Yamaha TRX850 Enthusiasts Forum

1st pic is stock crank which basically everyone on this forum has.


2nd pic.. You can see where partial "knife edge" has taken place. Being a dry sump, knife edge was not needed at all, but its quite good at weight removal. You can also see where a fair bit of material has been removed from each side of one of the lobes.


3rd pic.. 60% weight of original rotating mass. That means the centre shaft is not counted, and anything that is pure cylindrical. Such as the snub at each end, the gears, etc.. This basically means the lobes and the counter balances. 629g removed in total. (CMED = the guy who did it, its his own personal mark for future reference)


4th pic, you can clearly see where they thinned out one of the lobes / counter balances.. And you can see the how much of the lobe is removed on an taper.


They told me that they fairly much cant take any more out because of the design of it. If it was a V-twin, would have been MUCH more drematic material removal. They showed me a superbike crank for a R1, it had 50% TOTAL weight reduction. It went in about 4kg, came out 2kg.. It was scary how much material they remove.

You cant see it in these pics (well easily) but the total diameter of the crank, has also been reduced by an unknown amount. Where the CMED is engraved, that surface is fully machined. As are the rest of the lobes. Should have taken a before and after measurement.. Such is life.

Enjoy..

have you had the crank balanced for use with specific pistons or was this just an exercise in weight loss?

wot he said, and, wouldn't You need to lighten the balance shafts as well?

its matched to 907cc pistons + carrillo rods.

Weight reduction DOES NOT provide more power. hp and torque are NOT increased at all.

All weight reduction does is allow the engine to spool up faster.. Best example is this.
in neutral, at idle, slam the throttle open, measure the time it takes to hit the rev limiter. That time is now reduced because you engine can spend less energy trying to rotate that hunk of metal around.

@ hansj
balance shafts are to offset pistons and rods. yes they have to be touched slightly, but its VERY minimal. its possible to leave them alone in my case. (but when would i ever leave anything alone ? )

Rotating mass is they key to making a bike produce "power". And by power i mean "be efficient".

The more weight you can pull out of rotating pieces, the more your engine can transfer to the wheel, faster.
MotoGP bikes are inherently clever in this area. Look at Rossi's rear sprocket, and compare it to your own. Have a look at how much weight he cuts out. Now think of EVERY rotating part in your engine. gearbox gears, shafts, even your front sprocket. Everything can be lightened. At the cost of durability / life.
The more material you take off something, the weaker you make it. The less life it has. Obviously cranks will last a fair while, but sprockets, gears, primary / secondary gear shafts, etc.. the more you take out, the less they last. MotoGP has a HUGE budget (40mil AUD a year, so says a certain head engineer who lives nearish to me).
Sprockets / gears are replaced every race. They last a weekend, then sent off for X-Ray testing. If they come back perfect, the specific engineer says "well, they haven't started to fatigue yet, so theres some material that can be removed." They literally WANT them to come back with hair line fractures between every tooth on the gear. So they know the limits.
Remember last season (2007) philip island, rossi's motor basically blew up ? They cut out soooo much weight to get power to the ground faster, at the cost of ruining his bottom end. And the fact that he was possibly experimenting with direct injection (which fiat did.. 5 years ago ? now the ferarri enzo (which fiat own) now utilises DI..?.. do the maths people)
Given that they use X octane fuel, they have a limit of 19,000rpm, are 800cc, the physical limits (well, as far as current know physics are concerned) they can only produce Xhp.. So they experiment on removing load.
Pneumatic valves. They already have crank case positive air pressure. Why not utilise that for a valve return ? instead of springs. Less load on the cam to push the valve open. etc.. (desmo valve anyone ?)

All i am doing with my spare engine is changing a few key things about it. Variable spark control, fuel injection, lightened crank / pistons.

Last thing i have to do, in the "major" mod department is off-set the barrels by 2degs. Basically, where the barrels bolt to the upper crank case housing, im going to make the barrels tilt slightly.. Anyone have a guess why ?
(and im welcome for anyone to show me im a total moron and dont need to, im prepared to read / learn pros and cons on anything here. So please help me !! this engine is a pure experiment..)

Quan-Time wrote:
Last thing i have to do, in the "major" mod department is off-set the barrels by 2degs. Basically, where the barrels bolt to the upper crank case housing, im going to make the barrels tilt slightly.. Anyone have a guess why ?

Good stuff QT

I'm going to guess that you are attempting to create symmetrical gas flow on a 5 valve head to generate stronger swirl during the intake stroke?

Not sure I follow...

What You're saying is that You'll take material off from either bottom of barrels, or the surface on the crankcases, in order to tilt the barrels, in comparison with the engine? Not tilting the engine? Tilting barrels compared to something else, or will the barrels/head have the same configuration?

If that's correct, only thing that will change (well almost, but I don't see any big effects of the other changes) will be cam timing, or am I completely lost here? But I fail to see why it wouldn't be easier to change the camsprockets, so I'm probably barking up the wrong tree...

Fun stuff though, keep it up QT!!!

QT,,,,, how much power do you expect to get out of the motor ??

My guess as a pure mug would be something to do with anersha??? If its reving faster not higher to compensate in some way???

umm,, i actually replied, but my net connection dropped out at the exact same time.. doh !

@ phuk
i want LESS swirl and more linear flow. EFI wants lower swirl factor, carbies want MORE swirl.

@ hansj

Hope this helps give an example, and a hint.

@ steve speed
125hp @ wheel is what i want, but so far im calculating 118 - 120hp (theoretical) wheel hp. So yer.. wait and see.

@ cobbadiggabuddyblooo
"inertia" is what your thinking of. Umm, by lightening the crank, i have indeed changed its inertia potential. As ive said before somewhere, one superbike team (suzuki from memory) lightened everything, and where the starter motor goes, put a huge solid lump in there. To increase rotating mass. They changed it per track to change the power curve. It DOESNT increase / decrease power, it just changes delivery time.
But no, angled barrel does not increase inertia or spool up rate.

try again...that will throw the centre of the piston, gudeon all little further towards the front of the crank and to do with rotation(still workin on my anersha theory just prob use different turms let alone inglish) downward force being a little more forward upon the crank type thingo if you draw a line straight down from the centre of the gudgeon to the crank. But I spose this force is still being transfered straight down the rod to the crank... yes ... gets the creative juices flowing this does

This intern ...ok turn then...would change the angle of the piston upon the rod and transfering power from downward pressure upon the piston to the conrod type jobby.

more downward pressure on the rear of the conrod to help push it forward toward the direction of rotation

i like your thinking.. You are trying.

OK., it DOESNT effect hp or torque power, but it DOES effect when they come in. Ill give you another example of long conrod VS short conrod.


See how the LONG conrod is more verticle, while the SHORT one is still on a big angle ?
If you were to push down on the LONG conrod piston, you transfer more power to the crank than the SHORT setup. This is because of the angle.

More torque from a longer conrod. BUT if you have a short conrod, and slightly tilt the barrel, you dont increase torque, you just move the curve around. By laying it back a touch, you max torque come on EARLY in the rpm range. Thus getting to max power earlier.

Hope this help. (as you probably guessed, im a very "visual" person.. i love drawings and pictures...)

So... a longer rod gives a torque peak higher up and a shorter rod (haha) gives a torque peak lower down, but runs out of breath quicker?

Hey hey not bad for a old rock n roll sound roadie ..was sorta gettin there with the piston angle. Much the same as changing the length on a horn loaded pa box.
Tuning the box to a certain frequency, longer horn like a sub w bin lower the frequency.. different length horn loaded boxes need different delay times at the cross over so all signal transfered from subs, lows, mids and highs meets at a point at the same time.Just utilizing an analigy I can relate to..
Anyone out there remember a book i read over 20yrs ago...Zen and the art of motorcycle maintainence. Now wheres the beer rider...

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