Freshen up 2000 YZ 426

Are you sleeving the cylinder for the 98mm piston or just bore, repate & pray that the wall is thick enough? EDIT: Don't forget you will need a custom made head gasket for that 98mm piston, cosmetic does great work and has done that size before for the same bike.

Edited by jojo1224

good point about wall thickness jojo, i posted on my thread a question about 444,s breaking and was wondering if the aluminum cylinders got to thin and flexed causing binding or side loading of the piston and rod destroying the motor.it has occured to me that possibly a steel sleved big bore might be a longer life combination

I going to let the shop that doing the bore job tell me which way to go with the bore job they will know better than I know my self.

And thanks for the heads up about the head gasket..

Are you sleeving the cylinder for the 98mm piston or just bore, repate & pray that the wall is thick enough? EDIT: Don't forget you will need a custom made head gasket for that 98mm piston, cosmetic does great work and has done that size before for the same bike.

And the porting has begain if I can find my camara I post some pictures.

I did some research on head gaskets I have one made for the 98mm Big bore piston.

I read both they had the cylinder bored and replated and others sleeved with a steel sleeve I will let the shop let me know whats better for what I want the bike for.

After get this done I will install a WR transmission give the bike some longer legs, I do more research I like to put a lowwer first gear in the bike at the same time for the single track goat trails.

Edited by marv02

Let me reiterate: DO NOT have some gorilla with a grinder who "knows what he's doing", or who has some sort of general porting theory in his little mind monkey around with your cylinder head. Because of the dynamics of the three valve intake and its effect on air flow into the combustion chamber, it is far easier to loose power by porting a YZF than it is to gain any.

If you have anyone other than someone who has a proven record with 5 valve Yamaha heads work it over, you're on your own.

Thanks Gray but he knows what he doing.

Let me reiterate: DO NOT have some gorilla with a grinder who "knows what he's doing", or who has some sort of general porting theory in his little mind monkey around with your cylinder head. Because of the dynamics of the three valve intake and its effect on air flow into the combustion chamber, it is far easier to loose power by porting a YZF than it is to gain any.

If you have anyone other than someone who has a proven record with 5 valve Yamaha heads work it over, you're on your own.

Edited by marv02

Sent the cylinder out to get resleeved with a Steel Sleeve I talked to the place who doing it they said even with the smaller 97mm piston they recommend a steel sleeve with a 98mm what I using they say steel is more or less a must the Aluminum will crack at the cylinder skirt area.

They are also looking into a head gasket for it I told them add to the price if they can or have one already.

Edited by marv02

good decision marv, more than a couple of big bore 426+ motors have blowen up. i bought a wr trany off a guy who did up a 444 for super moto ---it lasted 32 hrs and nuthing bad about crank works but they had rebuilt the crank with a new rod. the rod snaped at the botom of the stroke and the cylinder was broken. top end was fine

whats it going to cost you to get your cylinder done?

$230.00 est.

good decision marv, more than a couple of big bore 426+ motors have blowen up. i bought a wr trany off a guy who did up a 444 for super moto ---it lasted 32 hrs and nuthing bad about crank works but they had rebuilt the crank with a new rod. the rod snaped at the botom of the stroke and the cylinder was broken. top end was fine

whats it going to cost you to get your cylinder done?

I have been looking for a good used WR transmisson so far no luck if I find one at a good price I pick it up but if all the topend parts come back first I put the motor back together for now.

I hearing I should get the topend part back end of next week or the next week.

I will do the WR down the road when I find a good deal on one but with my luck as soon as I get the motor back together I find a killer deal on a transmission.

I am interested in seeing the 98mm sleeved cylinder, I have a cracked 97mm cylinder that could be repaired with a steel or aluminum sleeve. Those wr transmission are sure hard to find, I have been looking for one for a while but it can wait for now because I have a spare crank I want to get stroked first.

I don't know if this might interest you, but there is a eline stator for a 426 in the classifieds for $300. Link here

No thanks no night riding for me it be a crash waiting to happen :jawdrop:

some times its cheaper to just buy a used wr bottom end and strip out the trany

I been looking.

some times its cheaper to just buy a used wr bottom end and strip out the trany

200 is what i payed the last 2 times,the first one had new low hrs wr top gears and the other one i,v yet to open up it could just be a pile of whore out crap

so uhhh ware are you at on this build? hope your not still grinding on that head lol, i slowed down on colecting parts for my build as cristmas is all most here and we,r going to do some traveling so the spending is changing patterns for a bit

Ya my jug is back from getting bored for the new piston.

I just E-Mailed Cosmetic Gaskets about having them make me a custom topend gasket kit.

I still looking for a Transmission from a WR but no big hurry.

Very Happy found a complete WR transmission on E Bay for $99.00 and ordered all the gaskets now I need to wait for them to show up and put the bike back together.

So I put a 3mm big bore kit, Ported the head, WR trans 450 Carb, Hot Cams, the bike should be a beast the way I like them.

I going to order the custom head gasket tomarrow It comming together.

I am going to paint the frame as long I have to pull the botton end out of the frame to split the cases to install the WR transmission in it cant wait to get back together and take for a ride.

Pulled the bottom end apart today starting to get things cleaned up so when the WR trans parts show up I can put back together.

I did notice someone has been inside the motor before looks like the worked on the couter balancer once apond a time but what I read thats normal for a 2000 YZ 426.

All the bearings seems to been nice and tight so no reason to change them crank seems tight all bearings on the crank seems good.

Looked at the shifter forks little to no wear on them but this was a first for me most motors only have 2 shafts for the shifter forks and they float on the shifter shafts,

This motor had 3 shifter fork shafts and they are rolled pinned in place and the shifter shaft slide on the case housngs it self somethig new for me.

3 shifter forks is normal but 2 are on 1 shaft and the 3rd on it own shaft by it self and they float on the shaft not rolled pinned to the shafts them self.

I have pulled many motors before this new.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now