Another Big Bore Kit thread

[URX111]

I've been reading and found out that the 1971 has a 256 engine. Now the kits are for a 447 engine, won't fit mine. Unless I put in 447 rods, looks like a lot of work. Then I got to thinkin , I could change the pistons. I would need a custom made piston , a motorcycle mechanic told me he could get them for around $200.00 apiece. It would be the same demission's as the kit pistons only change the pin height , move the pin down on the pistons 6mm's . Does this sound right or does anyone know who would stock this piston ?

 

[650Skull]

I think your mechanic means up the piston....................Lots of good information and advice on the 256 pistons and con-rods in your first thread. Maybe that's where you read about them

If you can get 2 pistons specially made for a 256 engine for $200.00 each that is cheap. Usually a company like wiseco would need an order of at least 12 to make it worth their while or else the cost would be exorbitant. Well they probably wouldn't do it

 

[URX111]

Your right Snake, it is up. I reread your post in my other thread and came to the conclusion that I may just go in another direction. What you wrote in my other thread sounds good. Until I get better and out of here , I can't get at my bike. When I get out of here I can talk to the man that's going to help me and go from there. Until then I'll keep reading and post once in a while, to see what other people have to say about my thoughts. Sense the 256 engine is a grenade waiting to happen, I don't see any reason to build it up to grenade.

TNX Paul

 

[drgonzo]

Is the 256 engine that fragile? In stock form, from my experience, no. I do not have big bore experience. I am considering building one with stock cam and 700cc or 750cc kit.
I have absolutely HAMMERED on my stock XS2 engine for probably. Ran three seasons of AHRMA, one race at Daytona with the throttle pinned, tucked in on the banking at absolute top speed for several second each lap for 8 laps, plus practice, x 2 days. I've never been farther than the clutch on bottom and valve adjustments on top.
I'd love to hear from someone with experience with a modified 256.

 

[RC4MAN]

The 256 engine is no more fragile than the 447, they were only built 3 years, there's way fewer of them so there's little interest in making high performance parts for them. As I understood it the change was made to achieve a smoother running engine.
Shame because I too have a 256 series engine that I'd like to pump out to 750.
Every once in a while between Mike's XS, YamahaXS650, XS650 Central you can find a kit but I just looked and none currently have the parts.
If you find them let me know.

 

[drgonzo]

If you find them let me know.

http://www.hoosracing.com/new650750engineparts.html

 

[gggGary]

The conventional wisdom is that the 256 rod 22mm small end is thin and prone to stretching. It was a "hangover" from very early needle bearing small ends. An oopsie by a company who mainly built 2 strokes before the xs.
Failure tends to be catastrophic,with a rod finding sunshine through the front of the block

 

[URX111]

Thanks drgonzo : There it is , just what I was looking for. The more I read the more I think I will go with new 447 rods and the Big Bore Kit for the 447 engine. Is this doable ? Will the case accept the Big Bore Cylinders ? Will the 256 heads fit on the cylinders ? This way it all comes in at about $600.00 I'm not a racer but my bike has been driven to L.A. CA. twice back and fourth , from S.F. CA. and it still runs good. I did break a timing chain though after I got back the first time. My friend put a new chain in and drove the second time , back and fourth . That's 760 miles for one trip .

 

[46th Georgia]

I've been reading and found out that the 1971 has a 256 engine. Now the kits are for a 447 engine, won't fit mine. Unless I put in 447 rods, looks like a lot of work. Then I got to thinkin , I could change the pistons. I would need a custom made piston , a motorcycle mechanic told me he could get them for around $200.00 apiece. It would be the same demission's as the kit pistons only change the pin height , move the pin down on the pistons 6mm's . Does this sound right or does anyone know who would stock this piston ?

Why not just buy a 447 engine. Plenty of them on ebay.

 

[650Skull]

Thanks drgonzo : There it is , just what I was looking for. The more I read the more I think I will go with new 447 rods and the Big Bore Kit for the 447 engine. Is this doable ? Will the case accept the Big Bore Cylinders ? Will the 256 heads fit on the cylinders ? This way it all comes in at about $600.00 I'm not a racer but my bike has been driven to L.A. CA. twice back and fourth , from S.F. CA. and it still runs good. I did break a timing chain though after I got back the first time. My friend put a new chain in and drove the second time , back and fourth . That's 760 miles for one trip .

Then there is the Cam chain sprocket on the crank shaft..............The 256 and 447 cam shaft sprockets have different sets of teeth. Can't mix and match them, has to be 256 sprockets on the crank and cam or 447 on the crank or cam. Can swap them both over to the other engine but has to be as a pair.

So for example. If you put in a 447 engine but you want to use the 256 cam. you will need to take the 447 cam sprocket and put it on the 256 cam. This would be the thing to do as the early 256 cams are a little hotter than the later 447 cams

 

[650Skull]

It Happens.........