ok completely unrelated... hey, it's the off season

[ratonabike]

i grew up riding Motocross, and though all i can think about is drag racing now, and sold my last MX bike 2 years ago, i still occasionally check out the MX scene... my fav brand has always been Yamaha... well, i was just watching a Supercross race on tv, and then checked out the Yamaha website to get the latest on their latest MX race bike, The 2010 YZ450F... other than switching from 2-stroke engines to 4-stroke engines a few years ago, there haven't been too many radical changes in the sport... but the new YZ450F, DOHC, titanium valved, 4-stroke water cooled motor has two big engineering changes that blew me away...

one, is that the engine is now rearward facing, instead of leaning forward like traditional motorcycle engine designs (or at least, in the dirt bike world of single cylinder bikes)... in an effort to lower the balance center of the bike (as handling is critical in MX), as well as putting the intake in the front of the bike, with the exhaust coming out the rear, for obvious advantages in a straight-through intake/exhaust design...

but what caught my eye the most, which would be of interest to u guys, is they offset the cylinder in relation to the crank, something i don't think i've ever seen in any engine design anywhere ever (though i wouldn't doubt if someone back in 1920 did the same thing, as is usually the case for 'new' engineering ideas)... the idea is to have the connecting rod straight up and down (100% vertical) on the power stroke, "...minimizing piston friction against the cylinder wall that could rob power (for) ...quicker response". of course this also means that the connecting rod is more angled on the opposite stroke, though i don't know what adverse effect that could have on the motor,.,..

anyway, if you're into engines, even though this is a car site and not a motorcycle site, engines are engines, it doesn't matter what they're in, and motorcycles always seem to be one step ahead of cars when it comes to engine advances... so if you're interested, check out the Yamaha website to check out that engine... definitely interesting to say the least... i wonder if an offset cylinder design will make it to future car engines!

http://www.yamaha-motor.com/sport/products/modelinnovation/209/0/innovation.aspx

[Waylon]

WOW! Now that's cool. My only thought is that the piston must have a very short skirt because skirt to rod clearance would be the biggest issue that I could see on the upward stroke with that much angle. And sure you loose the friction on the downward stroke, but I would think you have a lot more friction on the upward. That motor has about a 2.4" stroke and about a 3.95" rod length and if my math is correct, that would put the rod at about a 53 degree angle with the crank when it's at the middle of the upward stroke. In comparison, a BBC with a 4" stroke and a 6.135" rod would have about a 71 degree angle. That seems like it would put a lot of side load on the piston as it moved up and would wear the cyclinder wall quicker.

Yamaha (2.4 because it's the full length of the stroke)
acos(2.4/3.95) = 52.584 degrees

BBC (2 because it's 1/2 the length of the stroke)
acos(2/6.138) = 70.974 degrees

Disclaimer: It's been a long day at work so my calculations may not be correct, but I think they are.

[ratonabike]

well, i'll assume your math is correct since i don't know that math that would calculate those angles (though now because of you i'm researching the math so i can calculate that myself)... yeah, from the small video of the cutaway of the engine, the skirt definitely is very short... obviously, like you said, it would have to be to prevent contact with the rod... as far as the friction, i wonder that maybe because the piston on the return/exhaust stroke is after the power stroke, then there's less sideloading (at least compared to the power stroke), so friction would be less and not an issue... idk, maybe the friction is not less, and they figure the improvement in throttle response was worth the extra friction on the return stroke... i just wish i had a CNC machine and a big block of aluminum, it would be interesting (and cool as hell), to build a V8 block with offset cylinders... they would be offset inboard (i think i have that right), narrowing the V8 too.... hmmmmmmm

[Waylon]

I don't think you could physically do it with a V8 because one bank of pistons pushes to the bottom of the crank and the other side pushes to the top of the crank. You definately could not do it without having different rod lengths or a VERY odd valvetrain setup, all of which I don't think would work. It will be interesting to see if Honda or Toyota come out with something similar in the next few years with their 4-bangers though.

[ratonabike]

hmmm... right, on a V8 the offset would be the opposite on each side.... but, why different rod lengths? wouldn't the other side, the other bank of 4 cylinders, just be a mirror of the other, facing the opposite way? true, i would expect an inline engine (4,6, etc), be the way to do it... w