Piston size : new to four stroke

hello

 

i am new to four stroke, and would like to change my piston and rings on my yz 450  2012.

 

in 2 stroke, for yamaha they used A,  B,C,D piston sizes

 

 

what happens for four stroke? do you keep putting the same piston size over and over?For oem pistons i have seen  only one size for my bike.

 

if you do not know the piston size that was in, what do you recommend doing?

 

Thank you for answering

hello

 

i am new to four stroke, and would like to change my piston and rings on my yz 450  2012.

 

in 2 stroke, for yamaha they used A,  B,C,D piston sizes

 

 

what happens for four stroke? do you keep putting the same piston size over and over?For oem pistons i have seen  only one size for my bike.

 

if you do not know the piston size that was in, what do you recommend doing?

 

Thank you for answering

No ABDor C pistons. Just the stock bore size. You should take it to a competent machinist or other to see if your bore is in spec. When or if it gets out of spec. you can buy a new cylinder or have yours re-plated. Check in your shop manual for the bore specs.

Measure the bore with a bore gauge and order the piston accordingly. 

Measure the bore with a bore gauge and order the piston accordingly. 

 

This should read, "Measure the bore with a bore gauge and order the CYLINDER accordingly".  It was just stated that there is only one available piston size to be ordered, and as long as we're talking about OEM parts, that's entirely true.  Some of the aftermarket suppliers make pistons in alternate sizes, but only in increments of .0001" so you can decide between .0018" or .002" clearance, if that's your deal.   Just realize that both the OEM cylinder and piston are built to within .00025".  

 

The measurement of the bore is far more critical.  The maximum wear tolerance at any one point in the bore is .002" variation from being round through any cross section, or dead straight vertically.  The fact that the Nikasil plating is likely to be no more than .002" thick anywhere is a major consideration.  

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