Gonna need some Big Time help with my 426...

ok, i need some help, big time...on the last trip out my 2000 yz426f died on me, wouldn't restart at all...brought it home, tried to diagnose...

first thing...spark plug...the part that is in the chamber is all rusty. uh oh...second thing, coolant is low/non existant...drain the oil out of the case...ahhhh theres the coolant.

so, after various searches, it looks like it could be the head gasket, or even worse, a cracked cylinder...anything else?

I've decided to try to tackle this, with the help of this forum, if you all don't mind. I'm in the process of taking it a part, taking lots of pictures for reference, and to post with questions once I get into the engine. Which brings me to my first question. should this be an engine out of the frame process? would there be any reason to keep it in the frame? I'm thinking, take it out of the frame, take the engine apart, and try to find anything that could be wrong...take the head to a machine shop to check tolerances, and same with the cylinder, and replace the piston, rings, etc...then, after getting it all back together, put it back into the frame, and try to figure out any starting issues then...

if it turns out there's more damage than can be repaired, then I may have to change directions...but I want to try and tackle this myself. As far as previous experience, I've done a top end on a 2 sroke before...haha (I'm I getting in over my head?)

Does the kicker move? worse case scenario your timing jumped, Valve hit a piston and pushed it into the jug cracking it.

If your good at following directions and your observant and careful then yes its easy. If you like to rush and dont pay attention dont even try it.

My advise is rip the top end off its probably due anyway. Thats the only way to tell what happened. Everything else is speculation or a guess until its apart..

oh, top end is due...

kicker moves just fine.

i'm kind of in between observant and careful and sometimes rush to get it done...something like this, I'll force myself to research read and read again, then research some more and take my time...

so, you say take the top end out with still in the frame, or do everything out of the frame?

Its up to you, I take mine out and put them on the bench and clean the hell out of everything. If it was mine it would get a crank, clutch, basket and head rebuild depending on the hours it has on it and how well it was maintained. I mean it is 9 years old after all and I have been seeing a lot of 426 threads lately. Its up to you. you will need a fly wheel puller and a few basic tools to do the top end and chain..

clutch was good on it...really didn't want to touch the bottom end...but if i pull the motor out, maybe...head rebuild is in the plans...i have a basic mechanics socket set, gonna pick up a torque wrench, anything else?

A good set of narrow feeler gauges in the correct size range( i got mine from motion pro). A good quality TQ wrench, I use snap on. If you over tighten the cam caps its game over. They are only supposed to be 7.2lbs i believe. TQ specs and sequence are very important so be sure to pay attention to them. Its a easy procedure, im sure once you finish it you will feel confident in doing it more often.

thanks...gonna pick up some feeler gauges and look at getting a nice torque wrench.

ok, got the majority of the bike apart. engine is almost out. i think i'll powder coat the frame since it's this far apart.

now, when disassembling the engine for inspection, is there a certain procedure? i know there is a certain sequence when assembling, but how about disassembly? and what should I be looking for, exactly?


What size socket do I need to get the nut off the swingarm pivot?

And I've got all the nuts,bolts that hold the head/cylinder together but nothing is budging. Any ideas?

Yes. The procedure is detailed very clearly in your owner's service manual. If you don't have one, download one at http://www.yamahaownershandbook.com.au/index.php

RTM Dont attempt to do it blind if its your first motor.

And I've got all the nuts,bolts that hold the head/cylinder together but nothing is budging. Any ideas?

are you taking the motor out or top end off?

Well, I put all the nuts/bolts back on and waiting to get the right sized socket to get the swingarm pivot off. I was going to leave it in but I'm also going to wait to get a hold of the manual.

And I've got all the nuts,bolts that hold the head/cylinder together but nothing is budging. Any ideas?

You should have removed 4 head bolts and 4 nuts. Did you?


gotta hold of a factory service manual...been reading and studying the cam/cylinder head section before I loosen another nut or bolt...

looks like i need to remove the cams in the exact way the manual states...any hints not in the manual...before i remove, should i be checking anything like timing? - which will be harder as i won't be able to follow the manual as i have an auto decompression cam (which one i do not know as the P.O. said they were either hot cams or a 03-05 OEM...how would i be able to tell?)

and the engine is still in the frame, as i'm still wondering what size the nut on the pivot is...(the largest metric socket i have is a 19mm and it's too small, and i don't have any SAE that fit ???)

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