71 yamaha xs

[doughboi916]

is there any difference in performance with the older 650 motors? im going to go look at a 71 friday.. just curious?

 

[doughboi916]

yes no maybe so?

 

[5twins]

They were supposed to be a bit more powerful with a few more HP but I also heard the top ends weren't as strong. Also, all the parts are harder to get and more expensive. Unless I was fully restoring one, I wouldn't bother. For basic use and riding around, you're better off with the later 447 motor.

 

[XSLeo]

As 5twins says a bit more power. I think if I had one and it needed a rebuild I would replace the internals with 447 internals.

 

[Punkskalar]

I know the early cam profiles are more aggressive, and the heads are much nicer castings in the ports. I prefer to use them on my own builds... The rod pins are 22MM which are a "weak" point, but I've never seen a broken one. Nothing I would be afraid to ride, build, modify, etc... 447 Engine parts swap right in and are cheap to find...

 

[5twins]

Punkskalar, when you say you prefer to use them, do you mean just the head or the whole motor? The reason I ask is because I was recently given an XS-1B motor and I'm wondering what to do with it. I didn't really want to run the whole thing but could I swap parts to my newer engine, like the head for instance? I know the cam won't work because of the different sized sprocket. How about the cylinders, will they swap to a newer 447 motor?

 

[Punkskalar]

I prefer the head and the cam from the early motors. The Cylinders and the head will swap over just fine. The cam will swap as well, you just have to remove the stock gear and replace it with a 447 gear.

 

[5twins]

I assume that means pressing the sprocket off and on. I have a 12 ton press. If I made fittings to hold the cam upright, that 12 tons should be enough, right? How about alignment? Do you just scribe lines from the cam notch up onto the sprocket, then verify TDC in a motor afterwards (hole for ATU pin pointing straight up @ TDC)? This intrigues me. I would love to use that head and cam in my newer motor.

 

[Punkskalar]

Yeah, you'll definitely want to degree the cam to TDC. I've swapped sprockets using a 2 ton Drake Press before, so you'll be fine on that...

 

[doughboi916]

thanks for the info guys.. i hope the guy still has the bike, i will find out tonight.....450 bucks..

 

[cra-z1]

Since I had issues with my 72 crank I decided to use a 447 crank. The 447 crank does not have the weights as does the 256 crank, which have been known to loosen and come out causing all sorts of problems. I rebuilt it using 256 rods. The wrist pins are smaller but I will not be winding it out. I think the stock 447 develops more rod side wear compared to a 256 rod due to the length. It has to do with the angle of the rod at TDC or something like that. The 256 rod sits at TDC slightly longer than the 447 rod. Someone can chime in on this. My main goal was to keep the characteristics of the 256 motor but enabled me to use the cam components of the 447. I still used the 256 cam but I used a mega cycle adjustable sprocket for dialing in the cam better. Mega cycle will press on a collar and then their 447 sprocket bolts to that. Much easier than having to press the stock sprocket on and off several times if your trying to dial it in. If you want you can use the 447 crank/pistons and do what I did on the cam.