Always a "D" piston

[clw]

I have a B cylinder, did I read correctly a few years back in MXA that all rebuilds should use a "D" piston? That the cylinder will wear and the 0.01mm difference between an "A" and a "D" piston wouldn't matter anymore.

The parts jockey at the Yamaha shop said to use what's stamped only.

Thanks

 

[86 RM125]

The only wat to tell would be to have the bore measured. If the bore is worn enough the larger D sized piston might work.

 

[oxygen]

It does not matter what´s written on the cilinder.You have to measure bore and then order a right piston.

 

[sillygoose27]

Do you need a special measuring tool to measure it with?

 

[MikeT]

A side note. The Weisco replacemwnt piston only comes in one size. I don't know what letter it matches up to but I have always used one with no problems. I would call Weisco and ask them what size their piston is in diameter, then check your manual for the Yamaha sizes corresponding to each piston size. Then you can see what will work.

 

[fuzzy]

The wiseco is more than likely equivilant to the D. You can put a D into a brand new cyl. It's 'factory recommended' to go A-B-C-D, then new cyl w/ A. Of course no one in their right mind would ever buy a new cyl at that point!

 

[clw]

Fuzzy:
"A" is the smallest
"D" the largest,
were you thinking the opposite?

 

[fuzzy]

Nope. A "D" is still within the piston clearance limits of a brand new cyl.