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800screws

rebuilding a 426 top end

6 posts in this topic

this is going to be funny to alot of you, but what do u have to do? buy a piston kit and timing chain...anything else? what do u have to do to valves?

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It really depends on how worn out it is, how long you want it to last, how much money you have to spend, and any considerations to additional performance.

At a minimum, replace the piston, rings and cylinder with all new Yamaha parts. Unless you want more displacement, it's better to take this route than to have the cylinder re-worked. There are some exceptions, but given the nature of your question I would assume you're satisfied with the 426 as is. BTW- the factory cylinder and piston is of a very good quality at a great price.

The head and drive train is a different story. You can replace only the stuff that is worn out, or you can replace everything. Again, depending on budget and need.

Often the seats, cams, arms, guides and chain will be in good shape. But given the low cost of the chain, it may be worth it just to replace it.

At a minimum, you may find that you can get away with just replacing any worn valves. This includes having the new valve seated and possibly a new guide pressed in.

My guess is that unless you have some experience in this you may want to take the head to a shop that can examine and advise accordingly. A full work over would involve guides, seats and valves.

And of course you'll want all new seals, rings and gaskets.

I guess you already know that it's not like a rebuild on a two-stroke.

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that's the problem!! lol, i could do a 2 stroke in a half hour on my lt250r, but this i have no idea. i can adjust valves, but that's as far as i know.

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Take the head to a reputable shop and have them clean it, inpsect and change the valve seals at a minimum (cost me $80 earlier this year). There's no need to buy a new cylinder unless yours shows signs of wear. Get a new piston, rings, timing chain and gasket set then hone the cylinder. Done.

If your jug is bad you can get a 2mm bore, Wiseco piston kit and Cometic gasket kit for $350 shipped from Lukes Racing. I've got about 20-25 hrs on my 444cc rebuild and have had no issues.

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Take the head to a reputable shop and have them clean it, inpsect and change the valve seals at a minimum (cost me $80 earlier this year). There's no need to buy a new cylinder unless yours shows signs of wear. Get a new piston, rings, timing chain and gasket set then hone the cylinder. Done.

If your jug is bad you can get a 2mm bore, Wiseco piston kit and Cometic gasket kit for $350 shipped from Lukes Racing. I've got about 20-25 hrs on my 444cc rebuild and have had no issues.

With all due respect, a visual inspection will not reveal a cylinder that is out of round or distorted.

Additionally, you can order all new Yamaha components on-line for about $300.

And I've run Wiseco piston kits before, which is great for bumping the power up a bit, but I don't think you'll get the miles you would from the factory stuff.

However, all that for $350 is a great price.

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My local dealer has a complete top end for a 426 that he is blowing out! It includes - cylinder , piston , rings , head , valves , cam and gaskets. I am pretty sure that he was asking 1000.00 for everything and it was all brand new. The dealer is Delta Sports Center in Delta, Utah. Phone # is 435/864-3432

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