80 HP at 8700RPM by Herb Becker

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Fast Eddie said:
I picked up on your point that: ' It really makes no difference whether it is a heavy flywheel or a heavy rear wheel that adds mass to the system since any component subject to angular acceleration (shafts, gears, hubs, rims, etc) affects the system in the same way'.

Now, I'm not gonna do your water tyre experiment! But many modern bike mags have agreed on the results of fitting lighter carbon fibre wheels to bikes and all note, state, record faster acceleration as a result.
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Absolutely, lighter wheels can make a significant difference. I experienced this first hand decades ago when my brother had a vintage European 10 speed bicycle with steel wheels and utility tires on it. He fit alloy wheels and some light tires and it was startling how fast you could accelerate and how responsive the bike was after the wheel/tire change. Totally transformed the bike.
 
The point of the "minutiae" discussion was headed towards the ability to analyse the crankshaft speed graphs with
various weights of flywheels, and even wheels, on test on a dyno....

I've had a few lightweight bicycles, and a heavy one or two. With such contrivances, you'd have to be careful that
lighter wheels were contributing to an overall considerably lighter bicycle, its not just flywheel weight coming into play here.
I've not had a bicycle on a dyno though, I'd have to say.....
 
The wheel mass affects the way the wheel precesses (gyroscopic effect) when you turn it about the vertical axis. This is the reason that the 750 Vtwin Moto Guzzis tend to mishandle when they are turned by the rider. The inline crank tends to make the front of the bike rise and fall as the crank is turned when spinning.
 
Presumeably thats why the Dr John Guzzi could win the Battle of the Twins at Daytona ?
The racing dentist...

80 HP at 8700RPM by Herb Becker


And why the Reg Pridmore R90S did so well.

But we diverge, muchly.....
 
acrotel wrote;
The inline crank tends to make the front of the bike rise and fall as the crank is turned when spinning.
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Eeerrmm I'm not aware of that on my Guzzi. The longtitudinal crank might rock the machine to the right when blipping the throttle when stationary, but this isn't noticeable to the rider when the machine is rolling! Although it's effects are obviously influencing the machine all of the time as stated below.

Taken from Wiki;
Longitudinal crankshaft mounting is associated with a torque reaction that tends to twist the motorcycle to one side on sharp acceleration or when opening the throttle in neutral and in the opposite direction on sharp deceleration. Many modern motorcycle manufacturers correct for this effect by rotating flywheels or alternators in the opposite direction to that of the crankshaft.[
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Reggie said:
acrotel wrote;
The inline crank tends to make the front of the bike rise and fall as the crank is turned when spinning.
Click to expand...

Eeerrmm I'm not aware of that on my Guzzi. The longtitudinal crank might rock the machine to the right when blipping the throttle when stationary, but this isn't noticeable to the rider when the machine is rolling! Although it's effects are obviously influencing the machine all of the time as stated below.[
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Having ridden an old 850 Le Mans, I can confirm that the V twin Moto Guzzi were notorious for compressing the rear suspension when the throttle is suddenly shut off –you didn’t get it when ridden gently though :!:
 
Back in the 1980s or 1990s there was a crazed Hydrogen Peroxide, rocket drag bike. I can't remember the riders name. Some people told him that his rear tire was burning rubber. This couldn't be because the R wheel was free-wheeling like the front wheel - being a rocket propelled bike. Then they showed him photos. It turned out the the bike was accelerating so quickly that the Rear tire couldn't spin up fast enough to keep up with the bike - so it was lagging behind and burning rubber. He went to a smaller lighter R tire to fix that problem - it spun up quicker and didn't smoke. This is an extreme example of unwanted flywheel effect.

I also saw a photo of him defining the rules and the officials by making a run without a helmet with only one hand on the bars - the other hand held up in a defiant fist. His antics got him banned from the events - made him a bit of a hero for me.
 
Bernhard said:
Having ridden an old 850 Le Mans, I can confirm that the V twin Moto Guzzi were notorious for compressing the rear suspension when the throttle is suddenly shut off –you didn’t get it when ridden gently though :!:
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Still having an old LeMans in my collection, although its a while since its been ridden :(, and having owned a few BMs and other shafties,
I can confirm that shafties do rise and fall with throttle. Its the sitting DOWN on the suspension thats the problem - when braking hard approaching sharp corners.
Race schools teach you to hold a little bit of throttle while braking right into such corners, so it doesn't sit down.
They also teach to hold a little rear brake while accelerating out of such corners.
Also mostly applicable to chain drive bikes going fast.
But you all knew that anyway....

I'd also comment that the LeMans is the most planted feeling bike on the road I've ever ridden, it never did anything unusual or scary or bad to me.
That heavy clutch and throttle and gearchange is a bit agricultural though, you have to work at riding it = not as fun as a Commando.

My, we have diverged a long way from Herbs bike.
 
P.S. When you do the math, two identical engined bikes, one with heavy flywheel and one with light flywheel, have to have done the same amount of work* to cover the same ground - the ole hare and tortoise effect.

You CANNOT gain or lose horsepower by adding or subtracfting flywheels.

*Air resistance might need to subtracted from this equation to make it balance.
 
Enough about flywheels. Lets get back on track with Herb's bike.

Here's what I'd rather you all discussed - Its ripe for differing opinions.

Herb's head on the left is a bathtub design with big valves. Another of Herbs heads on the right - stock combustion chamber shape with big valves.

80 HP at 8700RPM by Herb Becker


Both motors put out about the same HP at 7000RPM (on the same dyno).

Here's another bathtub.
80 HP at 8700RPM by Herb Becker


Fire away.
 
I ran bath tubs like Herbs in a Triumph, it was fitted with a Norton crank and was 840cc. I ran 11.25:1 CR and it would run on pump fuel without issue.

A stock Triumph T140 can ping and knock on its stock 7.3:1 CR.

I kinda concluded that the bathtubs worked !
 
When you weld the head to create the bathtub shape, doesn't that soften it ? What is the heat treatment required to bring the aluminium back to strength so a valve guide does not split a port ? How do you stop the head from distorting ? I have a friend who has done this to Harley heads with good results.
 
Dances with Shrapnel said:
Jim,

Who did the combustion chamber sculpting on this head? It looks like some nice work and appears to retain the ferrous valve seats.
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I don't think those are original ferrous valve seats. Too large, at least the intake. Exhaust might be stock. When you weld the head up like that, you pretty much always have to re-cut the seat insert pockets, needing at least a little larger insert. I'm a little surprised. Most of the big valve conversions I've seen used bronze seats of one alloy or another.

Ken
 
Bad choice of words on my point Ken.

All the reworked heads I have seen for race applications have non ferrous valve seats. It just strike me as odd that the head was welded and then ferrous seats were used.
 
Dances with Shrapnel said:
Jim,

Who did the combustion chamber sculpting on this head? It looks like some nice work and appears to retain the ferrous valve seats.

jseng1 said:
Here's another bathtub.
80 HP at 8700RPM by Herb Becker
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This is an Australian customer. They did the head work over there. Its an exotic motor with lightweight internals, a 90 deg Ro Dy crank and custom 90 deg cam. He has his own particular formula for porting & HP production.

Very nice work but looks a little shroudy to me. For instance - at .4" valve lift it looks like there would be less than .4" lateral clearance between the valve and the combustion chamber. If you measure a stock head this way you will see that there is just enough lateral clearance around most of the valve for each given amount of lift. Going to big valves makes it even worse because the valve head is closer to the sides. Ideally you need a larger spherical dome for larger valves (at least around the valve heads). You've got to have a generous amount of side clearance around the valve (more than the lift) or you're defeating your own purpose.

I've been using the Tucker tungsten alloy valve seats with good results - very hard and no wear or recession. Can't see using bronze seats unless its for Titanium valves.
 
jseng1 said:
Can't see using bronze seats unless its for Titanium valves.
Click to expand...

Bronze has better thermal conductivity and a thermal coefficient of expansion closer to aluminum.

Not too often that you see a chamfer quench area on a Commando cylinder head. There is a lot of work that goes into that and and to matching the pistons and setting up clearance.
 
Dances with Shrapnel said:
jseng1 said:
Can't see using bronze seats unless its for Titanium valves.
Click to expand...

Bronze has better thermal conductivity and a thermal coefficient of expansion closer to aluminum.

Not too often that you see a chamfer quench area on a Commando cylinder head. There is a lot of work that goes into that and and to matching the pistons and setting up clearance.
Click to expand...

You've got to hand it to him for the craftsmanship. See custom domed lightweight pistons for those chambers below. Yes there are nice things about bronze seats - especially for racing. But the tungsten alloy is great for low maintenance street bikes - especially the exhaust valves.

BTW - the butt end of a drill bit is as quick easy tool for measuring the clearance around the valve (.4" drill bit at .4" lift for example).

80 HP at 8700RPM by Herb Becker
 
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