Single Bearing vs Dual Bearing Engine


Can anyone tell me the difference? What advantage one has over the other, if any? Power difference, I'm new to the Flatheads and looking for general information. Thank you
We always used the dual bearing engines for the simple fact of a true bearing on each side of the crank, and less drag than the bushing type motors. jmo
My personal opinion is it doesn't matter. Some of the very best engines across our dyno (our own engines and from other big name builders) have been single bearing. Mind you, it's not the bearing configuration that made them any better than another.

Consider this...A ball bearing is not designed to carry a lateral load. It is designed to carry / roll free when loads are placed vertically upon it. Unfortunately, when you enter a turn with your go-kart, the weight of that 6+ pound flywheel pulls the crank laterally due to centrifugal force and now that extra flywheel side ball bearing is expected to carry that lateral load. In reality, it can't do that as well as a bushing. In fact, if you pull the flywheel to the right enough to take up the crank endplay while you're dynoing the engine (by pushing on the pto side coupler and crank) you'll lose rpm due to the drag caused by the ball bearing being loaded in a way that it was never designed to handle. This is the reason that many years ago WKA had to address and make a rule to prohibited radial bearings and the likes on cranks. Now, on a limited, or open, you see guys preferring the single bearing blocks because of the issues of breaking the case under the flywheel side ball bearing where the oil drainback area is. With stockers pushing 7200 today, we're not all that far away from limited and open rpms of a few years ago. Could this "rattling" effect be causing other problems (ring flutter, ring seating, etc) with our flatheads today? Something to consider at least.

Look at it this way... If ball bearings were so great, we'd have them in the front hubs of all of our every day drivers (pick-up trucks, etc.) No, we have taper bearings in almost all cars on the road today -- Why? Because they can handle the side loads placed on them so much better than a ball bearing ever could.

With that said, all of the new R4 flathead blocks available are dual bearing because that's what the factory felt the majority of kart engine builders wanted (and that's probably correct.) For years, you saw engine builders list their pricing as a "standard" shelf engine with single bearing, and their "national level" engine with dual bearing. After awhile it was pretty much expected by the racers.

If you're looking at used flatheads, don't get caught up in single or dual bearing arguments -- be more concerned with overall performance of the engine. I look primarily at the intake port size, volume, shape, and seat alignment. Almost all of my own kids' engine are single bearing -- if I felt it was that important to have dual bearing blocks, you bet I'd have them for my kids. :)

Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
Has anyone ever tried to fit angular contact bearings into a dual bearing flathead? Obviously not for stock WKA flatheads. I was thinking more for flathead opens.
I dont think it realy matters i got a open flathead we turn it 10,500 rpm with no problem and we got both in the wka engines and had no problems otis said its all in your head dual bearings.
We'll I gess the best would be to mechean the crank or block and put a needle bearing thrust washer to take up the lateral load then u would have the best of both worlds I build vintage snowmobile oval race motors and I put one thrust on the crank and it keeps the heat down in the lower end when hard cornering
That's exactly right , and would be the setup for a bushing block open, because the bushing does not take care of that lateral load at all. It's the boss that the bushing is in and the side of the crank that gets loaded. On most kart tracks it's never seen as an issue, oil is trapped between the crank and boss and keeps things turning without much friction thru the turn and then when you hit the straight the crank can move back over and collect some oil again. We built some bushing blocks for use in 1/4 midget racing, their track was a circle, the crank stayed loaded on the bushing boss constantly and after several laps with all the oil forced out it grooved and burnt the boss with the friction generated. We switched to a bearing block and solved the problem. For karting I prefer the bushing block, it does not have more drag than a bearing, and when you add up all the clearance a bearing setup has, bearing to case, internal cl. , crank to bearing, it's more clearance overall than a bushing so the crank is a little less stable and more air gap has to be set between coil and flywheel. As was mentioned above there's nothing much under the bearing boss , so a limited or modified will bust it if it's not reinforced, those are some of the reasons it's my preference. Jon
Seems like we would be discussing a tapered bearing in our right front hub instead of our engines lol. I remember seeing these some where at one time. Popatop racing where were you buying the needle bearing thrust washers from? How much RPM were you turning those snow mobile motors? Are ceramic bearing tolerances any tighter than the standard roller bearings we all run?
I build my own ceramic hybrid roller bearings and make them with the same play or more than with steel balls. But u can make them tighter the ceramic balls expand 3 times less then steel at the same temp
I make them take a bearing apart and let me know what size the ball is then I will price it out and let u know how much I can make them for
We raced flatheads for over ten years and never owned a dual bearing. It was all about the ports. Better flow is where the hp is. Interesting conversation on the thrust issue, I never gave it much thought. Seems that flatheads are making a little comeback.
Its an own preference on which on eyou want to use, you really can't see or feel a difference, I have an engine with dual bearings and one with bearing and bushing, two exact same motor and parts, but I cant tell no difference, but that's my honest opinion.
I believe most would agree that the Europeans make the best kart engine in the world. I have never seen one with duel row bearings.
I would find it hard to believe if someone told me they do that for any other reason other than the single row bearings are better.
Comments, compliments, criticisms and questions always welcome.
I believe most would agree that the Europeans make the best kart engine in the world. I have never seen one with duel row bearings.
I would find it hard to believe if someone told me they do that for any other reason other than the single row bearings are better.
Comments, compliments, criticisms and questions always welcome.
All they arent talking double row bearings, its a term to describe the engine has bearings on both sides,.