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Time for the 420 Update

8 posts in this topic

I now have 8 months of track time and 6 moto's in on the 420 big bore kit. Results - Perfect. I have experienced no problems with the top end or bottom end. On the track the biggest difference is with starts and low end snap out of corners.

MX results:

Race 1

Moto 1 - 2

Moto 2 - 2

Overall - 2

Race 2

Moto 1 - 4

Moto 2 - 5

Overall - 4

Race 3

Moto 1 - 2

Moto 2 - 2

Overall - 2

6 race Series - 110 points to date. The WR420 is currently parked in 1st for the series. 3 more races to take the series.

Also -

Going to a 19 inch wheel made a huge difference in my cornering speed. The bike seems to hook up much better, while leaned over for the corner.

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James,

Who was the manufacturer of your big bore kit,

and

how much did it cost?

Kevin

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99 WR, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark, got forked by Pro Action.

AMA, NETRA

For clarification: WE'LL be having a KICK ASS time in Moab!! Right Mitch?!!

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Shite!!

9 hunnie for a 420 kit!

You can buy OEM 426 bits and do it for almost under 1/2 that price.

Anyone tried it with 426 bits..

I've been informed by another sorce that the 426 parts WILL fit..

Sorry to whoever I was disputing this with! :)

------------------

--

**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

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Matt,

What was the final verdict on the cylinder/piston swap w/ a 426? I know it was the small end bearing, or was it the big end bearing, or was it both? :)

------------------

99 WR, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark, got forked by Pro Action.

AMA, NETRA

For clarification: WE'LL be having a KICK ASS time in Moab!! Right Mitch?!!

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Rich Rohrich has been using OEM 426 parts on his big bore project and confirmed that the 426 rod does work on the 400 crank. Only the small end is bigger. You need the new rod if you plan to use the OEM 426 piston, or the new larger Wiseco. He also listed a guy who apparently does good a good job with crank work if anybody is interested.

Brad

[This message has been edited by Brad (edited 07-19-2000).]

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Kevin:

I've finally realised not to believe anything I read in mags..

I had 3 mags that all said different!!

You will need the 426 rod to be installed as the small end diameter IS larger.

The bottom end diameter is the same BUT the rod is thicker around the bearing.

Basically its a matter of replacing the rod with a 426 one and then reassembling with the 426 jug and piston.

------------------

--

**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

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I send my cyclinder off to Eric Gorr last Monday for the Weisco / Cometic 420 Kit. Eric indicated the cyclinder was off to National Chrome for boreing and plating and said I should have it back next Thursday and I can't wait. Right now boredom has set in with 1999 WZ 400 parts in baggies all over my garage waiting for my new big bore piston, cyclinder and gaskets to show up.

I rejetted my carb using James D. EKP needle in the #3 a 50PJ and a 168MJ should work great with the 420. So my scoot will have new jetting a 420 to go with the DSP CF airbox, porting and Vortex ignition. Should be real interesting on how it works out.

This bike had about 4000 miles on it and basicaly looked brand new inside. There was absoultly no signs of blow by or any other bad things to see. All cam bearing surfaces look perfect and not a single mark inside the cyclinder. I took apart a perfectly good performing engine in the hopes of making it better---time will tell the real story!!!!

BORED

Clark

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