701/Big Bore Porting Question

[BROSS]

If you are going to take a 701 61X, and resleeve it to a 84mm sleeve do you have to open the transfer ports, going up the sleeve because the bore opening 1-2mm. In the center of the cylinder its not very thick to start with, not much room to open it up. Any imput will help out, thanks Billy

 

[SUPERTUNE]

Mostly depends what brand sleeve you use... I have ported through before and now know how far I can cut. I saved some old cracked castings and cut them up with a sizzler wheel to find where they were thin. Not a job for the DIY'r. Now if you have a machine shop to use and lots of time...go for it like I did when I got started, I hated resleeving...now that I've done hundreds, I don't mind doing them now except the time it takes (too long).

 

[BROSS]

My father is going to bore the old sleeves out, and we have access to a full machine shop, the cylinder are ported lightly and I was just wondering if and how much to open them up, thanks for the reply.

 

[Watty]

Yeah, I'm wondering the same thing. I have a 61x cylinder that has been bored to 84mm (not re-sleeved) and wondering how much the tranfers should be opened up to accomodate the extra cc's. It's not a hi-po engine or anything, just needs to be reliable. I guess they could be just left standard, and be down a little on power?

Any thoughts?

 

[SUPERTUNE]

You shouldn't need to bore out the sleeves on a yamaha 61X/62T cylinder just put them in the oven for 1 hour at 375 degrees and should come right out , maybe a little proding with a punch and a small hammer. The only ones I bored out were a real rusty one and maybe another one that broke a rod and beat it up so bad it wouldn't slide out. I only bore the block about .100 thousandths more for the big bore sleeves, so not much is lost in transfer area, you can make up most of that loss by doing other mods with the engine set-up and port mapping for a specific target RPM for freestyle, a little more transfer work is required for a higher RPM target like when using a dry pipe set-up.