Stroker WR450F

7 replies to this topic
  • 2grimjim

Posted June 25, 2008 - 11:50 AM


Hot Rods Products has a stroker crank for the YFZ450 (yeah, I know...that's a four wheeler) p/n 4173. The only difference that I can find between the YFZ and WR 450 cranks is the wrist pin diameter. There may be other subtle differences like balance factor or crank mass (weight), but dimentionally they appear close enough to interchange, save for the 1mm bigger wrist pin (use a YFZ piston in the WR?).

Has anyone tried to use the Hot Cranks YFZ stroker crank in a WR 450?

  • tweav

Posted June 25, 2008 - 12:27 PM


I don't know what year bike your working on ,but on a 07 +wr450 the stator side of the crank is completely different then the yfz 450 . so it will not fit on the later ones for sure.

  • 2grimjim

Posted June 25, 2008 - 02:08 PM


It would be on an '03 WR450.

I know that the '07 and later WR450's are completely new machines; very little in the bottom end interchanges with the '03-'06.....tranny is completely different (shafts are about 1.5mm wider) and so on.

The YFZ still is based on the '03-'06 WR engine and quite a few parts will interchange.

Steahly uses the same part number for all YFZ's and '03-'06 WR's flywheels and the Yamaha p/n for the starter gear on the end of the crankshaft is the same (5TG-15515-01-00).

  • mikeythefokker

Posted June 25, 2008 - 07:55 PM


If you look on the site that sells the ice cube big bore kits, they have a big bore stroker kit that is made for the wr.

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Posted June 26, 2008 - 11:48 AM


If you look on the site that sells the ice cube big bore kits, they have a big bore stroker kit that is made for the wr.

I'd go that route. What you are wanting to do should work because the big to-do thing to the 04/05 YFZ was to switch to a WR crank to make it a 450 from a 440. Email one of the quad engine builders and ask. I might word it like - I bought a hybrid with a 2003 WR motor and it needs a crank. Will the stroker YZF cranks work?

Heres a few

  • tweav

Posted June 26, 2008 - 11:59 PM


these guy's sell 3 stroker kit that will fit your bike


  • MountainMax

Posted June 28, 2008 - 07:01 PM


I wonder how much more power the big bore/stroked 511 version makes, sounds awesome to me, If i ever loose any internal engine parts, a big bore/stroker would be the way I would fix it.

  • elcubeo

Posted September 08, 2009 - 06:44 AM


Hey there guys--

I'm in the market for a big-bore and stroker crank. Guess why?
I blew the small end of my stock con rod to chunks!

Upon initial inspection, the only things broken are the jug (windowed pretty nice!), con rod, and piston. The transmission is ok (coasted her about 1 mi down hill to the trailer, better than being 1 mi below the trailer...). The cylinder head and valves escaped remarkably unscathed, shy of a few piston-deck love marks.

I had a JE 14:1 std/std 450cc setup with hotcams shafts and an aftermarket exhaust. I liked the power, but not the $7.00/gal fuel and all the extra lo rpm detonation no matter my jetting. I race harescrambles and I dont really need that explosive of power delivery but i want to be able to pour it on when the opportunity presents itself. I see that my old GNCC hero Scott Summers has a good idea for his race Husky 510. He lowers the compression ratio to soften the power hit and make it more durable for abusive racing conditions. It's still about as fast as the 450 but it's more chuggable and impossible to break. Basically i wish i could install a 1987 XT600 engine in my awesome handling bike.....

Thus I am thinking of using all yfz parts to do a 511cc bb/stroker (478bb x 471stroker). My bike is an 06 so I dont think i will have issues with the crank snouts. I like the idea of stepping up from an 18mm wristpin to a 20mm wristpin (stronger maybe?). I might open up the combustion chamber slightly around the valve pockets while leaving stock quench area. I'm thinking about milling a slight dish in the center of whatever piston i end up using. Then it will roll over on the e-start like a lazy old utility quad.

I dont like the idea of assembling these kits without balancing something. I know from my drag car experience that a 6000 rpm v-8 can benefit greatly from a good internal <.1g balance job, so why not a 13,000 rpm single? I really dont forsee any of these parts being mass produced and being balanced to that precision. Also, has anyone found any balance shaft tech info, as far as what its actually balancing...and what i will have to change with +3mm stroke?

Maybe none of this crap matters, and I am the problem. I bet if i rode it like an XT600 and kept the rpm down I wouldnt break anything. But 250f rpm feels so good... what should I do?


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