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#526201 - 02/03/14 10:20 am On A65 motor, 90 degree crank Vs 270 degree crank.  
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Allan Gill Offline
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I am posting this here as I think it will generate more interest, also this is what I am considering with my to-be LSR motor (unless someone can tell me that I can't run it in the 650 pushrod class)

Here are my understandings of the 2 setups, I don't doubt that I have it all wrong so my mind is open to being corrected.

Firstly (not that it matters much to the assembly side, but something I'd like cleared up)

The figure of 90 degrees is:
The relation of the big end, being in relation to the crank centre point and little end (when the opposing cylinder is at TDC) that 90 degree point is measured at the big end

and not - the big ends are at 90 degree intervals to each other, with the 90 degree point being measure at the cranks centre point


(If this isn't clear, I will do a drawing demonstrating what I mean)

Moving on.

With a 90 degree (firing order) Piston one comes to centre, fires and then Piston two comes to centre and fires, you then have 2 consecutive exhaust strokes. In my mind its function is similar to that of a single cylinder but with the offset stroke advantage.

With a 270 degree (firing order) you still have 2 consective firing strokes and exhaust strokes like with the 90 degree, but as its firing order is closer to that of the 360 degree parallel twin but again with the advantage of having the off set crank.

I can imagine there are possibly torque gains with the 90 degree and RPM gains with the 270 degree???? either way they have a reputation for being smoother at higher RPM.

The advantage of having the off set crank is: with a parallel crank, both pistons are reaching point of TDC at the same time, slowing down as it reaches the change of direction (upwards forces to downward forces)
With the off set crank, Piston two is accelerating as Piston one is reaching TDC, the force of the second piston reduces the slowing down forces which are inherent with a parallel crank.

Many thanks for your time.


beerchug
#526209 - 02/03/14 10:57 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Running from demons in WNY
ECTA and SCTA have no restrictions on crankshaft, firing order, bore and stroke so long as the displacement is with in the class.
LSR on pavement is a long drag race LSR on non pavement is a bit less of sprint off the line due to traction problems.
If a different crankshaft phasing is a power advantage at high rpm then it can be useful.


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#526238 - 02/03/14 1:24 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Yer I can imagine the salt is a PITA for traction, however at such a long running range, any added torque from either configuration can mean running higher gearing and probably mean slipping the clutch more anyway - I wouldn't like to pretend I know anything as I haven't got the foggiest.

Good though with the regulations, I would like to fit a Norish crank (possibly one piece/billet???) in time, when they get up and running and I get a bit less poorer grin


beerchug
#526245 - 02/03/14 2:10 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Two Alpha Offline
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Originally Posted By: Allan Gill
I can imagine there are possibly torque gains with the 90 degree and RPM gains with the 270 degree????

I don't think that will be the case Allan, any torque/rpm gain/loss should be the same for either.
As I see it, the main difference between the two is which piston goes through TDC 90 degrees in front of the other one.

Just make sure your cam and the crank are twisted the same way. smile

edit: Fascinating stuff really, some good info here. Smoothness

Last edited by Two Alpha; 02/04/14 1:41 pm.

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#526248 - 02/03/14 2:33 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Two Alpha]  
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Allan Gill Offline
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Originally Posted By: Two Alpha


Just make sure your cam and the crank are twisted the same way. smile


Yes, I can see that getting very painful very quickly.

Is there any advantage between the 2 types? Or am I making assumptions out of nothing??

I'd happily avoid a 180 crank as used on the cb Honda engines. Everything about the ridding and running was just wierd.


beerchug
#526250 - 02/03/14 2:39 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Ger B Offline
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NL
Quote:
I don't think that will be the case

At marine engineers school in the 19-sixties we had to calculate torque [Nm] and power [kW] out bore, stroke of the engine and the measured average pressure of the running engine.
In the formulea we just added all piston top area's irrespective of the position of the cranks in relation to oneanother.
So a twin with a certain bore and stroke has twice the torque of a single with the same bore and stroke.

Ofcourse these are average values over the course of the revolution.

Don't ask too much details and difficult questions please. The last time I measured pressures and calculated, was on board in the 19-seventies. Shi... we do not have a grey hair smily.


Ger B

#526255 - 02/03/14 2:48 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Al, Moto Guzzi 90 degree twins fire at 270 and 450 degrees of crank rotation. My 1000 Guzzi goes smoother with higher revs.
And the sound,so gutsy....


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#526318 - 02/03/14 7:55 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: NickL]  
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Originally Posted By: NickL


Offset crank is the way to go but 90 degs? why? is it so it's easy to set up on an auto? because cams are easily available?
Why didn't Phil Irvine at Vincent use 90 degs? it would have been easier. Don't quote modern triumphs at me either 'cos they have balance shafts etc.

Nick


Maybe Irving wanted a compact engine? And narrow V's were more common engineering then...90 degree engines are long like the older Ducati.. or wide if mounted at a right angle to the frame.
I believe in theory 90 degrees gives best balance...But in reality something around 76 degrees works almost as well with less bulk.
And also the frame is important as some designs are better at resolving vibration.


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#526369 - 02/04/14 4:12 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Smooth would be nice but not a necessity. Just as long as it doesn't shake itself into pieces.

Power gains over a 360 crank are what I am after.


beerchug
#526371 - 02/04/14 5:30 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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What Allan has stated in his first post is not a 90 degree crank as such but a "whatever it is to get the correct tangential relationship" degree crank. ie 76deg in a triumph twin etc.
but as this changes with stroke and rod length etc Allan explained it as a relationship between the crank centre point, big end and little end being at 90 degrees in relation to each other when the other piston is at TDC.

Personally I doubt anyone would know any difference between this and a crank twisted to fire exactly 270 / 450 but nothing wrong with details.

As to firing intervals, I think a 90 / 630 would shake your balls off at high speed and play havoc with the primary drive. The idea is to keep the crank acceleration and deceleration loads as constant as possible, this would not seem to be logical in a 90/630 but may I be wrong.

Good luck Allan,
Julian


Royal Enfield Works Trials
BSA Super Rocket Scrambler
BSA Gold Star Scrambler
Triumph Bonneville 1966
Laverda 750SF
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BSA Rocket 3
Norton Commando 850
Moto Morini 3-1/2 Sport
Moto Guzzi Le Mans 1
Ducati MHR 1980
#526377 - 02/04/14 7:18 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Pete R - R.I.P. Offline
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The crank you're decribing would be about 76.35 degrees offset for an A65.That's OK from a momentum point of view,where one piston is stopped and the other is moving at maximum piston speed.It would allow the engine to idle with the least amount of flywheel inertia.Flywheel inertia is not a bad thing to have,for other reasons.

This won't give you the least amount of imbalance.When the 2 cylinders are each 38 degrees from TDC,the total imbalance is still quite high.Going to a 270 degree crank will reduce total imbalance.

You'll probably get a word from Mark Parker soon,telling you this is the way to go.It works well for him.

There is no way that this can actually produce more torque or power,although it might give that illusion to the rider.

#526383 - 02/04/14 8:32 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Pete R - R.I.P.]  
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Julian Offline
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Originally Posted By: Pete R

There is no way that this can actually produce more torque or power,although it might give that illusion to the rider.


Absolutely correct.
Although it can make the power more useable also.

I would have thought that a nice heavy flywheel would / May be the way to go and a good thing for a speed record bike that does not need to accelerate at lightning knots. (nor can do due to grip)

Julian


Royal Enfield Works Trials
BSA Super Rocket Scrambler
BSA Gold Star Scrambler
Triumph Bonneville 1966
Laverda 750SF
Laverda "1000"SF
BSA Rocket 3
Norton Commando 850
Moto Morini 3-1/2 Sport
Moto Guzzi Le Mans 1
Ducati MHR 1980
#526416 - 02/04/14 12:50 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Allan Gill Offline
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I know Pushrod Tom always recommends not reducing flywheel weight when used for this application.

On a track bike I can see the benefits of the lighter crank.

Julian, good to hear you again, how is the A10?


beerchug
#526424 - 02/04/14 2:12 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Pete R - R.I.P.]  
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Originally Posted By: Pete R
The crank you're decribing would be about 76.35 degrees offset for an A65.That's OK from a momentum point of view,where one piston is stopped and the other is moving at maximum piston speed.It would allow the engine to idle with the least amount of flywheel inertia.Flywheel inertia is not a bad thing to have,for other reasons.

This won't give you the least amount of imbalance.When the 2 cylinders are each 38 degrees from TDC,the total imbalance is still quite high.Going to a 270 degree crank will reduce total imbalance.

You'll probably get a word from Mark Parker soon,telling you this is the way to go.It works well for him.

There is no way that this can actually produce more torque or power,although it might give that illusion to the rider.


Pete, so you're saying a 90 degree crank has the least imbalance and there's no top end power difference between a 360 degree crank and 90 ---76 degree crank?


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#526502 - 02/05/14 3:48 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Hillbilly bike]  
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Originally Posted By: Hillbilly bike
Originally Posted By: Pete R
The crank you're decribing would be about 76.35 degrees offset for an A65.That's OK from a momentum point of view,where one piston is stopped and the other is moving at maximum piston speed.It would allow the engine to idle with the least amount of flywheel inertia.Flywheel inertia is not a bad thing to have,for other reasons.

This won't give you the least amount of imbalance.When the 2 cylinders are each 38 degrees from TDC,the total imbalance is still quite high.Going to a 270 degree crank will reduce total imbalance.

You'll probably get a word from Mark Parker soon,telling you this is the way to go.It works well for him.

There is no way that this can actually produce more torque or power,although it might give that illusion to the rider.


Pete, so you're saying a 90 degree crank has the least imbalance and there's no top end power difference between a 360 degree crank and 90 ---76 degree crank?


Vibration is a funny old thing Mike as I am sure you know well,
In "theory" if it vibrates less it is giving more power as vibrations are a product of energy dissipation, However, just because our "seat of the pants" says it vibrates less, it does not mean it actually does, maybe it's just spread out differently, or in a different vector etc. or even if it does vibrate less the power gain from this alone would be un-measurable in real terms.
Power is "as Mike Duckworth summed up" the Size of the bang times the number of bangs per minute. Balancing or phasing does not change this! It may tame it though, or allow an engine to rev more and thus give more power as a secondary result.

Hi Allan,
A10 on the side-lines due to work and other projects but running well, Better and better as I slowly run it in with my limited time available. Sorting some tiny improvements etc. Will power test it soon hopefully but it goes like hell.

Looking forward to seeing this project take shape!

Best regards,
Julian


Royal Enfield Works Trials
BSA Super Rocket Scrambler
BSA Gold Star Scrambler
Triumph Bonneville 1966
Laverda 750SF
Laverda "1000"SF
BSA Rocket 3
Norton Commando 850
Moto Morini 3-1/2 Sport
Moto Guzzi Le Mans 1
Ducati MHR 1980
#526510 - 02/05/14 7:01 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Julian]  
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Running from demons in WNY
So.....if different crankshaft phasing offers no power advantage at high rpms....Then for limited duration racing like drag or LSR where vibration isn't an issue,...there's nothing to be gained for spending 2000 bucks on a new crank and special camshafts.....Unless you need to buy a new billet crank for durability or stroking for more displacement...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#526515 - 02/05/14 7:59 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Hillbilly bike]  
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Only in so much as it "may" allow you to run a higher RPM, or give some other secondary gain to allow you to achieve more power through normal means.

In short, You hit the nail on the head.

Julian


Royal Enfield Works Trials
BSA Super Rocket Scrambler
BSA Gold Star Scrambler
Triumph Bonneville 1966
Laverda 750SF
Laverda "1000"SF
BSA Rocket 3
Norton Commando 850
Moto Morini 3-1/2 Sport
Moto Guzzi Le Mans 1
Ducati MHR 1980
#526639 - 02/05/14 9:43 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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The strength factor in racing is a big factor and can't be ignored.


beerchug
#526670 - 02/06/14 3:49 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Fully agree Allan,
Strength is usually one of the best "investments" you can make on any race / performance type engine.

Good thread this, looking forward to seeing how it goes together.

Julian.


Royal Enfield Works Trials
BSA Super Rocket Scrambler
BSA Gold Star Scrambler
Triumph Bonneville 1966
Laverda 750SF
Laverda "1000"SF
BSA Rocket 3
Norton Commando 850
Moto Morini 3-1/2 Sport
Moto Guzzi Le Mans 1
Ducati MHR 1980
#526672 - 02/06/14 4:12 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Allan Gill Offline
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Could be a good while off before it becomes an engine. Funds have dried up cry


beerchug
#526680 - 02/06/14 6:03 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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90+270= 360 they are the same offset depending how you look at it. I think it reduces load on the crank, std stroke versions can be quite smooth at rpm probably similar to a triple, that is a big advantage if you tune it for power at similar RPM levels they have similar strokes and the A65 head is probably better to work with. It seems to have a disproportional advantage with a 79-80mm bore, probably because it effects the breathing window with big valves. I use 44.5 inlets with 39 to 40mm exhausts. 90 or other similar offset cranks have a drive advantage and can be lighter while retaining flywheel effect probably difficult to measure on a dyno unless two motors had the exact same specs. A combination of exhausts head carbs cam and compression is what you need to juggle to get best power and the higher up the rpm range, that can stay together and be usable, the more power you will get in theory.


mark
#526681 - 02/06/14 6:09 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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Mark Parker Offline
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PS if you build a 90deg you will want to use it for your street motor.


mark
#526696 - 02/06/14 8:39 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Mark Parker]  
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Allan Gill Offline
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Originally Posted By: NickL
Originally Posted By: Mark Parker
PS if you build a 90deg you will want to use it for your street motor.



That's where the fun starts,,,, My license can't stand any more 'Nicks' and it's been that way for bloody years!
The 12 point system over here sucks! so do the coppers!

Nick


Sounds like the UK! Would I be right thinking your an ex-pat?

Originally Posted By: Mark Parker
PS if you build a 90deg you will want to use it for your street motor.


It might get some use on the street, can't keep a bike standing for too long grin

Originally Posted By: Mark Parker
90+270= 360 they are the same offset depending how you look at it. I think it reduces load on the crank, std stroke versions can be quite smooth at rpm probably similar to a triple, that is a big advantage if you tune it for power at similar RPM levels they have similar strokes and the A65 head is probably better to work with. It seems to have a disproportional advantage with a 79-80mm bore, probably because it effects the breathing window with big valves. I use 44.5 inlets with 39 to 40mm exhausts. 90 or other similar offset cranks have a drive advantage and can be lighter while retaining flywheel effect probably difficult to measure on a dyno unless two motors had the exact same specs. A combination of exhausts head carbs cam and compression is what you need to juggle to get best power and the higher up the rpm range, that can stay together and be usable, the more power you will get in theory.

Many thanks for your input Mark,
That was roughly my assumption, but its good to get it from first hand as opposed to my guessing. Although both versions of the crank are 90 degrees either way, it was the firing intervals that got my interest and the wonder how one would better over another in various circumstances. I hadn't really thought about flywheel weight, but I guess because of any increased inertia you could very well be right - a lighter flywheel could accelerate quicker! Taller gearing and the use of Monoblocks or GP's would/could hamper any off the line issues.


beerchug
#527224 - 02/09/14 1:58 pm Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: NickL]  
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Two Alpha Offline
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Originally Posted By: NickL
Having ridden BSA A65 based versions with 360 deg, 68 deg, 76 deg, 180 deg. Norton cranks and various piston and rod arrangements i still think that the 68 deg version of the set worked best. All the technical sides of things point to it as well (with long rods). Rotational acceleration, rod ratio etc.
What's the story/theory behind the 68 deg. version? It doesn't seem to fully mesh with the theory behind either the 90 degree, or Phil Irving's 76 degree. Are you able to share it's stroke, and rod length?

Originally Posted By: NickL
Offset crank is the way to go but 90 degs? why? is it so it's easy to set up on an auto? because cams are easily available?
As I understand it, the 90 deg crank has better overall balance. At any given rpm, when either piston is momentarily stationary at tdc or bdc, the other piston will be going the same speed no matter which of the other positions it is at. Not quite maximum speed, but close.
With the 76 degree crank, when either piston is momentarily stationary at tdc, the other piston will be moving at maximum speed (crank throw to rod angle is 90 degrees). This is the optimum situation to combat the inertia created by the momentarily stationary piston.
The downside to the 76 degree crank is that when either piston is at bdc, the other piston will be moving at quite a bit less than maximum speed (crank throw to rod angle is 62 degrees). The 76 degree crank would have more variation in the momentum of the flywheel than the 90 degree crank, more vibration.
It's too bad you hadn't also ridden a 90 degree for comparison.

Originally Posted By: NickL
Why didn't Phil Irvine at Vincent use 90 degs? it would have been easier.
Hard one to answer, hope it wasn't because he just overlooked doing the calculations for bdc. I don't recall having seen his write-up on the 76 degree, have to track that down and give it a good read. Perhaps his determination was that the trade-off was worth it. Either way, it's a shame that Triumph rejected his tremendous idea. They could have done a small limited run to test the waters, the buying public would have made the right choice easy for them.

Thanks for all your posts Nick, very interesting stuff.


BSA
Matchless
Triumph
#527476 - 02/11/14 8:24 am Re: On A65 motor, 90 degree crank Vs 270 degree crank. [Re: Allan Gill]  
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The rod length compared to the stroke I think had a bearing on Phil's calculated angle. My 90deg needed to be rubber mounted to be smooth. I couldn't guess at which offset would be better. 90 degree is less confusing to plot out and set up ignitions. The latest port alterations I made have a really nice effect, really suits using it on the road. There's a corner on my way home from work, 2nd gear, low RPM, it curves for nearly 180deg before switching back, probably go into it at 50-55MPH and accelerate through while banked well over, the amount of power and control the throttle gives plus the sound reflected from both pipes on the side near the ground, is pretty fun. I used to have a fairly fast 855 then 880cc T150V but there was no way it could punch out of a corner like this thing, and I'm sure the offset crank angle contributes.


mark
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