Piston Size

[trentjanelle]

Hey Guys,

I'm trying to rebuild my engine and i have come to a road block.

I have just removed my pistons and measured them and come up with 74.95mm in diameter. can someone tell me if this is the standard measurement of the standard piston. Mikesxs on tells me what mm over and the 1st 2nd 3rd or 4th rebuild and not the actual piston size.

while i'm there is there anything i should be on the look out for when i'm rebuilding it... it's already apart.

Thanks heaps guys

Trent

 

[Scrambled]

Maybe try looking at 650 Central . They have more tech info on that site .

 

[trentjanelle]

will do thanks

 

[hotdog]

75mm is the original bore size, you need to measure the difference between the piston/s and the size of the bore. If you're Lucky you might get away with re-ringing & reusing the pistons & a quick hone out.

Hey Guys,

I'm trying to rebuild my engine and i have come to a road block.

I have just removed my pistons and measured them and come up with 74.95mm in diameter. can someone tell me if this is the standard measurement of the standard piston. Mikesxs on tells me what mm over and the 1st 2nd 3rd or 4th rebuild and not the actual piston size.

while i'm there is there anything i should be on the look out for when i'm rebuilding it... it's already apart.

Thanks heaps guys

Trent

 

[650Skull]

Why you would get directed to 650central for maybe the info............

Hotdog is right and all the info you need for specs is in these threads here and here

 

[jay760]

75mm is the measurement given but always 74.***, Yamaha match the pistons to the barrels, you will find a number stamped in the top of the piston and a number printed on the liners, the clearance is the difference between these two numbers.

 

[Scrambled]

Why you would get directed to 650central for maybe the info............

Hotdog is right and all the info you need for specs is in these threads here and here

Why ? Because he was looking at Mikes XS and they did not list the stock piston size , my manual is out in the shed, I was in my underwear and it is - 15 out when I answered that. I know eventually someone would answer the guys question , he wanted to know the stock bore size. Mikes is very short on details .

 

[5twins]

Clean the tops of your pistons. Somewhere on there you should find a 3 digit number stamped. That is the decimal portion of your original piston size, as in 74.XXXmm. If you're measuring 74.95mm now, that's probably an original stock bore piston. Compare that number to what's stamped on the piston top and you'll see how much it has worn.

As mentioned, there is another number stenciled on the side of the cylinder liner where it hangs out the bottom of the jugs. That is the fractional portion of the original bore size, as in 75.XXXmm. The factory clearance spec is .050-.055mm so subtract your piston size from the bore size and see where you're at. If you're in spec or at least pretty close, you can probably get away with just re-ringing this time. Next time you're in there, you'll probably want to bore it.