YZ400F piston clearance

[E74]

I have a YZ400F that when I bought apparantly had a new top end,  it has .50 oversize piston which measures 85.00 millimeters exactly (The piston seems to be brand new) the bore is exactly 85.50 millimeters and is perfectly parralell and has hone marks in it, is this the standard amount of clearance?, the piston seems to move around a lot in the bore and slap against it?, is this normal?


Thanx,

Darren

[ChrisACT]

0.5mm is way to much.

[Rosco400]

3 to 4 thou or .12mm to.16mm about right

[Lozza]

It has not been bored correctly if there are no hone marks inside,bores need a cross hatch pattern for a host of reasons.If it measures 85.50 exactly I'm afraid it's going to have to go out to 85.75 or 86mm depending on the next piston size is.As the cylinder must be machined with a boring bar to 0.05mm under size then honed out to the correct size.Piston and bore sizes are labeled 2 different ways.Wossner for example quotes the piston size and the clearence eg 84.94 (0.06) meaning the bore size is 85.00mm. Wiseco quote the bore size eg 85.00(0.06). I doubt the piston will measure 85.00 exactly either Isn't 3 thou = to 0.075mm and 4 thou = to 0.10mm Rossco

[Rosco400]

Yeah see what happens when ur away from the tools so long 40" = 1mm, 20"=.5, 10"=.25, 5"=.125c Dumb freakin accountants should do there sums first

[caps 999]

really the logical thing to do is have the barrel bored to the piston your using then theres no guess work as moulds and metal shrinkages can play a factor in the piston size so technicly certain pistons can vary +-.05mm so if you need to go o.s the buy your piston and work from there

[E74]

Thanks guys, looks like I need to buy some new gear for this...

[oldyzman]

Would seemm that you hae a standard piston and the bore is 2nd oversize yammy or 1st oversize wiseco. as yamaha generally goes in steps of 0.25 and wiseco for yamaha goes in steps of 0.5.
OLDYZMAN