Lightened crank (pics included)

[Kayla]

Anyone out there remember a book i read over 20yrs ago...Zen and the art of motorcycle maintainence.

P.S. Kayla I could be a real male and come up with a few laughs about rods and talk n running outa breathe but I'll bite my tongue and let the other half of my geminian nature take ahold

I tried reading that book recently but only got about 40 or so pages in. Oh, and I thought the 'short/long rod' thing might raise a few titters

As for tilting the barrels to achieve this, can you not 'simply' skim the required amount off the barrel surface? Why does it have to be tilted?

[Quan-Time]

kayla basically got it in one.
longer rod = torque curve is earlier in the rev range
short rod = torque curve later in rev range.

Ill point out with longer rods you have MORE rotating mass, which means your potential peak RPM is reduced because you have more mass to push around. But with lightened stuff, this isnt a huge issue anyway.

Also note that shorter rods which can yield crazy peak RPM wear out MUCH faster than longer rods. F1 cars have in the order of 24 - 25mm stroke, the TRX has 67.5mm stroke, and the rod length in F1 is also quite short, but obviously offset a touch. Its part of the reason that allows them to spin to 19,000rpm.

[cobbadiggabuddyblooo]

Well done Karla... and as for zen..well it just utilises the analogy of motorcycle maintainence on looking after your body mind and soul.
Am in the proccess myself of writing a book on epilepsy(suffered it for the past 22yrs) and a audio mixing console as the anagogy. Both working on electrical impulses and emotions(muso's just releasing there emotions thro the medium of music), inputs and outputs,phasing,dynamics, balancing the mix, much the same as your motorcycle too.(some bikes sing, some cry, some growl) I'm constantly fine tuning my mind,body and spirit to deal with the challenge(without medication) to win the race.

[Trixz]

@ QT

You're SICK (well at least the person who does it)


WOW, this is a technical and interesting topic, with a result that makes me go

Greetz
Gerben

[dirty trix]

Ill point out with longer rods you have MORE rotating mass, which means your potential peak RPM is reduced because you have more mass to push around. But with lightened stuff, this isnt a huge issue anyway.

Also note that shorter rods which can yield crazy peak RPM wear out MUCH faster than longer rods. F1 cars have in the order of 24 - 25mm stroke, the TRX has 67.5mm stroke, and the rod length in F1 is also quite short, but obviously offset a touch. Its part of the reason that allows them to spin to 19,000rpm.

Couple of things about the rod length and rod/piston ratios in general.

You've got a maximum theoretical piston speed based on the metallurgy you are working with - a rough guide of about 24 m/s is pretty much critical speed on a bike engine, so aiming beyond that you'd better have spent up huge on the carillos or similar.
Consider how much a piston out of a trx weighs and then imagine that running the full 4 stroke cycle say 10000 times per minute... imagine the force on the rod and especially on the little end (the big end and crank should be strong enough given proper lubrication)

Can't just go the lightest option either - alloys are not chosen just because of their weight reduction, also their strength and wear characteristics. For instance, Carillo rods are generally fecking heavy..... but you choose them for a reason.


This may help explain Quans experiments a little easier. great little piece if you can fill in some of the gaps yourself.

http://www.epi-eng.com/piston_engine_te ... ration.htm

[Quan-Time]

Most pistons (the alloy they use) can handle around 24m/s constantly, load dependent. 67.5mm stroke and around 10,500rpm will exceed this. Shorter stroke allows more rpm. if i destroke the crank to 63.25, while maintaining my oversize pistons, ill get 849.5cc, and be able to rev to 11.500rpm before i hit this limit. By allowing the engine to breathe up top a bit, you can extract extra power more efficiently.

Because im using full race spec pistons, they are designed to handle a shade over 24m/s, and are VERY light while still being strong.
Hold your arm out infront of you, move it up and down as fast as you can. Now do it while holding a full bottle of water. You cant do it as fast. Now do it with a half empty (or half full ) bottle. You move faster than the full bottle, but not as fast as holding nothing obviously.
This is "releasing potential energy". You can never make an engine 100% efficient, hell 90% is almost impossible. 85% is getting to be VERY good for what an internal combustion can provide. By removing excess weight, your allowing more energy to be transferred into the crank and out of the piston / conrod assy.

Having lighter pistons, different conrod and lightened crank, im NOT making more power. All im doing is allowing more energy to be transferred. Why do you think a motogp bike is SOO light, and why each year manufacturers claim less and less engine weight. Its also why many people fight the "unsprung" weight on bikes. Rotating mass is the same thing.
Put 5kg weights on each leg, ride a push bike as fast as you can. measure that speed. Now put the 5kg weights in a bag and put it on your back. Now attach it to the axles of your rear wheel / frame somewhere (full rigid frame). Each time the speed will change according to where the weights are placed, and how well energy can be transferred.

[Kayla]

This may help explain Quans experiments a little easier. great little piece if you can fill in some of the gaps yourself.

http://www.epi-eng.com/piston_engine_te ... ration.htm

Thanks for that Now I have a headache

[dirty trix]

You can blame me when bf/husband/gf (hey we're equal opportunity here) complains.

Or make them read it and they will also have a headache and then there is no-one missing out.

[dandywarhol]

Hi Quan - are you remembering/aware that the gudgeon pin isn't central in the piston?
It's offset to a) reduce thrust slap and b) to give the big end an easier time at full pressure - the crankpin isn't directly under the piston - kinda like standing on a cycle crank at TDC - the bike won't move!

[Quan-Time]

yes, i am very much aware of this. That was taken care of in the piston manufacture process. I must admit tho, not many ppl realise that.. Aint you a clever boy

[dandywarhol]

yes, i am very much aware of this. That was taken care of in the piston manufacture process. I must admit tho, not many ppl realise that.. Aint you a clever boy

I should be - it's my job..............

[Greg]

I love this thread...

Greg