will this work for my cam swap?

last week i was riding my 02 426 and it locked up going across the field. well a local mechanic told me that it probably threw the timing chain off in which case i would have to replace all my valves as well. so i was thinking and i think im going to do the cam swap while im at it, so i have some questions...

1) will and 04 yz450 cam work or does it have to be an 03?

2) do you guys think this is what is wrong with my bike if not wat?

3) when i rebuild it are there any other mods you guys think i should do?

i was thinking of doing this:

444 kit

13:1 piston

2+ oversize valves heavy springs

port and polish but im afraid all this would make it unreliable and i would have to rebuild it alot

plz help me soon thanx:bonk: :mad:

1> '03-'05 YZ450 exhaust cams are all the same.

2> Maybe. Won't know 'til it's apart.

3> Your choice on the bore kit. The piston could force you to use race gas, although it usually doesn't. Don't use anything other than OEM valves. You don't need the oversized ones, and there isn't anything more reliable than Yamaha stuff.

Porting and polishing will have a complete zero effect on reliability. It alters no moving parts or wear surfaces. However, it has to be done correctly, or there will be little benefit, and may even cost horsepower. On the other hand, a port job done right can add an amazing amount of power without changing anything else. Because all the same engine componenets remain in place, there is no change in the durability of the engine.

so basically the bore kit and the port and polish are all i need and it should help me alot without sacrificing reliablity? What would be the best place to have a port and polish done?

OK so i took the cam cover off the motor on my 426 and a the mechanic that said the timing chain was off was wrong its still on and appears to be in good shape. heres the questions i have now......:mad: When i took the spark plug out it was saoked with water and iim not sur what to think im not sure if this is where the bike fell over and layed over night on its side in the rain after it locked or if the rod broke and busted through the cylinder because isnt there a water cavity around the cylinder? please let me know what you guys think thanx for all the help so far all you guys are a great help thanx a miilion

You left it lying in the rain on its side? Cool.

Water either came in from outside after the fact, or from a head gasket or broken cylinder. It's going to have to come apart to diagnose it.

Yea and it fell over sometme in the middle of the night and i didnt find it ntil the next morning

thnx again:worthy:

Like Grayracer said, until you get it opened you won't know. The timing chain coould appear fine even if it jumped a tooth or more. You need to look at the valves and piston to tell, and use the timing marks on the rotor to let you know if you are aligned for TDC. If it locked up and you think it is a rod you have to take the top end off to tell, unless you have a hole in the cylinder or cases. If that is so you have my profound sympathy.

Personally I would do what you need as far as destroyed parts, rod, piston valves etc and use stock parts except for a 450 DCM. I used the stock yamaha cam from an 03 450, like Grayracer said, any 03-05 should do the trick. Put everything back right with stock stuff including the Yamaha valves (super reliable and well made), skip the porting and big bore unless you are riding full throttle all the time, at the rev limiter, and enjoy the bike. this 426 is reliable and fast as is.

Get a Yamaha (not Clymers or Haynes) shop manual and get to work. this site can walk you through the work, just search some and ask about what you don't find.


Thanx Bill, there are no holes on the outside of the cylinder or cases or anything like that the thing that really worried me was the water i found on the plug. what should i look for on the valves ive never messed with valves on anything before? thanx

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