yz 426 busted after 3rd outing gutted

4 replies to this topic
  • supershaun

Posted December 05, 2010 - 10:24 AM


Im kinda confused which way to turn i bought this 426 (bored to 440) being told the engine had just been totally rebuilt ive since found out it was the top end only. to cut a long story short the big end is shot, the pistons been tapping the head, it smokes quiet bad and the whole engine looks like its been run low on oil , ive caught the symptoms early , as ive stripped it before the motor went pop.

So im kinda after a guide price of the repair bill
new crank ?
piston rings ?
gaskits ? plus any other items (4 strokes are kinda confusing im used to honda cr 250 )

if i spend money repairing the bike will it last if maintained correctly ?
every 426 here in the uk seems to suffer with rod failure this is my first 4 stroke bike and ive lossed all faith in 4 strokes now . I loved the bikes power but i cant afford expensive rebuilds. Any help and advise cheers in advance

  • Birdy426

Posted December 05, 2010 - 11:02 AM


rod kit is about 100 USD on e-bay. Crank rebuild labor is about 100 usd as well...shop around for best prices and quality...

If the piston isn't all dicked up from tapping the head, rings will be about 30 USD mail order from Wiseco or JE, depending on whose piston you have. All up, plan on spending about another hundred for gaskets, seals, o-rings and the like. Main bearings are about 100 bucks and are only available from Yamaha (TT store or other mail order for best prices).

If the motor really has been run low on oil, take a real good look at the cam bearings and oil pump.

What sort of condition are the valves in? Has the piston been kissing them? If the valve heads/stems are bent they will fail in a hurry. Stainless valves and springs from a 400 or '00 426 are a drop in (use the right springs...same year as the valves!) for about 150 USD if you need them (again, mail order or tt store to get a good price), and here it's about 125 USD to get the seats cut. Want to check the guides as well...if the piston has been hitting the valves, and the heads/stems are bent, that will accelerate wear on the guides.

Most of the bottom end bearings can be sourced from a local bearing supply house rather than Yamaha...a bit over 100 USD to replace all of them...don't know if you will need to or not...

If it's been run low on oil, take a good look at all clutch components as well...

As far as it seeming like all the 426's in the UK need cranks, put it in perspective...the newest of these bikes is an 02, so it's nearly 9 years old. Most folks do valves, rings, pistons, etc when they "rebuild" but leave the crank alone so they don't have to split the cases. As the needle and ball bearings in the crank/mains roll, rather than slide like the rings/cylinder and valves/guides, the crank/mains tend to last longer, so for the first top end job, that's ok. With most of these bikes being turned over to a third or fourth owner before a second top end rebuild, no one really knows if the cranks have received any love in the past, so they do the top ends and are surprised when the cranks grenade.

As far as reliability, remember, the motor is 8, 9, or even 10 years old. If you spend the time really inspecting everything (gear teeth and dogs in the transmission for wear and cracking, bearings for slop (or just replace them all), oil pump for wear (or replace it), cam chain gears for wear, valves and head for wear, and don't try to cheap screw anything (in other words, make sure everything is within servceable spec or new), you will have an as new motor. From the factory, with normal maintenance, these motors were (are) as reliable as a claw hammer.

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  • Gunner354

Posted December 05, 2010 - 11:08 AM


This is why I buy new bikes.
I have over 300 hrs on one of my 09 yz450's without any motor work. A well maintained bike will last a long time. Talk is cheap. You just don't know when buying used. Sorry but you are an example of that .

  • brentn

Posted December 05, 2010 - 02:39 PM


Not all of us can afford a new bike, for some of us it is literally impossible. I think it's unfair to say "you deserve it, you bought used"

If you have to buy used, he is right and you just don't know what your going to get. Alot of people just get on the bike and ride, but IMO if you want to be safer than sorry you need to start inspecting parts.
You don't necessarily have to replace them if they are in spec, but you should be prepared to pull the top end and the jug and inspect the piston, check the rings, make sure the valves are sealing, check the clearance. It's alot of work but it's worth it to know that the bike is good to go.
Your still taking a risk, but at least if you find a problem you can fix it before it turns into a disaster.

  • supershaun

Posted December 06, 2010 - 12:04 PM


Thanks all for your comments im going to have to juggle the pennies around christmas to see if i cant get this bike fixed and up and running cheers all for your help.....

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