Hi Guys, i have just got a new project and i would like some advice please. the piston has the number 68 on it and is in a chewed up condition no rings left and the barrel has the battle scars . i think it has been rebored in the past from 66 mm ?  could it be rebored again or is there a limit ? and if it can be rebored again would that be cheaper than finding a barrel on E bay or something and buying a new piston ?thanks for any help  Jez....

Without knowing how large the bore is now and the amount of damage it's hard to say if it can be bored again. Best to take it to a machine shop and have them measure it, they can also tell you how bad it is and how far it will need to be bored. I believe the service manual will tell you max bore. If all else fails you can have it sleeved or yes go to feebay. Just my opinion, others will vary.

+1 on measuring.

It seems unusual to me for the piston to be marked "68" and have that be the size. Yamaha pistons would only go up to 67mm. Anything beyond that would usually be aftermarket forged, most likely Wiseco. And Wiseco usually has a whole string of numbers.

You might just be seeing a random stamping? What are ALL the numbers on the piston top or is that the only one? And where is that number located? (Yamaha size stamp is usually near intake side of crown... on exhaust/arrow side there are often random numbers that probably meant something... not sure anyone knows exactly what.)

I am interested if the A 125 and 175 model piston and cylinder interchange with ct and at reed. I know the 74 125 is very similar in many ways.

"I am interested if the A 125 and 175 model piston and cylinder interchange with ct and at reed. I know the 74 125 is very similar in many ways."


69-73 AT/CT and 74-76 DT125/175 cylinders/heads/pistons can all be swapped around as "sets". 

Of course the early cylinders were piston port so you might need carb and/or jetting going between piston port and reed valves.  1976 stopped using the autolube injection into base of cylinder so you need to add fitting to carb if you have earlier carb...  or if you have 76 and use earlier cylinder you need to plug banjo fitting hole in base of cylinder on earlier cylinder..

Don't forget that 175 and 125 use different small end rod bearings if you are swapping displacements. 

Though out the years I have used Yamaha blaster pistons on my CT3 175. But if you go that route you will have to remove 3mm from the bottom skirt of the piston. With the blaster pistons you can go two steps over the step four Yamaha pistons, up to 1.5 mm over stock pistons..

Hi fellas, i have just measured the piston and it seems to be 66 mm . i have tagged in some pictures . let me know your thoughts . L O L . cheers