6m6 650 question

[tbaer]

i have a 650(6m6) sitting around and I am wondering how far can i bore it and what mm and brand of piston.

 

[SUPERJET-113]

Last bore on a 6M6 650 cylinder is 81mm(701cc).
Go with some Pro-X or Vertex.
If you wanted to save some more money the WSM Platinum series are good too.
Radney at Xscream xmeatal give good deals on Vertex too.

 

[Matt_E]

Last bore on a 6M6 650 cylinder is 81mm(701cc).

I've had one bored to 82mm before. Been running great for 2 years, no issues.
The bottoms of the sleeves were not as thin as 61X sleeves at 84mm.

 

[SUPERJET-113]

Really hmm. I was always remembering 701 from back when I did it like 15 years ago on a 6m6. If your doing it now, then it must be possible.
Ya the sleeves are thick on that cylinder, thats for sure. Those things have the worst stock porting ever.

 

[Matt_E]

We had a spare 650 cylinder and 82mm pistons, so I ported it and got it bored.
We put it on a 62T bottom end with dual 38's and a stock 701 head.
We had an initial high compression problem, but I don't remember how we solved it.

Ran it with a Riva Red pipe. It ran about as well as a home-ported and piped 701.

 

[vomitspot]

i need some oem 6m6 rings if your ditching the 650 stuff
jason

 

[jetski9010]

if you bore out a 650 to a 701 can you use the race logic porting specs for a 701 or can the 650 exhaust port not be opened up that much? Also if you have a coffman 650 pipe do you need to bore your head pipe to help the bigger bore?

 

[Matt_E]

The water jacket is closer to the exhaust port, so you can't go quite as wide.

 

[tbaer]

i had a friend of mine port it already, but i think i will bore it to 81mm. I have the 6m6 pistons and rings they are in very good shape. i haven't measured them but they have an "F" on the top of them. can anybody tell me what the "F" is for?

 

[SUPERJET-113]

They are new pistons? What brand?

 

[tbaer]

they are the pistons that were in the motor when i bought it. they just have an f on the top of them. what the he!! does the "f" mean?

 

[Matt_E]

It means Front.