whats the differece

[Myowncreation]

Whats the difference between a xs650 with a 447 serial# and a 256 serial#

 

[Tim of DO THE TON]

Some differences in the engine mostly. Frame differences also making the front ends incompatible (steering tube is shorter on the 71-73 frames I think).

The 256 engines had I believe a more aggressive cam profile, and some (earliest?) might have had longer rods? Others will chime in on that.

447 engines are all pretty much identical and all parts interchange through the years.

 

[5twins]

256 engines had many differences in the top ends compared to the 447 motors. Different pistons, rods, cam chains, and cam sprockets were the biggies. Cylinder and head castings differed slightly having a smaller gasket area between the cylinder and head. The cam is said to be a little hotter and the ports a bit better shaped, or at least cleaner cast. Early heads, up to '71, use four 3 hole valve covers. I have one of these early heads and would very much like to try it out on my 447 motor some day.

 

[scott s]

I have a ~72-ish 256 engine. What would it take to run that head and cam on a '78 447 engine?

I'm pretty sure the head bolts right on, but what's the difference in the cam chain and sprocket? Can it be made to work?

 

[gggGary]

You would have to press the sprocket from a 447 cam onto the 256 cam different number of teeth. AFAIK

 

[vr3506]

You will have problems with a 256 cam and tuning the engine with the later BS38 carbs.
Have no experience with BS34's on a 256 cam
A 256 cam will improve bottom power

 

[lakeview]

I don't want to sound like a wet blanket, but if one's intention was to hot rod a 650 engine, would it not make sense to start with something only a decade or so old, and maybe something that had underpinnings to support 60 or 80 hp?
I decided a Harley touring machine needed more power, ultimately I have a 113 c.i. engine that makes the Road Glide dance, in a way, but at the cost of thousands of dollars and a lot of down time, and if I choose to compare speed, in a safe legal setting of course, the only thing you can beat is other dressers. One of the regular contributors here characterized these 650's as "stately" and maybe getting one working good and reliable and looking like you want it should be the goal. end rant

 

[scott s]

You will have problems with a 256 cam and tuning the engine with the later BS38 carbs.
Have no experience with BS34's on a 256 cam
A 256 cam will improve bottom power

Why is that? Carbs will run anything with the right jetting, needle settings, etc.

 

[ReycleBill]

I don't want to sound like a wet blanket, but if one's intention was to hot rod a 650 engine, would it not make sense to start with something only a decade or so old, and maybe something that had underpinnings to support 60 or 80 hp?
I decided a Harley touring machine needed more power, ultimately I have a 113 c.i. engine that makes the Road Glide dance, in a way, but at the cost of thousands of dollars and a lot of down time, and if I choose to compare speed, in a safe legal setting of course, the only thing you can beat is other dressers. One of the regular contributors here characterized these 650's as "stately" and maybe getting one working good and reliable and looking like you want it should be the goal. end rant

It's not really about making sense-- it's about trying different things and learning the results for one's self. From any sort of practical point of view you are 100% correct but who says our toys must always be practical?

 

[mrriggs]

I don't want to sound like a wet blanket, but if one's intention was to hot rod a 650 engine, would it not make sense to start with something only a decade or so old, and maybe something that had underpinnings to support 60 or 80 hp?

Only if your goal was to have the fastest bike. In which case, why would you start with a 650 anything?

Personally, I like to hot rod things because I like to hot rod things. It's all about the journey, not the destination. The XS650 engine is a dirt simple design, easy to work on, and relatively cheap.

For comparison, a guy at work had an SV650. Clearly the better choice for a race bike. But even simple maintenace was a daunting task compaired to the XS. Took him over an hour to change the plugs which is a five minute job on an XS. When it came time to adjust the valves he sold the bike and bought something older. He is competent enough to do the valves himself, he just didn't want to go there.

Back on topic...

The 256 cam is hotter than the 447. It has more intake duration and a tighter lobe separation, similar to a Shell #1 but with less lift.

447 - Duration 231° In/Ex - LSA 106° - Lift 0.388"
256 - Duration 244° In / 236° Ex - LSA 100° - Lift 0.372"
Shell #1 - Duration 250° In/Ex - LSA 100° - Lift 0.405"

 

[vr3506]

Why is that? Carbs will run anything with the right jetting, needle settings, etc.

That's the problem, you don't have the right needles and if they exist, try to find them. It was not possible with the standard XS needles and different jets.
specially round 60-75 Mph the bike didn't responce right.
I tried this twice and a friend of mine tried it once. We've spent many hours to try to get it right. After putting on some old XS2 BS38's the bike ran almost immediately correct and just needed some fine tuning.

Jan