Dakar bikes ?

[kellymac530]

So I have loved watching the Dakar for many years. Sadly coverage in the USA is spotty. We get a daily 30 minute recap of each of the 4 major catagories. The only deeper info on the equipment is the occasional editorial piece, but they are minimal.

So I have a few questions for anyone who may know about the current bikes.

I know the Hondas are modified, but are clearly based on the CRf450 motor, they showed one with the tupperware off and it was clearly a Uni-cam motor.

The Huskys I am guessing are based on the TC and TE 449 motor, I think that is all that they are building in the 450 class now...but maybe they are based on an older motor?

The Yamaha I see are running 2 different bikes, one based on the last gen motor like a WR or pre 2010 YZ and the other is clearly based on the new rearward facing front injected rear exhausted motor, as you can see the big loop exhast out on the side nest to the swing arm.

But what are the KTMs running? Are they still using an RFS based motor, a modified Xc4, the new 450 SXf motor or maybe a detstroked or smaller bore version of the new 500?

Any knowledge out there?

[roadracer]

The KTM 450 RR is based on the newest 450sx motor, according to the literature.

[davesupreme]

Originally Posted by roadracer

The KTM 450 RR is based on the newest 450sx motor, according to the literature.

i dunno about that.... i just read somewhere that the RR motor is 97x60mm, and that ain't in any of the production bikes....

[roadracer]

I think those specs are for the 2011 bike and ktm just didn't update the website.

[kellymac530]

Bore and stroke mean very little to a factory race team.
There are many BxS combos that will fit in under the 450cc limit. Even MX teams play with bore and stroke to move the revs and torque around.

That is what Doug Dubach did for Yamaha in the 90s....years of testing different combos until they had what they tought worked the best.

KTM factory team could take an RFS or SXS or Xc4 motor and change the BxS as easily as most of us could do a valve adjustment...

Anyone have a pic of any of the last Dakar bike motors?

[davesupreme]

really?.... i wanna see you find a 60mm KTM crank.....

[snatchy]

Originally Posted by davesupreme

really?.... i wanna see you find a 60mm KTM crank.....

you seem a bit testy?

here you go;
http://www.motorcycle-usa.com/25099/...-450-SX-F.aspx

[davesupreme]

Originally Posted by snatchy

you seem a bit testy?

here you go;
http://www.motorcycle-usa.com/25099/...-450-SX-F.aspx

yeah you right!..... first i've seen.... i play w/the RFS motors.... thought that 60mm was just for the factory rally motor.... interesting.....

[snatchy]

Have a read through this thread if you want a bit more info on the engines and the minor bits that are different from 450sx engines;
http://www.advrider.com/forums/showthread.php?t=718817

[davesupreme]

WOW...... i wish i could afford that....

[kellymac530]

Dave,
All it takes is repositioning the crank lower rod pin to change stroke.
I am not saying you or I can or would do it, but it really not that hard especially if you could get the outer crank halves undrilled for the crank pin.

People build stroker cranks all of the time for cars and motorcycles.

On race car motors we have added welding to one side of a crank rod surface and then machine the journal back to round but offset to lengthen or shorten a stroke the reharden the crank with heat treating. Over simplifying the process here, but that is basically it.

With a motorcycle crankshaft blank it would be some simple machine work for a factory to move a crank pin and make any stroke that they want...within reason of course, based on crank case room.

These could build you a crank in whatever size you want:

http://thumperracing.net/

As well as a cyliner in any bore you could want...it just money right. Hey that guy in the other link paid 50k AUD for a Dakar replica....OUCH....I am sure you could build a 97X60 motor for a few grand if that is what you wanted.

[davesupreme]

yeah, i follow the RFS section at KTMTalk alot... lotta bore and stroke voodoo, they all wanna build 78mm stroked 6xx+'s, which sound pretty cool..... i just converted my 450 SMR to a dirtbike, and it's 64x95. you can hear the difference in these dakar motors w/the shorter stroke, more RPMs, almost smoother, high speed stuff...... i bet they really haul azz....

[kellymac530]

For sure dave. When the rotating mass is smaller there is usually less wear on the bottom end parts. Sometimes less torque, but those guys are running fast and up in the Rrs alot, even in the sand they seem like they run a low gear and spin em up.

Cool stuff though.

[davesupreme]

yeah, all the peeps over at KTMTalk wanna build 78mm strokers, and it's supposed to eat the lower end pretty fast, bearings, crank spread, etc....... i was at barber last year for a track school, and i think a guy had a 560 SMR, cause' he passed me on the straight pretty hard.... but they're all supposed to blow up quick..... i'm sure that short stroke longevity thing is what they're lookin' for at dakar....

[kellymac530]

Spinning them up is for sure...Did anyone see those shots from day 6 {I think 5 or 6} of them just rippin down that beach for miles tapped out..100+ for long stretches laid down on the tank tryin to squeeze every inch of speed out of them....gotta be hard on a 450 motor, even with a short stroke, to ring its neck that hard for that long. I used to stress on the hiway at 80+ on my 530 for more than a few seconds...not that I didn't trust the bike, just a single wrung out like that for any stretch just give me the creeps after a bit...