270 Question
- Thread starter norsa1
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I wonder where these myths come from.
I start the Vincents all the time and they are , if anything, easier to start than the Commando which is an easy starter as well. The Vincents do require use of a compression release. Once the technique is learned, they are one kick wonders, hot or cold.
The 1360, which is quite different than an original Vincent, does require starting on the rear cylinder. That was expected due to the high compression (10.5 to one) big squish bands and large displacement. I'm surprised that it is even possible to kick start that one.
With the 1000 CC bikes it's just kick and go.
Glen
I start the Vincents all the time and they are , if anything, easier to start than the Commando which is an easy starter as well. The Vincents do require use of a compression release. Once the technique is learned, they are one kick wonders, hot or cold.
The 1360, which is quite different than an original Vincent, does require starting on the rear cylinder. That was expected due to the high compression (10.5 to one) big squish bands and large displacement. I'm surprised that it is even possible to kick start that one.
With the 1000 CC bikes it's just kick and go.
Glen
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All the more recent Hinkley Triumph twins are 270 with balance shafts. The 961 has a balance shaft. A friend of mine's £17,000 961 was suffering from bad vibes, went back to the factory for a new crank. The "old" one ( about 1100 miles) had broken the welded up joints. I have a 675 street triple in my stable. It's mental. You can blow off almost everything on four wheels without going above 7000 rpm but there's a whole different world above 7000
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Actually....
All the recent triumph twins come in either 270 or 360 degree versions depending on the model. Anything that competes in a segment where it's desirable for the bike to be "american" sounding gets the 270 (scrambler, all the twin cruiser types, etc...) anything that is supposed to sound British get the 360 (bonnie, thruxton, etc...). If anything it's a good chance to go down and try out one of each to see the exact difference. There is a small power difference (~10% in favour of the 360, but that's probably just because of cam profile choices).
As for the advantages, it's mainly the disadvantages of the 360 that stand out. They are harder to balance (primary balance issues without a balance shaft, large weights on the balance shaft to counter that), and they have large amounts of crankcase volume change. With a 270 you somewhat alleviate both of these things (but not to the extent that a 180 crank does). With a 180 you end up with a nasty rocking couple in exchange for the primary balance, but that can actually be balanced out easily with a fairly small balance shaft. The 360 was commonly used because it gives an even firing order and lets you cut a large amount of cost by essentially twinning a single cylinder design, keeping one carb for both cylinders, and making it relatively straight forward to use a frame meant for a single with a twin of the same balance factor.
All the recent triumph twins come in either 270 or 360 degree versions depending on the model. Anything that competes in a segment where it's desirable for the bike to be "american" sounding gets the 270 (scrambler, all the twin cruiser types, etc...) anything that is supposed to sound British get the 360 (bonnie, thruxton, etc...). If anything it's a good chance to go down and try out one of each to see the exact difference. There is a small power difference (~10% in favour of the 360, but that's probably just because of cam profile choices).
As for the advantages, it's mainly the disadvantages of the 360 that stand out. They are harder to balance (primary balance issues without a balance shaft, large weights on the balance shaft to counter that), and they have large amounts of crankcase volume change. With a 270 you somewhat alleviate both of these things (but not to the extent that a 180 crank does). With a 180 you end up with a nasty rocking couple in exchange for the primary balance, but that can actually be balanced out easily with a fairly small balance shaft. The 360 was commonly used because it gives an even firing order and lets you cut a large amount of cost by essentially twinning a single cylinder design, keeping one carb for both cylinders, and making it relatively straight forward to use a frame meant for a single with a twin of the same balance factor.
Fast Eddie
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I thought it was only some variants, ie Scrambler and America. I thought the 'standard' Bonnie and Thruxton etc were still 360?84ok said:
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the statement I made is accurate including this year (2015) the current models of bonneville/thruxton, etc... are 360. Scrambler, america, other cruisers are 270. Take different coils, wiring, etc..., but same basic castings. except for the crank/cam.
Fast Eddie
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+1 on that.worntorn said:
My 1000 has 8:1 CR and provided the de-compressor is used, its a doddle to start! It is SO docile too. If i did it again I'd go for 10:1 and 105 cams.
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midnightlamp said:
I nearly bought a Scrambler a while back, was all set, till I heard it fire up! Them there 270 cranks just spoil an otherwise good twin in my book!
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t100 was 360, same years, after that it all went 270
http://en.wikipedia.org/wiki/Triumph_Bonneville_T100
http://en.wikipedia.org/wiki/Triumph_Bonneville_T100
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norsa1 said:
You need TWO 170 Lb men , or a four story building . :mrgreen:
. 
The Olde ' bring up to T.D.C. trip , BUT one cyl will have the next soon after , where you need the other - with the next later .
Gearing , the Triumph ( real ones 0 get THREE compressions if you do it right, the Norton TWO ( with a 360 crank ) . so the RGM gets more cylinders per swing .
Basically , you need to get the crank rotateing so it throws itself over compression . Thus the kick start engagement is ANOTHER process , when Cyl's positioned .
Throwing yourself up a story or two , foot on crank , pawl engaged - gets it M O V I N G , and your WEIGHT cARRIES IT THROUGH . uNLESS THE ADVAnce is stuck .
The other bleedy thing is the bleedy ignition . Best to leave it OFF untill the cyliders are primed . this is compulsary with a 2Mc & No Battery . ANYWAY .
swinging it over ign. on , if it ' bumps' its fired off the prime , so you have to do it again - ad infinitum . CHOKES / Damp Carbs ( ticklers ) are mandatory .
all this on a COLD motor of course . Winter in C ANADA :shock: :lol: :x :twisted: try a b low lamp , Nitro , ignition improver , anytghing . :twisted: :twisted: :wink:
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Not to pick an argument here 84, but....go to each of these links and click on specs then engine:
http://www.triumphmotorcycles.com/bikes ... /scrambler
http://www.triumphmotorcycles.com/bikes ... t100-black
http://www.triumphmotorcycles.com/bikes ... 5/thruxton
http://www.triumphmotorcycles.com/bikes ... peedmaster
etc... and you will find the firing interval listed for each of the motors. I would trust this substantially more than a wikipedia article I could edit right now to say otherwise :mrgreen:
and you will find that:
I'm also familiar with the concept of mechanical traction control and why yamaha chose to do the R1 with a cross plane crank. That started with dirt trackers building twingles and harley being very very competitive by changing the firing order on their V's. A 270 twin making 70 hp at the crank with good tires and proper suspension...does not need that sort of consideration you can really agressively ride one of those bikes and not be needing any sort of traction control to keep the rear wheel in check. There are also two firing order available for a 270 twin, one of which is more balanced, (which fires each piston on alternate rotations of the crank) and one which fires them 90 degrees apart. If I understand right, almost no commercially produced motorcycles chose the latter firing order.
Things change on dirt, and when traction is very very limited and the control of the rear wheel while sliding is critical.
Things also change when yamaha used it on the M1 (which is where they pulled the cross plane crank design from), which has ~250hp and weighs 330lbs. Even an R1 may benefit from that @ 180hp and 400lbs. A sluggish new bonnie certainly does not benefit from it in the same way.
http://www.triumphmotorcycles.com/bikes ... /scrambler
http://www.triumphmotorcycles.com/bikes ... t100-black
http://www.triumphmotorcycles.com/bikes ... 5/thruxton
http://www.triumphmotorcycles.com/bikes ... peedmaster
etc... and you will find the firing interval listed for each of the motors. I would trust this substantially more than a wikipedia article I could edit right now to say otherwise :mrgreen:
and you will find that:
midnightlamp said:
I'm also familiar with the concept of mechanical traction control and why yamaha chose to do the R1 with a cross plane crank. That started with dirt trackers building twingles and harley being very very competitive by changing the firing order on their V's. A 270 twin making 70 hp at the crank with good tires and proper suspension...does not need that sort of consideration you can really agressively ride one of those bikes and not be needing any sort of traction control to keep the rear wheel in check. There are also two firing order available for a 270 twin, one of which is more balanced, (which fires each piston on alternate rotations of the crank) and one which fires them 90 degrees apart. If I understand right, almost no commercially produced motorcycles chose the latter firing order.
Things change on dirt, and when traction is very very limited and the control of the rear wheel while sliding is critical.
Things also change when yamaha used it on the M1 (which is where they pulled the cross plane crank design from), which has ~250hp and weighs 330lbs. Even an R1 may benefit from that @ 180hp and 400lbs. A sluggish new bonnie certainly does not benefit from it in the same way.
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A 360 twin can use a balance shaft (or a pair if you want to reduce the rocking couple) to balance out the crankshaft quite a bit. On a non-balance shaft 360 twin with a 100% balance factor, at TDC and BDC the net momentum up/down from the piston velocity change is countered by the flywheel weight and at 90degrees before/after TDC/BDC there is an unbalanced lateral force from the same weight. With a balance shaft (which is geared to spin in the opposite direction) you can put a weight such that it counters this force using a 50% balance factor weight (and dropping the crank to 50% BF. End result would be that at TDC/BDC, the balance shaft weight and the crank weight (@ 50% each) would counter the vertical motion of the piston together, and at 90/270degrees the balance shaft weight and the crank weight (@50% each) would be pointing in opposite directions and counter each other. You can also do this same setup with a single. The issue is that this is a LOT of work, and spinning a small shaft @ 50% of the crank weight is a lot of loss as that shaft and the gear drive has inertia associated with it. The other issue is that this still doesn't result in a truly balanced single/360twin!
As for the Norton, the 270 does offer two unique advantages that aren't just "sound" based. One is that the engine balance is very good (with balance shaft), since the engine then has perfect primary balance, nearly perfect secondary balance, and a nearly regular firing interval, resulting in smooth running. The only unbalanced part is that the single balance shaft produces a rocking couple. However, the engine case is eating the imbalance, and taking extra load from the balance shaft...which is not great, and there is extra inertia from the balance shaft, which is also...not good. As for the second advantage, the pistons are never at rest so the power delivery is smoother at very low rpms, and there is less of a need for flywheel inertia to keep the engine running (which lets you run a smaller total inertial mass). While all of this sounds good, it's not really a cheap way to build a bike, nor does it really go with the whole "sort've like a commando" approach. It's very confusing that this much effort was put in on the bottom end of that bike, and they stuck with a pushrod top end.
Now before anyone takes this info as design guidance and people start calculating feet between power pulses and getting caught up in the engineering mind games...one should always take a step back and ask...."why really is too much vibration?" "why do I even want a parallel twin, as opposed to one of the other many engine arrangements" "why did norton swap the fork/caliper from the proper arrangement on the '84 to the backwards one of the '85". It's those basic questions (or at least two of them) that get you pointed in the right direction. People often forget that the reason why people liked parallel twins and singles is the power delivery and the reasonable vibes. A dynamically balanced single/twin is a very reasonable ride if set up right and I doubt anyone would really complain with a competently set up low displacement one, within a reasonable rev-range. Take away the simplicity...and you loose a lot of the good.
As for the Norton, the 270 does offer two unique advantages that aren't just "sound" based. One is that the engine balance is very good (with balance shaft), since the engine then has perfect primary balance, nearly perfect secondary balance, and a nearly regular firing interval, resulting in smooth running. The only unbalanced part is that the single balance shaft produces a rocking couple. However, the engine case is eating the imbalance, and taking extra load from the balance shaft...which is not great, and there is extra inertia from the balance shaft, which is also...not good. As for the second advantage, the pistons are never at rest so the power delivery is smoother at very low rpms, and there is less of a need for flywheel inertia to keep the engine running (which lets you run a smaller total inertial mass). While all of this sounds good, it's not really a cheap way to build a bike, nor does it really go with the whole "sort've like a commando" approach. It's very confusing that this much effort was put in on the bottom end of that bike, and they stuck with a pushrod top end.
Now before anyone takes this info as design guidance and people start calculating feet between power pulses and getting caught up in the engineering mind games...one should always take a step back and ask...."why really is too much vibration?" "why do I even want a parallel twin, as opposed to one of the other many engine arrangements" "why did norton swap the fork/caliper from the proper arrangement on the '84 to the backwards one of the '85". It's those basic questions (or at least two of them) that get you pointed in the right direction. People often forget that the reason why people liked parallel twins and singles is the power delivery and the reasonable vibes. A dynamically balanced single/twin is a very reasonable ride if set up right and I doubt anyone would really complain with a competently set up low displacement one, within a reasonable rev-range. Take away the simplicity...and you loose a lot of the good.
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