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View Full Version : yfz 450 top end rattle?


matt 1980
07-13-2009, 01:53 AM
hi, can anyone help with this one!

it all started with the piston going sideways in the barrel the bike locked up . we stripped it down the only dammage was the barrel and piston no dammage to bottom end or head at all.
seen as it was stripped i got a new hot rods crank and rod and a cylinder works big bore kit that is supposed to bolt straight on with no need to change anything ..
we carefully assembled the engine and fitted it back in the bike
when we fired it up lastnite after first checking the timeing is right and turning the engine by hand to check it all moves without things hitting each other!
we then had a rattle quite loud sounds like its comming from the top of the engine ??
we are not sure what it could be ?? any ideas?

thanks
matt
kyledvor61
07-13-2009, 02:56 AM
check your valves. could be out of spec
matt 1980
07-13-2009, 06:34 AM
thank bud .. ill try that . i dont know anything much about the head and clearences on the valves etc any tipps on gaps etc?
Fast350ex
07-13-2009, 01:47 PM
Intake- .006
Exhaust- .009

Also check cam chain tension.

Use a mechanics stethoscope and listen around the motor to justify.
matt 1980
07-13-2009, 02:03 PM
thanks all the help much appreiciated
matt 1980
07-13-2009, 02:18 PM
going back to the valves .. the top end was fine before the bottom end re build .. no rattles, how could it now start rattling ?
can taking it off etc effect it like that?
kyledvor61
07-13-2009, 02:59 PM
That, I'm not sure on. But I always check the valves whenever I have the valve cover off anyway.

and yes check your chain tensioner. There is an up and a down side to it.
matt 1980
07-14-2009, 11:39 AM
one other thing we are a bit worried about is the cylinder works big bore kit.. it all came boxed up but we only had enough rings for to make the oil one and one other piston ring above .
there is a slight groove up above that one but doesnt look deep enough for a ring and we wernt supplyed enough for that one any way ..
is this normal for this kit does anyone know?

thanks for any help
matt
ae13291
07-14-2009, 12:58 PM
also keep in mind when the engine seizes the cam sprokets on the yfz's can actually spin on the cam, there not held on by bolts, t think the sprockets are pressed on there. in your situation i think its your timing chain, it sure sounds like thats the issue, check the tensioner make sure its released