farm tractor- there was so much added weight because of the FOPS and 4 added seats and the rear tool carrier which was added it just absorbed it all at low idle.


The only way to cancel any low idle bounce is to add a grill guard(if possible) and front weights to cancel the delivered momentum at the flywheel at low idle due to the front engine mounts for the three cylinder engines.



leon

 

[KennyV]

Back to the OP initial question...
The more cylinders you have the smoother it will TEND to be....

This really is not of great importance to a tractor...


I have never thought my tractor (L4200) vibrated too much compared to a 5 or 6 cylinder.... If I go to idle with the AC and stereo on I'm not disappointed in the feel of things... KennyV

 

[LBrown59]

***there seems to be a lot of complaints about the Kubota B7800 and B3200 being vibrators when compared to 3 CYL versions of similar sized tractors. .

That's why I don't like the 4 cyl diesels.

Gas engines seem to do better with even numbers of cyls;while diesel engines appear to work better with odd numbers of cyls.

 

[ultrarunner]

Nothing like the old Buick Straight 8 for smoothness or a modern BMW straight 6...

 

[PHILIP8N]

That's why I don't like the 4 cyl diesels.

Gas engines seem to do better with even numbers of cyls;while diesel engines appear to work better with odd numbers of cyls.

The inline 6, gas or diesel, even number of cylinders, is about as closed to a natrually balanced engine you can ask for. 99.5% of all semi tractors use 6 cylinder inline diesel engines. Philip.

 

[KennyV]

Nothing like the old Buick Straight 8

Yeah.. I had a '48 ...great car. But I found the weak part of the engine... Babbitt bearings. KennyV

 

[rScotty]

Thanks for the replies, I was just wondering because I am looking at moving up in tractor size and all the JDs have 3 cyl and the Kubotas have 4 cylinders for about the same HP.

I design similar products and it often comes down to how much effort the manfacturer wants to put into smoothing out the inbalance - engine designers have no problem designing and balancing either number. Which is just another way of saying it's where designers decide to spend their money. For example, sleeved cylinder liners may cost more than directly bored blocks - but they also cool better so money can be saved in other areas. It's all trade offs. The cost of an additional cylinder's parts has to be considered against the cost of a driven balance shaft required by using a lesser number of cylinders. Often these basic decisions look more like politics than engineering.

I've got a three diesel tractors of 2, 3, and 4 cylinders.

The two cylinder is a low end direct injection Yanmar built to be absolutely bulletproof and cheap. It shakes. It has also not needed any maintenance in 30 years and still starts and runs same as it did when new.

The 4 cylinder is a new Kubota 60 hp turbo. I'd rate the engine construction as a good conservative motor design built with an eye on cost. It has some vibration, but not much or in any way objectional, but I notice I do tend to work at a RPM where it "feels" best.

The 3 cylinder is mid-30s HP non-turbo indirect injection type - also built by Yanmar. The quality of design and construction is obviously above the norm for tractors. It's also shows more thought in accessibility for routine maintenance. It is weirdly vibration free at all RPM - almost like an electric motor.

BTW, torque rules! Not HP, because HP is just torque times RPM. And unfortunately, engines are HP rated at full RPM...even though we tractor guys rarely run them that way. In fact, if torque is equal or close, a smaller motor can actually put out more HP by simply spinning it faster. Think about Torque first, then how RPM affects HP when comparing. High torque at low RPM also vibrates way less.
Enjoy! rScotty

 

[leonz]

So true , so true. I have the first 5 cylinder Isuzu Truck I have ever owned and its a great truck with the 5 banger Vortec -ithe 2008 is the last year that they contracted with GM to build trucks for them. I still have the 1995 4 by 4 (4 cylinder gas) that I bought new and it need frame work but is as good as new and I can still buy parts so its going back on the road this winter after the frame repairs.

 

[whistlepig]

I design similar products and it often comes down to how much effort the manfacturer wants to put into smoothing out the inbalance - engine designers have no problem designing and balancing either number. Which is just another way of saying it's where designers decide to spend their money. For example, sleeved cylinder liners may cost more than directly bored blocks - but they also cool better so money can be saved in other areas. It's all trade offs. The cost of an additional cylinder's parts has to be considered against the cost of a driven balance shaft required by using a lesser number of cylinders. Often these basic decisions look more like politics than engineering.

I've got a three diesel tractors of 2, 3, and 4 cylinders.

The two cylinder is a low end direct injection Yanmar built to be absolutely bulletproof and cheap. It shakes. It has also not needed any maintenance in 30 years and still starts and runs same as it did when new.

The 4 cylinder is a new Kubota 60 hp turbo. I'd rate the engine construction as a good conservative motor design built with an eye on cost. It has some vibration, but not much or in any way objectional, but I notice I do tend to work at a RPM where it "feels" best.

The 3 cylinder is mid-30s HP non-turbo indirect injection type - also built by Yanmar. The quality of design and construction is obviously above the norm for tractors. It's also shows more thought in accessibility for routine maintenance. It is weirdly vibration free at all RPM - almost like an electric motor.

BTW, torque rules! Not HP, because HP is just torque times RPM. And unfortunately, engines are HP rated at full RPM...even though we tractor guys rarely run them that way. In fact, if torque is equal or close, a smaller motor can actually put out more HP by simply spinning it faster. Think about Torque first, then how RPM affects HP when comparing. High torque at low RPM also vibrates way less.
Enjoy! rScotty

It's not that simple. Torque does not always rule. Torque is best for motors that pull loads and do work. At the drag strip horsepower will win the race.

 

[easygo]

Yeah you are right. But if I remember correctly the OP was looking to upgrade his/her tractor not a dragster.

This is a very informative thread. I'm lovin' it.

 

[Crash101]

I am wondering what the advantages and disadvantages are to diesel engines making the same horsepower, but with one more or less cylinder. Is there a mileage or efficiency advantage to one? More or less torque? Please clue me in.

This one is always sure to produce many responses. In reality the number of cylinders do little in providing more or less power, or efficiency. Fewer cylinders are cheaper, more are generally smoother, with some exceptions. A four stroke engine makes a complete cycle in two revolutions, or 720 degrees. This constant is what makes an inline four cylinder engine the worst for vibration. When two pistons are up, two are down (720 degrees divided by 4=180 degrees apart). With three cylinders, one is coming up and one is coming down while the other is up being fired. Like poker, three of a kind can be better than 2 pair.

 

[whistlepig]

I am wondering what the advantages and disadvantages are to diesel engines making the same horsepower, but with one more or less cylinder. Is there a mileage or efficiency advantage to one? More or less torque? Please clue me in.

The more cylinders the better on engines of equal size and horsepower. Each cylinder does less work thus less wear and tear. Also less load build up between the firing of the cylinders. Better power transfer. This was the demise of the old John Deere two cylinders.

 

[_RaT_]

Excellent comments from you, Ford and of course DickB. My smoothest diesel was a International 454 with 3 cylinders. My L48 and my L3830 shared the same rods, piston sizes but the L48 was 4 cylinder and the L3830 was 3. They were equally smooth. My L4850 is 5 cylinder and is no more or no less smooth than my previous 3 or 4 cylinder engines.

Two engines of the same size can have different bores and strokes. They can also be tuned differently. While what you say is very often true, but it's not gospel.

Most inline-three cylinder engines employ a crank angle of 120 degrees, and are rotationally balanced. However, since the three cylinders are offset from each other, the firing of the end cylinders induces a rocking motion from end to end, since there is no opposing cylinder moving in the opposite direction as in a inline six that is inherently balanced. In other words, the cylinder firings induce a vibration.

The inline-four layout is the simplest design that is in perfect primary balance. However, it suffers from a secondary imbalance that causes minor vibrations in smaller engines.

Primary balance and secondary balance refer to vibrations at the first and second harmonic of the crank's rotational frequency, respectively. Higher order harmonics also exist, but as the orders increase, the magnitudes decrease, thus orders higher than the second are typically neglected.

So all this crap means that neither is the winner, and it all depends on what the manufacturer creates. My two John Deere tractors are both three cylinder engines. The little 455 has to idle around around 1600 rpm to be smooth. The bigger 790 does nicely at 800-1000 rpm.




Agreed. If you see two models with the same hp ratings, look for the torque specs. Chances are that the four cylinder will have more cubes and more torque. FYI - turbos tend to give you more power toward the top of the rpm band.

 

[_RaT_]

If this is true it makes me wonder why the GM (Isuzu) and the Ford V8 diesels have always been less than they could be compared to the 6 cylinder from Cummins. Even today I would take the Cummins over the Ford or Isuzu but not by as much as I once would have. On the other hand, I would gladly take the Cummins but you can keep the Dodge body. :laughing:

The more cylinders the better on engines of equal size and horsepower. Each cylinder does less work thus less wear and tear. Also less load build up between the firing of the cylinders. Better power transfer. This was the demise of the old John Deere two cylinders.

 

[whistlepig]

If this is true it makes me wonder why the GM (Isuzu) and the Ford V8 diesels have always been less than they could be compared to the 6 cylinder from Cummins. Even today I would take the Cummins over the Ford or Isuzu but not by as much as I once would have. On the other hand, I would gladly take the Cummins but you can keep the Dodge body. :laughing:

We are getting off the subject but an inline six cylinder is the best motor ever made. Gas or diesel.

 

[SPYDERLK]

The more cylinders the better on engines of equal size and horsepower. Each cylinder does less work thus less wear and tear. Also less load build up between the firing of the cylinders. Better power transfer. This was the demise of the old John Deere two cylinders.

Hummm... Then you must be assuming that the pistons, pins, rods, crank and bearings are of equal strength and quality. My guess would be that a smaller piston will be coupled with smaller components because the loads would be less. Kind of blows the argument. It all depends on what the manufacturer designs.

Consider also the thermal detriment of going to too many cyls. ... In any given displacement, more cyls causes more combustion chamber area. This means more of the heat of combustion goes into the metal parts instead of producing mechanical power.
larry

 

[rScotty]

It's not that simple. Torque does not always rule. Torque is best for motors that pull loads and do work. At the drag strip horsepower will win the race.

I'm not sure that helps. The whole object of a tractor is to run at slow speeds and slow RPM. In fact, the slower the better - as long as there is enough power available to get the work done. Torque is what we want available when reducing the RPM is more important than increasing it.
rScotty

 

[kuboman]

Consider also the thermal detriment of going to too many cyls. ... In any given displacement, more cyls causes more combustion chamber area. This means more of the heat of combustion goes into the metal parts instead of producing mechanical power.
larry

I think displacement determines combustion area and fuel used not the number of cylinders

 

[Rob-D]

Nothing like the old Buick Straight 8 for smoothness or a modern BMW straight 6...

Interesting that you say that. BMW specifically states that the inline six is much smoother than the V6 which they believe has inherent balance issues.

The BMW 6 on the 325 I owned years ago was a sweet engine!

My friend has a 990 Deere with a 4 and it was much smoother than the 3 on my 2720. The 2720 may have been too light for the three, I'll see what happens when the 3320 gets here. The 2320 seemed smoother than the 2720. Less HP for the weight.

Rob

 

[LD1]

I think displacement determines combustion area and fuel used not the number of cylinders

I agree.

Two engines of the same displacement and same storke length with the only difference being 3cyl vs 4cyl, they will have exactly the same piston surface area. And depending on combustion chamber type/shape, that will be the same also.

Some 3cyl engines may seem to operate smoother than some 4cyl's. This is all in what the MFG does to reduce the harmonics and vibrations. But the bottom line is, the more power strokes per revolution, the smoother the engine will generally run, due to less time in between "explosions". 12 and 16 cylinder engines run extreemly smooth compaired to 6 and 8 cylinder engines.

But there are more than just the # of cylinders that contribute to percieved vibrations. Its all in what the MFG does to curb the vibrations. More agressive cam profiles and timing can make an engine "seem" to run rougher or smoother. Hydraulic vs solid lifters. Roller vs solid cam.

In general however, two engines constructed exactally alike, the 4cyl will typically be smoother.

To the OP: There are many different engine sizes and styles in the 3 and 4 cylinder tractor market. All MFG make them different. You have to test them for yourself and be the judge. Example:A JD 3cyl may be smoother than a Kubota but a kubota 4cyl may be smoother than a JD. Maybe even one JD 3cyl is smoother than another 3cyl JD of different size. There are way more variables other than just 3cyl vs 4cyl.