Need info about cranks

[GreasyC]

I've got a 256 engine I'll be rebuilding over the winter. Not sure what I want to do with it yet but I'm looking over what I've got right now and the crank is pretty beat. The copper is worn out in the small ends and the left rod measures at the wear limit for side to side play.

Searching for replacement 256 rods hasn't gotten me anywhere so far. Anybody have a lead on that?

I'm doing some reading up on cranks right now because it's my first time messing with it and I have a couple general questions:

- Every crank balancing description I can find online assumes you can take the rods off and attach bobwieghts to the pins. That's not going to happen on an XS crank without tearing it apart so how do they balance this type of crank?

- On that topic, what is this type of crank? Most cranks seem to be made up of bell shaped counter weight sections, but the XS is all round wheels with some holes in them. Does this style have a name?

 

[burns]

I believe the 256 cranks had lead counter-weights (which by reputation were prone to wander off on their own), so when you refer to "holes" in your crank I'm wondering if your crank met that fate (i.e. the counter weights are gone).

 

[GreasyC]

Hmm, now you got me wondering too! I'll get some pics of what I'm looking at tonight.

 

[5twins]

Most economical route would probably be to throw a 447 crank in it.

 

[rebel542]

If you lost one of those lead weights it would have chewed your engine up. To run a 447 crank you're going to have to change pistons to 447 also. From what you're describing you can probably run what you've got for many more miles. Hope this helps.

P.S. I may have a couple of 256 rods laying around if you're interested.

 

[cra-z1]

Depends what you are building. If your just going to throw it in a rat bike you can just put a 447 crank in it. You will need to use a cam from a 447 engine also along with all the cam parts. If your restoring or want to keep the characteristics of the 256 engine as I did when restoring the 72 here is what I did. Yes the 256 has weights that can loosen and fall as did one of my 72 cranks which resulted in a locked crank. The second crank had a loose weight. I was told these can be tightened ???. You can buy NOS rods on e-bay if you watch but Heiden Tuning does offer a aftermarket rod for the 256. I bought a used 447 crank that was ok and 256 NOS rods. I had Falicon press the new rods along with bearings ect. Then they balanced it and welded the crank. No more worry about the weight. Another issue I was fighting was the drive gear on the crank. Both my 256 motors had a chewed up gear. Now the 447 crank uses a different cam chain. In order to keep your 256 cam you will need to use an adjustable cam from Megacycle. They press on a collar and you can then bolt a 447 sprocket to that. This allows you to dial in the cam easily when reassembling the engine. Mike has oversize 256 pistons with updated rings which I used to complete. You will need to also use the newer cam chain adjuster for the 447 engine. So what you have is an engine with 256 characteristics but you have a crank that will not lock up. Also updated cam parts which are easier to get a hold of. Costs a little but it was well worth it for me. The engine runs very smooth and has kept the 256 characteristics.

Buy the way the weights are not lead but a special metal which I can't remember the name. I also have the 256 crank with the loose weight if you want to give it a try. The rods are in pretty good shape.

 

[hard_y_rd]

Going to hi-jack here a little... If you have a good 256 crank supposedly, can the weights that are known to fall out be welded to prevent a breakdown. I'm currently rebuilding a 256 motor.

 

[GreasyC]

This is good stuff, thanks guys. This is not a restoration so it's not really important to me to keep the 256 guts but if switching to a 447 crank means I need buy 447 pistons and 447 cam as well at that point I'd probably be tempted to skip the stock stuff and do something more fun. Better make sure about what I've got first. Here's the crank:

All four wheels have holes like that with nothing in them (except the pins of course). On the section you can't see behind the primary gear there's a much smaller hole, also empty. I can see straight through all four plates looking down it.

Here's one of the small ends:

Sorry for the bad lighting but that's bare steel on the left side of the ID and copper on the right. Both rods look like this but this one is a little worse.

 

[hotdog]

To help identify your crank the following would help - what numbers do your rods have on them, what is the I.D. of your little end & what is the length of the rods.

 

[XSLeo]

As hotdog said the numbers on the rods tell you if it's a 256 or 447 crank. It's possible a PO has swapped the crank.
Leo

 

[GreasyC]

The rods say:

256 (some weird symbol) E
256 (some weird symbol) D

I.D. of the small end is 22mm

 

[XSLeo]

Those are the 256 rods. I might do as other suggest, get a good 477 crank and pistons, use a 447 cam. Change out the chain tensioner. It will look the same and run about the same. Maybe not quite as strong but close.
Leo

 

[GreasyC]

I checked out the rods at Heiden tuning and wow, is that $200 EACH? I think you guys are right, doesn't look like keeping it 256 inside is the way to go. My idea for this project is to keep it original where I can but where I can't to use something better than stock. If I can't keep the engine stock I'll probably use it as an opportunity to do something a little more fun, maybe try the rephase and a bit hotter cam than the stock 447 one.

I'm still curious to learn more about cranks if anyone wants to talk about them. I don't see any of those lead weights mentioned earlier in mine. And I'm still wondering why these cranks look so different from all the other parallel twin cranks I can google up. I know it doesn't matter for my build, just finding it interesting.

 

[cra-z1]

Yes those rods don't come cheap. I found NOS rods for under 100. Here is a picture of the weights on the 256 crank. They are located on the drive side only. I do not think you can weld them in place and it would change the balance. As you can see they are of a different material. They go all the way through. I think by peening the material you could tighten them up

 

[cra-z1]

I think what you have is a XS1 or XS1b crank. No starter gear. The weights may have come into play when yamaha decided to add a starter in 72. That crank may be worth some money to someone who is restoring an early XS1/XS1b?. There are some other differences on those early engines. Maybe someone can chime in to explain them.

 

[GreasyC]

Yeah mine is a 71. The fiche shows both a 256-11442-01-00 and a 306-11442-03-00 for that part up until 74 where there's only the 306 but it makes sense that the switch really happened in 72 when the starter appeared. But there really seems to be no weights in mine. Does that mean mine vibrates even more than 72 on? Interesting. I'm starting to get the impression Yamaha didn't put much effort into balancing these things. Even the weights on yours, I don't think it makes sense to put them only on one wheel. From what I've read the counterweight is supposed to be spread 50-50 on either side of each piston to do it's job right.

 

[cra-z1]

I think they needed to add weight when they machined the teeth on the gear. They machined a lot of metal out and that was the way they got it back to equal the other side of the crank. Each wheel is probably within a certain range of weight which was tolerable.

 

[rebel542]

Not sure about why they added the weight but cra-z1's theory sounds good to me. The other differences in the engines are the head, no square valve cover and cases without indention for starter. Those are just 2 of many. It also holds half a quart more oil than the electric start engines.

 

[GreasyC]

That does make sense, probably right. I guess if you squint your eyes at the holes in the xs650's crank wheels and consider that area is mostly gone it sort of adds up to the bell shaped counterweights in other cranks. I'm thinking of things like this triumph crank:

Or yamaha's modern parallel twins like the TRX/TDM:

That yamaha one seems to have different shaped weights on either side of the rods. Wonder what that's supposed to do?

 

[rebel542]

Yes. Same principal. The large holes in your 650 crank are balance holes. BTY, that Triumph crank is a 270/90 degree as is the Yamaha crank pic you posted.