Any gueses?

[johnmarchetta34]

You most likely could get by with cleaning the aluminum off the cylinder walls and install a new piston. Most importantly, make sure the combustion temps are cooler. Start by opening the top screws 3 turns, power should be down. Then slowly close them until response and power is adequate. The idea is to stay slightly rich of peak power, that is a lot rich of peak heat.

I agree, but since I have everything apart and there is mild scoring on the cylinder, I am going to bore everything 1mm over to be safe.

 

[fastgtfairlane]

No need to go 1mm over if .5mm over will do the job. Just extra work with no gain and eliminating possible rebore in the future.

 

[WFO Speedracer]

No need to go 1mm over if .5mm over will do the job. Just extra work with no gain and eliminating possible rebore in the future.

Ditto don't go any farther O/S than you need to go to clear the scoring and get the cylinder back round, if .25mm will do it then go .25mm .

You have to go several mm's before you realize any performance gains , Yamahas won't bore out that Far.

Send it to whoever is boring the cylinder and let them determine what needs to happen is my best suggestion.

 

[johnmarchetta34]

Ditto don't go any farther O/S than you need to go to clear the scoring and get the cylinder back round, if .25mm will do it then go .25mm .

You have to go several mm's before you realize any performance gains , Yamahas won't bore out that Far.

How far can you go on a yam cylinder?

 

[WFO Speedracer]

701 will go out 3mm to 84mm which is the stock 760 bore size

62T cylinder has much thicker sleeves than the 61X cylinder does .

 

[Big Kahuna]

701 will go out 3mm to 84mm which is the stock 760 bore size

32T cylinder has much thicker sleeves than the 61X cylinder does .

Well, I have seen some 61x Cylinders punched out to 85mm.............. But the skirts were paper thin!!!!!!!!! Not recommended but it ran really good until it didnt!

 

[WFO Speedracer]

Yeah I don't even like going 84.5 on the 760 cylinders , I can't imagine how thin those 61x sleeves would be bored that far, I won't go past 84.5 on a 760 cylinder , you are correct they are way too thin at that point .

My 650 SX cylinder is bored 2mm over , it had to go that far to take out the huge gouge in the cylinder that a piston pin dug into it, I got it that way so , you gotta do what you gotta do.