Freshen up 2000 YZ 426

I getting ready to tear into my 426 to freshen up the topend in to the bike I dont how many hours are on the topend or bottem end I a the 3rd ownner.

I was thinking about a 444 big bore kit what I dont like about it you cant over bore the cylinder again if something go's wrong down the road.

Is a High compressin piston worth it with the stock bore.

I want to have a good port job done on the head from a good know shop.

I already have hot cams in the motor I going to reuse so what kind of power should I get out of the bike.

I put a new cam chain when I installed the hot cams in the motor about 10 runing hours ago.

The bike has SS valves in it already the year 2000 came with them I have them checked and have the vavle seats lapped but they seem fine.

I was thinking about a 444 big bore kit what I dont like about it you cant over bore the cylinder again if something go's wrong down the road.

Not a concern, unless you break a chunk out of it. When you wear out the stock bore, you have two choices:

  1. Replace the cylinder
  2. Bore it straight and repair it if necessary, then replate and hone it back to its original size.

These same two options are available whether the cylinder is stock or 3mm oversized.

I going to get hold of Ron Hamp get some info from him prices and save up and send him the topend let him do his magic.

As for the bottom end I going to wait until it starts acting up mean while look for a WR gear box.

I E-Mailed Ron Hamp today So I hope he gets back to me with a reply soon.

Edited by marv02

What luck went to do a family outting with my Daugthers new ATV so I went and fired all the bikes up the Daughters new bike fired up the wifes bike after draining the gas and puttting new gas it it fired right up.

The Yamaha time before last was beening a pig fro some reason to get running today 5 kicks it fired up as normal I wacthing the exhaust wacthing it to clear out habit after all these years of riding.

I noticed there was a shiny sliver glitter floating in the exhaust not good and it was smoking a little blue smoke I was hopping it was some water in the pipe that was burnning off it did not go away not good.

I pulled the endcap off the silencer hopping that was stuff just stuck in it fired the bike back up still shiny sliver glitter floating in the air still not good.

I now think it's the coating has worn off the cylinder now I going to have to rebuild it sooner than I was planning to.

Edited by marv02

sounds like a good excuse to send that cylinder to mileniem and get that 444 big bore done.

i been thinking about what it would cost me to ship my 400 cylinder and have it redone i,m guesing a rebore replating and shiping and how expensive is a 444 pistion compared to stock

I just ordered a Wossner Piston kit Pn# 8525d300 it's a 97.98 and stock compression I have a local place I have do the bore and the recoating they always done me right in the past.

This make the bike a 452.5 but we wont tell the 450 ownners this just tell them it's stock.

I waiting for Ron Hemp to get back to me about the porting the head and if the cam set up will work or if he has a better cam set up.

Edited by marv02

Try this web site to find a piston set up for your bike I happen to have a good place local I going to have them Bore and replate my Cylinder I sure if you look arounf=d you can find a local place to do the bore for you also.

http://www.wossnerpistons.com/products/mode/filter?sort=name&order=ascending

sounds like a good excuse to send that cylinder to mileniem and get that 444 big bore done.

i been thinking about what it would cost me to ship my 400 cylinder and have it redone i,m guesing a rebore replating and shiping and how expensive is a 444 pistion compared to stock

i just won a new 2002yz426 crank pistion assembly off ebay 176 bucks and i have a other little collection of stuff to go on it.

that 452 number sounds better than 400 or 426etc and i have the wr3/4/5th gears so next comes a auto cam and a big bore cylinder of some sort

I been searching for a WR Transmission but so far no luck But I been reading other are just replacing the 5th gear only I might go that route my self so I have the OD for the long wide open fire road where I live.

i just won a new 2002yz426 crank pistion assembly off ebay 176 bucks and i have a other little collection of stuff to go on it.

that 452 number sounds better than 400 or 426etc and i have the wr3/4/5th gears so next comes a auto cam and a big bore cylinder of some sort

i used to want to do that but i heard that its a mighty big jump from 4th to 5th i think it might of been greyracer who statedat least go wr 4th and 5th but 3/4/5from a wr just flowed better after yz 1st and second- i cant remember exactly it was a long time back

If I was you I put a new rod and bearing on the crank before I put in the cases that is a lot of work to find out the used crank you just installed is bad.

When I split my cases to put the WR 5th gear in I going to put a new rod and bearings as long as I in there But I have a HYD press If mine12 ton wont do it I have a 50 TON at work I can use.

Like I say if you have it that torn down that far do it right I sure you dont want to tear it back apart for a simple fix you could done when it was apart the first time around.

i just won a new 2002yz426 crank pistion assembly off ebay 176 bucks and i have a other little collection of stuff to go on it.

that 452 number sounds better than 400 or 426etc and i have the wr3/4/5th gears so next comes a auto cam and a big bore cylinder of some sort

Hum nice to know this I look for a complete WR trans then off Flee Bay I hope I find one before I get everything else done so I can do all at one time Or I do the topend and one day I do the bottem end latter :p .

sounds like a good excuse to send that cylinder to mileniem and get that 444 big bore done.

i been thinking about what it would cost me to ship my 400 cylinder and have it redone i,m guesing a rebore replating and shiping and how expensive is a 444 pistion compared to stock

If I was you I put a new rod and bearing on the crank before I put in the cases that is a lot of work to find out the used crank you just installed is bad.

When I split my cases to put the WR 5th gear in I going to put a new rod and bearings as long as I in there But I have a HYD press If mine12 ton wont do it I have a 50 TON at work I can use.

Like I say if you have it that torn down that far do it right I sure you dont want to tear it back apart for a simple fix you could done when it was apart the first time around.

He got a brand new crank still in the box off ebay for $176 not a used one. I was watching that auction and but I was at work when it ended.

perfect auction ,no competition ,jojo is right marv its a brand new yamaha crank assembly still in a unopened yamaha packing, it was listed as a (crankshaft piston assembly)

i think it was the best way to go for me-new iron better rod than a 400 so now i can run 426 or big bore stuff easily, the 400 rod has a smaller piston pin hole than 426 rods and their not as beefy as the 426 rods.

Peaceofwork, earlier you said you want a 444 (97mm) piston and have your 400 cylinder bored and replated well it wont work, there isnt enough cylinder left. Also if you want to get rid of that new crank left me know. That is the last thing I need to get my 426 going again, I had the my big bore 444 cylinder crack and fill the bottom end with coolant during a ride. I have all new bearings, gaskets, seals, new oem cylinder, wiseco piston, and a rod kit but the local crank guy has had my crank almost 2 months now.

Edited by jojo1224

I still looking for a 4th and 5th WR transmission parts I found new for $270.00 But still looking for the best deal.

thanks for the hint jojo i,m learning as i go and used wore out 426 cylinders are cheap on ebay- how about i sell you a cheap 400 cylinder?i even have a good 400 crank rod and piston for you cheap since you run antifreeze through your new bottom end bearings any how.

I have a great lead on A head for my bike it's on Chad Reeeds it never been used it sitting on a shelf It's sure nice nice knowing old racers like my self :goofy:

Edited by marv02

I having the head ported by a friend that knows what he doing for free that a great price.

Us old 50 years old ex Mxer's stick together and help each other out when we can.

I still waiting for my new big bore piston to show up then I taking the Cylinder down to anouther Old Ex racer thats going to hook me up.

Now I still have to find a WR transmission.

This is going to be one nice desert fun bike I think it might be able to run up there with my old KTM 560 RFS 6 speed transmission the KTM was a nice bike but heavy and I never felt 100% on the bike it felt nose heavy I always worried about dropping front wheel into a whop.

But the KTM had stupid topend speed what I miss it was the only dirtbike I ever ownned you back out of it the KTM had the topend pucker factor thats for sure.

Edited by marv02

The new Big bore 98mm piston showed up need to take down sometime next week to get bored and replated.

I going try high velocity porting this time around I got mixed feed back for my old school race buddies but hey what I read it might be the hot ticket instead of getting the ported the old school way hogging them out :banghead:

Edited by marv02

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