Rebuilding 2012 YZ250. NO A,B,C,D Pistons?

So I am about to order a new top end for my YZ250 and am browsing the parts lists. Cylinder is an 'A'.

 

Looks like the part number fro the Piston,Rings, Gaskets is 1P8-11630-00-00. There is no mention of piston sizing A-D. Are all OEM pistons now the same size? 

IMO order a "D" sized piston on any cylinder with second, third or fourth piston.

Once I had to use a "D" piston in a brand new "B" cylinder to get within piston clearance.

Order them individually. You need "A" piston, 1P8-11631-00-A0. Rings and gaskets are common.

 

I tried reverse lookup 1P8-11630-00-A0 at online parts catalogue of yamaha motor japan. But , such part did not exist. The set can not be designated its size of the piston.

It may be the part number of spare piston set as accessories of the new bike.

measure the bore dont guess,not worth it

When ordering an OEM top end kit it will usually, if not always, come with a D piston. I have read here on TT in this forum that a D is always the best thing to run in a used cylinder. 

Ok cheers guys. How do you find the individual part numbers for the A, B, C and D pistons (online)? I cannot seem to find it in the manual. 

 

 

Ideally I would have the piston before I pull it apart that way I dont have to have the engine apart/off-line for multiple weeks.

Why would you order an oem part that is inferior to a Wiseco, and costs more? Just get Wiseco. There are no downsides if you think logically.

You have to measure the bore and pick the appropriate sized piston. Take the cylinder to your local machine shop and they will measure it with a bore gauge for free or a few bucks max. I would not stand behind a motor I built by guessing piston to cylinder clearance. If its too tight it will 4 corner seize when the piston warms up and expands. Then you will need a cylinder and possibly a crank

Why would you order an oem part that is inferior to a Wiseco, and costs more? Just get Wiseco. There are no downsides if you think logically.

 

Wiseco has a downsides like a one size fits it all policy. Woessner delivers a forged piston in 3 different sizes and throws even a single ringed piston in its assembly. 

Wiseco GP pistons are good quality

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