426 stroker


15 replies to this topic
  • Scotty426

Posted April 10, 2005 - 08:25 PM

#1

How come about 9 shops have a 444 stroker for the 426 engine, but none bigger? If you are going to take the 450 out to 508, you can't do more for the 426? Balance issue? Crankcase narrower? Both could be overcome. It's got me scratching my head. Thanks in advance.

  • Guest_BrandonV_*

Posted April 11, 2005 - 05:13 AM

#2

Powroll can modify your crank and turn it into stroker. That and the 97mm piston will get you to 459cc's (I think). Search for some of YZDad posts, he's got that setup.

  • cowboyona426

Posted April 11, 2005 - 10:11 AM

#3

YZDAD1 had a Powroll modified crank (+2m stroke by moving the rod pin) and a +2mm piston to make a YZ 459. I plan on having him modify my motor this summer like the one he used to have.

  • HyBridYZ426

Posted April 13, 2005 - 03:50 PM

#4

can you use the jug from a 450f?

  • cowboyona426

Posted April 13, 2005 - 03:52 PM

#5

Hybrid- probably not. The 450F has a lot longer rod than a 426F, so the jug would also be longer. I don't think it would line up with the top motor mount (headstay) when you were done unless you used a 450 jug, rod, and head.

  • Scotty426

Posted April 15, 2005 - 10:29 AM

#6

How sure are you cowboy? I didn't realize that the 450 cylinder was taller. I heard they were trying to lower the center of gravity with a shorter head so a longer cylinder would seem to be a little backwards but I'm not doughting you. I wonder why? Seems like YZdad paved the way for us. I'm in no hurry yet. I want to try the YZ cam next, then evaluate my ability to stay alive on the bike. Low end torque makes life easier but a good pilot can make it work either way. Thanks for the insight. I'll study this and post again.

  • felony

Posted April 15, 2005 - 07:59 PM

#7

i saw a Falicon stroker kit on ebay a while ago,it took the 426 up to 488cc! it went to like 4 something with the stock bore.it also had the spacer plate for the cylinder

  • cowboyona426

Posted April 16, 2005 - 11:42 AM

#8

05 YZ 450- 95mm bore by 63.4mm stroke
02 YZ 426- 95mm bore by 60.1mm stroke

Those specs came from the Yamaha website. Based on that, they could have either went with a slightly taller cylinder or lowered the crank slightly to accomodate the longer stroke as compared to the 426.

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  • PowerFiend

Posted April 16, 2005 - 09:11 PM

#9

05 YZ 450- 95mm bore by 63.4mm stroke
02 YZ 426- 95mm bore by 60.1mm stroke

Those specs came from the Yamaha website. Based on that, they could have either went with a slightly taller cylinder or lowered the crank slightly to accomodate the longer stroke as compared to the 426.


The third option, they went with a shorter rod. :naughty:

  • Scotty426

Posted April 17, 2005 - 05:26 AM

#10

I might seek out some Yamaha dealer mechanics and see about the cylinder length. A shorter rod jives with what I know about stroking. If they had spare cylinder length, no harm. The problem is if you get the piston rocking by going too low out the bottom of the stroke/cylinder. Either way, it seem like I'd have to buy 2 full kits, big bore and crank mods.This will put the hurt on my wallet sho-nuff. For trail riding, the stroke mod should be first I guess. It makes the torque I want. Bottom line, little brother has a 525 KTM and lets me know about it. He wants to stroke it!!!????????? I do stall the 426 trying to keep up with these dudes I ride with in these tight nasty trails (90% of my riding). A flywheel weight is the next mod, but I wonder if the end state(big bore, longer stroke, flywheel weight) will vibrate badly. Yeah, I know you wont have to rev this combination as high to get stratospheric power, but the countershaft is designed to counter the vibration around a certain weight range. Would this thing vibrate like a tractor? I like my motors smoothness. I wonder if someone uses heavy metal to re balance a crank like a car engine crank? My wallet is groaning. Trade the 426 for a 450? I have plenty of set up money in the 426 plus the extra trans gear. I bought the Yamaha for its power and reliability. Hmmmmmm. She's tough like a tank- before I start messing with it. I will likely do....something. I look for trouble.

  • cowboyona426

Posted April 18, 2005 - 03:21 PM

#11

The third option, they went with a shorter rod. :naughty:


I'm confused as to how a shorter rod would increase the stroke on the 450... :D :naughty:

  • PowerFiend

Posted April 23, 2005 - 06:33 PM

#12

I'm confused as to how a shorter rod would increase the stroke on the 450... :naughty: :naughty:


:D I didn't say that it would increase the stroke, it was in reply to:

Based on that, they could have either went with a slightly taller cylinder or lowered the crank slightly to accomodate the longer stroke as compared to the 426.


The easiest thing for them to do would be to put in a shorter rod with the stroked crank to put the piston in the same relative position. The pistons are different, so I assume that they played with piston pin height also. :D

  • grayracer513

Posted April 23, 2005 - 09:06 PM

#13

05 YZ 450- 95mm bore by 63.4mm stroke
02 YZ 426- 95mm bore by 60.1mm stroke

Those specs came from the Yamaha website. Based on that, they could have either went with a slightly taller cylinder or lowered the crank slightly to accomodate the longer stroke as compared to the 426.

This is just some general info for you guys to think about. The problem is that when you add to the stroke, the piston goes farther up toward the head by half the additional stroke (the other half goes farther down the cylinder). There 3 ways of compensating for this.

> Shorten the connecting rod. Shortening the rod by half the added stroke keeps the same deck clearance. There is, however, a ratio of rod length to stroke that is considered best for performance and longevity, and these need to be evaluated and understood before taking this approach. Changes in the length of the rod affects the angle at which it bears on the crank during the power stroke. Yamaha may have gone to a longer rod to make a change in this angle for a specific reason, probably to improve the engine's performance at high RPM.

> Move the wrist pin higher in the piston. This is the approach typically taken by automobile engine builders, but it requires new pistons made from scratch for the purpose. And, you can only raise the pin until it runs into the oil rings. The home builder can sometimes sort of accomplish this by removing material from the piston crown equal to half the added stroke. The limit to this is in how much material is in the piston crown, and how near the crown the top ring will be after the modification.

> Increase the height of the cylinder. Once again, you're looking for half the added stroke. So, in a case like the Powroll kit, just a thick base gasket (1mm) may be all that's needed. With OHC engines, the length of the cam chain can become a limiting factor.

  • cowboyona426

Posted April 24, 2005 - 09:51 PM

#14

Thanks for the explanations PowerFiend and grayracer :naughty:

  • Scotty426

Posted April 27, 2005 - 07:16 AM

#15

For the record I emailed the guy who did both the 2mm stroke and the 2mm bore and piston (459cc ish) and he said reliability is good and no added vibration. Wow. Now the age old questions....how to pay for it, and how to explain it to my pretty wife?

  • cowboyona426

Posted April 27, 2005 - 10:57 AM

#16

If you figure that one out Scotty, please let me know!!! :naughty:





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