Where can i get a new std bore piston for yamaha rd 350

Whenever a motor is taken apart so that you can install piston rings, it is rather common to replace many other parts at that time.
Commonly, all of the replaceable bearings ( crank & cam) are changed.
Also commonly, the engine block is bored so that new pistons can be fitted, because of wear on the cylinder walls.
Commonly, an inside micrometer will tell the technician how much to bore the block.
The block is usually bored from .010 up to .040.
If the block is so bad that a .040 will not be big enough, the block is scrapped out.
Then, "oversized" pistons and rings are fitted to the new size hole.
You would measure the size of the bore to tell which size rings to buy.
God bless your efforts.

Model: Yamaha RD 350 Year: 1986 Category: Classic Rating: 76.9 out of 100. Show full rating and compare with other bikes Engine and transmission Displacement: 347.00 ccm (21.17 cubic inches) Engine type: Twin, two-stroke Power: 63.00 HP (46.0 kW)) @ 9000 RPM Top speed: 190.0 km/h (118.1 mph) Compression: 6.0:1 Bore x stroke: 64.0 x 54.0 mm (2.5 x 2.1 inches) Fuel control: Membrane & power valve Cooling system: Liquid Gearbox: 6-speed Transmission type,
final drive: Chain Chassis, suspension, brakes and wheels Front tyre dimensions: 190/90-18 Rear tyre dimensions: 110/80-18 Front brakes: Dual disc Rear brakes: Single disc Physical measures and capacities Weight incl. oil, gas, etc: 170.0 kg (374.8 pounds) Fuel capacity: 20.00 litres (5.28 gallons) Other specifications Further information Parts and accessories Our partner CMSNL ships low cost OEM motorcycle parts to Australia, Austria, Bahamas, Belgium, Canada, China, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hong Kong, Hungary, Iceland, India, Ireland, Italy, Japan, Kuwait, Latvia, Lithuania, Luxembourg, Macedonia, Malta, Montenegro, The Netherlands, New Zealand, Norway, Poland, Portugal, Serbia, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, Taiwan, Ukraine, United Kingdom, The United States and more. Or check out parts and accessories from our other partners.

you have to buy a new bore kit which u fetch u around 5k

The std bore is 54mm and some available piston sizes are (Vertex Pistons)

53.93
53.94
53.95
53.96
53.97

It depends on how deep the gouge is. Having it bored and a new oversized piston may set you back more than a new stock piston and cylinder.

faulty piston cast, or too hot of a plug for too long will rusult the same.

You need to check clearance betwween piston and bore.It should be 1 1/2 thou clearance at the base(widest part)of piston.If it is less than this or more than 2 thou (0.002")then you will get problems.

Make sure it has been bored properly and that bore diameter is the same throughout the length.

Ring gaps should be about 7 thou,and no less or you will get seizing.

If you have a powervavle it should be set correctly too.I raced RD 350s for nearly 10 years and there is so much you can do but it can take time, but I will help you if you are interested.I could give you starting points for tuning if you can tell me carb size,whether you have expansion pipes,airfilter type etc ,etc.Oh dond forget not to fit plugs that are too hot like a bp6hs etc. as you can hole your piston too.

In the mean time check the piston,bore and rings and get back to me if you need more help.

first off what country are you in ???? the 1979 rd 350 was an air cooled engine, same as 250 . the 1989 engine was water cooled with yamahas ypvs exhaust valve both very differnt in design although some frame and body parts cross over.the manual for the air cooled is: isbn 0 85696 505 7 . i dont have the water cooled number but could find it you require. the rd was exported under various different names ie: rd , rz , ypvs and so on. you can contact me @ [email protected]. hope this helps.

did you re-jet the carbs?

The bike will still run even at 7:1 or a little lower, but the specifications call for about 10:1.