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Twin Cylinder Design Theory #727759
03/06/18 6:11 pm
03/06/18 6:11 pm
Joined: Feb 2018
Posts: 53
Oklahoma
T
Tracey Spear Offline OP
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Oklahoma
Here's a question for the true engine mechanics out there. This is something probably elementary I should know, but don't.

In the vertical twins, both pistons rise and fall at the same time, sometime firing both at the same time, sometimes alternating. But this design has inherent vibration that is difficult to balance out.

Why isn't the crank designed so that the pistons alternate? Wouldn't that balance out better?

Obviously there is something fundamental I'm missing.

Tracey

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Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727760
03/06/18 6:15 pm
03/06/18 6:15 pm
Joined: Aug 2001
Posts: 7,550
scotland
triton thrasher Offline
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No vertical twins fire together.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727761
03/06/18 6:25 pm
03/06/18 6:25 pm
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Posts: 7,550
scotland
triton thrasher Offline
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One up-one down (180 degree) four stroke twins have been sold in large numbers by Honda. Their old CD range of single carburettor twins in the 1960s were 360 degree, like a Brit twin, but the CB twin carburettor twins were 180 degree, for better balance. It's supposed to be hard to make a single carburettor work well on an uneven-firing twin, such as a 180 degree.

As well as wanting to sell single carburettor twins, the British factories believed that an even exhaust note was a selling point. The 250 Norton Jubilee is supposed to have been tried as a 180 degree twin, as a prototype, but reached the market as a 360.

A 180 degree twin evens out most of the up and down imbalance of the pistons changing direction, but balance is not perfect. The engine is rocked from side to side as its pistons change direction at top and bottom of their stroke. Also, two pistons changing direction at the same time in either type of twin takes a bit of energy out of the flywheel and gives the whole engine unit a kick in the opposite direction of rotation from that of the crankshaft.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727767
03/06/18 6:46 pm
03/06/18 6:46 pm
Joined: Feb 2018
Posts: 53
Oklahoma
T
Tracey Spear Offline OP
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Thanks Triton, nice reply

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727768
03/06/18 6:58 pm
03/06/18 6:58 pm
Joined: Feb 2018
Posts: 53
Oklahoma
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Tracey Spear Offline OP
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Oklahoma
Hey Triton! Since your name brought it to mind. What the hell's going on with three cylinders? Are they spaced 120 degrees?

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727771
03/06/18 7:20 pm
03/06/18 7:20 pm
Joined: Aug 2015
Posts: 1,248
Bolton Lancs UK
A
Andy Higham Offline
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The smoothest twin cylinder configuration is a 90 deg V twin, a "boxer" flat twin is also quite well balanced
As far as parallel twins go the 360 degree version is about as bad as it gets, the 180 degree twin has less primary vibration but secondary high frequency vibration can be a problem. Some people have had good results with crank pins spaced 90 degrees apart


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727772
03/06/18 7:30 pm
03/06/18 7:30 pm
Joined: Aug 2001
Posts: 7,550
scotland
triton thrasher Offline
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Originally Posted by Tracey Spear
Hey Triton! Since your name brought it to mind. What the hell's going on with three cylinders? Are they spaced 120 degrees?


BSA/Triumph triples were 120 degree.

Some Laverda triples were 180 degree: one up, two down.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727773
03/06/18 7:34 pm
03/06/18 7:34 pm
Joined: Aug 2001
Posts: 7,550
scotland
triton thrasher Offline
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My own 650 Triton doesn't feel bad until it gets well past 6,000 rpm and I don't do those revs often.

It "doesn't feel bad" but I did literally lose fillings from my teeth when I first put it on the road.

That's a 360 degree twin.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Andy Higham] #727785
03/06/18 9:02 pm
03/06/18 9:02 pm
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Posts: 2,742
New Hampshier USA
MikeG Offline

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Originally Posted by Andy Higham
The smoothest twin cylinder configuration is a 90 deg V twin, a "boxer" flat twin is also quite well balanced
As far as parallel twins go the 360 degree version is about as bad as it gets, the 180 degree twin has less primary vibration but secondary high frequency vibration can be a problem. Some people have had good results with crank pins spaced 90 degrees apart


My Hinckley Bonneville is called a 270 degree twin, any different than a 90 degree in terms of operation, or just a matter of reference between left and right cylinder? The bike is pretty smooth, but the balance shafts probably have a lot to do with that as well.


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727787
03/06/18 9:03 pm
03/06/18 9:03 pm
Joined: Aug 2012
Posts: 309
Hampshire, England
DoubleDiamond Offline
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I have a 280/80 crank for my A65. Unfortunately I haven't yet run it with the correct timing and camshaft as I bought it as a 270/90 crank!!

It has a 50% balance factor and sounds a bit like a V twin. It also had the Nova 5-speed gearbox fitted which was a dream in use.


BSA: '71 B175; '68 B25; '71 A65; '71 A75
Triumph: '87 T140; '72 T150v
Re: Twin Cylinder Design Theory [Re: MikeG] #727792
03/06/18 9:34 pm
03/06/18 9:34 pm
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scotland
triton thrasher Offline
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Originally Posted by MikeG

My Hinckley Bonneville is called a 270 degree twin, any different than a 90 degree in terms of operation, or just a matter of reference between left and right cylinder? .


They must think 270 degrees sounds more intriguing than 90.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727814
03/07/18 12:40 am
03/07/18 12:40 am
Joined: Nov 2012
Posts: 658
Isle of Wight, UK
K
koan58 Offline
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TT,

"One up-one down (180 degree) four stroke twins have been sold in large numbers by Honda. Their old CD range of single carburettor twins in the 1960s were 360 degree, like a Brit twin, but the CB twin carburettor twins were 180 degree, for better balance. It's supposed to be hard to make a single carburettor work well on an uneven-firing twin, such as a 180 degree."

As far as I know, all the early twins (C, CA, CB this and that) were 360 cranks. I got my initiation on a CD175, which was such. I suspect the CB175 was the earliest (Honda) experiment with a 180 crank.
My mate's CB175 certainly made me envious (schoolboys) due to its prettier styling, but almost identical in performance (my CD had long megas, can you imagine the noise at 10,000rpm?).

When they went to the CB200, it was back to 360, as were the others in the range.

For reasons only known to Honda, they played with 180's on their 450 and 500 twins around this time, I find this amusing:

"While not receiving much praise from critics and riders alike, Cycle World took note of its comfortable and roomy seat in its 1975 test, writing, "Unusual in that it is brown in color, it is long enough to carry a briefcase or passenger without crowding the rider. And the padding is soft enough for comfort. Believe us, without this seat you couldn’t ride a 500T very far and get off smiling.""

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727817
03/07/18 12:52 am
03/07/18 12:52 am
Joined: Nov 2012
Posts: 658
Isle of Wight, UK
K
koan58 Offline
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Isle of Wight, UK
"It's supposed to be hard to make a single carburettor work well on an uneven-firing twin, such as a 180 degree."

I don't know how real this is, many V-twins share a carb?

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727821
03/07/18 1:28 am
03/07/18 1:28 am
Joined: Nov 2012
Posts: 658
Isle of Wight, UK
K
koan58 Offline
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Isle of Wight, UK
" Tractors like hardleys' are probably ok."

Yes, I know where you're coming from. The first time I messed with one, was a homemade lowrider shovel, running dreadfully.

I'd never met such a system where its wasted spark could actually fire and damage the engine if the timing were way out.

I've yet to meet a Hardon Colluder who does his tappets and timing.

Re: Twin Cylinder Design Theory [Re: Les P] #727822
03/07/18 1:30 am
03/07/18 1:30 am
Joined: Aug 2001
Posts: 5,099
Stone Creek OH USA
R
Rich B Online happy

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Stone Creek OH USA
XS650 Yama was a 360 twin just like the Brit twins. It was also 75 X 74 mm stroke. Hands down, best 4 stroke twin from Yamaha in that era. It was also a tooth rattler. The crank was a pressed up crank like a 2 stroke. They could be made to rev.


Life is too short to drink cheap, bad beer.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727824
03/07/18 1:42 am
03/07/18 1:42 am
Joined: Nov 2012
Posts: 658
Isle of Wight, UK
K
koan58 Offline
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Definitely, a good solid bike. Kawasaki have done some similar since (W etc). Never popular with the crowd though.

Re: Twin Cylinder Design Theory [Re: NickL] #727829
03/07/18 2:09 am
03/07/18 2:09 am
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Stone Creek OH USA
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Rich B Online happy

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Yes, the XS650 could become a bit “fragile” when raced. The crank and rods were definitely a weak link.

Had a 750 version (Wiseco big bore kit) that ended up being the most spectacular blow up I have ever been involved with. You could see the transmission standing in front of the bike eek There was nothing left between the bottom of the cylinder head and top of the sump plate. Both rods were simply gone. Actually tweaked the one down tube where bits exiting the engine caught the front motor mount bolt on the bits road to freedom.

That was the end of my involvement with those engines for flat track.


Life is too short to drink cheap, bad beer.
Re: Twin Cylinder Design Theory [Re: Rich B] #727831
03/07/18 2:34 am
03/07/18 2:34 am
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Posts: 4,527
Owego, NY, USA
Mark Z Offline
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Originally Posted by Rich B
XS650 Yama was a 360 twin just like the Brit twins. It was also 75 X 74 mm stroke. Hands down, best 4 stroke twin from Yamaha in that era. It was also a tooth rattler. The crank was a pressed up crank like a 2 stroke. They could be made to rev.


I saw a lot of successful Yama flattrackers back in the seventies, XS650 engines bored to 750. One advantage they had over the Brit twins was a center bearing on the crank, which necessitated the pressed-up crank and horizontally-split crankcase. Yeah they could rev; I'm sure the OHC helped.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727845
03/07/18 3:09 am
03/07/18 3:09 am
Joined: Nov 2012
Posts: 658
Isle of Wight, UK
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koan58 Offline
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Just because an extra bearing in the middle looks like a good idea doesn't mean it is in practice.

Where in most Brit twins, crank flex is just accepted, the centre bearing in an AJS is trying to play "Kiing Canute" against the tide, in a parallel twin.

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727847
03/07/18 3:14 am
03/07/18 3:14 am
Joined: Jun 2013
Posts: 94
Texas, USA
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Ray Elliott Offline
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After my Brit bike business closed about '76 i went to work in the Honda & Yamaha business. Selling XS650s was a terrible chore & Yamaha forced them on the dealers. It really was easier to sell a Brit twin as the few buyers actually wanted one. The XS650 buyer really wanted a CB750 but hadn't the budget. Warranty claims were low & unlike Triumph/BSA/NVT Yamaha paid the dealer's claims.


Ray Elliott
---
A65, A70, A75, T120, T140, T150, T160
Re: Twin Cylinder Design Theory [Re: NickL] #727849
03/07/18 3:33 am
03/07/18 3:33 am
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Owego, NY, USA
Mark Z Offline
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Originally Posted by NickL
The other advantage was, they had rich owners or wealthy sponsors.



Ha, yes, I guess that's why I never heard about the blowups - they didn't hobnob with the renegades.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Twin Cylinder Design Theory [Re: Mark Z] #727864
03/07/18 11:13 am
03/07/18 11:13 am
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Stone Creek OH USA
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Rich B Online happy

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There were few XS650 based flat track bikes that were consistently competitive. The power delivery was a balance of having enough power and avoiding wheel spin. Usually wheel spin won. It took a unique rider to master the power delivery. There were precious few of those.

The ignition was always a crap shoot. The stock points cam drive was Mickey Mouse, the crank mounted units would work, but not consistently.

Cranks/rods were delicate. It took money to keep the bottom end alive. You had to have the crank welded to keep it from twisting under the stress of racing. Even with the crank pins tack welded to flywheel, the welds would break and the crank would twist. There were special rods, but even those, when available, had a finite life.

Yamaha and Kenny Roberts gave up on the engine. It hit a ceiling of development and there was no more to be had.

The engine had a brief run in flat track around the time of the demise of BSA/Triumph and the intro of the alloy XR750. But the XS run was brief. As the XR become more available and developed, the XS was done.

I will admit, the XS taught me a lot about chassis set up, ignition, timing, gearing, and tires in flat track. I got lots of practice finding a combination that allowed traction out of the corners. When it worked, the line between working and not working was incredibly thin.

An XR or Triumph was simple by comparison.


Life is too short to drink cheap, bad beer.
Re: Twin Cylinder Design Theory [Re: NickL] #727869
03/07/18 2:02 pm
03/07/18 2:02 pm
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Posts: 2,742
New Hampshier USA
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[quote=NickL]Another variation is the Twingle, firing one cylinder after the other using small crank offset angles.
Having used various offsets, yes the vibration and power area can be changed using different
offsets, the rod ratio and other factors need to be considered.

Thank you for that memory jog! I remember a few Puch/Sears Twingles around when I was younger, but never paid much attention to them. After a google search I see I missed something unique. I knew that the cylinders shared a common combustion chamber, but never knew they were not synched together.

Last edited by MikeG; 03/07/18 2:04 pm.

1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
17 Triumph Bonneville

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727887
03/07/18 6:28 pm
03/07/18 6:28 pm
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DMadigan Offline
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It sounds as though you guys are saying this is a waste of time?
[Linked Image]
[Linked Image]
I have not had the time to work on it of late. I have to have a head and cylinder cast up. Yes, I know JHill makes a cylinder but with an 80mm bore it would need 5/16" head bolts which in aluminum with the course thread means a 1/4" core to the bolts. I want through bolts into the cases by the four corner bolts.
I still have to change the rods to CR500. Otherwise the cylinder would have to be shortened by 3/4"!
I found an investment caster that is willing to work with me on the new triple clutch housings and this now seems a possibility.

90 deg. parallel twins change the vibration from vertical/horizontal to less vertical/horizontal with a rocking couple. Years ago I worked out the forces and moments on an A65 with 360, 180 and 90 deg. offsets.
Offset Force Moment
360 9174*w 0
180 4520 *w 690*w
90 3290*w 1159*w

Where w is the reciprocating weight of one cylinder.
On L twins the moment is reduced because the distance between cylinders is far less. On H*rleys (H*rlies?) the rods are coincident so there is no moment but weaker rods due to the fork and wobbly cranks due to the long throw. Ask how often XR750 cranks were rebuilt.
To the original question, a 360 crank is cheaper than 180 (both rod journals can be ground at the same time). Remember, BSA/Triumph were into cheap, not racers. Riders feel less of the horizontal vibration than vertical so balance factors were biased this way. Watch a Brit twin idling on the side stand. The front wheel oscillates fore/aft. A Japanese twin will show little movement.
The H*nda 250/350 six cylinder racers had pressed together cranks but seemed to hold together enough for Hailwood. Race engines always need more maintenance than a street engine.

Re: Twin Cylinder Design Theory [Re: DMadigan] #727892
03/07/18 7:47 pm
03/07/18 7:47 pm
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scotland
triton thrasher Offline
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Originally Posted by D Madigan
It sounds as though you guys are saying this is a waste of time?


The man that made time made plenty o' it.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727895
03/07/18 9:24 pm
03/07/18 9:24 pm
Joined: Aug 2001
Posts: 4,081
argyll. scotland, uk
gavin eisler Online content
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argyll. scotland, uk
The Velocette Roarer was a different twin, contra rotating cranks geared together, fllywheel bob weights cancel each other out, con rod waggles also cancel out.
link has a vid with sound.
http://www.classicbikeswapmeet.com/featured-bike-2015/


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727921
03/07/18 11:33 pm
03/07/18 11:33 pm
Joined: Apr 2005
Posts: 2,410
Bega NSW Australia
Mark Parker Online content
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Bega NSW Australia
An interesting thing about a 90degree configuration is the reduction in peak dynamic load by about 45% compared to the 360degree style. In effect giving a healthy increase in the cranks ability to sustain higher loadings. Such from increased rpm etc.

BSA/Triumph's early experimental DOHC 350s 180degree cranks were plagued with breakages until redesigned. It's hard to see from the limited drawings of the original but it has a central flywheel like the 360 style, and maybe they put just the one counterbalance on it rather than treating the two pins to their own counterweights as with the redesigned unit which fixed the problem.


mark
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727945
03/08/18 2:31 am
03/08/18 2:31 am
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DMadigan Offline
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Mark,was that the Turner 350 DOHC (the same "engineer" that stepped on valve springs with his heel to check strength)?
Nick, what makes a 90mm 90 deg EN40 crank legal and this not? I do not know what the latest AHMRA rules are. They seem to change by who is winning against the regulars. Are not those cranks "one off" or does someone have a quantity on the shelf? The only parts not modified from off the shelf are the pin for the crank offset and the middle bearing plate.
This bottom end might not interest most people but when the cylinder and head are done it gives another option for a 750cc A65 using a standard style crank.
The target is to have something different. Same with building the Wenco framed R3 racer.
How about an electric A65? Toss the crank and clutch, put in an electric motor, rebuild the cylinder as the radiator, hide the batteries in the fuel tank, controller in the oil tank. Just thinking.

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727955
03/08/18 3:49 am
03/08/18 3:49 am
Joined: Apr 2005
Posts: 2,410
Bega NSW Australia
Mark Parker Online content
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Turner. But I think it was D Hele that limited the hp because he didn't like the look of a tall head. The intakes were at a low angle with no metal in the casting to fix it. They had top guys spending heaps of time on it when it really needed redesigning around good ports. The best it gave was 34hp when high 40s should have been possible.


mark
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727965
03/08/18 6:54 am
03/08/18 6:54 am
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Posts: 2,410
Bega NSW Australia
Mark Parker Online content
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The Yamaha guys on their forum speaking of offsetting cranks bemoan the weakness of the centre bearing area?


mark
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727969
03/08/18 8:02 am
03/08/18 8:02 am
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DMadigan Offline
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Nick, not upsetting, just curious to what I perceived as a dislike for this modification over what has been done before. Higher RPM might be possible, but first the experiment. A four valve is possible. I already have one drawn. The disadvantage is finding a usable piston/valve set. With the two valve I have readily available parts from the XS. I have found 7mm stem auto valves as another source and about 1/3rd the cost of A65 valves.
Perhaps you did not notice that this crank is 90 degree.
Doug Hele tried an OHC on a triple and did not find any significant improvement. The problem was the ports, not the valve actuation method.
Four valves and water cooling would be fairly obvious for the scrutineers, yes? With this the only visible difference will be the corner through studs which can be "justified" by the larger bore weakening the cylinder near the base.
One thing that I do not understand is allowing an 8 valve Westlake or Norish head/cylinder for the Triumph but not one for the BSA? What difference does it make if it was not actually made back then. It could have been. The technology was there and Triumph did it eventually.
Mark, the centre bearing area is much wider on an XS with the two bearings and camdrive. I just have the single ball bearing.
The electric A65 would need a "breadbin" tank for the batteries.

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727974
03/08/18 9:35 am
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Triumph's modern 900 4valve head flows 180cfm an A65 head can easily do that without the port being particularly huge, and bolt straight on. For a 744 to make power to 8500rpm you only need around 160cfm-170cfm and a stock cam. If you wanted to run over 9,000rpm 180-190cfm and stock cam would do it. 200cfm for power at 10,000rpm if you want to go there, and I'd be all for that, it would be nice to see how it sounded.

I made alloy cyls with a particularly strong area around the flange they are thick everywhere, the cut outs for the base nuts go in closer but it's more likely to break the case than cyl, why I had the breather hole welded up and a brace fitted, And have the breather through the primary case like a T140.


mark
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #727977
03/08/18 11:05 am
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In 1972 BSA three talented men were working on a planned 750 twin with a well designed 4 valve head, they were testing it as just one cyl and it was making 46hp. It shows what a difference well designed breathing makes, a 350 single making 12-14hp more than the 350 twin.

In 1971 BSA were winning in all forms of motorcycle competition, F750, MX, 24hr Endurance, flat track. The F750s were very exotic, imagine if BSA had stayed in the industry to put a 92hp smooth running 750 onto the market in 1973-4.


mark
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #728180
03/10/18 2:59 am
03/10/18 2:59 am
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There is a lot more to it than just primary vibrations which can easily be cancelled out over a specific rev range with counterbalances.
In fact the BSA crank does balance out fairly well between 4000 & 6000 rpm.
Other considerations are things like rocking couples which on anything other than a 360 twin can be far more difficult to manage.
Then there is induction balance, not a factor with a carb per cylinder but a big problem with single carbs.
You also have to consider the plane of the vibrations, front - back, up - down, get them wrong and the bike becoms unrideable .
A 360 twin is vibration wise a big single and what works with singles was fairly well known .
We also tend to forget that now days we have computer modeling so can work out vibrations on different engine layouts in 0.01 deg increments , in real time watching the screen.
back in the day this was a job for a team of engineers working with slide rules and took days for each configuration.
Then the new design had to be made in metal and tested, this was not cheap.
Post WW II profit levels on motorcycle plummeted which is one reason why a lot of companies closed up shop


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Trevor
Re: Twin Cylinder Design Theory [Re: BSA_WM20] #728196
03/10/18 9:09 am
03/10/18 9:09 am
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Originally Posted by BSA_WM20
There is a lot more to it than just primary vibrations which can easily be cancelled out over a specific rev range with counterbalances.

"Easily" is an optimistic statement. You can counterbalance all of the primary imbalance, but you're introducing a roughly equal imbalance at right angles to the imbalance you corrected. So, you only partially balance the reciprocating parts (% balance factor) and go for a ride, to see how it feels.


Quote

back in the day this was a job for a team of engineers working with slide rules and took days for each configuration.
Then the new design had to be made in metal and tested, this was not cheap.


Drilling and plugging the flywheels is relatively cheap, I'd say. Sometimes the makers didn't bother with proper testing and just kept the same balance factor as some previous model.

Quote
Post WW II profit levels on motorcycle plummeted which is one reason why a lot of companies closed up shop


The Brit factories went from a captive market immediately post-War, to a collapse in the UK home market after 1959, as normal people stopped using motorbikes as everyday transport.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: Tracey Spear] #728374
03/12/18 7:47 am
03/12/18 7:47 am
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[quoteDrilling and plugging the flywheels is relatively cheap, I'd say. Sometimes the makers didn't bother with proper testing and just kept the same balance factor as some previous model.
][/quote]

Engine has to come out of the frame then get the cases spilt then have the work done on the crank then reassembled and put back in a frame then taken out for testing.
Not cheap in any sense of the word. so we are talking about what 3, 4, 5 man days which equates to the gross profit on how many machines?
Then do this a dozen or more times and your seasons profit from that model can vanish before your eyes.
This is the justification to supporting racers with factory special machines or parts that they will fit & test for free.

Now days we can shove the crank on a machine, spin it up and get a dynamic balance at a variety of engine speeds.
Back in the day it was all calculations & seat of the ( testers) pants .

And as you know it is not just a case of drilling a hole 1/2" deeper .
To get the balance dynamically stable oft it is many holes in very precise locations.
I have never had crank dynamically dalanced but have done a few statics.
A flat mate got his Honda 4 crank dynamically balanced and there were small holes every where.


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Trevor
Re: Twin Cylinder Design Theory [Re: BSA_WM20] #728418
03/12/18 5:53 pm
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Originally Posted by BSA_WM20
Originally Posted by me
Drilling and plugging the flywheels is relatively cheap, I'd say. Sometimes the makers didn't bother with proper testing and just kept the same balance factor as some previous model.


Engine has to come out of the frame then get the cases spilt then have the work done on the crank then reassembled and put back in a frame then taken out for testing.
Not cheap in any sense of the word. so we are talking about what 3, 4, 5 man days which equates to the gross profit on how many machines?
Then do this a dozen or more times and your seasons profit from that model can vanish before your eyes.
This is the justification to supporting racers with factory special machines or parts that they will fit & test for free.


Have you moved on to a subject other than makers finding a suitable balance factor to routinely use on the cranks they built, for the bikes they sold to the public?

Triumphs at one time experimented with different weights of plug in a threaded hole in the flywheel. They changed the plug through an access in the crankcase and rode the bike round a test track. Then they came into the pits and tried a different plug and rode it again, just to see if the vibration was better or worse.

Do you disagree that is a quick, easy and cheap way to test different balance factors?

Quote
Now days we can shove the crank on a machine, spin it up and get a dynamic balance at a variety of engine speeds.
Back in the day it was all calculations & seat of the ( testers) pants .

And as you know it is not just a case of drilling a hole 1/2" deeper .
To get the balance dynamically stable oft it is many holes in very precise locations.
I have never had crank dynamically dalanced but have done a few statics.
A flat mate got his Honda 4 crank dynamically balanced and there were small holes every where.


Nobody could ever dynamically balance a crankshaft with calculations or the seat of their pants.

Static balance adjustment can certainly be a case of drilling a hole deeper and/or wider.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: triton thrasher] #728425
03/12/18 7:30 pm
03/12/18 7:30 pm
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Originally Posted by triton thrasher
Triumphs at one time experimented with different weights of plug in a threaded hole in the flywheel. They changed the plug through an access in the crankcase and rode the bike round a test track. Then they came into the pits and tried a different plug and rode it again, just to see if the vibration was better or worse.

I suspect this was a fairly common practice in the industry, and possibly even by racers. Phil Irving notes in "Tuning For Speed" that drilling and plugging tapped holes in the crankcase allows for the simple addition or removal of flywheel weights to experimentally determine a suitable balance factor.

Re: Twin Cylinder Design Theory [Re: Tracey Spear] #728435
03/12/18 10:21 pm
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Tungsten's density 2.5 times that of steel would make it a popular material for the inserts.


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Re: Twin Cylinder Design Theory [Re: triton thrasher] #728458
03/13/18 3:58 am
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Quote
The Brit factories went from a captive market immediately post-War, to a collapse in the UK home market after 1959, as normal people stopped using motorbikes as everyday transport.


So that puts me very much in the abnormal category


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Trevor
Re: Twin Cylinder Design Theory [Re: triton thrasher] #728459
03/13/18 4:03 am
03/13/18 4:03 am
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Quote
Triumphs at one time experimented with different weights of plug in a threaded hole in the flywheel. They changed the plug through an access in the crankcase and rode the bike round a test track. Then they came into the pits and tried a different plug and rode it again, just to see if the vibration was better or worse.

Do you disagree that is a quick, easy and cheap way to test different balance factors?


OK I will go stand in the dunces corner with the tall funny hat on.
Not a set up I had considered or even though about.


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Trevor
Re: Twin Cylinder Design Theory [Re: BSA_WM20] #728460
03/13/18 6:25 am
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Originally Posted by BSA_WM20
Quote
Triumphs at one time experimented with different weights of plug in a threaded hole in the flywheel. They changed the plug through an access in the crankcase and rode the bike round a test track. Then they came into the pits and tried a different plug and rode it again, just to see if the vibration was better or worse.


Not a set up I had considered or even though about.


Do you fancy trying it, or at least the drilling part?

A Pre-unit Triumph, for instance , has quite good access to the flywheel, from underneath.


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Re: Twin Cylinder Design Theory [Re: NickL] #728462
03/13/18 6:31 am
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Originally Posted by NickL
Yes, tungsten is what is normally used. BUT it is normally welded in not tapped and screwed.
With something like a vinnie where you can go across the crank, not so bad but screwing a
1/2 inch or so plug into the circumference of an iron flywheel then spinning it to 7k or so may
cause a few mishaps. Not so bad with steel but it's the fact that iron likes to explode in that
sort of situation that would concern me.


That makes sense. Adding something permanent, that could find its way out and hit the cases, would be unwise.

I think J Healy said that Triumph, in their latter days, didn't bother rebalancing for the 1971 frame, or the 750 engine.

I also think it was Frank Damp who said that Norton sent Atlas cranks out to a contractor for balancing and the contractor just drilled a few credible-looking holes and sent them back, without doing any actual balancing.


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