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Message started by pg on 10/28/15 at 17:15:28

Title: Firing Order
Post by pg on 10/28/15 at 17:15:28

I have been looking at a Triumph Bonneville. Beautiful bike, classic and refined with some of today's technology. I was reading about how the firing order varies between the various Triumphs. The Bonneville utilizes a 360 degree order or both pistons go up and down at the same time. What would be the benefit of that as opposed to a 180 degree? At 865 cc, that is really a big two piston thumper...

Best regards,

Title: Re: Firing Order
Post by Kris01 on 10/28/15 at 18:12:12

Like any thumper, it's probably very torquey as opposed to a high RPM screamer.

Title: Re: Firing Order
Post by gizzo on 10/28/15 at 19:38:51

A: Val Page wanted his Speed Twin (therefore brit twins forever) to behave like a single because Brits feared change, but with more RPM and power + easier starting
B: It makes it easier to feed 2 cylinders with 1 carb
C: It sounds cool
D: Less rocking couple at expense of primary vibration

Take your pick.

FWIW 360 deg twins have often been rephased to 270 deg. Makes them really smooth and sound like a Ducati. I think the Yamaha TRX850 is 270?

Title: Re: Firing Order
Post by HovisPresley on 10/28/15 at 20:34:23

Val Page had left Triumph and Edward Turner taken over the design for the Speed Twin.
Turner had basically inherited the design which he both retained and altered, mainly due to financial reasons.

pg, I think 'modern' Triumph twins have 360* or 270* cranks depending on the model.
With 270 you get the peak torque at lower revs, but lose out slightly with top-end hp..... I think

If the weather stays okay, I might try to arrange a short test ride of the two at my local dealer

Title: Re: Firing Order
Post by mpescatori on 10/29/15 at 00:26:17

We all know what a 360° twin crankshaft looks like.

A 180° crankshaft on a 4-stroke twin is essentially the same as a crank in a 2-stroke twin.

A 270° crankshaft on a 4-stroke is a very original idea; the cranks are at 270° (or, at 90°) which means they are at right angles to each other, as in an "L";
this allows for a very smooth and balanced engine provided your name is Guzzi or Ducati (or Honda CX at best)
but if the engine is a side-by-side twin, the engine will sound a bit "Harley-ish" and the crank counterweights will have a helluva hard time keeping the vibrations down.

Not as lumpy as a 180° 4-stroke twin (not that I've ever seen any) but still lumpy...

IMHO...

Title: Re: Firing Order
Post by gizzo on 10/29/15 at 03:22:42

Well, a Ducati (and Guzzi) crankshaft has both conrods on the one crankpin, but has the cylinders at 90 deg instead, but we know what you mean. If the cylinders were folded up, it would indeed be a 360 deg parallel twin. Likewise, a 270 deg crank on a parallel twin behaves somewhat like a folded up 90 deg V twin.

Here's a link to an article I read a while ago about a guy making 270 deg cranks for XS650 engines
http://www.trademotorcycles.com.au/spannerman-tech-advice/1407/improving-the-yamaha-xs650-technical-advice/

Title: Re: Firing Order
Post by pg on 10/29/15 at 05:31:50

Quote:

I think 'modern' Triumph twins have 360* or 270* cranks depending on the model.

After doing a bit of research that is correct. Although, it looks like more manufacturers are producing a 270*.

Pesci:

I heard a Ducati for the first time at the end of summer. I never imagined that an engine could sound that good. Actually, he passed me at about 55mph on the "dragon".

Anyway, thanks for the insight gents.

Best regards,

Title: Re: Firing Order
Post by HovisPresley on 10/29/15 at 07:22:51

pg, have you seen the new Triumph T120 and Thruxton 1200cc models?

Title: Re: Firing Order
Post by pg on 10/29/15 at 07:32:02

Yeah, they are phenomenal!

Best regards,

Title: Re: Firing Order
Post by Gus on 10/29/15 at 09:20:15

So am I to understand that the Honda cx is timed at 270 degree's! That must be why they sound and run so smooth. I've always been attracted to the cx because of the way they run.

6A77627464667368756E070 wrote:

Title: Re: Firing Order
Post by oldNslow on 10/29/15 at 10:27:25

Quote:

I think 'modern' Triumph twins have 360* or 270* cranks depending on the model.

Not any more. Looks like the new motors in the 2016 models are going to all be 270.
Triumph says that based on their market research that's what their customers (or potential customers) prefer.

The Scrambler is staying the same for one more year, but I think it had a 270 crank already.

http://www.motorcyclistonline.com/long-awaited-2016-triumph-bonneville-is-here-new-bikes-2016-motorcyclist-magazine-first-look

Title: Re: Firing Order
Post by Rodger on 12/19/15 at 19:38:20

Two *ahem* "advantages" to a 360° vertical twin:

1) as previously mentioned, one carburetor could service 2 cylinders

2) only one set of points/condensor/coil required, firing one cylinder on compression, the other cylinder on exhaust..so-called "waste spark"