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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: 3,868
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
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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: 2,380
Bega NSW Australia
Mark Parker Offline
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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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Posts: 3,700
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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
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Bega NSW Australia
Mark Parker Offline
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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
Joined: Apr 2005
Posts: 2,380
Bega NSW Australia
Mark Parker Offline
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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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Posts: 3,700
ca, us
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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
03/08/18 9:35 am
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Posts: 2,380
Bega NSW Australia
Mark Parker Offline
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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
03/08/18 11:05 am
Joined: Apr 2005
Posts: 2,380
Bega NSW Australia
Mark Parker Offline
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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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Sydney Australia
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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


Bike Beesa
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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scotland
triton thrasher Offline
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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
Joined: May 2004
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Sydney Australia
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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.


Bike Beesa
Trevor
Re: Twin Cylinder Design Theory [Re: BSA_WM20] #728418
03/12/18 5:53 pm
03/12/18 5:53 pm
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Posts: 7,419
scotland
triton thrasher Offline
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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
Joined: Oct 2001
Posts: 1,137
Sydney, Oz
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Shane in Oz Offline
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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
03/12/18 10:21 pm
Joined: Aug 2001
Posts: 7,419
scotland
triton thrasher Offline
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Tungsten's density 2.5 times that of steel would make it a popular material for the inserts.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: triton thrasher] #728458
03/13/18 3:58 am
03/13/18 3:58 am
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Sydney Australia
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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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Sydney Australia
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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
03/13/18 6:25 am
Joined: Aug 2001
Posts: 7,419
scotland
triton thrasher Offline
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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.


Amateur Loctite enthusiast.
Re: Twin Cylinder Design Theory [Re: NickL] #728462
03/13/18 6:31 am
03/13/18 6:31 am
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scotland
triton thrasher Offline
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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.


Amateur Loctite enthusiast.
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