Yeah. I don't know if you recall or not, but at one time several years ago, it was indexed into 500GP "By mistake", but it stayed there awhile....that's what Doug and I were referencing. Jack called the bluff by buying a bike (or 2) and starting a build. He then asked for clarity, and it was removed.
Its a 180 crank..... Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up. The 180-degree crankshaft was now one piece (it was built-up on the 400 and 425), and ran on three automotive-style plain bearings instead of balls and rollers as before. I wonder why any of the bigger vert twins (triumph, Norton, etc) didn't have 180 cranks.....???
There's an outfit in Canada that cuts & re welds cranks that has done 360 Brit cranks. Lack of development was certainly a contributing factor to the demise of the Brits.
So they make a 180 out of a 360? Dang, that changes cams and everything don't it? The 180 crank just makes more sense to me, and I believe its most of the reason the small Hondas make such good power, and I was wondering why it wasn't adopted into the bigger twins. What I hear you saying chuck, is the 360 is cheaper? A lot of the even smaller Honda are 360 cranks for some reason. 180 cranks seem to be isolated, used sparingly, and was just wondering why.
One reason for the popularity of 360 degree cranks is they allow the use of one carburetor and a single ignition system using a wasted spark. The advantage of the 180 degree crank is less pumping losses since the crankcase volume remains relatively constant. I am sure there are other considerations as well.
OK, that makes sense....so pointing back to the "360 is cheaper" scenario. Man, 180 just makes so much more sense to me mechanically / power-wise.
180 definitely has to be smoother.....on a twin 180, its a boom every 2 strokes (opposite cylinder, lets not get carried away on the two strokes here!).....that's gotta make more power than a boom every 4 strokes. I do think it makes more top end power because its smoother, and the motor can rev higher. Whats the redline on an old triumph?
:up:The 180 fires at 180 and 540 intervals. The 180 has the uneven firing order. It is smoother since the pistons are always opposite one another but it does have a rocking-coupling. 180+540+=720. The 360 is just like a big single but split into two halves hence the vibration. The firing pulses are spaced evenly. 360+360=720. Not saying you are wrong but I don't think the inherent advantages and disadvantages are that great a difference. I can't think of any good direct comparisons though Honda did change the CB450 from a 360 to a 180 for some reason. Maybe it was an attempt to quell some vibration but the ones I've had still vibrate more than the SR500 I had. The only modern contrast I can think of is Triumphs Bonneville (360) and Scrambler (270) but I don't know which one makes more power or revs higher or whatever. Maybe someone familiar can chime in. Good talk CY.
I don't know but I would think the Triumph 650s relatively small bore 71mm and long stroke 82mm have more to do with limiting its rpms than does its crank configuration due to its high piston speed. I think you are right, that the 180 had more rpm potential but it's hard to compare 350s and 650s.
Valve train is the limiting factor, not crank. Light valves / rockers / keepers all help. 6500 rpm on a stocker maybe. 500's would rev higher, 7500. Crank fails at 70hp if not reinforced.
Good stuff fella's, thanx. Well, how big an advantage it is would be up for discussion I guess....I'm not saying its massive or anything, but I am saying there is a difference, with the plus side going to the 180, and I'm really wondering why that was not exploited more? The closest thing I see to a number would be the difference in redline.....which should drive a difference in power at some point. The Triumph redline numbers Chuck listed are right around 25% less than the 180 crank Honda 350.....350 Factory numbers are around 10K. To sum things up, any opinions on why the 360 setup became more prominent than the seemingly more efficient 180 setup? I'm leaning twds cost, but I'm also thinking the 1 more carb, cam and ignition changes, appear to be worth it.....or it would be to me. I've kinda left the 270 out just to not muddy the waters, but I know there are people who rephrase their 360's to 270's, so that says something about the 360's as well. Then there anomalies also, like the XS with 360deg AND Dual carbs anyway.....kinda leads AWAY from the cost analogy. These are the things I ponder.
I see what you are saying about valvetrain Chuck.....OHC vs Pushrod....but I did a quicksearch XS, couldn't find redline, but the HP and Torque numbers are all close to 7,000 RPM.....so, the redline might be slightly higher than that, BUT still pretty close to the RPM numbers you listed. And still a difference from the 180 Honda. Actually, the numbers you listed are actually pretty darn good for pushrod.
Brad, I think the Honda fires at 180 and has a wasted spark.....no 540....confirm? Just for the record, I know 540 is 3 x 180......I'm thinking it fires at every 180, with a wasted spark.